JPH0357424B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a ground fault detection device suitable for use in detecting ground faults in a live system.

[Conventional technology]

The technology for detecting ground faults in live power transmission lines is well established, partly because the transmission lines are simple, but in the case of system systems, the wiring paths are complex like a network. The reality is that the technology has not yet been established because it involves difficult problems such as the fact that the signal current is small and the influence on it must be minimized.

[Problem that the invention seeks to solve]

The present invention was made to solve these problems, and its purpose is to create an extremely small and simple device that can detect ground faults in live systems that involve complex problems. This is achieved through a unique configuration.

[Means for solving problems]

In order to achieve the above object, the present invention includes a series circuit consisting of an oscillator, a resistor R1, and a capacitor C1 connected between a power supply placed in a main cubicle and the ground, and a series circuit between each slave cubicle and the ground. A measuring device is provided which has a capacitor C2 connected to the oscillator, and a synchronous rectifier circuit that synchronously rectifies the output of a transformer that clips the power line for each slave cubicle using the output of the oscillator, and connects the output of the synchronous rectifier circuit to ground. It is configured to be obtained as a fault detection signal.
Hereinafter, a case where the present invention is applied to a power monitoring system will be described.

〔Example〕

FIG. 1 is a circuit diagram of an embodiment of a device according to the present invention. In the figure, 10 is a main cubicle in which a power control circuit and the like are built-in, and 11, 12, . These cubicles constitute a power monitoring system. Es is a DC power supply located in the main cubicle 10, L1 and L2 are power supplies
This is a power line that leads Es to each slave cubicle 11, 12, . . . In addition, in the figure, two power lines L
1, L2 is shown, but in reality, the power source Es is connected to each slave cubicle 11, 1 by multiple lines.
2. It is now supplied to... OSC has a very small value (about 60mV) compared to the voltage of the power supply Es.
an oscillator that produces a sinusoidal voltage of , R1 is a resistor, and C
1 are capacities, which are arranged within the main cubicle 10. One end of the oscillator OSC is connected to the negative pole side of the power supply Es, and the other end is connected to the resistor R1 and capacitor C.
It is grounded through one series circuit. C2,C
3 indicates a capacitor (or a capacitor for noise prevention) connected between each slave cubicle 11, 12, . . . and the ground.

M1, M2... are clip-type transformers T.
1, T2..., each transformer T1, T
2... are always clipping the power lines L1, L2 for each slave cubicle 11, 12.... The outputs of the transformers T1, T2... are the outputs of the oscillator OSC in the synchronous rectifier circuits provided in the measuring instruments M1, M2...
Vi is rectified as a synchronous signal, and the synchronous rectified output is analog indicated or digitally displayed in the measuring instruments M1 and M2, and output signals S1 and S
2... is sent to a buzzer (not shown).

The operation of the detection device according to the present invention having such a configuration will be explained as follows. In addition, current measuring device M
The current transformers T1, T2, . . . 1, M2 keep the power lines L1, L2, . The power supply voltage Es is supplied into each slave cubicle 11, 12... through power lines L1, L2..., and the main cubicle 10
At the same time, each control circuit in the slave cubicles 11, 12, . . . is in an operating state. in this case,
The oscillation output of the oscillator OSC is added to the power supply voltage Es as a minute signal. Equivalent circuits of the ground fault detection portion in each slave cubicle 11, 12, . . . in such a power monitoring system are shown in FIGS. 2A and 2B. FIG. 2A shows an equivalent circuit when no ground fault occurs, and FIG. 2B shows an equivalent circuit when a ground fault occurs. In FIG. 2, the same elements as in FIG. 1 are given the same symbols as in FIG. 1. Transformer T
1, T2... clip the power lines L1, L2.

The detection signals of transformers T1, T2... are generated by the oscillator OSC.
is synchronously rectified by the output Vi of the result,
The measuring devices M1 and M2 detect only the effective portion of the signal voltage Vi, and the output of the effective portion is indicated or displayed and is output to the outside as a buzzer signal S1 (FIG. 1). In the case where a ground fault does not occur as shown in the equivalent circuit of FIG.
(C3,...) power lines L1, L2...
This current flows into the measuring device M as an imaginary current.
1, M2 does not output this.

