JPH0247175B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting whether a ground fault has occurred on either side of a branch line in an ungrounded high voltage distribution system.

When a ground fault occurs in a high-voltage distribution line, for example, as shown in Figure 1, the high-voltage distribution line is pulled out via the high-voltage bus 2 in the substation 1, the disconnector 3, and the zero-phase current transformer 4. 5 and each branch line 6, and the accident point G is on the load side from the branch point,
A maintenance engineer will be dispatched to the location and, for example, alternately open and close the pole-mounted high voltage switches S ₁ , S ₂ ,...Sn, such as high pressure air switches, and retransmit power while communicating with substation 1. An accident is caused and an accident investigation is conducted.

However, in the case of a so-called ghost accident, where a ground fault occurs for a short time due to temporary contact with a bird, animal, or tree, and disappears when the accident investigation begins, there is no other option than waiting for the next accident to occur. , it is difficult to detect during patrols, etc.

For this reason, zero-phase current transformers and zero-phase transformers are installed in pole-mounted high-voltage switches, etc. on the main line and each branch line.
A detection device has been devised that compares the phases of the fault current and zero-sequence voltage detected by each sensor and displays which branch line the fault has occurred on.

However, this current-voltage phase comparison method has the following problems.

First, high-voltage cables are increasingly being used in recent high-voltage power distribution lines (the same applies in the premises of private electrical facility facilities), and as a result, the ground capacitance has increased significantly. This inevitably results in a drop in the zero-sequence voltage caused by the same resistance value in a resistance ground fault accident, for example, and a detectable fault occurs when the ground fault current is large, in other words, the degree of damage increases. I have no choice but to become It is also possible to increase the sensitivity by amplifying the low zero-sequence voltage, but doing so may cause malfunctions due to the so-called residual voltage that normally occurs in high-voltage distribution lines, so it is not possible to increase the sensitivity without limit. Therefore, the detectable ground fault current has to be kept at a relatively low sensitivity. In addition, if a three-phase bulk zero-phase current transformer is placed inside a pole-mounted high-pressure air switch, etc., the wires will bend significantly, and to avoid this, if a large oval zero-phase current transformer is used, For example, it is impossible to detect minute ground fault currents. Furthermore, the zero-sequence voltage detector may also become a weak point in the line.

The present invention aims to solve these problems and provide a detection device that can reliably determine the accident side using a simpler method that does not use a zero-phase voltage detector.

First, to explain the principle of the present invention, when a single-line ground fault occurs on one line at a branch point of an ungrounded high-voltage distribution line as shown in Figure 2, zero-sequence current flows from all lines toward this fault point. Flow into. Considering the branch point, it is natural that some current flows from the intact line through the branch point to the fault point. In Fig. 2, i _g indicates the magnitude of the ground fault current.

If the ground fault current sensitivity settings of the detectors on both sides are set to high sensitivity so that minute ground fault currents can be detected, both detectors can be detected even if a fault occurs on one side, depending on the magnitude of the fault current on the ground fault side. There is a fairly high probability that the device will display an operating message.

This is the reason why a non-grounding type earth fault directional relay is required, and the voltage/current phase comparison method is also one of the methods to prevent this.

The present invention focuses on the fact that when a ground fault occurs on one side of a branch line, there is a large difference in the ratio of the absolute values of zero-sequence currents flowing from other branch lines to this fault point, and utilizes this fact. The determination is made by

That is, considering the ground fault zero-sequence current flowing in the distribution line, as shown in the second diagram, from the substation bus 2 to the fault point A
The current value flowing towards fault point A is the sum of the currents flowing in from other feeders connected to this substation bus 2 through the ground capacitance, and the current value flowing towards fault point A from the healthy branch line is the The value is several times larger.

However, this is a comparison in terms of ratios, and there is a wide range in absolute values. In other words, for example, when the fault side is about 20A, which is close to a complete ground fault, the healthy side is 500mA.
(This value is determined from the overall ground capacitance of the same substation bank, the ground capacitance of the healthy branch line, the resistance value of the ground fault, etc.) If this is the case, then the fault side has a high resistance ground fault, When the fault current is about 100mA, the healthy side is only about 2.5mA.

For this reason, as shown in Figure 3, zero-phase current transformers 9 and 10 (both of which are connected to three CT
Consists of. ) output on each display 11, 1
2 to the main body side, comparison sides 13, 14 and 15, 16, and create a comparison circuit as shown in Figure 5.
Depending on the larger value, the operation of that side is displayed.

Embodiments of the present invention will be described below with reference to FIGS. 4 and 5. In order not to reduce the insulation strength of the high-voltage distribution line 17, for example, as shown in FIG. High voltage pole switch 19
One high-performance feed-through current transformer is built into each phase inside the pushing switch (a combination of three detects zero-sequence current. Two of these can also be used to detect short-circuit current). ), input the outputs from the above three current transformers installed on the two branch lines, or the main line and the branch line, at a height visible from the ground on each pillar 18, and compare them. Then, a display 20 is attached to each side to indicate which side the accident occurred. If the switch 19 is an automatic switch, the display signal is relayed to open the switch 19. In addition, in Fig. 4, 21 is a contact line,
22 indicates the substation side, and 23 and 24 indicate the load side.

