JP7623643B2 - Insulation Resistance Monitoring Device - Google Patents

Description

The present invention relates to an insulation resistance monitoring device that can monitor the insulation resistance of an object to be measured both when load power that operates a load device is not being supplied and when it is being supplied.

Patent Document 1 describes an application-type measuring instrument that monitors the insulation resistance of a measurement object that includes a set of multiple power lines that supply load power from upstream to downstream, and a load device that operates with the load power supplied from the power lines. This application-type measuring instrument is connected to a grounded (earthed) part and the measurement object, and applies a voltage between the grounded part and the measurement object. This voltage is divided by the insulation resistance of the measurement object and a reference resistor inside the application-type measuring instrument, and the application-type measuring instrument calculates the insulation resistance of the measurement object relative to the grounded part by measuring the voltage across the reference resistor.

JP 2017-173176 A

In conventional application-type measuring instruments, the supply of load power is stopped and the load equipment is stopped, and then a voltage corresponding to the insulation resistance of the object being measured is measured. Therefore, the conventional technology has the problem that, although it can monitor the insulation resistance of the object being measured when load power is not being supplied, it cannot monitor the insulation resistance of the object being measured when load power is being supplied.

The present invention has been made to solve the above-mentioned problems, and aims to provide an insulation resistance monitoring device that can monitor the insulation resistance of a measurement object both when load power that operates a load device is not being supplied and when it is being supplied.

In order to achieve this object, the insulation resistance monitoring device of the present invention monitors the insulation resistance between a grounded part and a measurement object comprising a set of multiple power lines supplying load power from upstream to downstream and a load device operated by the load power supplied from the set of power lines, and comprises an application-type measuring instrument connected to the power lines and the ground part, respectively, and a leakage current measuring instrument that monitors the leakage current generated in response to the insulation resistance of the measurement object when the load power is supplied, and the application-type measuring instrument measures the insulation resistance between the measurement object including the power lines and the measurement object. By applying a voltage between the power line and the ground while the power line is disconnected from the ground except for the insulation resistance of the power line and the connection to the ground via the application-type measuring instrument, a current generated in accordance with the insulation resistance of the object to be measured, or a voltage converted from that current, is measured, and the leakage current measuring instrument includes one current measuring instrument that collectively measures the magnetic fields generated in each of the multiple power lines of a set when power for the load is supplied, and measures the total current flowing through those power lines based on the magnetic field, or multiple current measuring instruments that individually measure the current flowing through each of the multiple power lines of the set.

In addition, the insulation resistance monitoring device of the present invention monitors the insulation resistance between a grounded part and an object to be measured, the object having a set of multiple power lines that supply load power from upstream to downstream and a load device that operates by the load power supplied from the set of power lines, and includes an electromagnetic switch that opens and closes a ground wire connecting one of the power lines and the ground part, an application-type measuring instrument connected to each of the power lines and the ground part, and a current measuring instrument that measures the current flowing through the ground wire, and with the electromagnetic switch closed, measures with the current measuring instrument a leakage current generated in response to the insulation resistance of the object to be measured when the load power is supplied, and with the electromagnetic switch open, the application-type measuring instrument applies a voltage between the power lines and the ground part via the insulation resistance of the object to be measured, thereby measuring the current generated in response to the insulation resistance of the object to be measured, or a voltage obtained by converting that current .

Note that "grounded part" includes not only parts that are electrically connected to the earth (such as the housing of a load device), but also the earth itself. Furthermore, connection to a large conductor that is not connected to the earth, such as the frame of a vehicle, ship, or airplane, is also called "grounding," and a grounded "grounded part" includes large conductors such as frames and things connected to those conductors.

According to the insulation resistance monitoring device of claim 1, the application-type measuring instruments connected to the power line and the ground respectively apply a voltage between the power line and the ground while the measurement object including the power line is not connected to the ground except for the insulation resistance of the measurement object and the connection to the ground via the application- type measuring instrument. This voltage application generates a current corresponding to the insulation resistance of the measurement object connected to the application-type measuring instrument, and this current is input to the application-type measuring instrument. The application-type measuring instrument measures this input current or a voltage obtained by converting this current. Since this measurement uses the voltage applied by the application-type measuring instrument rather than the load power, the insulation resistance monitoring device can monitor the insulation resistance of the measurement object using the application-type measuring instrument even when the load power is not being supplied.

The leakage current meter is equipped with one current meter that collectively measures the magnetic fields generated in the multiple power lines of a set when power for a load is supplied, and measures the total current flowing through those power lines based on the magnetic fields, or multiple current meters that individually measure the current flowing through each of the multiple power lines of a set. Even in the latter case, the total current flowing through the set of power lines can be calculated by adding up the measurement results of the multiple current meters. Basically, the total current flowing through the set of power lines when power for a load is supplied is the same as the leakage current generated according to the insulation resistance of the object being measured. Therefore, the insulation resistance monitoring device can monitor the insulation resistance of the object being measured when power for a load is supplied using the leakage current meter. As a result of the above, the insulation resistance monitoring device can monitor the insulation resistance of the object being measured both when power for a load is not being supplied and when it is being supplied.

The insulation resistance monitoring device according to claim 2 has the following effect in addition to the effect of the insulation resistance monitoring device according to claim 1. A set of power lines is three AC electric wires that make up a three-phase, three-wire circuit. One end of each of the three resistors is connected to the three AC electric wires individually, and the other ends of the three resistors are combined together. An application-type measuring instrument is connected to the other combined end, and the application-type measuring instrument is connected to the AC electric wires via the resistors.

Since the three resistors have the same resistance, the sum of the currents generated in each of the three resistors by the load power supplied from the three-phase, three-wire AC power line is approximately 0 A, and the combined voltage at the other end of the resistors is also approximately 0 V. This makes it difficult for the current and voltage based on the load power to be input to the application-type measuring instrument.

Note that "same resistance value" includes cases where the resistance values differ within a range of ±5%.

The insulation resistance monitoring device of claim 3 has the following effect in addition to the effect of the insulation resistance monitoring device of claim 2. An upstream transformer is disposed on the three AC electric wires upstream of the position where one end of each of the three resistors is connected. This upstream transformer transmits load power from the upstream side to the downstream side by electromagnetic induction while insulating the AC electric wires upstream and downstream of its own position.

Therefore, the application-type measuring instrument can measure the current or voltage generated by applying a voltage according to the insulation resistance of the object to be measured downstream of the upstream transformer. As a result, the insulation resistance monitoring device can monitor the insulation resistance downstream of the upstream transformer without having to cut off the AC electric wire midway to monitor the insulation resistance of a part of the AC electric wire and stop the supply of power to the load.

The insulation resistance monitoring device according to claim 4 has the following effect in addition to the effect of the insulation resistance monitoring device according to claim 1. The set of power supply lines includes a positive line connected to the positive pole of a battery that outputs DC power as load power, and a negative line connected to the negative pole of the battery. The application-type measuring instrument is connected to the negative line and a ground while being directly disconnected from the positive line. Since the potential of the negative line with respect to the ground is close to 0 V, it is possible to prevent current and voltage based on the DC power from being input from the negative line to the application-type measuring instrument even while DC power is being supplied to the load device.

In addition, because the battery is considered to be a low-resistance conductor, the positive and negative wires connected via the battery are considered to be a single wire. This allows the insulation resistance monitoring device to measure the current or voltage corresponding to the insulation resistance of not only the negative wire but also the positive wire using an application-type measuring instrument, and to monitor the insulation resistance of the positive and negative wires.

According to the insulation resistance monitoring device of claim 5, in addition to the effect of the insulation resistance monitoring device of any one of claims 1 to 4, the following effect is achieved. A grounding line connecting a power line connected to an application type measuring instrument and a grounding part is opened and closed by an electromagnetic switch. By opening the electromagnetic switch to disconnect the power line from the grounding part, it is possible to prevent the current generated by the application of voltage by the application type measuring instrument from flowing directly between the grounding part and the power line without passing through the insulation resistance. Therefore, by measuring the current or voltage with the electromagnetic switch open, the application type measuring instrument can accurately measure the current or voltage according to the insulation resistance of the object to be measured.

On the other hand, leakage current measuring instruments use a current measuring instrument to measure the current when the electromagnetic switch is closed. In this closed state, leakage current that occurs in the object being measured when power is supplied to the load is more likely to return from the ground to the power line through the ground wire. Furthermore, because the power line upstream of the measurement position of the current measuring instrument (the position where the current is measured by the current measuring instrument) is connected to the ground wire, leakage current that passes through the ground wire is more likely to bypass the current measuring instrument. As a result, the leakage current measuring instrument can more accurately measure or calculate the leakage current when power is supplied to the load.

According to the insulation resistance monitoring device of claim 6, in addition to the effects of the insulation resistance monitoring device of any one of claims 1 to 4, the following effects are achieved. The set of power lines includes a set of main electric wires on the upstream side and a plurality of sets of branch electric wires each branching off from the set of main electric wires. A plurality of load devices are connected to each set of branch electric wires. The earth leakage measuring device includes a main measuring device,
The current meter of the trunk meter measures the current flowing through the trunk meter upstream of the sets of branch conductors (either together or individually), allowing the trunk monitoring device to easily measure or calculate the total leakage current of the load devices connected to the sets of branch conductors.

According to the insulation resistance monitoring device of claim 7, in addition to the effects of the insulation resistance monitoring device of any one of claims 1 to 4, the following effects are achieved. The set of power lines includes a set of upstream main electric wires and multiple sets of branch electric wires each branching off from the set of main electric wires. Multiple load devices are connected to each set of branch electric wires. The leakage current measuring device includes a branch measuring device, and measures the current flowing through the set of branch electric wires (together or individually) with a current measuring device of the branch measuring device. This allows the branch measuring device to measure or calculate the leakage current of the load device connected to the set of branch electric wires without being affected by the leakage current of the load devices connected to the other branch electric wires.

