JPH039275A - Leakage current detector for cable line - Google Patents

Abstract

PURPOSE:To inform the decision result made from a comparison with a reference value to a substation from an origination part in a line by monitoring a charge current for a sheath of the cable line and indirectly detecting a 2-phase current constituting the cable. CONSTITUTION:The charge currents for the sheaths of the lines 5a (phase A), 5b(phase B) are measured by current transformers 11a,11b and the phase shift of 120 deg. is made for an output from the transformer 11a in a phase current detecting part 10. In a comparison decision part 20, the signal of the phase A is made to a rectangular wave with a cycle in the time t1-t3 by a waveform forming circuit 21 and the signal of the phase B is made to a sine wave with the same cycle. When a leakage current exists in the line, the signal of phase B inputted to a mask circuit 22 is shifted in a certain amount from the signal of phase A and a current at the plus side of phase B is detected in the time t1-t3 without being masked. This signal is detected, smoothed and changed to a DC voltage signal, then, when it is beyond the reference value, the output of the mask circuit is made to 'H' and a switch in the origination part 30 is made to be ON to output a specified signal. This output is supplied to an earth line 3 of the cable line 5c through a current transformer 11c, and the decision signal is informed to the substation, etc., through the cable line.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a cable line leakage current detection device used for monitoring cable lines, particularly ungrounded cable lines.

(Prior art) When a ground fault occurs on a cable line, it is necessary to immediately disconnect the faulty section in order to prevent wide-area power outages, induction failures, and major accidents.

If a ground fault occurs in a power transmission line that uses a grounding method such as direct grounding or resistance grounding, a relatively large ground fault current will flow, so this can be detected using a ground fault relay, etc., and the ground fault can be quickly detected. The area where the accident occurred is being separated.

(Problem to be Solved by the Invention) By the way, when the power transmission voltage is low, the so-called non-grounding type is adopted because it is easy to insulate the cable line and the transformer. In this case, even if a - line ground fault occurs, the ground fault current is relatively small and power transmission can continue as is. However, in the case of cables or equipment in which poor insulation or the like has occurred, it is preferable to quickly find the faulty part and repair or replace it.

That is, it has been desired to develop a more practical leakage current detection device that is suitable for rapid detection of minute leakage currents at such failure locations and for centralized control in substations and the like.

The present invention has been made with attention to the above points, and can be installed at various locations on a cable line, and when a leakage current is detected, the result can be automatically notified to a substation, etc. The object of the present invention is to provide a leakage current detection device.

(Means for Solving the Problems) A leakage current detection device for a cable line according to the present invention includes a phase current detection section that detects phase currents of at least two phases of a cable line from a charging current of a cable sheath, and a phase current detection section that detects phase currents of at least two phases of a cable line, and A comparison/determination unit that compares the phase difference between the phase currents of the two phases and determines the deviation of the phase difference from a reference value, and a determination signal that displays the determination result of this determination unit, is transmitted into the cable line. The device is characterized in that it includes a transmitter that transmits.

(For A) The above device monitors the charging current of the cable sheath of the cable line, thereby indirectly detecting the phase currents of the two phases forming the cable line. The phase difference between the two is usually
The temperature is set at 120°C. However, when a leakage current occurs due to a ground fault or the like, the phase difference deviates from 120°C. If there is this deviation, a determination signal is generated.

This determination signal is transmitted from the transmitter via a cable line and notified to a substation or the like.

(Example) Hereinafter, the present invention will be explained in detail using embodiments shown in the drawings.

FIG. 1 is a block diagram showing an embodiment of the cable line leakage current detection device of the present invention.

Before going into the explanation of FIG. 1, the principle of operation of the apparatus of the present invention will first be explained with reference to FIGS. 2 and 3.

FIG. 2 is an explanatory diagram showing the sheath grounding state of a general ungrounded cable line.

As shown in the figure, in a cable line that employs an ungrounded type, only one end of a sheath 2 covering a conductor 1 of a power cable is grounded by a grounding wire. A relatively large voltage is usually induced in the sheath 2 by the transmission voltage of the conductor l of the cable. Therefore, the sheath 2 is grounded to prevent danger, but when both ends are grounded, a loop is formed by the ground return path, and a large induced current flows through the loop. Therefore, especially in the case of a non-grounded cable line, the sheath 2 is often grounded at one end as shown in FIG.