The circuit of the display 20 is constructed as shown in FIG. That is, the inputs from the zero-phase current transformers ZCT-A and ZCT-B installed on the two branch lines A and B are respectively transmitted to the over-input protection circuits 25A and 25B and the amplifier circuit 2.
6A, 26B, AC/DC conversion circuit 27A, 27B
is connected to the first level detection circuit 28 and the comparison circuit 29 through the first level detection circuit 28 and the comparison circuit 29.
8, if it is above the set level, it goes directly to the output circuit 30, and the comparator circuit 29 outputs it only when A>B (in the case of A branch, it is the opposite on the B side), and the second level detection circuit 31 Output circuit 30 via
It is connected so that it enters the The output uses a relay circuit to display lamps, mechanical targets, etc. Note that the above circuit can be easily constructed using known hardware technology.

The reason for providing the first and second level detection circuits 28 and 31 in the above circuit is as follows.

The problem with this invention is that if a ground fault occurs on the power supply side from the branch point, a zero-sequence current proportional to the ground capacitance on the load side from the branch point flows toward the power supply side in both branch lines. . The comparison circuit 29 compares the magnitude of the two and outputs the larger one, but this is a malfunction.

Therefore, when a complete ground fault occurs on the power supply side, the magnitude of the fault current that flows backward is a [mA] (A side),
If b [mA] (B side), when a resistance ground fault occurs, compare the fault current value flowing to the A side and B side,
When the ratio is a:b, the circuit is configured so that it does not operate.

When a ground fault occurs on the load side of either A or B, the control circuit will not operate because the ratio of a:b is much larger than the ratio of a:b, as described above.

However, if this is done, if a one-line ground fault such as a:b occurs simultaneously on the load side of both branch lines, both lines will not operate.

Here, a [mA] and b [mA] are the values at the time of a complete ground fault, so as long as there is a ground fault on the power supply side, these values will not be exceeded. Therefore, the circuit is configured such that both values are set as threshold values, and if the values are larger than these values, the output is output even if both are at the same time. This threshold is level 1.

By estimating the ground capacitance of both branches and narrowing the range a:b as much as possible, it is possible to further narrow the inoperable region in the case of simultaneous ground faults in both branch lines.

As long as either side exceeds the a:b range, one side will operate first, followed by the other side.

The probability that a ground fault will occur in both branch lines at the same time is small, and the probability that both are high-resistance ground faults that are lower than the threshold (level 1) and that a: b is extremely small. It will be done.

Furthermore, the above non-operating region is the value at which the distribution substation operates (in this case, it is dominated by the zero-sequence voltage)
This is a very low range, and it can be said that it always operates whenever a distribution substation operates. That is, even in the worst case, when the distribution substation is in operation, it is possible to issue an operation indication in series.

Since the present invention is configured as described above, it will not malfunction no matter how small the sensitivity current setting value is set. For example, if the sensitivity current setting value is set to about 60 mA, even a slight ground fault such as contact with a tree will not occur. It is possible to provide a detection device that can detect the accident side reliably and with high sensitivity using a simpler method than the conventional detectors described above.

[Brief explanation of drawings]

Figure 1 is a model diagram of a branch line of a high-voltage distribution line.
A conceptual diagram showing, for comparison, the current values flowing through each part of the line when a single-line ground fault occurs on a single branch line. A conceptual diagram showing the relative magnitude of short circuit currents. Figure 3 is an explanatory diagram of inputs to the display of the branch line ground fault fault detection device on the opposite side and comparison side, respectively. Figure 4 is an illustration of the present invention. FIG. 5 is a block diagram illustrating the circuit of the display device in the same embodiment. 17... High-voltage distribution line, 18... Utility pole, 19... High-voltage pole-mounted switch incorporating a through-type current transformer, 20... Display device.

Claims (1)

[Claims] 1. At a branch point of an ungrounded system high voltage distribution line,
A high-sensitivity feed-through current transformer that does not reduce the insulation strength of each branch line is installed, and a comparison circuit is installed to mutually compare the minute ground fault currents detected by this current transformer. The display is connected so that the input from each current transformer passes through an over-input protection circuit, an amplifier circuit, an AC/DC conversion circuit, and then enters a first level detection circuit and a comparison circuit. Then, if it is above the setting level, it goes directly to the output circuit, and the comparison circuit outputs it only when there is a difference between the inputs from each of the zero-phase current transformers, and goes through the second level detection circuit to the output circuit. A high-voltage distribution line/branch line ground fault detection device equipped with a fault point indicator that is connected in the following manner. 2. The high-voltage distribution line/branch line ground fault detection device according to claim 1, wherein the fault point indicator is attached to a utility pole at a height visible from the ground.