According to the insulation resistance monitoring device of claim 8, a ground line connecting one of a set of multiple power lines to a ground is opened and closed by an electromagnetic switch. An application-type measuring instrument connected to the power line and the ground applies a voltage between the power line and the ground through the insulation resistance of the object to be measured , with the electromagnetic switch opened to disconnect the power line from the ground. This application of voltage generates a current corresponding to the insulation resistance of the object to be measured connected to the application-type measuring instrument, and this current is input to the application-type measuring instrument. The application-type measuring instrument measures this input current or a voltage obtained by converting this current. Since the measurement uses the voltage applied by the application-type measuring instrument, not the load power, the insulation resistance monitoring device can monitor the insulation resistance of the object to be measured by the application-type measuring instrument even when the load power is not being supplied.

Furthermore, when the electromagnetic switch is closed, leakage current that occurs in the object to be measured when load power is being supplied is more likely to return from the grounded part through the ground wire to the power line. Because the current flowing through this ground wire is measured by the current meter of the leakage current meter, it is easier to measure the leakage current that occurs in response to the insulation resistance of the object to be measured when load power is being supplied by the current meter. In other words, the insulation resistance monitoring device can monitor the insulation resistance of the object to be measured when load power is being supplied by the leakage current meter. As a result of the above, the insulation resistance monitoring device can monitor the insulation resistance of the object to be measured both when load power is not being supplied and when it is being supplied.

1 is a circuit diagram showing an insulation resistance monitoring device according to a first embodiment and an electric circuit of an object to be measured; FIG. 2 is a block diagram showing the electrical configuration of an application-type measuring instrument. 11 is a flowchart of a periodic measurement process executed by a CPU of the voltage-type measuring instrument. 1 is a graph showing changes over time in insulation resistance measurement results and predictions for the future. 1A is a block diagram showing the electrical configuration of a leakage current meter, and FIG. 1B is a flowchart showing a leakage current measurement process executed by a CPU of the leakage current meter. FIG. 11 is a circuit diagram showing an insulation resistance monitoring device and an electric circuit of a measurement object according to a second embodiment. FIG. 11 is a block diagram showing the electrical configuration of an application-type measuring instrument and an earth leakage measuring instrument in a second embodiment. 13A is a flowchart of a periodic measurement process in the second embodiment, and FIG. 13B is a flowchart of an earth leakage measurement process in the second embodiment. FIG. 11 is a circuit diagram showing an insulation resistance monitoring device and an electric circuit of a measurement object according to a third embodiment. FIG. 13 is a circuit diagram showing an electrical circuit of an insulation resistance monitoring device and an object to be measured according to a fourth embodiment. 1A is a graph showing the change over time in current values measured by two current transformers, and FIG. 1B is a graph showing the change over time in leakage current values.

Preferred embodiments will now be described with reference to the accompanying drawings. First, an insulation resistance monitoring device 20 and an object to be measured in a first embodiment will be described with reference to FIG. 1. FIG. 1 is a circuit diagram showing a schematic diagram of an electrical circuit of the insulation resistance monitoring device 20 and the object to be measured. The object to be measured includes a set of three AC electric wires 11, 12, and 13 that constitute a three-phase three-wire AC circuit, and a load device 14 that is connected to the set of three AC electric wires 11 to 13.

The AC power lines 11 to 13 are power lines that supply three-phase power (load power) from an upstream pole transformer or the like to a downstream load device 14. Three-phase power is three-phase AC power, and three-phase AC is three single-phase AC power of the same voltage that flows through each of the AC power lines 11 to 13, each shifted in phase by 120°.

The load device 14 is an electric circuit that operates with three-phase power supplied from a set of AC electric wires 11 to 13. An example of the load device 14 is a three-phase induction motor. The load device 14 is housed in a housing 14a that is D-type grounded (earthed) via a grounding wire 18. The load device 14 is directly connected to the AC electric wires 11 to 13 within the housing 14a.

The ground wire 18 is an electric wire connected to a ground electrode embedded in the earth. The ground wire 18 connected to the housing 14a, the isolation transformers 21 and 22 described below, and the voltage-applied measuring instrument 30 may be the same electric wire, or may be separate electric wires connected to each other via the earth.

The insulation resistance monitoring device 20 is for monitoring the insulation resistance between the grounding part, such as the grounding wire 18, the housing 14a, or the earth, and the measurement object. The insulation resistance monitoring device 20 includes insulation transformers 21, 22 arranged midway along the AC electric wires 11-13, combined resistance parts 23, 24 connected to the AC electric wires 11-13, an application-type measuring instrument 30 connected between the combined resistance parts 23, 24 and the grounding wire 18, and leakage current measuring instruments 50a, 50b arranged on the AC electric wires 11-13 downstream of the insulation transformers 21, 22, respectively.

An isolation transformer 22 is arranged on the AC electric wires 11 to 13 downstream of the isolation transformer 21. The isolation transformer 21 includes a primary winding 21a connected to the AC electric wires 11 to 13 upstream of its arrangement position, a secondary winding 21b connected to the AC electric wires 11 to 13 downstream of its arrangement position, an iron core (not shown) around which the primary winding 21a and secondary winding 21b are wound, and a housing 21c that houses the primary winding 21a, the secondary winding 21b, and the iron core.

Similarly, the isolation transformer 22 includes a primary winding 22a, a secondary winding 22b, an iron core (not shown), and a housing 22c. In order to allow leakage currents generated within the isolation transformers 21 and 22 to escape to the ground, the housings 21c and 22c are connected to the ground wire 18 and are grounded.

Here, of the AC electric wires 11 to 13, the parts connected to the primary winding 21a of the isolation transformer 21 are referred to as upstream wires 11a to 13a, the parts connecting the secondary winding 21b of the isolation transformer 21 and the primary winding 22a of the isolation transformer 22 are referred to as intermediate wires 11b to 13b, and the parts connected to the secondary winding 22b of the isolation transformer 22 are referred to as downstream wires 11c to 13c.

The isolation transformer 21 transmits three-phase power from the upstream lines 11a-13a to the intermediate lines 11b-13b by electromagnetic induction while insulating the upstream lines 11a-13a from the intermediate lines 11b-13b. Similarly, the isolation transformer 22 transmits three-phase power from the intermediate lines 11b-13b to the downstream lines 11c-13c by electromagnetic induction while insulating the intermediate lines 11b-13b from the downstream lines 11c-13c.

The isolation transformer 21 can transform the voltage on the primary winding 21a side and transmit it to the secondary winding 21b side by making the number of turns of the primary winding 21a different from the number of turns of the secondary winding 21b. However, it is also possible to make the number of turns of the primary winding 21a and the number of turns of the secondary winding 21b the same and not to perform a transformation by the isolation transformer 21. Similarly, it is also possible to perform a transformation by the isolation transformer 22, or not.

In addition, the intermediate lines 11b to 13b and downstream lines 11c to 13c downstream of the isolation transformers 21 and 22 are all maintained in a state of being unconnected to grounded parts such as the grounding line 18. In other words, the downstream sides of the isolation transformers 21 and 22 are not grounded to type B.

The combined resistance unit 23 includes a resistor 23a having one end connected to the intermediate line 11b, a resistor 23b having one end connected to the intermediate line 12b, and a resistor 23c having one end connected to the intermediate line 13b. The other ends of these three resistors 23a to 23c are combined with each other. The other ends of the combined resistors 23a to 23c are connected to the voltage application type meter 30 by a combined electric wire 23d.

The three resistors 23a to 23c have the same resistance value. As a result, a graph showing the time change in the current generated in each of the three resistors 23a to 23c by the three-phase power supplied from the intermediate lines 11b to 13b is similar to a graph showing the time change in the voltage of the intermediate lines 11b to 13b (a graph in which the phases of single-phase AC of the same voltage are shifted by 120°).

Therefore, at any given time, the sum of the currents flowing through resistors 23a to 23c is approximately 0 A. Therefore, the current flowing through composite wire 23d, which is the combination of these currents, is approximately 0 A, and the voltage combined in composite wire 23d is also approximately 0 V. Note that the current and voltage based on the three-phase power are set to approximately 0 because a small amount of current and voltage may also be generated in composite wire 23d when the balance of voltages between intermediate wires 11b to 13b is lost.

In addition, "the same resistance value" includes cases where the resistance values of each resistor differ within a range of ±5%. Even if the resistance values of the three resistors 23a to 23c differ slightly, a small amount of current and voltage may be generated in the composite electric wire 23d.

Similar to the combining resistor unit 23, the combining resistor unit 24 includes resistors 24a to 24c, one end of which is connected to each of the downstream lines 11c to 13c. The other ends of the combined resistors 24a to 24c are connected to the voltage application meter 30 by a combining wire 24d. Because the resistors 24a to 24c have the same resistance value, the current flowing through the combining wire 24d based on the three-phase power is approximately 0 A, and the voltage combined by the combining wire 24d is also approximately 0 V.

In this way, by connecting the application-type meter 30 to the AC power lines 11-13 via the combined resistance units 23 and 24, it is possible to make it difficult for the current and voltage based on the three-phase power to be input to the application-type meter 30. As a result, it is possible to eliminate the need to disconnect the application-type meter 30 from the AC power lines 11-13 when supplying three-phase power, and to eliminate the need for an electromagnetic switch for connecting and disconnecting it.

Even if the electromagnetic switch is provided, if the electromagnetic switch cannot be opened due to a malfunction such as welding, the combined resistance units 23 and 24 can make it difficult for the current and voltage based on the three-phase power to be input to the application-type meter 30. Therefore, by using the combined resistance units 23 and 24, the application-type meter 30 can be kept connected to the AC wires 11 to 13 even when three-phase power is being supplied.

The voltage application type measuring instrument 30 has a terminal E connected to the ground wire 18, a terminal a connected to the intermediate wires 11b to 13b via the composite wire 23d and the composite resistance section 23, and a terminal b connected to the downstream wires 11c to 13c via the composite wire 24d and the composite resistance section 24.

