JP2009079958A - Apparatus for detecting ground-fault current of resistance value - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus which facilitates determining the presence of a ground-fault current of a resistance value and value reliability and is practical and economical. <P>SOLUTION: An apparatus such as a molded case circuit breaker, a ground-fault interrupter, a relay, and a measuring instrument provided with a means for detecting a ground leakage current of an electrical path and detecting the magnitude of a leakage current due to a resistance ground fault on the basis of a phase shift between its magnitude and a voltage of the electrical path is provided with a means for detecting a ground-fault current of the resistance value, displaying or outputting its magnitude each time, and displaying or outputting an error range of computation results corresponding to the magnitude of the phase shift between the ground leakage current and the voltage of the electrical path together. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The invention of the present invention is a device having 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. Or, it relates to a device such as a leakage relay or a measuring instrument.

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 ground fault current. Even if the detection accuracy of the phase difference is the same, the influence on the calculation result of the resistance 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 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 an attempt is made to detect a resistance ground fault current of 1 mA with an accuracy of ± 10%, the accuracy can be guaranteed only by detection errors other than the phase difference. Is always limited to a leakage current of 6.3 mA, that is, the phase difference angle range is limited to 0 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 where errors are likely to occur, it will be extremely difficult. It is necessary to improve the accuracy of detecting the phase difference, 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, relays, and measuring instruments, display the error range of the measurement along with the magnitude of the detected resistance ground fault current to make it easier to judge the presence of the resistance ground fault current and the reliability of the value. To do. In addition, it is intended to provide a practical and economical device by doing so.

Therefore, in the first aspect of the invention, means for detecting the ground leakage current of the circuit, detecting the resistance ground fault current based on the magnitude and the phase shift from the circuit voltage, and displaying or outputting the magnitude each time. Detecting a resistance ground fault current characterized by comprising means for displaying or outputting the error range of the calculation result according to the magnitude of the phase shift between the ground leakage current and the circuit voltage. A device is provided.

According to a second aspect of the present invention, an apparatus having means for detecting the resistance ground fault current has a means for detecting the resistance ground fault current and displaying or outputting the magnitude each time. An apparatus for detecting a resistance ground fault current according to claim 1, wherein the apparatus is a ground fault relay.

According to a third aspect of the present invention, there is provided the apparatus for detecting a resistance ground fault current according to claim 1, wherein the apparatus having means for detecting the resistance ground fault current is a measuring instrument. .

According to the present invention, there is a means for detecting a ground leakage current in the circuit, detecting a resistance ground fault current based on the magnitude and a phase shift from the circuit voltage, and displaying or outputting the magnitude each time. In the device, the error range is displayed and output according to the magnitude of the phase shift between the ground leakage current and the circuit voltage, so whether the detected resistance ground fault current really exists and how reliable the value is Can be easily determined. Further, by providing the device with such an error range display and output device, it is possible to obtain a device having a phase shift detection accuracy that does not interfere with practical use, thereby reducing 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 a commercial voltage to the electric lines 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 a single-phase three-wire electric circuit or a three-phase three-wire electric circuit with a delta connection and one-pole grounding can be applied in principle.

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 circuit 2 and a ground-fault leakage current Ior flowing in the ground-fault resistor 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 zero-phase current and the current signal handled by the detection circuit, but may be included in the arithmetic circuit 1007.

Generally, 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. The current flowing through the ground fault resistor 5 linearly corresponds to those waveform distortions. However, the current flowing through the ground capacitance 4 changes relatively as the frequency increases because the impedance changes with respect to the frequency of the waveform distortion component. 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. In this case, the circuit voltage corresponds to the ground voltage.

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 from the absolute magnitude of the phase difference and the zero-phase current. This will be described with reference to FIGS.

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 signal and the zero point of the current signal, and the phase difference is calculated as 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.

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.

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.