Here, FIG. 3 shows an equivalent circuit of such an ungrounded cable line. That is, the cable lines 5a, 5b, 5 connected to the ungrounded YΔ transformer 4
Since the sheath 2 is grounded at one end as shown in FIG. 2, its equivalent circuit can be replaced with capacitors Ca, Cb, and Cc whose one end is grounded.

Here, the power supply voltage is expressed as a vector value for each phase, Ea,
Eb and Ec are the phase currents, and Ia and Ib are the phase currents.

Assuming Ic, the following equation is satisfied vector-wise if there is no leakage current.

Ia+Ib+Ic=0 Here, if a single line ground fault occurs, a resistor R is connected in parallel to one capacitor C, as shown by the broken line in FIG. For example, if this ground fault resistance R is “0”
”, each phase current satisfies the following relationship vector-wise.

Ia=Ib+Ic That is, before the ground fault occurs, Ia, Ib, and Ic are out of phase with each other by 120 degrees, but after the ground fault occurs, the phase voltage E1 of the cable line 5a becomes "O". ”, the phase between the phase currents Ib and Ic changes to 60°.

The device of the present invention captures this change and generates a determination signal.

Note that due to the line current flowing in the cable line, a charging current flows through the bond wire 3 in the sheath 2 shown in FIG. The line current of the cable line corresponds to this charging current, and by measuring the charging current of the sheath of each phase, it is possible to detect the phase difference between the phase currents.

FIG. 1 shows a circuit constructed based on the above principle.

The illustrated circuit includes a phase current detection section 10, a comparison determination section 20,
A transmitting section 30 is provided.

The phase current detection unit 10 extracts sheath charging current from a current transformer lla attached to the grounding wire 3 of the cable line 5a and a current transformer llb attached to the grounding line 3 of the cable line 5b, respectively. The phase current detection section has a 120° phase shifter for one input signal.
A phase circuit 12 is provided. This phase circuit can match the phases of input signals corresponding to the two-phase currents of the cable line 5a and the cable line 5b in a healthy state by using a circuit including a delay circuit or the like.

The comparison/judgment section 20 includes a waveform shaping circuit 21 and a mask circuit 2.
It consists of 2.

The waveform shaping circuit 21 is a circuit that converts a sinusoidal input signal into a rectangular waveform output signal. The mask circuit 22 is a circuit that masks the input signal waveform corresponding to the phase current of the cable line 5b directly input from the phase current detection section 10 using the rectangular waveform signal input from the waveform shaping circuit 21, and outputs the result. be. This circuit is composed of, for example, a NAND gate (NAND). If the phase difference between the input signals corresponding to two phase currents is more than 120 degrees, the mask circuit 22 outputs a high level when the phase difference is detected, and outputs a low level in other cases. This is a working circuit.

The transmitter 30 includes a transmitter that transmits a determination signal indicating that a shift has occurred when the output of the mask circuit 22 is at a high level. For example, this determination signal has a frequency of 10 to 200 KHz.
It is assumed that the carrier frequency of about 100 MHz is modulated by an identification signal unique to the transmitter.

The above circuit operates as follows.

First, the charging current of the cable sheath of each cable line 5a, 5b is measured from the current transformers lla, llb,
When inputted to the phase current detection unit 10, the output of the current transformer lla is inputted to the comparison determination unit 20 with a phase shift of 1'20°C. Here, the cable line 5a will be called the A phase, and the cable line 5b will be called the B phase.

In the comparison/judgment section 20, when the waveform shaping circuit 21 shapes the waveform of the input signal, as shown in FIG. 4(a),
The A-phase signal input to the mask circuit 22 is at time t, ~t
It becomes a rectangular wave whose amplitude repeats with a cycle of 3. On the other hand, the B-phase signal input to the mask circuit 22 is a sine wave having the same period as the rectangular wave, as shown in FIG. 4(b).

The mask circuit 22 masks the + side signal of the B-phase signal between times t1 and t2. Furthermore, one side of the B-phase signal is masked between time t2 and time t3. As a result, when the phases of the input signals to the mask circuit 22 match both the A phase and the B phase, the output of the mask circuit 22 becomes a low level, and the transmitter 30 does not operate at all.