The application-type measuring instrument 30 applies a voltage between terminal E and terminal a or terminal b, thereby generating a current according to the insulation resistance of the measurement object (AC electric wires 11-13, load device 14) connected to terminal a or terminal b. The application-type measuring instrument 30 measures the voltage converted from this current, and calculates and monitors the insulation resistance from the voltage.

The current generated in the AC wires 11-13 by the application of voltage by the application-type measuring instrument 30 does not flow beyond the isolation transformers 21, 22. Therefore, when the application-type measuring instrument 30 applies a voltage between terminals E and a, it can measure the voltage generated according to the insulation resistance of the intermediate wires 11b-13b, secondary winding 21b, and primary winding 22a (hereinafter referred to as "measurement object a") connected to terminal a among the measurement objects when the application-type measuring instrument 30 applies a voltage between terminals E and a terminal, it can measure the voltage generated according to the insulation resistance of the downstream wires 11c-13c, secondary winding 22b, and load device 14 (hereinafter referred to as "measurement object b") connected to terminal b among the measurement objects when the application-type measuring instrument 30 applies a voltage between terminals E and b.

In this way, the insulation resistance monitoring device 20 can monitor the insulation resistance of the measurement objects a and b downstream of the isolation transformers 21 and 22, using the isolation transformers 21 and 22 located upstream of the connection position of the terminals a and b. Also, the insulation resistance monitoring device 20 can monitor the insulation resistance of the measurement object a upstream of the isolation transformer 22, using the isolation transformer 22 located downstream of the connection position of the terminal a.

Conventionally, to partially monitor the insulation resistance of a measurement object including the AC electric wires 11-13, it was necessary to disconnect the AC electric wires 11-13 midway. However, in the insulation resistance monitoring device 20 of this embodiment, by providing the insulation transformers 21 and 22, it is possible to partially monitor the insulation resistance of the measurement object without disconnecting the AC electric wires 11-13 midway. In other words, in the insulation resistance monitoring device 20, it is not necessary to disconnect the AC electric wires 11-13 and stop the supply of three-phase power in order to monitor the insulation resistance of the measurement object.

Specifically, a method for calculating the insulation resistance of measurement object a (intermediate lines 11b-13b, etc.) connected to terminal a using the application-type measuring instrument 30 will be described. First, when a predetermined voltage V0 (e.g., 250-1000V) is applied between terminal E and terminal a, a current corresponding to the insulation resistance of measurement object a is generated. The application-type measuring instrument 30 converts this current into a voltage V1 using a reference resistor 40 (see Figure 2) installed inside the application-type measuring instrument 30, and measures this voltage V1.

This will be explained from a different perspective. The voltage V0 applied between terminal E and terminal a by the application-type measuring instrument 30 is divided mainly between the insulation resistance of the measurement object a, resistors 23a to 23c, and the reference resistor 40. The application-type measuring instrument 30 measures the voltage V1 applied to the reference resistor 40 out of this divided voltage.

Here, if the insulation resistance value of the measurement object a is R1, the resistance value of the combined resistance part 23 (the combined resistance value of the three resistors 23a, 23b, and 23c) is R2, and the resistance value of the reference resistor 40 is R3, then the formula V1 = V0 x R1 / (R1 + R2 + R3) holds. Since the voltage V0 and the resistance values R2 and R3 are known in advance, the insulation resistance value R1 of the measurement object a can be calculated by measuring the voltage V1.

Similarly, when measuring the insulation resistance of measurement object b (downstream lines 11c-13c, etc.) connected to terminal b, the application-type measuring instrument 30 applies a voltage V0 between terminal E and terminal b, measures the voltage V1 across the reference resistor 40, and calculates the insulation resistance value R1 of measurement object b from the measurement result. In this case, the resistance value of the combined resistance part 24 (the combined value of the resistance values of the three resistors 24a, 24b, 24c) is R2.

The application-type measuring instrument 30 is powered by the storage battery 25, not by the three-phase power supplied from the AC power lines 11-13. Furthermore, the application-type measuring instrument 30 measures the voltage corresponding to the insulation resistance using the voltage it applies itself (the power of the storage battery 25), so it can monitor the insulation resistance of the measurement objects a and b even when three-phase power is not being supplied.

In addition, to measure the insulation resistance of measurement objects a and b using the application-type measuring instrument 30, the measurement objects a and b must be disconnected from grounded parts such as the ground wire 18. However, measurement objects a and b, including intermediate lines 11b-13b and downstream lines 11c-13c, are maintained in a state of being disconnected from the ground wire 18 because there is no type B ground. Therefore, when measuring with the application-type measuring instrument 30, the work or process of disconnecting the measurement objects a and b from the ground wire 18 is not required. This simplifies the measurement using the application-type measuring instrument 30.

When disconnecting the AC wires 11-13 from the ground wire 18 during measurement with the application-type measuring instrument 30, it is preferable to stop the supply of three-phase power through the AC wires 11-13 before disconnecting them in order to prevent malfunction of the load equipment 14, etc. However, since there is no need to disconnect them, there is no need to stop the supply of three-phase power through the AC wires 11-13 during measurement with the application-type measuring instrument 30.

In addition, the combined resistance units 23 and 24 make it difficult for the current and voltage based on the three-phase power to be input to the application-type measuring instrument 30. As a result, even when the load device 14 is operating with three-phase power, the application-type measuring instrument 30 can measure a voltage corresponding to the insulation resistance of the measurement objects a and b while suppressing the influence of the three-phase power on the measurement results. Therefore, the insulation resistance monitoring device 20 can accurately monitor the insulation resistance of the measurement objects a and b even when the load device 14 is operating.

Next, the control of the application-type measuring instrument 30 will be described in more detail with reference to Figures 2 to 4. Figure 2 is a block diagram showing the electrical configuration of the application-type measuring instrument 30. The application-type measuring instrument 30 has a CPU 31, a flash ROM 32, and a RAM 33, which is a memory for rewritably storing various work data and flags when the CPU 31 executes a program, and these are each connected to an input/output port 35 via a bus line 34.

The input/output port 35 is further connected to a communication device 36, a measurement unit 37, a voltage application unit 38, and a switching unit 39, which are connected to an external control device 26. The external control device 26 is a device that analyzes the measurement results of the insulation resistance of the measurement object obtained from the insulation resistance monitoring device 20 (voltage application type measuring instrument 30) and controls the operation of the load device 14, etc.

The CPU 31 is a calculation device that controls each part connected by the bus line 34. The flash ROM 32 is a rewritable non-volatile memory that stores programs executed by the CPU 31, fixed value data, etc., and is provided with an application monitoring program 32a. When the application monitoring program 32a is executed by the CPU 31, the periodic measurement process of FIG. 3 is executed.

The measurement unit 37 is a device that measures the voltage applied to the reference resistor 40 built into the application-type measuring instrument 30. The reference resistor 40 is a load that has a predetermined resistance value that serves as a reference, and one end is connected to the switching unit 39 and the other end is connected to the ground 41. The voltage application unit 38 is a device that applies a positive DC voltage from terminal E to the ground wire 18, using the ground 41 as a reference potential.

The switching unit 39 is a circuit that connects one of the measurement objects a and b connected to the terminals a and b to the reference resistor 40 and the measurement unit 37, making it possible to calculate the insulation resistance of the measurement object a or b connected to the measurement unit 37.

The electrical path between terminal a and the measuring unit 37 is connected in an openable/closable manner by switch SW1, and the electrical path between terminal b and the measuring unit 37 is connected in an openable/closable manner by switch SW2. Switches SW1 and SW2 are switches that open and close the electrical circuit in response to instructions from the CPU 31, and remain open when not energized.

The switching unit 39 further includes a standard resistor 42 that is connected to the wire branching off from between the terminal E and the voltage application unit 38, and a switch SW3 that can open and close the standard resistor 42 and the measurement unit 37. The standard resistor 42 is a load having a predetermined resistance value. The switch SW3 may be provided between the wire branching off from between the terminal E and the voltage application unit 38 and the standard resistor 42.

Next, the periodic measurement process executed by the CPU 31 of the application-type measuring instrument 30 will be described with reference to FIG. 3. FIG. 3 is a flowchart of the periodic measurement process of the application-type measuring instrument 30. The periodic measurement process of the application-type measuring instrument 30 is executed periodically (e.g., every 10 minutes) while the power of the application-type measuring instrument 30 is turned on.

The periodic measurement process of the application-type measuring instrument 30 first sets n=1 to calculate the insulation resistance of the measurement object a (S11). Next, switch SWn (n: integer) is closed (S12). In the process of S12, which is immediately after the process of S11 in which n=1 is set, switch SW1 is closed to connect the measurement object a to the measurement unit 37.

As a result, a circuit for calculating the insulation resistance of the measurement object a is formed, and the voltage application unit 38 applies a positive voltage from terminal E to the ground wire 18 (S13). Next, it is confirmed whether a predetermined time has passed since the application of the voltage (S14). If the predetermined time has not passed (S14: No), the measurement value of the voltage generated according to the insulation resistance of the measurement object a is not stable, so the process of S14 is looped.

On the other hand, if a predetermined time has passed since the application of the voltage (S14: Yes), it is checked whether n≦2 (S15) to see if it is time to calculate the insulation resistance of the measurement object a or b. If n≦2 (S15: Yes), the time has come to calculate the insulation resistance of the measurement object a or b, so the voltage applied to the reference resistor 40 is measured by the measurement unit 37, and the insulation resistance of the measurement object a is calculated from the measurement result as described above (S16).

Next, the measurement result, the measurement object (measurement object a in the first process after the process of S11), and the date and time of measurement are transmitted to the external control device 26 (S18). The external control device 26 accumulates and analyzes the measurement result, as described later with reference to FIG. 4.

After processing in S18, switch SWn is opened for the next measurement (S19). In the first processing after processing in S11, switch SW1 is opened in S19, and measurement object a is disconnected from measurement unit 37. To confirm this disconnection, it is confirmed that the voltage corresponding to the insulation resistance is no longer detected by measurement unit 37 (S20).

