JPH0657036U - Leakage detector for single-phase two-wire circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an earth leakage detection device capable of accurately detecting a ground fault current that causes a fire or an electric shock accident even in an electric circuit where a large amount of leakage current is constantly present. [Effect] In a single-phase two-wire type electric circuit in which one wire is grounded,
The total leakage current signal of the single-phase, two-wire type electric line from the zero-phase current transformer whose primary side is the electric line or the ground line is the 9-line voltage waveform between two lines.
Since only the ground fault current is detected by sampling at the timings of 0 degree and 270 degree, there is an effect that the ground fault current can be accurately detected in a state in which the occurrence of unnecessary operation due to the electric circuit leakage current is significantly reduced.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a leakage detecting device for a single-phase two-wire type electric circuit.

[0002]

[Prior art]

 Conventionally, as shown in Fig. 13 and Fig. 14, the earth leakage detection device for a single-phase two-wire type electric circuit has a ground fault current flowing when the insulation between the electric circuit and the earth is abnormally lowered, and a ground electrostatic current between the electric circuit and the earth. The zero-phase current transformer ZCT detects the combined current with the leakage current that constantly flows through the capacitor, and outputs the leakage detection signal when the current value exceeds the set value.

[0003]

[Problems to be solved by the device]

 The above-mentioned conventional leakage detecting device for a single-phase two-wire type electric line has a small capacitance to ground and a small constant leakage current in an electric line having a short wiring length. Although it is possible to detect faults with high accuracy, on the other hand, in an electric circuit with a long wiring length, the capacitance to ground is large and the leakage current is always large. The sensitivity current setting value of the device has to be increased, which causes a problem that the ground fault detection accuracy is significantly reduced.

[0004]

[Means for Solving the Problems]

 In view of the problems of the conventional leak current detection circuit in a single-phase two-wire type electric circuit, the object of the present invention is to accurately detect a ground fault current that causes a fire or an electric shock accident even in an electric circuit with a large leakage current at all times. A single-phase two-wire type electric circuit in which one wire is grounded, and the single-phase two-wire from the zero-phase transformer whose primary side is the electric circuit or the grounding wire is provided. All leak current signals of the type electric circuit are sampled at the timings of 90 ° and 270 ° of the voltage waveform between two lines, and only the ground fault current is detected.

[0005]

According to the leakage detecting device in the single-phase two-wire type electric line configured as described above, the total leakage current is calculated from the ground leakage current which is the resistive leakage current component and the constant leakage current which is the capacitive leakage current component. And each current component waveform has a phase difference. The present invention pays attention to this point, and samples all the leakage current waveforms detected by the zero-phase current transformer at the timings of 90 ° and 270 ° of the two-line voltage waveform, that is, at the timing when the capacitive leakage current waveform becomes 0V. By ringing, only the ground fault current can be detected and the ground fault current can be detected with high accuracy regardless of the magnitude of the leakage current value at all times.

[0006]

【Example】

 FIG. 1 is an external connection diagram of the leakage detecting device for a single-phase two-wire electric circuit according to the present invention, and FIG. 2 is a block diagram of the leakage detecting device for a single-phase two-wire electric circuit according to the present invention. Further, FIG. 3 is a waveform diagram in a steady state, which is a 1: L relative earth voltage waveform and a 2: L relative earth capacity leakage current waveform. FIG. 4 is a waveform diagram at the time of occurrence of a ground fault, where 3: is a ground-capacity leakage current waveform, 4: is a ground-fault current waveform, and 5 is a total leakage current waveform. The present invention will be described below with reference to these drawings.

When a leakage current is generated in the electric circuit, a leakage current detection signal is output in steps a to h below. a: Total leakage current is detected by the zero-phase current transformer ZCT. b: Amplify by the amplifier. c: Full-wave rectification is performed by the full-wave rectification unit. d: The full-wave rectified signal is sampled by the sampling unit at timings of 90 degrees and 270 degrees. This sampling signal is generated by inputting a reference signal to the sampling pulse generating section through a transformer for the voltage between two lines of a single-phase two-wire type electric circuit. Note that the sampling value is almost 0 V in the steady state, and when the ground fault occurs, it becomes the instantaneous value of the peak of the ground fault current waveform. e: The sampled signal is held by the hold unit from the end of sampling to the input of the reset signal. As shown in FIG. 9, the output is a square wave whose peak value is the sampling value. The reset signal is generated by a reset pulse generator that outputs a pulse after t time using the sampling pulse as a trigger signal, and is input to the reset terminal of the hold unit. f: The voltage comparison unit detects whether the signal of e is equal to or higher than the threshold voltage, and if the signal is equal to or higher than the threshold voltage, outputs a square wave pulse having a constant voltage value in the same time width. g: When a square wave pulse is continuously input to the integrator, the voltage rises to a constant voltage after a fixed time. h: The voltage comparator detects that the output voltage of g, that is, the resistance ground fault of a set value or more continues for a set time or longer, and outputs a leakage detection signal.

FIGS. 5 to 12 show waveforms in a steady state in which only the electric line leakage is present in each of the steps a to h, and waveforms when a ground fault occurs, in which a ground fault is added to the electric line leakage.

[0009]

[Effect of device]

 The leakage detecting device for a single-phase two-wire electric circuit according to the present invention is a single-phase two-wire electric circuit in which one wire is grounded, and the single-phase from the zero-phase current transformer whose primary side is the electric path or the ground wire. By sampling the total leakage current signal of the 2-wire type electric circuit at 90 ° and 270 ° timing of the voltage waveform between the 2 lines and detecting only the ground fault current, only the leakage current due to insulation failure of the electric line or load can be detected. Since it is possible to detect the ground fault current, it is possible to detect the ground fault current with high accuracy while significantly reducing the occurrence of unnecessary operation due to the leakage current in the circuit.

[Brief description of drawings]

FIG. 1 is an external connection diagram of a leakage detecting device in a single-phase two-wire type electric circuit according to the present invention.

FIG. 2 is a block diagram of a leakage detecting device in a single-phase two-wire type electric circuit according to the present invention.

FIG. 3 is a waveform diagram in a steady state.

FIG. 4 is a waveform diagram when a leakage current is detected.

5 is a waveform diagram of step a in FIG.

FIG. 6 is a waveform diagram of step b in FIG.

FIG. 7 is a waveform diagram of step c in FIG.

FIG. 8 is a waveform diagram of step d in FIG.

9 is a waveform diagram of step e in FIG.

10 is a waveform chart of step f in FIG.

11 is a waveform diagram of step g in FIG.

FIG. 12 is a waveform diagram of step h in FIG.

FIG. 13 is an external connection diagram of a leakage detection device in a conventional single-phase two-wire type electric circuit.

FIG. 14 is a block diagram of a conventional leakage detecting device in a single-phase two-wire type electric circuit.

[Explanation of symbols]

 ZCT: Zero-phase current transformer.

Claims (1)

[Scope of utility model registration request] 1. In a single-phase two-wire type electric circuit in which one line is grounded, a total leakage current signal of the single-phase two-wire type electric line from a zero-phase current transformer whose primary side is the electric line or the grounding line, Sampling at the timing of 90 degrees and 270 degrees of the voltage waveform between two lines,
A leak current detection circuit in a single-phase two-wire electric circuit, which is characterized by detecting only a ground fault current.