JP4142137B2 - Measuring device of ground fault resistance and ground fault voltage in DC circuit - Google Patents

Description

[0001]
[Industrial application fields]
A measuring device used in DC circuits used in power plants, substations, plant factories, etc., to measure ground fault resistance and ground fault voltage in the event of a ground fault caused by insulation deterioration of control equipment, alarms and display devices, etc. About. In addition to the ground fault resistance and ground fault voltage, the measuring device obtains values representing ground fault conditions in the electric circuit, such as P-pole ground fault resistance, N-pole ground fault resistance, and ground fault rate , by calculation. . Therefore, this measuring apparatus can also measure a ground fault voltage when a ground fault occurs in a part of the solar cell.
[0002]
[Prior art]
As a prior art, there is a patent application number Japanese Patent Application No. 1-319855 “display device for ground fault resistance of a DC circuit”. With this technique, it is possible to measure a value such as a ground fault resistance in a DC circuit.
[0003]
[Problems to be solved by the invention]
However, the conventional method has the following two drawbacks.
[0004]
The first drawback is that when a ground fault occurs in the coil circuit of the control relay used in the load circuit of the DC circuit, the ground fault current is, for example, the P pole, the control relay coil, the ground fault point, and the 64D ground. Wire, 64D, N pole, then the ground wire switches from 64D to the measuring instrument and flows through P pole, the control relay coil, ground fault point, measuring instrument grounding line, measuring instrument, N pole, ground fault current When is large, there is a risk that the control relay operates (malfunctions) and an unexpected accident occurs.
[0005]
The second disadvantage is that it takes a long time to measure because the measurement accuracy is improved by switching the internal resistance twice to cope with the case where the capacitance of the DC circuit is large. The measuring instrument of Kohei 1-319855 required about 2 minutes for one measurement.
[0006]
OBJECT OF THE INVENTION
Among the first disadvantages, the malfunction of the control relay via 64D is considered separately as another problem. In the present invention, when a ground fault occurs and the ground line is switched from 64D to a measuring instrument. The first object is to prevent the control relay from malfunctioning, and the second object is to shorten the measurement time of ground fault resistance and ground fault voltage.
[0007]
[Means and means for achieving the object]
Connected to the positive electrode P / negative electrode N and ground electrode E of a DC circuit (generally not grounded except at 64D described later), and the ground fault point when the negative electrode N in the DC circuit is used as a reference When the voltage is the ground fault voltage and the ground fault resistance in the DC circuit is the ground fault resistance, the internal resistances between PE and EM in the measurement circuit for measuring the ground fault resistance and the ground fault voltage are the same ( when a ground fault in the path in a state where the midpoint grounded) is not occurred, the measured value of the "normal measurement" for measuring the ground resistance and ground voltage as the first data, land絡側(e.g. P side is In case of ground fault , measure the ground fault resistance and ground fault voltage in a state where the internal resistance between PE is smaller than the internal resistance on the non-ground fault side (between E and N in the above example). ”As the second data, and“ detailed measurement ”from the first data and the second data. In the measurement apparatus of the ground-fault resistance and ground voltage calculating the measured value, the internal resistance of the positive electrode P and a negative electrode N resistance of 64D between P over E and between E over N in "Normal measurement" (64D of P-E And the resistance on the non-grounded side in the “secondary measurement” (in this example, the internal resistance between E and N of the measuring device) is the internal resistance of 64D (in the above example). becomes smaller than when the ground fault current is through the 64D by the internal resistance) or more values between E-N of 64D, for example, the control even if the earth絡点was the control relay circuit the first object without use relay operates (malfunction) can be achieved. In addition, when the above-mentioned measuring device for ground fault resistance and ground fault voltage receives a “detailed measurement” command, When the data in the “normal measurement” has not yet reached a stable state, such as when the measurement device starts, “secondary measurement” is performed by switching the internal resistance to the measurement data when the data is stable. 1. “Detailed measurement” is performed with the measurement data obtained when the data at 1 reaches a stable state as another data. When the data of “Normal measurement” has reached a stable state, such as when the measurement device has been operating for a long time, the measurement data at that time is taken as one data, and “Secondary measurement” is performed by switching the internal resistance. 2. Perform “detailed measurement” by using the measurement data when the data in (2) reach a stable state as another data. When “secondary measurement” is performed immediately before the command, the measurement data from the “secondary measurement” performed immediately before is regarded as one data, and the data after “command” is stabilized. If the “detailed measurement” is performed by using the data at the time of arrival as another data, unnecessary measurement is not performed, so that the measurement time is shortened and the second object can be achieved.