If no voltage is detected in the process of S20 (S20: Yes), it is determined that switch SW1, which was instructed to open in the process of S19, was opened without any problems. Therefore, the voltage application by the voltage application unit 38 is terminated (S21), and n=n+1 is set for the next measurement (S22).

Next, it is confirmed whether n ≥ 4 (S23), and if n < 4 (S23: No), there are still unmeasured items, so the processes from S12 onwards are executed again. Specifically, if n = 2 in the process of S22, switch SW2 is opened and closed in the processes of S12 and S19, and the insulation resistance of measurement object b is calculated in the process of S16.

If n=3 in the process of S22, the switch SW3 is closed in the process of S12, and the voltage application unit 38 is connected to the measurement unit 37 and the reference resistor 40 via the standard resistor 42. Furthermore, since n>2 in the process of S15 (S15: No), the process of S17 is executed instead of the process of S16.

In the process of S17, the voltage applied to the reference resistor 40 is measured by the measurement unit 37, and the resistance value of the standard resistor 42 is calculated from the measurement result (S17). The voltage V0 applied by the voltage application unit 38 is divided between the standard resistor 42 and the reference resistor 40, so if the resistance value of the standard resistor 42 is R4, the voltage applied to the reference resistor 40 is V1, and the resistance value of the reference resistor 40 is R3, then the formula V1 = V0 x R4 / (R3 + R4) holds. By substituting each value into this formula, the resistance value R4 of the standard resistor 42 is calculated.

The measurement result calculated in the process of S17 is sent to the external control device 26 in the process of S18, with the standard resistor 42 as the measurement target. The external control device 26 compares the resistance value R4 calculated by the application-type measuring device 30 with the original resistance value of the standard resistor 42 that is determined in advance, and if the two are almost identical, it can be determined that the application-type measuring device 30 is operating normally.

In addition, a signal for calibrating the application-type measuring instrument 30 can be sent from the external control device 26 to the application-type measuring instrument 30 so that the resistance value R4 calculated by the application-type measuring instrument 30 approaches the predetermined resistance value of the standard resistor 42. Note that these normal operation and calibration judgments may be performed by the application-type measuring instrument 30 instead of the external control device 26.

After processing S18 when n=3, switch SW3 is opened in processing S19, and processing S20 to S23 is executed. In processing S23, n=4 due to the immediately preceding processing in S22 (S23: Yes), and all measurements have been completed, so the periodic measurement processing ends.

In addition, regardless of the value of n, if the measurement unit 37 detects a voltage in the process of S20 (S20: No), it can be determined that the switch SWn instructed to open in the process of S19 did not actually open due to welding or the like. In this case, error information that the switch SWn did not open is sent to the external control device 26 (S24), the voltage application by the voltage application unit 38 is terminated (S25), and the periodic measurement process is terminated.

For example, if switch SW1 does not open due to welding, causing an error, and the periodic measurement process is not terminated, and the process from S12 onwards is executed again to close switch SW2 to measure the insulation resistance of measurement object b, measurement object a and measurement object b will be connected. If three-phase power is supplied in this state or voltage is applied by voltage application unit 38, the application-type measuring instrument 30 and each part of measurement objects a and b may be damaged by the unintended voltage.

In contrast, if an error occurs in the process of S20 in which a voltage is detected (S20: No), the periodic measurement process is terminated, thereby preventing multiple measurement objects a and b from being connected to each other via the switching unit 39. As a result, the possibility of the application-type measuring device 30 or each part of the measurement objects a and b being damaged by an unintended voltage can be reduced.

Furthermore, the periodic measurement process may be controlled not to be executed until the error is resolved. This further reduces the possibility that the application-type measuring device 30 or each part of the measurement objects a and b will be damaged by an unintended voltage.

With reference to FIG. 4, the analysis performed by the external control device 26 on the measurement results of the insulation resistance of the measurement object a by the application-type measuring instrument 30 will be described. Note that the same analysis is also performed on the measurement results of the insulation resistance of the measurement object b.

As shown in Figure 4, the external control device 26 generates and displays a graph for the measurement object a with past insulation resistance measurement results on the vertical axis and date and time on the horizontal axis. In the graph in Figure 4, the solid line shows the change over time of the past measurement results (actual values), and the two-dot chain line shows the change over time of future measurement results (predicted values) as an extension of a straight line that approximates the actual measurement values using the least squares method. The graph in Figure 4 also shows the threshold value at which insulation resistance degradation is suspected with a dashed line.

When the past measurement result is below the threshold value, the external control device 26 notifies the administrator of the external control device 26 that the insulation resistance of the measurement object a is suspected to have deteriorated. At this time, the worker or operator who operates the load device 14 may be notified. When measuring the insulation resistance with the application type measuring device 30, the temperature and humidity at the time of measurement may also be obtained, and the insulation resistance may be corrected or the threshold value may be changed based on this information.

In the external control device 26, the date and time when the future measurement result will be below the threshold is predicted based on the change over time of the future measurement result (predicted value) and the threshold, and the date and time are displayed in the graph of FIG. 4. Therefore, the administrator of the external control device 26 can plan a schedule for maintenance of the measurement object a based on the date and time when the future measurement result will be below the threshold, and can also plan the ordering of equipment or parts that need to be replaced.

Returning to FIG. 1, the leakage current measuring devices 50a and 50b will now be described. The leakage current measuring devices 50a and 50b are devices that automatically and periodically measure the leakage current that occurs in the AC power lines 11-13 and the load equipment 14 (objects to be measured) when three-phase power is being supplied through the AC power lines 11-13 and the load equipment 14 is operating.

The earth leakage measuring instrument 50a includes a current transformer 57a through which a set of intermediate wires 11b-13b pass together, and a reference detection unit 58a that measures the voltage and phase occurring between the intermediate wires 11b and 12b. Similarly, the earth leakage measuring instrument 50b includes a current transformer 57b through which a set of downstream wires 11c-13c pass together, and a reference detection unit 58b that measures the voltage and phase occurring between the downstream wires 11c and 12c. The power that operates the earth leakage measuring instruments 50a and 50b may be supplied from the AC electric wires 11-13 via an electric wire not shown, or may be supplied from an electric wire other than the AC electric wires 11-13.

Note that the earth leakage measuring instruments 50a and 50b are configured in substantially the same manner, except for their different positions. Hereinafter, when the earth leakage measuring instruments 50a and 50b are described without distinction, they will be referred to as earth leakage measuring instruments 50. Similarly, when the current transformers 57a and 57b and the reference detection units 58a and 58b possessed by the earth leakage measuring instruments 50a and 50b are described without distinction, they will be referred to as current transformer 57 and reference detection unit 58, respectively. These are the same in the embodiments described below.

Current transformer 57 is a current measuring device formed in a ring shape so that the electric wire to be measured passes through it, and measures the current flowing through the electric wire at the pass-through portion. More specifically, current transformer 57 measures the magnetic field generated at the pass-through portion of the electric wire by the passage of current, and measures (calculates) the value of the current based on that magnetic field. Current transformer 57a is a zero-phase current transformer that measures the total current flowing through a set of intermediate wires 11b-13b. Current transformer 57b is a zero-phase current transformer that measures the total current flowing through a set of downstream wires 11c-13c.

When three-phase power is supplied by the AC power lines 11-13, if no leakage current occurs downstream of the current transformer 57, the total current passing through the AC power lines 11-13 will basically be 0 A, and the measurement result of the current transformer 57 will also basically be 0 A. On the other hand, when three-phase power is supplied, if a leakage current occurs downstream of the current transformer 57, the current transformer 57 measures the total current excluding the leakage current. In other words, the current transformer 57 can measure the leakage current occurring downstream of its own installation position.

In addition, even if the AC electric wires 11 to 13 downstream of the current transformer 57 are insulated by the isolation transformers 21 and 22, the current transformer 57 can measure the leakage current occurring downstream of the isolation transformers 21 and 22. This makes it possible to calculate the leakage current occurring downstream of the current transformer 57a and upstream of the current transformer 57b from the difference between the measurement results of the current transformer 57a and the measurement results of the current transformer 57b.

The leakage current measured by the current transformer 57 includes the leakage current Igc caused by the capacitance to the ground, and the leakage current Igr caused by the insulation resistance to the ground, which is directly related to the insulation resistance of the object being measured. The leakage current Igc not only increases in capacity according to the length of the AC electric wires 11-13 of the object being measured, but also increases in capacity due to harmonic distortion currents caused by the inverters, noise filters, etc. used in the load equipment 14.

The reference detection unit 58 is a voltage probe that measures the voltage and phase of the AC electric wires 11 to 13 that are the measurement objects. In this embodiment, the reference detection unit 58 detects the voltage cross points between the AC electric wires 11 and 12, but since none of the AC electric wires 11 to 13 are connected to a ground part such as the ground wire 18, it is also possible to detect the voltage cross points between the AC electric wires 11 and 13 or between the AC electric wires 12 and 13.

The leakage current meter 50 calculates the leakage current Igr of the object to be measured from the measurement results of the current transformer 57 and the reference detection unit 58. The leakage current meter 50 is not limited to calculating the leakage current Igr as the measurement result, and may also calculate the insulation resistance value of the object to be measured based on the leakage current Igr as the measurement result. The leakage current Igr and insulation resistance can be calculated using a known method, such as the method disclosed in Patent Publication No. 4945727.

In addition, the leakage current meter 50 may also obtain the measurement results of the current transformer 57 and the reference detection unit 58 so that the external control device 26 can calculate the leakage current Igr. In this specification, when the leakage current meter 50 monitors the insulation resistance of the object to be measured, this includes the calculation of the insulation resistance value itself, the calculation of the leakage current Igr caused by that insulation resistance, and the acquisition of the measurement results of the current transformer 57 and the reference detection unit 58.