The arithmetic circuit 1007 calculates the error range of the resistance ground fault current from the calculated phase difference, the ground leakage current, the magnitude of the resistance ground fault current, and the phase difference detection accuracy of the preset device. The error range may be displayed as ±% with respect to the calculated resistance ground fault current or may be displayed as ± mA. In the case of ±% display, it is the ratio of 18 (18 ') to 17 (17') in FIG. 4, and in the case of ± mA, 18 (18 ') may be displayed as it is. Reference numeral 1008 denotes an output means for outputting the result of the resistance ground fault current by the arithmetic circuit 1007. The output of the detection result is displayed as a level, a numerical value, or a signal. An error range display output means 1009 displays and outputs the above-mentioned error range calculated by 1007 as a ±%, mA, or mini-max range.

When the calculation by 1007 is performed by the method shown in FIG. 3, the phase difference between the circuit voltage and the ground leakage current uses a trigonometric function from the absolute value of the ground leakage current and the detected resistance ground fault current value. There is a way to ask.

According to the circuit breaker 10 shown in FIG. 1, the magnitude of the resistance ground fault current of the installed circuit can be detected and displayed, and since the error range can be known, the fact that there is a resistance ground fault current is displayed. Can also determine if it really is and whether the value is reliable.

In addition, when trying to detect the 1 mA resistance ground fault current given in the above example with an accuracy of ± 10%, if errors other than the phase difference measurement error can be ignored, the phase difference is 45 degrees. The permissible value of detection accuracy is ± 5 degrees, but if the phase difference is 85 degrees, the required phase difference detection accuracy is ± 0.5 degrees, and the phase difference is detected as the phase difference approaches 90 degrees. The demand for accuracy 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.

FIG. 5 and FIG. 6 show an embodiment in which a resistance ground fault current display function is added to the earth leakage breaker that breaks the circuit depending on the magnitude of 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) to open 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. Even with such a configuration, the same function as in FIG. 5 can be achieved. The earth leakage breakers shown in Figs. 5 and 6 display the magnitude of the resistance ground fault current for insulation failures that do not require emergency, and constantly monitor the degree of failure. However, such as electric shocks where the leakage current exceeds 30 mA. In case of an urgent accident, it operates in stages to cut off the electric circuit. At this time, since the detection error range is displayed at the same time for the display of the resistance ground fault current before the breaking operation, it can be known whether or not the displayed magnitude of the resistance ground fault current is reliable.

FIG. 7 shows a 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 1010 'relay operation, is it possible to constantly monitor the magnitude of the resistance ground fault current in the circuit in advance and is the magnitude of the resistance ground fault current displayed and output reliable? You can judge at a glance.

FIG. 8 shows a measuring instrument for resistance ground fault current. In the figure, reference numerals 1004 to 1009 are the same as those of the relay shown in FIG. 7, but the display means 1008 always displays and outputs the resistance ground fault current as a level or a numerical value. The current transformer 1004 may be a clamp type, and the electric circuit voltage may be temporarily connected to the electric circuit with an alligator clip or the like and supplied to the input circuit 1006. With such a measuring instrument, it can be determined at a glance whether the measured resistance ground fault current value is reliable.

In addition to circuit breakers, earth leakage 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 Configuration diagram of measuring instrument 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)

In a device that has a means to detect the ground leakage current of the circuit, detect the resistance ground fault current based on the magnitude and phase shift from the circuit voltage, and display or output the magnitude each time. An apparatus for detecting a resistance ground fault current, comprising means for displaying or outputting an error range of a calculation result in accordance with a magnitude of a phase shift from an electric circuit voltage. The device provided with the means for detecting the resistance ground fault current is a circuit breaker, earth leakage breaker or earth leakage relay having means for detecting the resistance ground fault current and displaying or outputting the magnitude each time. The apparatus for detecting a resistance ground fault current according to claim 1. 2. The apparatus for detecting a resistance ground fault current according to claim 1, wherein the apparatus provided with means for detecting the resistance ground fault current is a measuring instrument.

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