[0008]
[Explanation of Examples]
Since the 鳳 -Thevenin theorem is used to describe the present invention, the 鳳 -Thevenin theorem is illustrated in FIG. In FIG. 1, the circuit connected to V1 by R1 and connected to V2 by R2 is a circuit in which R3 = R1 * R2 / (R1 + R2) is connected to V4 = (V1 * R2 + V2 * R1) / (R1 + R2). equal. In FIG. 2 and FIG. 3, it is assumed that V22 is a ground fault pole and V21 is a non-ground fault pole. V25 corresponds to V22 when a unipolar ground fault occurs. When the ground fault of V22 is the main ground fault due to the bipolar ground fault, the voltage is closer to V22 than V21. When a unipolar ground fault occurs, R25 is a ground fault resistance. In the case of a bipolar ground fault, R25 is a composite ground fault resistance.
[0009]
First, when the internal resistance of each pole of the device of the present invention is the same as the internal resistance of each pole of 64D (DC ground fault relay) in “normal measurement”, even if the device of 64D is replaced with the device of the present invention electrically Since there is no difference, the ground fault current is the same.
[0010]
A case where the internal resistance of each pole of the device of the present invention is set larger than the internal resistance of each pole of 64D in “normal measurement” will be described with reference to FIG. In FIG. 2, when R21 = R22, V24 = (V21 + V22) / 2, which is the same in 64D and the device of the present invention. However, since R24 = R21 / 2 and the internal resistance of the device of the present invention is larger than the internal resistance of 64D, V23 is
The voltage obtained by subtracting the ground voltage from the ground fault voltage approaching V25, that is, the ground fault both-end voltage applied to both ends of the ground fault resistance R25 is smaller than that in the case of 64D, and the ground fault current is also smaller than that in the case of 64D. .
[0011]
Next, the case where the resistance on the non-ground fault side is made larger than the value of 64D and the resistance on the ground fault side is made smaller than that in “secondary measurement” will be described with reference to FIG. Assume that the resistance of the non-ground fault electrode of the present invention is R21, and the resistance of the ground fault pole side of the present invention is a combined resistance of R22 and R27 equal to R21. When R27 is not provided, it is the same as FIG. 2 of “normal measurement”, and as described with reference to FIG. 2, the ground fault current is smaller than that in the case of 64D. If 3 with R27, at both ends of the negative voltage of the ground node when the pole N was based is moved to the ground絡極side (V22 side) than in the case of absence of R27 2 ground fault resistor R25 The ground fault current becomes small compared to the case where the voltage across the ground fault is 64D. To summarize the above, the resistance on the non-ground fault pole side is made larger than the value of 64D, and the resistance on the ground fault pole side is made smaller than that, so that the ground fault current is smaller than the case where 64D is connected. Therefore, when a ground fault occurs in the control relay coil circuit, there is no possibility that the control relay operates and safety is ensured.
[0012]
Although the internal resistance of each pole of 64D varies depending on the manufacturer and model, the general internal resistance of each pole of 64D is 30 kΩ. Therefore, if the internal resistance of the device of the present invention is designed to be, for example, 50 kΩ, in most cases it will be larger than the internal resistance of 64D, so that the ground fault current is smaller than the ground fault current when 64D is connected. Thus, an apparatus in which the first object of the present invention is achieved can be obtained.