Next, the control of the earth leakage measuring instrument 50 will be described with reference to Figures 5(a) and 5(b). Figure 5(a) is a block diagram showing the electrical configuration of the earth leakage measuring instrument 50. Figure 5(b) is a flowchart of the earth leakage measuring process executed by the CPU 51 of the earth leakage measuring instrument 50.

The earth leakage measuring instrument 50 has a CPU 51, a flash ROM 52, and a RAM 53, which is a memory for rewritably storing various work data and flags when the CPU 51 executes a program, and these are each connected to an input/output port 55 via a bus line 54. The input/output port 55 is further connected to a communication device 56, a current transformer 57, and a reference detection unit 58, which are connected to an external control device 26.

The CPU 51 is a calculation device that controls each part connected by the bus line 54. The flash ROM 52 is a rewritable non-volatile memory that stores programs executed by the CPU 51, fixed value data, etc., and is provided with a leakage current monitoring program 52a. When the leakage current monitoring program 52a is executed by the CPU 51, the leakage current measurement process of FIG. 5(b) is executed.

This leakage current measurement process will be described with reference to FIG. 5(b). The leakage current measurement process is executed periodically (e.g., every second) while the leakage current measurement device 50 is powered on. The leakage current measurement process first checks whether the load device 14 is powered on (S31).

If the power supply of the load device 14 is off (S31: No), no current flows through the AC power lines 11-13 and no leakage current is occurring in the measurement target, so the leakage current measurement process ends without measuring the leakage current.

On the other hand, if the load device 14 is powered on (S31: Yes), measurements are performed using the current transformer 57 and the reference detection unit 58, and the leakage current Igr occurring in the measurement object is measured (calculated) from the measurement results (S32). Next, the measurement results of this leakage current Igr, the measurement object, and the date and time of measurement are transmitted to the external control device 26 (S33), and the leakage current measurement process is terminated.

The measurement object transmitted in the process of S33 is information that makes it possible to determine whether the measurement was performed by the earth leakage measuring instrument 50a or the earth leakage measuring instrument 50b. This allows the external control device 26 to analyze the locations where the insulation resistance of the measurement object has deteriorated based on the measurement results obtained from the earth leakage measuring instrument 50.

The external control device 26 also performs an analysis on the measurement results of the earth leakage measuring device 50 in the same manner as the analysis method for the measurement results of the application-type measuring device 30 described with reference to FIG. 4. Specifically, when the leakage current Igr of the measurement object exceeds a predetermined threshold, the external control device 26 notifies the administrator of the external control device 26 that the insulation resistance of the measurement object is suspected to have deteriorated. At this time, the worker or operator who operates the load device 14 may be notified. The external control device 26 also predicts the date and time when the leakage current Igr will exceed the predetermined threshold and notifies the administrator.

As described above, the insulation resistance monitoring device 20 can monitor the insulation resistance of the measurement object when three-phase power is being supplied using the leakage current meter 50, and can also monitor the insulation resistance of the measurement object even when three-phase power is not being supplied using the application-type meter 30. This makes it easier to identify areas of insulation resistance degradation, for example, by comparing the insulation resistance when three-phase power is not being supplied with the insulation resistance when it is being supplied.

Furthermore, the insulation resistance monitoring device 20 can monitor the insulation resistance of the object being measured when three-phase power is being supplied using both the application-type measuring instrument 30 and the earth leakage measuring instrument 50. Since the measurement methods of the application-type measuring instrument 30 and the earth leakage measuring instrument 50 are different, it is easy to identify the location of deterioration in the insulation resistance by comparing the measurement results of both instruments.

Next, the second embodiment will be described with reference to Figures 6 to 8. In the first embodiment, the case where the downstream side of the isolation transformer 22 is not grounded to type B was described. In contrast, in the second embodiment, the case where the downstream side of the isolation transformer 22 is grounded to type B was described. Note that the same parts as in the first embodiment are given the same reference numerals and the following description will be omitted.

Figure 6 is a circuit diagram showing a schematic diagram of an insulation resistance monitoring device 60 and an electric circuit of an object to be measured in the second embodiment. The object to be measured in the second embodiment includes a set of three AC electric wires 11-13 constituting a three-phase three-wire AC circuit, and load devices 14, 15 connected to the set of three AC electric wires 11-13, respectively.

Of the set of AC electric wires 11-13, the set of downstream wires connected to the secondary winding 22b of the isolation transformer 22 includes a set of main electric wires 11c1, 12c1, 13c1 extending from the secondary winding 22b, and two sets of branch electric wires 11c2, 12c2, 13c2, 11c3, 12c3, 13c3 branching off from the set of main electric wires 11c1-13c1. The set of branch electric wires 11c2-13c2 is directly connected to the load device 14. The set of branch electric wires 11c3-13c3 is connected to the load device 15 via the isolation transformer 16.

The load device 15 is an electric circuit that operates with three-phase power supplied from the branch electric wires 11c3 to 13c3. An example of the load device 15 is a three-phase induction motor. The load device 15 is housed in a housing 15a that is grounded to type D via a grounding wire 18. An isolation transformer 16 is built into this housing 15a.

The isolation transformer 16 includes a primary winding 16a connected to each of the branch electric wires 11c3 to 13c3, a secondary winding 16b connected to the load device 15, an iron core (not shown) around which the primary winding 16a and secondary winding 16b are wound, and a housing 16c that houses the primary winding 16a, the secondary winding 16b, and the iron core.

The isolation transformer 16 transmits three-phase power from the branch electric wires 11c3-13c3 to the load device 15 by electromagnetic induction while insulating the branch electric wires 11c3-13c3 from the load device 15. In addition, the housing 16c of the isolation transformer 16 is connected to the housing 15a of the load device 15 and is grounded in order to allow leakage currents generated within the isolation transformer 16 to escape to the ground.

The insulation resistance monitoring device 60 includes an insulation transformer 22, a class B grounding wire 66 that connects the downstream side of the insulation transformer 22 to class B ground, an electromagnetic switch 67 provided on the class B grounding wire 66, a combined resistance unit 24, an application-type measuring instrument 61 connected between the combined resistance unit 24 and the grounding wire 18, and a leakage current measuring instrument 63 placed on the main electric wires 11c1 to 13c1 downstream of the insulation transformer 22.

The B-class ground wire 66 is an electric wire that branches off from the main electric wire 13c1 near the isolation transformer 22 and is connected to the ground wire 18 of the housing 22c of the isolation transformer 22. This provides a B-class ground for the downstream side of the isolation transformer 22. Note that the B-class ground wire 66 may also be directly connected to the earth to ground the main electric wire 13c1.

The electromagnetic switch 67 is a normally closed type switch that opens and closes the B-class grounding wire 66. When the electromagnetic switch 67 is not energized, the electromagnetic switch 67 closes (energizes) the B-class grounding wire 66 to ground the main electric wire 13c1, and when the electromagnetic switch 67 is energized, it opens (cuts off) the B-class grounding wire 66 to switch the main electric wire 13c1 to an ungrounded state.

The application type measuring instrument 61 applies a voltage between terminal a and terminal E, and measures a voltage corresponding to the insulation resistance of the measurement object connected to terminal a. A set of main wires 11c1-13c1 is connected to terminal a of the application type measuring instrument 61 via a combined resistance unit 24. Furthermore, the secondary winding 22b and branch wires 11c2-13c2, 11c3-13c3 are connected to the main wires 11c1-13c1, and the load device 14 is connected to the branch wires 11c2-13c2. Thus, the application type measuring instrument 61 can monitor the insulation resistance of the secondary winding 22b, main wires 11c1-13c1, branch wires 11c2-13c2, 11c3-13c3, load device 14, and primary winding 16a.

Note that because the branch electric wires 11c3-13c3 and the load device 15 are insulated by the isolation transformer 16, the application-type measuring instrument 61 cannot monitor the insulation resistance of the load device 15. In other words, the application-type measuring instrument 61 can monitor the insulation resistance of the measurement object downstream of the isolation transformer 22, excluding the load device 15.

The leakage current measuring device 63 includes a current transformer 57c through which a set of main electric wires 11c1 to 13c1 pass, and a reference detection unit 58c that measures the voltage and phase generated between the main electric wires 11c1 and 12c1. The main electric wire 13c1 downstream of the position where the B-class grounding wire 66 branches off from the main electric wire 13c1 passes through the current transformer 57c.

In addition, as explained in the first embodiment, even if the AC electric wires 11 to 13 (branch electric wires 11c3 to 13c3) downstream of the position of the current transformer 57c are insulated by the isolation transformer 16, the leakage current generated in the load device 15 downstream of the isolation transformer 16 can be measured by the current transformer 57c.

Furthermore, the current transformer 57c is penetrated by the trunk wires 11c1-13c1 before they branch into the branch wires 11c2-13c2 on the load device 14 side and the branch wires 11c3-13c3 on the load device 15 side. As a result, the leakage current meter 63 can easily measure the total leakage current of the load devices 14 and 15.

As shown in FIG. 7, the application type measuring instrument 61 differs from the application type measuring instrument 30 (see FIG. 2) in the first embodiment in that the switching unit 39 and terminal b are omitted, and terminal a is directly connected to the measuring unit 37 and reference resistor 40. Furthermore, the flash ROM 32 of the application type measuring instrument 61 is provided with an application monitoring program 62 that is different from that in the first embodiment. The rest of the configuration of the application type measuring instrument 61 is the same as that of the application type measuring instrument 30 in the first embodiment.

Furthermore, the flash ROM 52 of the leakage current meter 63 is provided with a leakage current monitoring program 64 that is different from the leakage current monitoring program 52a in the leakage current meter 50 of the first embodiment. The rest of the configuration of the leakage current meter 63 is the same as that of the leakage current meter 50 of the first embodiment.

The external control device 26 is connected to an application type measuring device 61, a leakage current measuring device 63, load devices 14 and 15, and an electromagnetic switch 67. The external control device 26 transmits the operating states of the load devices 14 and 15 and the open/closed state of the electromagnetic switch 67 to the application type measuring device 61 and the leakage current measuring device 63, and transmits a switching signal from the application type measuring device 61 to the electromagnetic switch 67.

