JPS586148B2 - Insulation monitoring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an insulation monitoring device for preventing electrical leakage accidents.

As a conventionally used earth leakage accident prevention device, for example, an earth leakage breaker ELB as shown in FIG. 1 is known.

This type of earth leakage breaker ELB usually includes a zero-phase current transformer ZCT, an amplifier AMP, trip contacts CTTa, CTTb, and the like.

Looking at a circuit in which loads Z1 and Z2 are connected to the output side of an isolation transformer T in which this earth leakage breaker ELB is used, and virtual insulation resistances r1, r2, and r3 are assumed at both ends of the loads Z1 and Z2, respectively, This virtual insulation resistance r1, r2, r
If 3 is infinite, no current will flow through the ground terminal E of the isolation transformer T1.

In this case, the output of the zero-phase current transformer ZCT is zero.

For example, when the virtual insulation resistance r1 takes a certain value, a leakage current flowing to the ground terminal E via the virtual insulation resistance r1 is added to the secondary current of the isolation transformer T1 in addition to the load current.

Since this leakage current flows only in one direction in the zero-phase current transformer ZCT, a signal is generated, which is amplified by the amplifier AMP to operate the trip contacts CTTa and CTTb.

Even when the virtual insulation resistance r is applied, the leakage current flowing through the ground terminal E flows in one direction in the zero-phase current transformer ZCT and generates a control signal.

However, when the virtual insulation resistance r3 is inserted, since both ends thereof are at the same potential as the ground terminal E, no leakage current flows and no signal appears in the zero-phase current transformer ZCT.

Also, a grounding terminal E must be provided on the output side of the isolation transformer T1 (G).

In other words, when using this type of earth leakage breaker ELB, it is not possible to completely monitor the insulation deterioration of wiring paths or load electrical equipment, and furthermore, it cannot be used in circuits where the secondary side is not grounded. There is a problem.

In view of these circumstances, the present invention aims to provide a device that can reliably monitor insulation deterioration in a circuit whose secondary side is not grounded.

When insulation deterioration occurs in the secondary wiring of an insulating transformer or connected electrical equipment, the present invention separates one cycle of AC voltage every half cycle, detects leakage current, and displays a display device based on one cycle. This is intended to operate protective devices, etc., and is particularly effective in detecting minute currents.

FIG. 2 shows a block diagram of the insulation monitoring device according to the present invention. In the figure, T1 is an isolation transformer, and Z is a load connected to the secondary side of the isolation transformer T1, for example, ME equipment,
Instrumentation equipment etc. are connected.

1 is a waveform discriminator for separating and capturing one cycle of leakage current based on an AC power supply every half cycle; and a second discrimination circuit 12.

2 is an I/V converter that converts the output of waveform discriminator 1 from a current signal to a voltage signal, and the signal due to leakage current is
It is given through a converter 2 and a waveform discriminator 1.

The /V converter 2 includes first and second converter circuits 21 and 22 connected in series with the first and second discrimination circuits 11 and 12, respectively.

Reference numeral 3 denotes a peak storage device which receives the voltage signal output from the I/V converter 2 and stores its peak value, and is connected in series with the first and second converter circuits 21 and 22, respectively, by a second peak hold circuit 31, 32 are connected.

4 is a buffer circuit that receives the output of the peak memory device 3 at high impedance and converts it into a low impedance voltage signal;
Puffer amplifiers 41 and 42 are connected in series with the first and second peak hold circuits 31 and 32, respectively.

Reference numeral 5 denotes an adder that separates every half cycle in the waveform discriminator 1 and adds the signals outputted from the 11th and 2nd buffer amplifiers 41 and 42 as low impedance voltage signals, and displays the sum signal of both on the meter 6. make it work.

A comparator 7 detects a signal applied to the display meter 6 and operates the external control circuit 8.

9 is a power transformer used as a power source for the insulation monitoring device, and 10 is a self-test circuit for the insulation monitoring device.

According to the device having such a configuration, for example, when an insulation failure occurs in the load Z, the display on the display meter 6 is determined by the leakage resistance due to the insulation failure, regardless of where the insulation failure occurs in the load Z. There is.

This is because the leakage current signal is separated every half cycle and a DC current based on a voltage determined by its peak value is added. This point will be explained in detail using the following embodiment.

Therefore, by looking at the display on the display meter 6, it is possible to know the state of insulation deterioration of the wiring and load, and it is also possible to operate alarms and other devices as necessary.

The circuit diagram shown in FIG. 3 shows the main parts of a specific embodiment of the insulation monitoring device according to the present invention, and the same parts as in FIG. 2 are given the same reference numerals.

In the figure, T is an isolation transformer, Z is a load, and the load Z is shown as a series load of a first load Z1 and a second load Z2.

r1, r2, and r3 indicate first, second, and third virtual insulation resistances, respectively; the first virtual insulation resistance r1 is on the power supply side of the first load Z1, and the second virtual insulation resistance r2 is on the power supply side of the first load Z1. 1. A third virtual insulation resistance r3 located between the second loads z1 and Z2 is connected to the power supply side of the second load Z2, and the other end is grounded.