When a ground fault occurs in each secondary cubicle 11, 12..., the current due to the ground fault flows through the ground fault resistance (or short circuit) Rx connected in parallel to the capacitor C2 (C3,...) as shown in Figure 2 (b). flows to the earth through it. The current flowing through this ground fault resistance Rx has a real part. This real part is measured by the transformer T in the measuring instruments M1 and M2.
1, T2... are extracted by synchronously rectifying them with the output of the oscillator OSC. This synchronously rectified real part output is given an analog indication in the measuring instruments M1 and M2, and is also output as a buzzer signal S1. As mentioned above, the power lines L1, L2
actually has multiple lines, and the transformers T1, T2... clip the multiple power lines L1, L2 all at once, but when the buzzer sounds and a signal is detected, the operator can Remove the clip and clip each power line to connect multiple power lines L.
Check which power supply line among 1 and L2 has caused the ground fault. Analog instructions when checking power lines L1 and L2 at once are provided by measuring instrument M.
1 and M2 operate as a level detector, and the digital indication for each line indicates the value of the ground fault resistance RX. In this way, the occurrence of a ground fault in the control system shown in FIG.
It is possible to detect every 1, 12, etc., and in which power supply line the occurrence occurred.

As shown in FIG. 1, the resistor R1 is inserted and connected between the oscillator OSC and the capacitor C1 in the main cubicle 10 in each of the slave cubicles 11, 12...
This is to prevent resistance Rx from becoming impossible to detect due to its imaginary component when the capacitance C2 (C3, . . . ) between the ground and the ground increases. This can be explained as follows. The equivalent circuit of FIG. 1 in a ground fault condition is shown in FIG. Here, when the oscillation frequency of the oscillator OSC is 750Hz, the impedance of capacitor C1 is X1, the impedance of capacitor C2 (C3,...) is X2, and the parallel resistance of ground fault resistor Rx and X2 is Rr, Rr is It is expressed by the following formula (1).

Rr＝(R1+αX2)＋(X1+αRx) ² /(R1+αX2)
...(1) However, α=Rx・X2/(Rx ² +X2 ² ) R1=20Ω, and the oscillation frequency of the oscillator OSC is
When X1 = 1Ω and X2 = 10Ω at 750KHz, the relationship between Rx and Rr is determined using equation (1) as follows.

When Rx = 0Ω, Rr = 20Ω When Rx = 20Ω, Rr = 27.4Ω When Rx = 50Ω, Rr = 54Ω When Rx = 100Ω, Rr = 26.8Ω When Rx = 200Ω, Rr = 26.05Ω When Rx = 1000Ω, Rr = 26.05Ω Equation (1) means that the limit of Rr is determined by R1 and ) is 26Ω, which is not preferable.

X2 to be able to detect 1KΩ as Rr is given by equation (1) assuming R1=10Ω: 1000=10+X2 ² /10 X2=√990×10=99.5Ω C2=1/2πfX2=2.22μF Therefore, C2= Using a 2.2μF (X2=100Ω), the relationship between Rx and Rr is calculated again using equation (1) as follows.

When Rx = 0Ω, Rr = 10.1Ω When Rx = 20Ω, Rr = 30.0Ω When Rx = 50Ω, Rr = 83.6Ω When Rx = 100Ω, Rr = 103.35Ω When Rx = 200Ω, Rr = 181Ω When Rx = 1000Ω, Rr = 1000Ω, and even if the capacitance C2 is large, the value of the ground fault resistance Rx in the open and short states can be clearly distinguished.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to obtain a ground fault detection device which is suitable for detecting ground faults in a system in a live line state and has a small size and simple configuration.

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing an embodiment of the ground fault detection device according to the present invention, and FIG. 2 shows an equivalent circuit of the device shown in FIG. 1. 10...Main cubicle, 11, 12...Slave cubicle, Es...Power source, OSC...Oscillator, R1...Resistor, C1, C2 (C3,...)...Capacitance, M1, M2
...Clip-type measuring device.

Claims (1)

[Claims] 1. A system system comprising a main cubicle and a plurality of slave cubicles, in which the output of a DC power supply placed in the main cubicle is sent to each slave cubicle via a power line. The fault detection device includes a series circuit consisting of an oscillator, a resistor R1, and a capacitor C1 connected between the power source and the ground, a capacitor C2 connected between each of the slave cubicles and the ground, and a series circuit of the slave cubicles and the ground. A measuring instrument is provided which has a synchronous rectifier circuit that synchronously rectifies the output of the transformer that clips the power line at each time using the output of the oscillator, and the output of the synchronous rectifier circuit is obtained as a ground fault detection signal. Ground fault detection device.