Next, referring to FIG. 8(a), the process when the application monitoring program 62 is executed by the CPU 31 of the application-type measuring instrument 61 will be described. FIG. 8(a) is a flowchart of the periodic measurement process executed by the CPU 31 by the application monitoring program 62. The periodic measurement process of the application-type measuring instrument 61 is executed periodically (e.g., every 10 minutes) while the power of the application-type measuring instrument 61 is turned on.

The periodic measurement process of the application-type measuring instrument 61 first checks whether the power to the load devices 14, 15 is off to determine whether the electromagnetic switch 67 can be opened (S41). If the electromagnetic switch 67 is opened to unground the main electric wire 13c1 when the power to the load devices 14, 15 is on, for example, noise generated when the load devices 14, 15 are operating cannot be dissipated to the ground from the class B grounding wire 66, and the load devices 14, 15 may malfunction.

When the power supply of the load devices 14, 15 is off (S41: Yes), opening the electromagnetic contactor 67 will not cause the load devices 14, 15 to malfunction, so the electromagnetic contactor 67 is opened (S42). Specifically, in the process of S42, a signal to open the electromagnetic contactor 67 is sent to the electromagnetic contactor 67 via the external control device 26, and the electromagnetic contactor 67 opens when it receives the signal.

After the process of S42, the processes of S13, S14, S16, S18, and S21 are executed as in the first embodiment, and the insulation resistance of the measurement object connected to terminal a is calculated and transmitted to the external control device 26. Next, the electromagnetic switch 67 is closed to ground the main electric wire 13c1 again (S43) so that the load devices 14, 15 will operate normally when the power is turned on, and the regular measurement process is terminated.

On the other hand, in the process of S41, if the power supply of the load devices 14, 15 is on (S41: No), the electromagnetic switch 67 is left closed to prevent malfunction of the load devices 14, 15 when the electromagnetic switch 67 is opened, and the periodic measurement process is terminated. If a voltage is applied to the ground wire 18 by the voltage application unit 38 with the electromagnetic switch 67 closed, a current corresponding to that voltage flows directly from the ground wire 18 and the B-class ground wire 66 to the main wire 13c1 without passing through the insulation resistance, and that current is input to the measurement unit 37. In this case, there is a risk that the insulation resistance of the measurement object cannot be accurately measured from the measurement result of the measurement unit 37.

In contrast, the application-type meter 61 measures the voltage using the measurement unit 37 with the electromagnetic switch 67 open and without supplying three-phase power to the load devices 14 and 15, so that the measurement unit 37 can accurately measure a voltage corresponding to the insulation resistance of the object being measured. As a result, the application-type meter 61 can accurately calculate the insulation resistance of the object being measured from the measurement results of the measurement unit 37.

Next, referring to FIG. 8(b), the process when the leakage current monitoring program 64 is executed by the CPU 51 of the leakage current meter 63 will be described. FIG. 8(b) is a flowchart of the leakage current measurement process executed by the CPU 51 by the leakage current monitoring program 64. The leakage current measurement process of the leakage current meter 63 is executed periodically (e.g., every second) while the power of the leakage current meter 63 is turned on.

As in the first embodiment, the leakage current measurement process first checks whether the load devices 14, 15 are powered on (S31). If the load devices 14, 15 are powered on (S31: Yes), it checks whether the electromagnetic switch 67 is closed (S52).

Basically, when the load devices 14, 15 are powered on, the electromagnetic switch 67 is closed to operate the load devices 14, 15 normally. Therefore, if the electromagnetic switch 67 is open when the load devices 14, 15 are powered on (S31: Yes, S52: No), an error has occurred, and the leakage current measurement process is terminated without measuring the leakage current.

On the other hand, if the electromagnetic switch 67 is closed in the process of S52 (S52: Yes), the electromagnetic switch 67 is operating normally, so the leakage current Igr occurring in the measurement object is measured (calculated) (S32). Next, the measurement result of this leakage current Igr, the measurement object, and the date and time of measurement are transmitted to the external control device 26 (S33), and the leakage current measurement process is terminated.

When the electromagnetic switch 67 is closed, leakage current generated in the object to be measured when three-phase power is supplied is more likely to return to the main wire 13c1 through the ground wire 18 and the class B ground wire 66. Furthermore, because the main wire 13c1 upstream of the current transformer 57c is connected to the class B ground wire 66, leakage current passing through the class B ground wire 66 is more likely to bypass the current transformer 57c. As a result, the leakage current meter 63 can more accurately measure the leakage current of the object to be measured when three-phase power is supplied.

Next, the third embodiment will be described with reference to FIG. 9. In the second embodiment, a leakage current meter 63 having a current transformer 57c through which a set of main electric wires 11c1-13c1 passes was described. In contrast, in the third embodiment, a leakage current meter 71 having a current transformer 57d through which a set of branch electric wires 11c2-13c2 passes, and a leakage current meter 72 having a current transformer 57e through which a class B ground wire 66 passes will be described. Note that the same parts as in the first and second embodiments are given the same reference numerals and the following description will be omitted.

Figure 9 is a circuit diagram that shows a schematic of the electrical circuit of the insulation resistance monitoring device 70 and the object to be measured in the third embodiment. The object to be measured in the third embodiment is the same as the object to be measured in the second embodiment.

The insulation resistance monitoring device 70 includes an insulation transformer 22, a class B ground wire 66, an electromagnetic switch 67, a composite resistor unit 24, an application-type meter 61, a leakage current meter 71 disposed on the branch electric wires 11c2 to 13c2, and a leakage current meter 72 disposed on the class B ground wire 66. The leakage current meter 71, 72 measure (calculate) the leakage current of the measurement object in the same manner as in the second embodiment, as shown in FIG. 8(b).

The leakage current measuring device 71 includes a current transformer 57d through which a set of branch electric wires 11c2-13c2 pass together, and a reference detection unit 58d that measures the voltage and phase generated between the branch electric wires 11c2, 12c2. This allows the leakage current measuring device 71 to measure (calculate) the leakage current of the load device 14 connected to the branch electric wires 11c2-13c2 without being affected by the leakage current of the load device 15 connected to the other branch electric wires 11c3-13c3.

When the electromagnetic switch 67 is closed, leakage current generated in the object to be measured when three-phase power is supplied tends to return to the main power line 13c1 from the Class B ground wire 66. The leakage current measuring instrument 72 is equipped with a current transformer 57e through which the Class B ground wire 66 passes. Therefore, the leakage current measuring instrument 72 can measure the leakage current generated in the object to be measured when three-phase power is supplied using the current transformer 57e.

Incidentally, since the leakage current meter 72 does not have a reference detection unit 58, it is not possible to calculate the leakage current Igr from the measurement results of the current transformer 57e. However, since it is only necessary to pass one Class B ground wire 66 through the current transformer 57e, there is no need to use a current transformer of a size or special shape to pass multiple electric wires together. This makes it easy to install the leakage current meter 72 on the object to be measured, and also makes it easier to reduce the manufacturing costs of the leakage current meter 72.

Next, a fourth embodiment will be described with reference to Figures 10 and 11. In the first to third embodiments, the insulation resistance monitoring devices 20, 60, and 70 that monitor the insulation resistance of a measurement object including three-phase three-wire AC electric wires 11 to 13 have been described. In contrast, in the fourth embodiment, an insulation resistance monitoring device 90 that monitors the insulation resistance of a measurement object that supplies DC power from a battery 81 to a load device 86 will be described. Note that the same parts as those in the first to third embodiments are given the same reference numerals and the following description will be omitted.

Figure 10 is a circuit diagram showing a schematic diagram of an insulation resistance monitoring device 90 and an electric circuit of a measurement object in the fourth embodiment. The measurement object in the fourth embodiment includes a battery 81 that outputs DC power (load power), a positive electrode line 84 connected to the positive electrode of the battery 81, a negative electrode line 85 connected to the negative electrode of the battery 81, and a load device 86 that operates with DC power supplied from the battery 81 via the positive electrode line 84 and the negative electrode line 85. Examples of the measurement object include automobiles, industrial vehicles, railroad vehicles, aircraft, ships, and other electric equipment that are driven by electricity.

The battery 81 is a power source that outputs DC power of a predetermined voltage (e.g., about 400 V) and has an internal resistance 82. However, the resistance value of this internal resistance 82 is low enough to allow the battery 81 to be considered a conductor similar to an electric wire, relative to the insulation resistance of the object being measured.

The positive and negative wires 84 and 85 are a pair of power lines for supplying DC power from the upstream battery 81 to the downstream load device 86. The load device 86 is an electric circuit that operates using that DC power. The load device 86 is housed in a housing 86a that is grounded to type D via a ground wire 18. When the measurement target is a vehicle or the like, the term "grounding" refers to connecting to a large conductor such as the frame of the vehicle, and the large conductor does not necessarily have to be connected to the earth.

The insulation resistance monitoring device 90 includes an application-type measuring instrument 30 connected between the negative electrode wire 85 and the ground wire 18, and a leakage current measuring instrument 92 that measures the leakage current of the load device 86. Terminal E of the application-type measuring instrument 30 is connected to the ground wire 18, and terminal a is connected only to the negative electrode wire 85. The application-type measuring instrument 30 applies a voltage between terminal E and terminal a, measures a voltage corresponding to the insulation resistance of the measurement object connected to terminal a, and calculates the insulation resistance from the voltage.

As described above, the battery 81 is considered to be a low-resistance conductor, so the application-type measuring instrument 30 can measure a voltage corresponding to the insulation resistance of the positive wire 84 as well as the negative wire 85, the battery 81, and the load device 86 among the measurement objects, even if terminal a is not directly connected to the positive wire 84. Therefore, the insulation resistance monitoring device 90 can monitor the insulation resistance of the positive wire 84, the negative wire 85, the battery 81, and the load device 86 based on the measurement results of the application-type measuring instrument 30.