The first and second discrimination circuits 11 and 12 each have a resistor R11.
and a diode D11, a resistor R12, and a diode D12 in series, the first discrimination circuit 11 is connected to the output end of the isolation transformer T1 to which the third virtual insulation resistance r3 is connected, and the The discrimination circuit 12 is connected to the other output terminal of the isolation transformer T1 to which the first virtual insulation resistance r1 is connected.

First and second converter circuits 21 and 22 are connected to the output ends of the first and second discrimination circuits 11 and 12, respectively.

The eleventh and second comparator circuits 21 and 22 are respectively composed of operational amplifiers Q11 and Q12.
1, the current signal applied to the input terminal of Q12 is taken out as a voltage signal output.

R21 and R22 each represent a feedback resistor.

Voltage signals obtained as outputs of converter circuits 21 and 22 are applied to peak hold circuits 31 and 32.

The peak hold circuits 31 and 32 are each composed of a diode D21 and a capacitor C11, and a diode D22 and a capacitor C12, and the respective capacitors C12 and C12 are charged to the peak value of the output voltage of the converter circuits 21 and 22.

These peak voltages are input to operational amplifiers Q21 and Q22 that constitute buffer amplifiers 41 and 42.

Since this input impedance is high impedance, discharge of the capacitors C11 and C12 constituting the peak hold circuits 31 and 32 is suppressed, thereby increasing the stability of operation.

R31, R41 and R32, R42 are feedback resistors, respectively, and G1=(R31+R41)/R31, G
The input voltage is amplified at a ratio of 2=(R32+R42)/R32.

R51 and R52 are resistors to which the output voltages of the buffer amplifiers 41 and 42 are applied, and constitute an adder 5 that adds the currents flowing through the resistors R51 and R52.

6 is a display meter, and a DC ammeter is used.

R6 is a detection resistor, and if this terminal voltage is used as a signal, an alarm or other protection device can be operated.

7 is a comparator that uses an operational amplifier Q3 to compare the voltage signal given from the detection resistor R6 with a reference voltage V0 given to the resistor in advance, and when the voltage signal exceeds the reference voltage V0, the positive/negative of the output is reversed. It works like that.

R8, R9, and R10 each represent a resistance.

8 is an external control circuit operated by the output of the comparator 7, and is composed of, for example, a transistor Q4, a relay coil X, and the like.

According to such a configuration, when the output of the comparator 7 is negative, the transistor Q4 is in an open state, and when it becomes positive, the transistor Q4 is closed, and current flows through the relay coil X to perform the necessary operation.

The power transformer 9 is connected to the output end of the isolation transformer T in parallel with the load Z, and although not shown, rectifies the output voltage and uses it as a power source for the insulation monitoring device.

Reference numeral 10 denotes a self-test circuit connected to the primary winding of the power transformer 9, in which simulated grounding resistors R1, R2, and R3 are connected to positions corresponding to virtual insulation resistors r1, r2, and r3, respectively.

S1, S2, S3 are simulated grounding resistances R1, R2, respectively.
This is a switch inserted in series with R3.

Note that any impedance may be used instead of the primary winding of the power transformer 9.

Next, the operation of the insulation monitoring device configured as above will be explained.

That is, if a ground fault corresponding to the virtual insulation resistances r1, r2, and r3 occurs in the load Z due to insulation failure, a leakage current flows in addition to the load current.

In the isolation transformer T, if there is a grounding fault in one place, no leakage current should flow, but the leakage current passes through the ground terminal of the I/V converter 2 of the insulation monitoring device and the waveform discriminator 1 to the isolation transformer T1. This is because an electric path is formed.

The leakage current flowing at this time is separated every half cycle depending on the position of the ground fault and the positive/negative direction of the power supply voltage, and flows through the first and second converter circuits 21 and 22.

This signal current is converted into a voltage by the I/V converter 2 and output, and the peak voltage is stored in the peak memory 3.

Then, the voltage is converted into a low impedance voltage signal by the buffer circuit 4, and a direct current is obtained from this voltage, which is displayed on the display meter 6.
It operates.

At this time, the signals obtained by separating every half cycle are added by current.

By the way, if this added current signal takes a different value depending on the location where the grounding fault has occurred, even though the grounding resistance is the same, correct judgment cannot be made.

However, according to the configuration of the present invention, the current signal is determined only by the value of the ground resistance, regardless of the position of the ground fault.

For example, consider the case where a virtual insulation resistance r2 is inserted.

The leakage current I(r) at this time is divided through the grounding circuits of the first and second converter circuits 21 and 22.