Here, the cable line 5a or 5b shown in FIG.
When a leakage current occurs, as shown in Figure 4 (C),
The B-phase signal input to the mask circuit 22 has a certain deviation from the A-phase signal shown in FIG. As a result,
When looking at times t2 to t3, the + side current of the B phase is not masked, and a part of it is detected as the output of the mask circuit 22, as shown in FIG. 4(d). This signal is converted into a predetermined DC voltage signal by a detector and a smoothing circuit (not shown) built into the mask circuit 22. This DC voltage signal level is compared with a preset reference value, and if it exceeds the reference value, the output of the mask circuit 22 is set to a high level. The sensitivity of the mask circuit's determination is adjusted by increasing or decreasing this reference value.

The transmitter 30 is switched on by its output,
The predetermined signal described above is output. This signal is supplied to the ground wire 3 of the cable line 5C via the same current transformer llc from which the sheath charging current is taken.

By the way, the device as shown in FIG. 1 is installed in a manhole or the like where the sheath of the cable line is grounded. Therefore, a power source is usually required to operate the circuit shown in FIG.

FIG. 5 shows a specific wiring diagram of such a power supply.

In FIG. 5, this circuit connects any cable line 5.
A current similar to the charging current explained in FIG. 1 is taken out from the current transformer 11 provided on the grounding wire 3 of A battery 45 is charged via a smoothing capacitor 44. The output of the battery 45 is supplied to various parts of the circuit shown in FIG. In this way, it is not necessary to prepare special power supply wiring or batteries for installing the device.

Note that the signal output from the transmitter 3o shown in FIG.
It is transported through the cable line as shown in FIG.

FIG. 6 is a wiring diagram showing an equivalent circuit of a cable line.

This circuit is a partial extraction of the circuit shown in FIG. has been done.

A current transformer LIC is attached to one side of this grounding wire 3, and when a judgment signal for displaying the judgment result described above is input from the transmitter 30 shown in Fig. 1, the judgment signal is transmitted to the cable line. 5c, capacitor Cc, capacitor c
b, the signal is transmitted through a loop formed by the cable line 5b and a part of the coil of the transformer 4. This determination signal is then transformed by the transformer 4 and is also transmitted to the secondary side of the transformer 4. In this manner, the determination signal reaches the substation or the like. Also at the substation, the determination signal is received using the same current transformer 51 and receiver 50 connected to the transmitter.

Incidentally, in the case of long-distance transmission, it is preferable to perform relay amplification of the determination signal at a portion such as the transformer 4 as necessary.

The present invention is not limited to the above embodiments.

The configuration of the phase current detection unit, the configuration of the comparison/judgment unit, or the configuration of the transmitting unit 30 may be replaced with known circuits having equivalent functions.

For example, a configuration may be adopted in which the grounding wires of each phase of the cable line are bundled and a single current transformer is installed, the zero-phase portion of the charging current is taken out, and the transmitting section 30 is activated when the zero-phase portion of the charging current is above a certain level. No problem.

(Effects of the Invention) The cable line leakage current detection device of the present invention described above detects the phase current of the cable line from the charging current of the cable sheath, and monitors the phase difference between the two to detect the leakage current. Therefore, the cable line condition can be monitored with high sensitivity with a relatively simple configuration. Furthermore, by transmitting the determination signal into the cable line, it is possible to construct a highly reliable system that centrally monitors the status of each part of the cable line at a substation or the like.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the cable line leakage current detection device of the present invention, FIGS. 2 and 3 are explanatory diagrams showing the operating principle of the device of the present invention, and FIG. 4 is the same as that of FIG. A time chart explaining the operation of the device, FIG. 5 is a wiring diagram showing an example of a power source for operating the device of the present invention, and FIG. 6 is a wiring diagram explaining the operation of the transmitter of the device of the present invention. . ---1--------Ground wire, a, 5b, 5cm---1-Cable line, ○----
-------- Phase current detection section, la, llb, 1lc
---1 current transformer, 0---------1 comparison/judgment section, 0-------------- transmitting section.

Claims (1)

[Claims] A phase current detection unit that detects phase currents of at least two phases of the cable line from the charging current of the cable sheath, and compares the phase difference between the detected phase currents of the two phases, and calculates the phase difference from the reference value of the phase difference. a comparison determination unit that determines the deviation of the
A leakage current detection device for a cable line, comprising a transmitter that transmits a determination signal indicating the determination result of the determination unit into the cable line.