JP5072086B2 - Device for detecting resistance ground fault current - Google Patents

Description

The invention of the present invention is a circuit breaker, earth leakage breaker, or earth leakage circuit having a means for detecting a ground leakage current in a circuit and detecting a resistance ground fault current based on the magnitude and a phase shift from the circuit voltage. It relates to a device such as a relay.

It is well known that the ground leakage current of the circuit includes a constant leakage current that flows through the capacitance of the circuit ground capacitance and the noise filter capacitance of the device, and a resistance ground fault current due to poor insulation.

Since the constant leakage current is a current flowing through the ground capacitance, the phase advances by 90 degrees with respect to the ground voltage, and the resistance ground fault current due to insulation failure is in phase with the ground voltage. Therefore, there is a phase difference between the circuit voltage and the ground leakage current that is determined by the ratio of the magnitude of the constant leakage current and the resistance ground fault current.

Therefore, a method is known in which only the resistance ground fault current due to insulation failure is classified based on the phase difference between the magnitude of the ground leakage current and the circuit voltage.
JP-A-2005-140532 JP 2006-71341 A

However, depending on the phase difference between the earth leakage current and the circuit voltage, the detection accuracy of the phase difference greatly affects the detection accuracy of the resistance ground fault current. Even if the detection accuracy of the phase difference is the same, the influence on the calculation result of the ground fault current is almost not when the phase difference is around 0 degrees, but is considerably large when the phase deviation is around 90 degrees.

Therefore, depending on the angle range of the phase difference of the ground leakage current with respect to the circuit voltage, the resistance ground fault current may not be detected with the required accuracy. For example, if the detection accuracy of the phase difference is ± 1 degree and the resistance ground fault current of 1 mA is to be detected with an accuracy of ± 10%, the accuracy can be guaranteed only for other detection errors other than the phase difference. Is ignored, the leakage current always has a magnitude of 0 mA to 6.3 mA, that is, the phase difference angle range is limited to 0 degrees to 81 degrees.

 In other words, the detection accuracy of the phase affects the detection accuracy of the resistance ground fault current, but if you try to guarantee the detection accuracy of the resistance ground fault current at a phase difference close to 90 degrees, which is likely to cause errors, Therefore, it is necessary to improve the accuracy of detection, which increases the cost of the apparatus.

Therefore, the present invention detects a leakage current to the ground of the circuit, and based on the phase difference between the magnitude of the circuit and the circuit voltage, detects a magnitude of the leakage current due to the resistance ground fault or a circuit breaker or a leakage current. In devices such as circuit breakers or relays, it is possible to easily determine whether there is a constant leakage current state in the circuit within a range where the required resistance ground fault current detection accuracy can be guaranteed. It is intended to provide an economical device.

Therefore, according to the first aspect of the present invention, the ground leakage current of the circuit is detected, the resistance ground fault current is detected based on the magnitude and the phase shift from the circuit voltage, and the resistance ground fault current is a predetermined magnitude. In a device provided with means for detecting that the current exceeds the value, the leakage current is always detected together with the resistance ground fault current, and the constant leakage current is set according to the detection sensitivity of the resistance ground fault current. The present invention provides a device for detecting a resistance ground fault current, characterized by comprising means for issuing an alarm when the value exceeds.

According to a second aspect of the present invention, the device for detecting a resistance ground fault current is a circuit breaker for issuing a warning when the resistance ground fault current exceeds a predetermined magnitude, or the alarm is a prior warning. The apparatus for detecting a resistance ground fault current according to claim 1, wherein the apparatus is a certain earth leakage breaker or earth leakage relay.

According to a third aspect of the present invention, the device for detecting a resistance ground fault current is a ground fault circuit breaker or an output that interrupts the circuit when the resistance ground fault current exceeds a predetermined magnitude. An apparatus for detecting a resistance ground fault current according to claim 1, wherein the apparatus is a leakage relay configured to generate a fault.

According to the present invention, the ground leakage current of the circuit is detected, the resistance ground fault current is detected based on the magnitude and the phase shift from the circuit voltage, and the resistance ground fault current has a predetermined magnitude. In a device equipped with means for detecting that the current exceeds the value, the leakage current is always detected together with the resistance ground fault current, and the value set according to the detection sensitivity of the resistance ground fault current If it exceeds the limit, it has a means to issue an alarm, so if there is a constant leakage current in the circuit where the required resistance ground fault current detection accuracy cannot be guaranteed, a predetermined resistance ground fault current is detected. In fact, it can be easily determined whether the detected output meets the required accuracy.

Further, by providing the device with such a warning means, it is possible to obtain a device having a phase shift detection accuracy that does not interfere with practical use, and it is possible to reduce the cost of the device.