In this 5, the first converter circuit 21 and the first discrimination circuit 1
1, and the current flowing through the second converter circuit 22 and the second discrimination circuit 12 as I2(r), I1(r)=[Es・Z2/ (Z1+Z2)]/(R1
1+r2)・・・・・・・・・(1) I2(r)=[Es・Z1/(Z1+Z2)]/(R1
2+r2) (2)

However, Es is the secondary voltage of the isolation transformer T2.

Therefore, the output voltages of the first and second converter circuits 21 and 22 are R21·I1(r) and R22·I1(r).
2(r) is obtained.

At this time, the capacitors C11 and C12 of the first and second peak hold circuits 31 and 32 are
Charges up to double.

The first and second buffer amplifiers 41 and 4 receive this voltage.
Since the amplification factors of 2 are G1 and G2 as described above, the output voltages E41 and E42 are as follows.

Therefore, if the internal resistance RM of the display meter 6 is taken into consideration, the current flowing therein will be as follows.

IM1=E41/(R51+RM+R6)...
...(5) IM2=E42/(R52+RM+R6)
(6) By the way, the characteristics of the pair of circuits that are processed separately every half cycle must naturally be configured to have the same characteristics, so R11=R12...・・・・・・(7) R21=R2
2・・・・・・・・・(8) G1=G2・・・・・・
・・・・・・(9) R51=R52・・・・・・・・・(■
0), the current IM flowing through the display meter 6 will be.

As is clear from equation (11), the current IM flowing through the display meter 6 has no relation to the eleventh second loads Z1 and Z2, and changes only depending on the value of the virtual insulation resistance r2.

Note that in the case of virtual insulation resistances r1 and r3, the first load Z
Needless to say, this corresponds to the case where the resistance of the first or second load Z2 is set to zero.

In a circuit having such a configuration, for example, even if the ground resistance is zero, the resistance R of the first and second discrimination circuits 11 and 12
Since resistors R11 and R12 are inserted as shown in equations (1) and (2), the value of leakage current can be suppressed by appropriately determining the values of these resistors R11 and R12.

This is extremely effective when using ME equipment as a load, but in medical settings, for example, in equipment used near the heart, even a few microamperes of current is said to be dangerous, so the maximum value of leakage current is It is possible to choose a safe value.

Regarding the self-test circuit 10, when an insulation monitoring device according to the present invention is installed, it is necessary to check the operation of the device.

In that case, the switch S1 of this self-test circuit 10,
It is best to turn on S2 and S3 and read the instructions on the display meter 6.

For example, if the same simulated grounding resistors R1, R2, and R3 are used, and no matter which switch is closed, the operation is normal unless the instruction changes.

Note that when using the same simulated ground resistance in terms of circuit configuration, the switches S1, S2, and S can be placed in the front stage, and one resistor can also be used in the latter stage.

Furthermore, it goes without saying that the detection resistor R6 that supplies a signal to the comparator 7 is not necessary if the external control circuit 8 is not required.

The objects to be controlled by the external control circuit 8 include various alarms, circuit breakers, changeover switches, and the like.

As explained in detail above, the present invention reduces the insulation deterioration of the load of the isolation transformer used with the secondary side ungrounded.
Detect leakage current by separating cycles into half cycles,
Convert each half-cycle current signal to a DC voltage,
The magnitude of the grounding resistance is displayed by adding the DC current based on this value.

In other words, regardless of the grounding position of the load, the voltage applied to the grounding resistor will reach the peak value that matches the power supply voltage by summing the sum for each half cycle of one cycle, thus achieving the purpose. It is.

Further, according to the insulation monitoring device of the present invention, it is possible to detect a leakage current of several microamperes, which improves accuracy and enables safer circuit protection than detection using a conventional zero-phase transformer.

[Brief explanation of drawings]

Fig. 1 is an earth leakage detection circuit diagram using a conventional earth leakage breaker, Fig. 2 is a block diagram of an insulation monitoring device according to the present invention, and Fig. 3 is a circuit diagram showing a specific example. Z1 is a load, 1 is a waveform discriminator, 2 is an I/V converter, 3 is a peak storage device, 4 is a buffer circuit, 5 is an adder,
6 is a display meter, 7 is a comparator, 8 is an external control circuit, 9 is a power transformer, and 10 is a self-test circuit.

Claims (1)

[Claims] 1. An I/V converter is connected to a waveform discriminator connected to both ends of the secondary side of the isolation transformer, and the I/V converter separates one cycle of the power supply voltage every half cycle to capture leakage current, An insulation monitoring device characterized in that a direct current is obtained every half cycle based on the peak value of the voltage output, and a leakage current is detected by adding these direct currents. 2. The insulation monitoring device according to claim 1, wherein a resistor is provided in the waveform discriminator, and the leakage current is limited by the resistor. 3. The insulation monitoring device according to claim 1, characterized in that an arbitrary impedance is connected to the secondary side of the isolation transformer, and a self-test circuit equipped with a simulated ground resistance is provided. 4. Insulation monitoring according to claim 1, further comprising a comparator that compares the signal based on the added DC current with a reference value, and an external control circuit that operates when the reference value is exceeded. Device.