[0013]
Note that the internal resistance of the device calculated by the 鳳 / Thevenin theorem for “normal measurement” and the internal resistance of the device calculated by the 鳳 / Thevenin theorem for “secondary measurement” are matched. In other words, the time constant becomes the same as the ground capacitance of the DC circuit, and the stabilization time becomes equal. If the stabilization time is equal, it is not necessary to take into consideration such as changing the waiting time during measurement, and the measurement is simplified.
[0014]
FIG. 4 is a view of an example for explaining claim 1 of the present invention. Although FIG. 4 shows using resistors and switches, the same applies to a circuit that is electronically controlled without using switches (not shown). In order to simplify the explanation, it is assumed that there is an N pole ground fault. Also, the resistance values of the resistors in FIG. 4 are all the same resistance value, and the resistance value is 50 kΩ. In “normal measurement”, when S3 and S6 are turned ON and the resistance between P and E is 50 kΩ and the resistance between N and E is 50 kΩ, the internal resistance calculated by the 鳳 -Thevenin theorem is 25 kΩ . When the voltage from the negative electrode N when the ground is removed to the ground drawing point is the internal voltage , the internal voltage is 0.5 Vpn. In this state, the value is larger than most 64D internal resistances. In the “secondary measurement”, when S2, S5, and S6 are turned ON, the resistance between P and E becomes 100 kΩ and the resistance between N and E becomes 100/3 kΩ, which satisfies claim 1 of the present invention. The internal resistance calculated by 鳳 ・ Thevenin's theorem is 25 kΩ, and the internal voltage is 0.25 Vpn. In this case, the internal resistance does not change between the two states of “normal measurement” and “secondary measurement”, so that the time constant when the state is switched is the same and the stabilization time is the same. In the “secondary measurement”, when S2, S4, and S6 are turned on, the resistance between P and E becomes 100 kΩ and the resistance between N and E becomes 25 kΩ, which satisfies claim 1 of the present invention. The internal resistance calculated by the 鳳 -Thevenin theorem is 20 kΩ, and the internal voltage is 0.2 Vpn. Since the internal voltage difference between the two states is as large as 0.3 Vpn and the internal resistance is close to that of “normal measurement”, the measurement time can be measured with high accuracy because the stabilization time is not so different.
[0015]
5, when the average of the conventional output voltage of the two states illustrated in ground fault resistance display device of the direct current circuit of Japanese Patent Application No. 1 over 319,855 is such that the intermediate voltage of the voltage between the P over N a It is a figure which shows one example of the change of the voltage of the earthing point when the negative electrode N is made into the reference | standard . The ground fault resistance is a value close to infinity on the N pole side. Normally, the ground fault resistance is always measured and displayed by the same method (internal resistance between P = E = internal resistance between E and N) as the method of measuring at 64D by “normal measurement”, and the measurement button is pressed. For example, when “Detailed measurement” is commanded, the internal resistance between PE <measurement with the internal resistance between PE and the internal resistance between PE and E> the measurement with the internal resistance between EI and Two measurements are performed, and the measured values of ground fault resistance and ground fault voltage are displayed from the two data. In this case, it is necessary to wait twice for the stabilization time by switching the internal resistance. In FIG. 5, the ground fault resistance is a value close to infinity on the N pole side. However, when the ground fault occurs and the ground fault resistance decreases, the grounding resistance when the negative electrode N shown in FIG. The voltage waveform at the point moves to the P side, and the voltage across the ground fault R25 at the time of the first half measurement increases, and the ground fault across the ground fault resistance R25 when connected to 64D. Exceeding the voltage at both ends causes the relay to malfunction.