A first embodiment of the present invention is shown in FIG. FIG. 1 shows an example in which a circuit breaker 10 with a resistance ground fault current detection display function and the circuit breaker 10 are installed in an electric circuit. In FIG. 1, reference numeral 1 denotes a transformer for supplying an electric circuit voltage to the electric circuits 2 and 2 ′, and the 2′-side terminal of the low-voltage side winding is grounded as 3. For convenience, the electric circuit will be described as a single-phase two-wire system, but the same principle can be applied to a single-phase three-wire electric circuit or a three-phase three-wire electric circuit with a Δ connection and a single-pole grounding type.

1001 and 1002 are switching contacts, and 1003 is an overcurrent detection element. When the current in the electric circuit exceeds a predetermined value, the overcurrent detection element 1003 acts on a switching mechanism (not shown) in a time period corresponding to the magnitude of the current. And 1002 are automatically opened. Reference numeral 1004 denotes a zero-phase current transformer that detects the difference between the reciprocating currents of the electric circuits 2 and 2 '. The current detected by the zero-phase current transformer 1004 is a zero-phase leakage current Io consisting of a constant leakage current Ioc flowing in the ground capacitance 4 of the electric circuit 2 and a ground fault leakage current Ior flowing in the ground fault resistance 5 due to insulation failure. It is.

Reference numeral 1005 denotes an input circuit for a current detected by the zero-phase current transformer 1004, which includes an over-input protection circuit, a filter circuit, an amplifier circuit, a phase shift circuit and the like as necessary. Note that the phase shift circuit is used for the purpose of correcting the phase difference between the actual zero-phase current and the current signal handled by the detection circuit, but may be included in the arithmetic circuit 1007.

In general, the voltage of the electric circuit includes harmonics and high frequencies due to the nonlinearity of the transformer 1 and the load current waveform with respect to the original commercial fundamental wave. Linearly. However, the current flowing through the ground capacitance 4 changes relatively as the frequency increases because the impedance changes with respect to the waveform distortion frequency. Therefore, it is desirable to remove harmonics and high-frequency components with a filter in order to detect a ground fault current of only a commercial fundamental frequency more accurately.

Reference numeral 1006 denotes an input circuit for an electric circuit voltage, which has an insulating circuit for the electric circuit, an over-input protection circuit as in the case of 1005, and a filter circuit if necessary.

Reference numeral 1007 denotes an arithmetic circuit that calculates the phase difference between the circuit voltage and the zero-phase current, and calculates the ground-fault current for the resistance and the constant leakage current due to the capacitor from the absolute magnitude of the phase difference and the zero-phase current. This will be described with reference to FIGS. In this case, the circuit voltage corresponds to the ground voltage.

In FIG. 2, 6 is a circuit voltage vector and 7 is a zero-phase current vector. The zero-phase current 7 is a combined current of a constant leakage current 9 due to a resistance ground fault current 8 and a ground capacitance. The arithmetic circuit 1007 calculates the phase difference θ between the circuit voltage vector 6 and the zero-phase current vector 7 from the time lag between the zero point of the circuit voltage and the zero point of the ground leakage current, and the phase difference is calculated to the absolute value of the zero-phase current vector 7. The magnitude of the resistance ground fault current 8 is calculated by multiplying by the cosine (cos) of θ. The constant leakage current is calculated by multiplying the absolute value of the zero-phase current vector 7 by the sine of the phase difference θ. Alternatively, the constant leakage current may be calculated from the ground leakage current and the resistance ground fault current.

FIG. 3 shows another method. FIG. 3 shows a method of calculating the magnitude of the resistance ground fault current 12 by integrating the instantaneous values of the circuit voltage 10 and the zero-phase current 11. (A) is an example where there is no phase difference between the circuit voltage and the zero-phase current. Since there is no phase difference, when the instantaneous values are multiplied, the value is doubled in the positive range of 0 or more. The average value is proportional to the resistance ground fault current.

(B) is an example in which the phase difference between the circuit voltage and the zero-phase current is 90 degrees. When the instantaneous values are multiplied, the average value is zero and the frequency is doubled. FIG. 3 is the same as the method by so-called synchronous rectification. The constant leakage current may be obtained by advancing the phase of the circuit voltage by 90 degrees by means of phase shifting means and taking the average value by integrating the instantaneous values of the zero phase current by the same method as (a) and (b). It may be calculated from the resistance ground fault current.