In addition, the potential of the negative wire 85 relative to the ground wire 18 is close to 0V regardless of whether the two are connected or not. Therefore, even while DC power is being supplied from the battery 81 to the load device 86, it is possible to prevent the current and voltage based on that DC power from being input from the negative wire 85 to the application-type meter 30. As a result, it is possible to eliminate the need to disconnect the application-type meter 30 from the negative wire 85 when DC power is being supplied from the battery 81, and to eliminate the need for an electromagnetic switch for connecting and disconnecting it. Therefore, the application-type meter 30 can be left connected to the negative wire 85 even when DC power is being supplied.

In some cases, the negative wire 85 is connected to a grounding portion such as the ground wire 18 or the vehicle frame to prevent noise from the load device 86, but in this embodiment, the negative wire 85 is kept disconnected from the ground wire 18. This makes it possible to eliminate the need for a task or process (such as opening and closing the electromagnetic switch 67 as in the second embodiment) to disconnect the negative wire 85 from the ground wire 18 when making measurements using the application-type measuring instrument 30. This simplifies measurements using the application-type measuring instrument 30.

Furthermore, since there is no need to disconnect the negative wire 85 from the ground wire 18 when making measurements with the application-type measuring instrument 30, there is no need to stop the supply of DC power through the negative wire 85 and the positive wire 84. In addition, since it is difficult for a current or voltage based on DC power to be input to the application-type measuring instrument 30 connected to the negative wire 85, even when the load device 86 is operating with DC power, the application-type measuring instrument 30 can measure a voltage corresponding to the insulation resistance of the object being measured while suppressing the effect of DC power on the measurement results. Therefore, the insulation resistance monitoring device 90 can accurately monitor the insulation resistance of the object being measured even when the load device 86 is operating.

The leakage current meter 92 is a device that automatically and periodically measures leakage current that occurs in the load device 86 and a part of the positive and negative wires 84 and 85 of the measurement object when DC power is supplied from the battery 81 to the load device 86. The leakage current meter 92 includes a current transformer 93 through which the positive wire 84 passes, a current transformer 94 through which the negative wire 85 passes, and a reference detection unit 95 that measures the potential difference between the positive wire 84 and the negative wire 85 (the voltage of the battery 81).

Current transformers 93 and 94 are current measuring devices formed in a ring shape so that the electric wire to be measured passes through them, and measure the current flowing through the electric wire at the pass-through portion. Current transformers 93 and 94 are configured to be able to measure DC current, but as their configuration is known, a description of this configuration is omitted. Reference detection unit 95 is a known voltmeter.

A method of monitoring leakage current using such a leakage current meter 92 will be described with reference to FIG. 10 and FIG. 11. FIG. 11(a) is a graph showing the change over time in the current value A1 of the positive electrode line 84 measured by the current transformer 93 and the current value A2 of the negative electrode line 85 measured by the current transformer 94. FIG. 11(b) is a graph showing the change over time in the value of the leakage current flowing from the load device 86 through the housing 86a to the ground wire 18.

The vertical axis of the graphs in both Fig. 11(a) and Fig. 11(b) is the current value [A]. The horizontal axis of the graphs in both Fig. 11(a) and Fig. 11(b) is the time [s]. Note that current value A1 is a positive value and current value A2 is a negative value, but Fig. 11(a) shows their absolute values.

In addition, in the graph of FIG. 11(a), the change over time of the current value A1 of the current transformer 93 is shown by a solid line, and the change over time of the current value A2 of the current transformer 94 is shown by a dashed line. Note that in FIG. 11(a), the solid and dashed lines are slightly shifted in the overlapping portions in order to make the graph easier to read.

When no leakage current is occurring in the load device 86, essentially all of the current that passed through the current transformer 93 (positive pole wire 84) passes through the current transformer 94 (negative pole wire 85). Therefore, during the time when no leakage current is occurring, the current values A1 and A2 of the current transformers 93 and 94 are the same in the graph of FIG. 11(a), and the leakage current value is 0 A in the graph of FIG. 11(b).

On the other hand, if leakage current occurs from the load device 86 to the ground wire 18, for example, the leakage current returns from the housing of the battery 81 to the inside of the battery 81, bypassing the current transformer 94. In other words, the current that passes through the current transformer 93 is divided into a normal route that passes through the current transformer 94 and a leakage current route that does not pass through the current transformer 94.

Therefore, at the time when leakage current occurs in load device 86, in the graph of FIG. 11(a), the current value A2 of current transformer 94 is lower than the current value A1 of current transformer 93, and in the graph of FIG. 11(b), the sum of these current values A1 and A2 (the difference between the absolute values of current values A1 and A2) is shown as the leakage current value. In this way, leakage current meter 92 can calculate the leakage current occurring in the measurement object downstream of current transformers 93 and 94 (on the load device 86 side) when DC power is supplied from battery 81.

Note that the voltage of the DC power output from the battery 81, that is, the potential difference between the positive electrode wire 84 and the negative electrode wire 85 (the potential difference measured by the reference detection unit 95) may fluctuate due to various factors. As shown in FIG. 11(a), the current values A1 and A2 of the current transformers 93 and 94 fluctuate in inverse proportion to this potential difference. In FIG. 11(a), the potential difference at the time the current value was obtained is shown above the graph of the current value.

In addition, since the leakage current, which is the sum of the current values A1 and A2, also varies inversely proportional to the potential difference, the graph in FIG. 11(b) shows the corrected (converted) leakage current value when the potential difference is 400V. Specifically, when the potential difference is 400V, the sum of the current values A1 and A2 is used as is as the corrected leakage current value. When the potential difference is 430V, the sum of the current values A1 and A2 is multiplied by 1.075 to obtain the corrected leakage current value. When the potential difference is 380V, the sum of the current values A1 and A2 is multiplied by approximately 0.95 to obtain the corrected leakage current value.

In this way, the leakage current meter 92 can more accurately calculate the leakage current that occurs according to the insulation resistance of the object being measured when DC power is supplied from the battery 81. Therefore, the insulation resistance monitoring device 90 can monitor the insulation resistance of the object being measured when DC power is supplied using the leakage current meter 92.

The control method of the leakage current meter 92 is substantially the same as the control method of the leakage current meter 50 of the first embodiment described with reference to FIG. 5(b), and during processing of S32, the current values A1 and A2 and the potential difference are measured, and the corrected leakage current value is calculated from them. The calculation of the insulation resistance based on this leakage current value may be performed by the leakage current meter 92, or may be performed by the external control device 26. Furthermore, the leakage current meter 92 may measure the current values A1 and A2, and the calculation of the leakage current may be performed by the external control device 26.

Although the present invention has been described above based on the embodiments, the present invention is not limited to the above-mentioned embodiments, and it can be easily assumed that various improvements and modifications are possible within the scope of the present invention. For example, the voltage applied by the voltage application unit 38, the magnitude of the output voltage of the battery 81, the intervals at which the periodic measurement process and the leakage measurement process are performed, the number of load devices 14, 15, and 86, etc. may be changed as appropriate.

In addition, the external control device 26 may be omitted, and the control performed by the external control device 26 may be performed by the voltage application type measuring device 30, 61 or the earth leakage measuring device 50a, 50b, 63, 71, 72, 92.In addition, either the voltage application type measuring device 30, 61 or the earth leakage measuring device 50a, 50b, 63, 71, 72, 92 may be omitted.

In the above embodiment, the application type measuring instruments 30 and 61 are described as generating a current according to the insulation resistance of the object to be measured by applying a voltage from the voltage application unit 38, and measuring the voltage converted from that current with the measurement unit 37. In contrast, the reference resistor 40 may be omitted and the measurement unit 37 may be an ammeter, so that the measurement unit 37 measures the current generated according to the insulation resistance of the object to be measured when the voltage is applied by the voltage application unit 38.

Furthermore, the present invention is not limited to the case where a positive voltage is applied from the voltage application unit 38 to the ground wire 18 via terminal E. For example, a positive voltage may be applied from the voltage application unit 38 to terminal a or b, and a current or voltage generated in response to the insulation resistance due to the application of the voltage may be input from terminal E to the application-type measuring instrument 30, 61. In this case, the current or voltage generated in response to the insulation resistance is measured by the measuring unit 37 connected to terminal E.

However, it is preferable to apply a positive voltage from the voltage application unit 38 to terminal E (ground wire 18). In this case, the insulation resistance measurement result is more likely to be lower than when a positive voltage is applied to terminals a and b, making it easier to determine the deterioration of the insulation resistance at an early stage.

In the first embodiment, the case where terminals a and b are connected to objects to be measured that are insulated from each other has been described. The number of terminals may be increased appropriately according to the number of objects to be measured that are insulated from each other, and the multiple terminals may be selectively connected to the measurement unit 37 and the reference resistor 40 by the switching unit 39. Furthermore, the switching unit 39 and multiple terminals may be applied to the second to fourth embodiments. Also, multiple voltage-type measuring instruments that omit the switching unit 39 and have only terminal a may be connected to multiple objects to be measured that are insulated from each other.

In the above embodiment, the insulating transformers 21, 22 are arranged in the AC electric wires 11 to 13, but these insulating transformers 21, 22 may be omitted. In this case, when monitoring the insulation resistance of a part of the AC electric wires 11 to 13 with the application-type measuring instruments 30, 61, it is sufficient to disconnect a part of the AC electric wires 11 to 13 from the other parts and to disconnect that part from the ground part such as the ground wire 18.

In addition, the combined resistance units 23 and 24 in the above embodiment may be omitted, and one of the AC electric wires 11 to 13 may be directly connected to the terminals a and b. In this case, however, it is preferable to provide switches SW1 and SW2 or an electromagnetic switch between the AC electric wires 11 to 13 in order to disconnect them from the measurement unit 37 when three-phase power is being supplied.