[0016]
FIG. 6 is a diagram showing an example of a change in voltage at the ground point when the negative electrode N is used as a reference by the apparatus of the present invention. Similarly, the ground fault resistance is close to infinity on the N pole side. Normally, the ground fault resistance value is measured and displayed in the same manner as that measured at 64D by “normal measurement”. When “detailed measurement” is instructed by pressing the measurement button, the ground fault resistance and ground Since the value related to the ground fault of the fault voltage is measured and displayed, and after returning to “normal measurement” after “detailed measurement”, the “normal measurement” value is used as one measurement value in the present invention, and the “secondary measurement” value is already set. Since one measurement value is used, the waiting time for the stabilization time by switching the internal resistance is only once, and the measurement time is about half that of the conventional measurement method described in the previous section.
[0017]
FIG. 7 is a diagram showing an example of a change in the voltage at the ground point when the negative electrode N is used as a reference by the apparatus of the present invention which has issued a command for “detail measurement” again immediately after “detail measurement” in FIG. It is. Similarly, the ground fault resistance is close to infinity on the N pole side. The voltage waveform shown before the measurement time in FIG. 7 is the voltage waveform at the ground point when the negative electrode N of the previous “secondary measurement” is used as a reference, and the value of this “secondary measurement” is directly used as one. As a measurement value, the value of “normal measurement” when it reaches a stable state after command is set as another measurement value. At this time, waiting for the stabilization time by switching the internal resistance is unnecessary, and the measurement time is further shortened. .
[0018]
The general method for using this device is to perform “normal measurement” and continue to output the first data in a stable state where the power has been turned on for a long time. When the command is issued, the internal resistance is switched instantaneously and "secondary measurement" is started. When the state is stabilized, the second data is output, and the first data and the second data are calculated. Output and display the values of ground fault resistance and ground fault voltage. At this time, since the waiting time due to switching of the internal resistance is one time, the measuring time is about half that of the conventional measuring method having two waiting times.
[0019]
As another method of use, there is a case where “detailed measurement” is executed by this apparatus when there is no ground fault and 64D is not operating, which is useful for preventive maintenance against a ground fault. In this case, equal to the voltage between the voltages and EN between P-E (Vpe = Ven) , it does not flows is ground fault current be switched internal resistance (Ie = 0), the control relay coil circuit No current flows, and therefore the control relay does not malfunction. Also, the measurement time is about half that of the conventional case as described above. Furthermore, as another method of using the apparatus of the present invention, “detailed measurement” can be continuously performed, and values relating to ground faults can be calculated and displayed every moment.
[0020]
What has been described above is further described with reference to a flowchart.
[0021]
FIG. 8 is an example of a flowchart of a conventional method. When there is a command for “detailed measurement”, the internal voltage is brought to the P pole side to perform “secondary measurement”, and then the internal voltage is brought to the N pole side to perform “tertiary measurement”. Calculate and display “detailed measurement” data. In this method, when the internal voltage is applied to a pole that is not a ground fault pole, the ground fault current becomes larger than that in the case of 64D, and there is a risk that the control relay malfunctions.
[0022]
FIG. 9 is an example of a flowchart of the method of the present invention, and shows a flow corresponding to the third item of claims 1 and 2. Since there is no “third-order measurement” compared to FIG. 8, the measurement time can be reduced to half or less than the conventional method. In addition, since the internal voltage is not brought to the non-ground fault pole side, the ground fault current is smaller than that in the case of 64D, so the control relay does not malfunction.
[0023]
【The invention's effect】
Before the apparatus of the present invention is connected to the DC circuit, 64D is connected and the ground line is neutrally grounded. This device measures and displays the ground fault resistance and the ground fault voltage instead of the 64D when a ground fault occurs. First of all, since the ground fault current when the ground wire is connected to the device of the present invention is less than the ground fault current in the case of 64D, the ground fault is not detected in the coil circuit of the control relay used in the load circuit. Even if this occurs, the relay does not malfunction, and there is no secondary accident caused by the malfunction of the control relay. Next, when “detailed measurement” is performed by the apparatus of the present invention, since the switching of “secondary measurement” is performed once, the measurement time is shortened to about half compared with the conventional one, and it is continuously performed. Thus, when “detailed measurement” is performed, the measurement time is further shortened. Thirdly, the difference in voltage between the ground points when the negative electrode N is used as a reference is sufficiently large so that the measurement accuracy does not deteriorate. Fourthly, the apparatus of the present invention can also measure the ground fault voltage of a solar cell.