Here, the detection accuracy of the phase difference between the circuit voltage and the leakage current and the detection accuracy of the resistance ground fault current will be described with reference to FIG. In FIG. 4, when there is a zero-phase leakage current 16 having a small phase difference θ1 with respect to the circuit voltage phase 15, if the detection error range of the phase difference is ± α, the error α with respect to the resistance ground fault current 17 to be detected The effect of is 18 and is relatively small with respect to 17. However, when the phase difference of the leakage current 16 ′ is large as θ2 with respect to the circuit voltage phase 15, the resistance ground fault current 17 ′ is small even if the phase difference detection error range is the same as ± α and the influence of the error α. Since it becomes as large as ± 18 ', it becomes relatively large with respect to 17', and even if the detection accuracy of the phase difference is the same, the detection accuracy of the resistance ground fault current greatly changes.

Therefore, the phase difference between the circuit voltage and the leakage current that can guarantee the detection result, in other words, the magnitude of the constant leakage current, is limited by the demand of the resistance ground fault current to be detected and the accuracy. As described above, when the detection accuracy of the phase difference is ± 1 degree, if the detection accuracy 18 when the resistance ground fault current 17 is 1 mA is to be guaranteed to 0.1 mA, 10% of 17, the resistance component of 1 mA. The phase difference between the circuit voltage and the zero-phase leakage current with respect to the ground fault current is within 81 degrees, or when the resistance ground fault current is 1 mA, the magnitude of the zero-phase leakage current is not within 6.4 mA. You will not be able to answer. In that case, the constant leakage current must be within 6.3 mA.

In FIG. 1, reference numeral 1008 denotes a means for outputting the result of the resistance ground fault current calculation by the arithmetic circuit 1007. When the calculation result exceeds a predetermined value, an output is generated by voice or a lamp or output at a contact. Reference numeral 1009 denotes an alarm output means capable of determining whether or not the calculation result satisfies the required accuracy. The constant leakage current calculated by the calculation circuit 1007 is a value set according to the detection sensitivity of the resistance ground fault current. Judge whether or not it is below and display / output. The display output may either output that the accuracy can be guaranteed or output that the accuracy cannot be guaranteed.

In FIG. 1, a detection sensitivity switching device (not shown) may be added. In that case, the value of the constant leakage current that can guarantee the accuracy corresponding to each desired detection sensitivity is also switched.

According to the circuit breaker 10 for wiring according to FIG. 1, the detection of a request at the initial stage of installation, for example, depending on whether the constantly leaking current is less than a value set according to the magnitude of the resistance ground fault current to be detected and the required accuracy. It is possible to easily determine whether the circuit can guarantee accuracy and whether the alarm can be guaranteed with accuracy when a predetermined resistance ground fault current is detected.

In addition, when trying to detect the 1mA resistance ground fault current mentioned in the previous example with an accuracy of ± 10%, if errors other than the phase difference detection error can be ignored, the phase difference is detected at 45 degrees. The tolerance of accuracy is ± 5 degrees, but when the phase difference is 85 degrees, the required phase difference detection accuracy is ± 0.5 degrees, and the phase difference detection accuracy becomes closer to 90 degrees. The demand for the device becomes stricter and the cost of the apparatus increases. However, if there are many cases where the phase difference is within 45 degrees when the resistance ground fault current to be detected is flowing in a general circuit, a device with a phase difference detection accuracy of ± about 5 degrees is sufficient. In the unlikely event that the phase difference is exceeded, it is practically sufficient to know that the accuracy cannot be guaranteed by an alarm.

5 and 6 show an embodiment in which a resistance ground fault current alarm function is added to an earth leakage breaker that breaks the circuit depending on the magnitude of the leakage current, and the operation is stepwise with respect to the leakage current. Reference numerals 1001 to 1009 in the embodiment of FIG. 5 have the same functions as those of the embodiment of FIG. In the figure, reference numeral 1010 denotes a trip device that acts on an opening / closing mechanism (not shown) and separates the contacts 1001 and 1002 and operates according to the determination result of the arithmetic circuit 1007. In this case, the leakage current can be either a ground leakage current or a resistance ground fault current. The embodiment in FIG. 6 is an example in which a leakage current detection circuit 1011 for driving the trip device 1010 is provided separately from the arithmetic circuit 1007. The earth leakage breaker shown in FIGS. 5 and 6 detects whether the resistance ground fault current is, for example, 1 mA or more in the case of an insulation failure that does not require an emergency, and an emergency such as an electric shock such that the leakage current exceeds 30 mA. In the case of an accident that requires an operation, it operates in stages so as to interrupt the electric circuit. At that time, it is possible to know whether or not the detection output of the resistance ground fault current detection before the interruption operation is performed within a range in which the accuracy can be guaranteed.