In the above embodiment, the leakage current measuring instruments 50a, 50b, 63, and 71 are described as calculating the leakage current Igr from the measurement results of the current transformer 57 and the reference detection unit 58. However, the reference detection unit 58 may be omitted, and the measurement results of the current transformer 57 may be used directly as the measurement results of the leakage current measuring instruments 50a, 50b, 63, and 71.

In addition, instead of the current transformers 57a, 57b, 57c, and 57d through which the set of three AC electric wires 11 to 13 pass together, three current transformers through which the three AC electric wires 11 to 13 pass individually and which measure the currents of the AC electric wires 11 to 13 individually may be provided in the leakage current measuring instruments 50a, 50b, 63, and 71. In this case, by summing up the measurement results of the three current transformers, the total current of the set of three AC electric wires 11 to 13, i.e., the same value as the measurement result by the current transformers 57a, 57b, 57c, and 57d, can be calculated.

In the fourth embodiment, the positive and negative wires 84 and 85 pass through the current transformers 93 and 94 individually. However, instead of the current transformers 93 and 94, a single current transformer through which a set of positive and negative wires 84 and 85 pass together may be provided. In this way, when a set of multiple electric wires passes through a current transformer together, the leakage current generated downstream of the current transformer can be easily measured. On the other hand, when a set of multiple electric wires passes through multiple current transformers individually, each current transformer can be made smaller, or a commercially available current transformer can be used.

In the third embodiment, a leakage current meter 71 having a current transformer 57d through which the branch electric wires 11c2 to 13c2 pass has been described, but a leakage current meter having a current transformer through which the branch electric wires 11c3 to 13c3 pass may also be provided. This leakage current meter can measure the leakage current of the load device 15.

In the above embodiment, the three AC electric wires 11 to 13 upstream of the connection position with the combined resistance units 23 and 24 pass through the current transformers 57a, 57b, and 57c. However, the three AC electric wires 11 to 13 downstream of the connection position with the combined resistance units 23 and 24 may pass through the current transformers 57a, 57b, and 57c. In either case, the current flowing between the AC electric wires 11 to 13 via the combined resistance units 23 and 24 does not bypass the current transformers 57a, 57b, and 57c, so that the current flowing through the combined resistance units 23 and 24 can be prevented from being measured by the current transformers 57a, 57b, and 57c together with the leakage current of the measurement object. In other words, the measurement accuracy of the leakage current of the measurement object by the current transformers 57a, 57b, and 57c can be improved.

Part of the configuration in the first to fourth embodiments may be applied to other embodiments. For example, the leakage current meter 63 of the second embodiment, which measures the leakage current generated in the load devices 14 and 15 together, and the leakage current meter 71, which measures the leakage current generated only in the load device 14, may be provided on the same measurement object. In this case, the leakage current of the load device 15 can be measured from the difference between the measurement result of the leakage current meter 63 and the measurement result of the leakage current meter 71.

In the second and third embodiments, the B-class ground wire 66 is branched off from the trunk wire 13c1. However, the B-class ground wire 66 may be branched off from the trunk wire 11c1 or the trunk wire 12c1. In addition, one of the intermediate wires 11b to 13b in the first embodiment, one of the downstream wires 11c to 13c, or the negative wire 85 in the fourth embodiment may be connected to the ground wire 18 by the B-class ground wire 66 in the second and third embodiments. In this case, the measurement is performed by the application-type measuring instrument 30 with the electromagnetic switch 67 provided on the B-class ground wire 66 open, and the measurement is performed by the leakage current measuring instruments 50a, 50b, and 92 with the electromagnetic switch 67 closed. Conversely, the B-class ground wire 66 may be omitted in the second and third embodiments.

In the above embodiment, the resistance value of the standard resistor 42 is measured by the application-type measuring instrument 30 to confirm the normal operation of the application-type measuring instrument 30. For purposes other than this confirmation of normal operation, the switch SW3 may be closed and each part of the measuring unit 37 and the switching unit 39 may be connected to the ground line 18 via the standard resistor 42. In this case, residual voltage and electrostatic capacitance parasitic in the application-type measuring instrument 30 can be discharged using the standard resistor 42.

In the above embodiment, the electromagnetic contactor 67 is a normally closed type contactor. However, a normally open type contactor that opens when de-energized and closes when energized may be used for the electromagnetic contactor 67. Also, a latch type contactor that maintains an open/closed state when de-energized and opens/closes in response to an electrical signal may be used for the electromagnetic contactor 67.

In the above embodiment, the current transformers 57a-57e, 93, and 94 are formed in a ring shape through which the electric wire to be measured passes, and are current measuring instruments that measure the value of the current flowing through the passed portion. However, these current transformers 57a-57e, 93, and 94 may be replaced with other current measuring instruments that can measure the value of the current flowing through the electric wire to be measured. An example of the other current measuring instruments is a non-ring type that measures the magnetic field generated in the electric wire when current is passed through it, and measures the value of the current based on that magnetic field. Another example of the other current measuring instruments is limited to those that measure the current of a single electric wire individually, and an example is one that uses a shunt resistor.

11, 12, 13 AC wire (power line)
11c1 to 13c1: main electric wire 11c2 to 13c2, 11c3 to 13c3: branch electric wire 14, 15, 86: load device 14a, 15a, 16c, 21c, 22c, 86a: housing (grounding part)
18 Ground wire (ground part)
20, 60, 70, 90 Insulation resistance monitor 21, 22 Isolation transformer (upstream transformer)
23a to 23c, 24a to 24c resistors 30, 61 application type measuring instrument 50a, 50b, 63, 71, 72, 92 earth leakage measuring instrument 57a to 57e, 93, 94 current transformer (current measuring instrument)
66 Class B grounding wire (grounding wire)
67 Electromagnetic switch 81 Battery 84 Positive wire (power supply wire)
85 Negative wire (power line)

Claims (8)

An insulation resistance monitoring device for monitoring insulation resistance between a grounded portion of a measurement object including a set of multiple power lines for supplying load power from upstream to downstream and a load device that operates by the load power supplied from the set of power lines, the device comprising:
an application-type measuring instrument connected to the power supply line and the ground portion, respectively;
a leakage current meter that monitors a leakage current that occurs in response to the insulation resistance of the measurement object when the load power is supplied,
the application-type measuring instrument applies a voltage between the power supply line and the ground in a state in which the object to be measured, including the power supply line, is disconnected from the ground except for the insulation resistance of the object to be measured and the connection to the ground via the application-type measuring instrument, thereby measuring a current generated in response to the insulation resistance of the object to be measured, or a voltage obtained by converting the current;
The insulation resistance monitoring device is characterized in that the leakage current meter includes a single current meter that collectively measures the magnetic fields generated in each of the multiple power lines of a set when power is supplied to the load and measures the total current flowing through those power lines based on the magnetic field, or a plurality of current meters that individually measure the current flowing through each of the multiple power lines of the set. The set of power supply lines is three AC electric wires constituting a three-phase three-wire electric circuit,
the insulation resistance monitoring device includes three resistors having the same resistance value, one end of which is connected individually to the three AC electric wires and the other end of which is combined together and connected to the application-type meter;
2. The insulation resistance monitoring device according to claim 1, wherein the voltage application type measuring instrument is connected to the AC electric line via the three resistors. The insulation resistance monitoring device according to claim 2, further comprising an upstream transformer that is arranged on the three AC electric wires upstream of the positions where the three resistors are connected at one end, and that transmits the load power from the upstream side to the downstream side by electromagnetic induction while insulating the AC electric wires upstream and downstream of the arrangement position. The set of power lines includes:
a positive pole line connected to a positive pole of a battery that outputs DC power as the load power;
a negative electrode wire connected to the negative electrode of the battery;
2. The insulation resistance monitoring device according to claim 1, wherein the voltage application type measuring instrument is not directly connected to the positive electrode line but is connected to the negative electrode line and the ground. a power supply line connected to the application-type measuring instrument, the power supply line being on an upstream side of a measurement position of the current measuring instrument, and an electromagnetic switch for opening and closing a grounding line connecting the power supply line and the grounding portion;
The application type measuring instrument measures a current or a voltage in a state where the electromagnetic switch is open,
5. The insulation resistance monitoring device according to claim 1, wherein the leakage current meter measures the current by the current meter with the electromagnetic switch closed. The set of power lines includes:
One upstream pair of main conductors;
and a plurality of sets of branch electric wires each branching off from the one set of trunk electric wires,
The load device is provided in plurality and connected to each of the sets of branch electric wires,
The insulation resistance monitoring device described in any one of claims 1 to 4, characterized in that the leakage current meter includes a main meter that monitors the total leakage current of the load devices connected to the multiple sets of branch wires by measuring the current flowing in the main wire upstream of the multiple sets of branch wires using the current meter. The set of power lines includes:
One upstream pair of main conductors;
and a plurality of sets of branch electric wires each branching off from the one set of trunk electric wires,
The load device is provided in plurality and connected to each of the sets of branch electric wires,
5. An insulation resistance monitoring device as described in any one of claims 1 to 4, characterized in that the leakage current meter comprises a branch meter that monitors the leakage current of the load equipment connected to a set of branch electric wires by measuring the current flowing through the set of branch electric wires using the current meter. An insulation resistance monitoring device for monitoring insulation resistance between a grounded portion of a measurement object including a set of multiple power lines for supplying load power from upstream to downstream and a load device that operates by the load power supplied from the set of power lines, the device comprising:
an electromagnetic switch that opens and closes a ground line that connects one of the power supply lines and the ground portion;
an application-type measuring instrument connected to the power supply line and the ground portion, respectively;
a leakage current measuring instrument having a current measuring instrument for measuring a current flowing through the ground wire, the leakage current being generated in response to the insulation resistance of the measurement object when the load power is supplied with the electromagnetic switch closed, and
Equipped with
The insulation resistance monitoring device is characterized in that the application-type measuring instrument applies a voltage between the power line and the ground through the insulation resistance of the object to be measured with the electromagnetic contactor open, and measures a current generated in response to the insulation resistance of the object to be measured, or a voltage converted from that current .

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