[Brief description of the drawings]
[1] Feng-Thevenin theorem illustration Figure 2 ground fault voltage across illustration ground voltage across diagram for explaining the first aspect of the present invention; FIG 4 shows the present invention FIG. 5 shows an output voltage in two states illustrated in the conventional DC ground fault resistance display device of Japanese Patent Application No. 1-319855 as an intermediate voltage between PN voltages. FIG. 6 is an example of the time chart of claims 1 and 2 of the present invention. FIG. 7 is the time chart of the present invention when continuously measured. FIG. 8 shows an example of a flowchart of a conventional measuring method. FIG. 9 shows an example of a flowchart of a measuring method of the present invention.
R: Resistance V: Voltage P: DC circuit positive electrode N: DC circuit negative electrode E: DC circuit ground electrode S: Switch Vpe: Voltage between positive electrode and ground electrode Ven: Voltage between ground electrode and negative electrode Ie: Ground fault Current (current flowing through the ground electrode)

Claims (2)

Connected to the positive electrode P / negative electrode N and the ground electrode E of the DC circuit, the voltage at the ground fault point when the negative electrode N in the DC circuit is used as a reference is the ground fault voltage, and the ground fault resistance in the DC circuit is the ground fault resistance. In the measurement circuit that measures the ground fault resistance and ground fault voltage, the ground fault resistance and ground fault voltage of the electric circuit in the state where the internal resistance between PE and EN coincide (midpoint grounding). The measured value in the “normal measurement” to be measured is the first data, and the internal resistance on the ground fault side (for example, between P and E when the P side is ground fault) is the non-ground fault side (between E and N in the above example) ) The measured value in the “secondary measurement” that measures the ground fault resistance and the ground fault voltage in a state where the internal resistance is made smaller than the internal resistance as the second data, and the “detailed measurement” from the first data and the second data. in the measurement apparatus of the ground-fault resistance and ground voltage to calculate a measured value as "in the" normal measurement " -E and E-N resistances are the internal resistances of the positive electrode P and the negative electrode N (64D P-E and E-N) of a DC ground fault relay (Nippon Electric Industrial Standard JEM: 64D, hereinafter referred to as 64D) internal resistance) value greater than and to "secondary measurement" the internal resistance (the example of the 64D internal resistance) between E over N of the non-ground side of the resistor (measuring device in the example of E-N of 64D between A device for measuring a ground fault resistance and a ground fault voltage in a DC electric circuit characterized by having a value larger than the internal resistance between). In the above ground fault resistance and ground fault voltage measuring device, when a “detailed measurement” command is received, When the data in the “normal measurement” has not yet reached a stable state, such as when the measurement device starts, “secondary measurement” is performed by switching the internal resistance to the measurement data when the data is stable. 1. “Detailed measurement” is performed with the measurement data obtained when the data at 1 reaches a stable state as another data. When the data of “Normal measurement” has reached a stable state, such as when the measurement device has been operating for a long time, the measurement data at that time is taken as one data, and “Secondary measurement” is performed by switching the internal resistance. 2. Perform “detailed measurement” by using the measurement data when the data in (2) reach a stable state as another data. When “secondary measurement” is performed immediately before the command, the measurement data from the “secondary measurement” performed immediately before is regarded as one data, and the data after “command” is stabilized. 2. The apparatus for measuring ground fault resistance and ground fault voltage in a DC circuit according to claim 1, wherein the detailed measurement is performed by using the data obtained when the data has been reached as another data.

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