5 and 6, the display unit 1008 can be omitted, and the trip coil 1010 can be suddenly driven when the arithmetic circuit 1007 detects a predetermined resistance ground fault current. In this case, if the display of 1009 is electrically backed up or if a mechanical latch mechanism is used, the circuit is cut off by driving the trip coil 1010 based on the detection accuracy required to cut off afterwards. You can determine whether it was done. The trip coil 1010 can be driven even when the leakage current always exceeds the required detection accuracy.

FIG. 7 shows an earth leakage relay that does not have a main circuit contact that interrupts the circuit. In the figure, reference numerals 1004 to 1009 are the same as those in FIG. However, the zero-phase current transformer may be installed outside the relay casing or built in. Further, the zero-phase current transformer is not provided in the electric circuit, but may be one that detects the ground leakage current of the B-type ground wire of the transformer. Reference numeral 1010 'denotes a relay, which outputs a contact to the outside instead of the circuit breaker of FIG. 5 or 6 interrupting the circuit. Alternatively, a signal may be output from the arithmetic circuit 1007 to the outside. In such an earth leakage relay, in addition to the relay operation of 1010 ', it is possible to detect the resistance ground fault current of the previous circuit, and whether the detected resistance ground fault current has the required accuracy. Can be distinguished at a glance.

Further, the display means 1008 is omitted, and the relay 1010 ′ is operated when the resistance ground fault current exceeds a predetermined value as described in “0029”, and the alarm means 1009 is activated when the relay is activated. You may make it show that the leakage current always exceeded the predetermined range.

In the above description, the display means 1008 has been described in the case where the detection sensitivity of the resistance ground fault current is one, but a plurality of display means may be provided in stages and selectively switched. In that case, it is necessary to always switch the upper limit value of the leakage current according to the resistance ground fault current to be detected. In addition, it is optional to add a means for calculating the leakage current constantly by the arithmetic circuit 1007 and displaying the value.

In addition to circuit breakers, earth leakage circuit breakers, relays and measuring instruments, it can also be used in addition to monitoring devices with other functions.

Configuration diagram of circuit breaker with resistance ground fault current alarm function according to the present invention Explanatory drawing of the method to detect the resistance ground fault current from the ground leakage current Explanatory drawing of the method to detect the resistance ground fault current from the ground leakage current Diagram explaining detection error due to phase difference between voltage and ground leakage current Configuration diagram of earth leakage breaker with resistance ground fault current alarm function according to the present invention Configuration diagram of earth leakage breaker with resistance ground fault current alarm function according to the present invention Configuration diagram of relay with resistance ground fault current alarm function according to the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Transformer 2, 2 '... Electric circuit 3 ... Grounding 4 ... Ground capacitance of electric circuit 5 ... Ground fault resistance 6 ... Voltage vector 7 ... Ground leakage current vector 8: Resistance ground fault current vector 9: Constant leakage current vector 10: Circuit waveform unit waveform 11, 13: Ground leakage current waveform 12, 14: Circuit voltage unit waveform Accumulated waveform of instantaneous value and instantaneous value of ground leakage current 15... Voltage vector 16, 16 '.. ground leakage current vector 17, 17' .. resistance ground fault current 18, 18 '.. detection error 1001, 1002 ... Main circuit contact 1003 ... Overcurrent detection element 1004 ... Current transformer 1005 ... Waveform shaping circuit 1006 ... Waveform shaping circuit 1007 ... Arithmetic circuit 1008 ... Display means 1009 ... Alarm means 1010 ... Trip carp 1010 '... Relay 1011 ... Leakage detector

Claims (3)

The earth leakage current of the circuit is detected, the resistance ground fault current is detected based on the magnitude and the phase shift from the circuit voltage, and it is detected that the resistance ground fault current exceeds a predetermined magnitude. In a device equipped with means, always detect a leakage current in combination with the resistance ground fault current, and if the constant leakage current exceeds a value set according to the detection sensitivity of the resistance ground fault current, an alarm is issued. An apparatus for detecting a resistance ground fault current, characterized in that it comprises means for emitting. The device for detecting a resistance ground fault current includes a circuit breaker for wiring that issues an alarm when the resistance ground fault current exceeds a predetermined magnitude, or a ground fault circuit breaker or a ground fault relay whose warning is a prior warning. The apparatus for detecting a resistance ground fault current according to claim 1. The above-mentioned device for detecting the resistance ground fault current is a ground fault circuit breaker that shuts off the circuit or a ground fault that generates an output when the resistance ground fault current exceeds a predetermined magnitude. 2. The apparatus for detecting a resistance ground fault current according to claim 1, wherein the apparatus is a relay.

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