JPS6155327B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a line selection ground fault protection relay device for a direct-to-ground polyphase AC circuit. There are three types of devices for extracting zero-sequence current in an AC circuit: a secondary residual circuit in each phase transformer, a tertiary zero-sequence shunt in each phase current transformer, and a zero-phase current transformer. Although they are used differently depending on the situation, zero-phase current transformers are generally used for high-sensitivity detection to protect ground faults in direct-to-ground low-voltage three-phase distribution lines applied to building facilities, etc. The reason for this is that each zero-sequence current extraction device generates residual current in the output system when normal load current is flowing, so in order to prevent the ground fault relay from malfunctioning due to this residual current, the operating current value must be higher than the residual current. This is because a zero-phase current transformer with a small residual current allows for more sensitive setting. This zero-phase current transformer is usually housed in a low-voltage closed power distribution board called a load center, along with current transformers for each phase used for shield breakers and short-circuit protection or measurement. In order to reduce the installation space, it is desired to be as small as possible, and for this purpose, it is necessary to downsize or reduce the size of equipment stored in the switchboard. The present invention was made in response to such demands, and by using a secondary residual circuit or a tertiary zero-phase shunt of each phase current transformer without using a zero-phase current transformer, equipment housed in a switchboard can be To provide a ground fault protection relay device which is compact in size and can accurately determine a ground fault in a protected line even when a residual current is generated from a secondary residual circuit of each phase current transformer. The purpose is to Hereinafter, one embodiment of the present invention will be described with reference to FIG. In the same figure, 1 is a secondary residual circuit of each phase current transformer provided in the protected distribution line, and the output current of this circuit 1 is assumed to be I ₁ . 2 is a single-phase current transformer installed on the neutral point grounding wire, and the output current of this current transformer 2 is I〓 ₂
shall be. 3 is an overcurrent detector that outputs an overcurrent detection signal when _I〓2 exceeds a certain value, 4 is a difference extractor that extracts the vector difference between _I〓1 and _I〓2 , and 5 is a difference extractor 4. 6 is a NOT circuit that inverts the output of the change detector 5, and 7 is the output signal of the NOT circuit 6 and the output signal of the overcurrent detector 3. This is an AND circuit that serves as a determination circuit that outputs a signal indicating an accident when inputted with the following. Next, the operation of the apparatus configured as above will be explained. In the absence of ground fault, each current is I〓 ₁ =
The residual current (I〓 ₀ 1〓) due to the load current, I〓 ₂ ≈0, therefore, since the overcurrent detector 3 is inoperative, the signal at its output section is "0". For this reason, AND
The output signal of circuit 7 is “0” regardless of the state of _I〓1 .
becomes. Now, if a line-to-ground fault F ₁ occurs in the protected line, I〓 ₁ ≒ I〓 ₀ 1〓 + 3 as shown in Figure 2.
I〓 ₀ , I〓 ₂ ≒ 3I〓 ₀ (However, I〓 ₀ is the zero-sequence current converted to the secondary side of the current transformer, and the transformation ratios of current transformers 1 and 2 are the same), and the difference extractor The output of 4 is I〓 ₀ 1〓=
I〓 ₁ - I〓 ₂ , which is the same as before the failure occurred. The output signal of the change detector 5 is "0", and the output signal of the NOT circuit 6 is "1". Here, I〓 ₂ = 3I〓 ₀
If is greater than or equal to the operating sensitivity of the overcurrent detector 3, the output signal of the detector 3 becomes "1", so the condition of the AND circuit 7 is satisfied and an output is generated. On the other hand, if a failure occurs in another line, I〓 ₁ = I〓 ₀ 1〓 as shown in Fig. 3, so I〓
₁
-I〓 ₂ ≠I〓 ₀ 1〓, a signal is generated at the output part of the change detector 5, and the output of the NOT circuit 6 becomes "0", so the condition of the AND circuit 7 is not satisfied, and the line is considered to be a healthy line. It is possible to identify a faulty line. Further, even if the residual current of the secondary residual circuit 1 fluctuates due to a short-circuit accident in the protected line or a large load fluctuation, the overcurrent detector 3 is inoperative and no output signal is generated. The above relationships are organized as shown in the table below.

【table】

[Table] Next, FIG. 4 is a diagram showing a specific example of the difference extractor 4 shown in FIG. 1. This extractor 4 is a differential circuit using a conventionally known operational amplifier 4a, and E ₁ = KI ₁ , E ₂ = KI ₂ (K is a proportionality constant).
Then, E ₀ =-(R ₀ /R ₁ E ₁ -R ₀ /R ₂ E ₂ )=-(R ₀ /R
₁ K ₁ I ₁ - R ₀ /R ₂ K ₂ I ₂ ), and as mentioned above, if the transformation ratios of current transformers 1 and 2 shown in Fig. 1 are the same, R ₁ = R _2. On the other hand, if the metamorphic ratio is different,
By arbitrarily selecting R ₁ or R ₂ , the difference in metamorphic ratio can be easily matched. That is, the transformation ratios of the current transformers 1 and 2 do not necessarily have to be the same, and any ratio can be applied. FIG. 5 is a diagram showing a specific example of the variation detector 5 shown in FIG. 1. In the figure, 8 is a fundamental wave passing filter, 9 is a difference extractor, and 10 is a level detector. The signal of the difference extractor 4 is introduced into a fundamental wave passing filter 8, and then the output signal of the filter 8 and the output signal of the difference extractor 4 are introduced into a difference extractor 9 to extract the difference. Then, this difference signal is introduced into a level detector 10, and if the difference signal is equal to or higher than the detection level, a signal is output. FIG. 6 shows waveforms at various parts in FIG. As is clear from this figure, when there is no change in the output signal of the difference extractor 4, the input and output signals of the filter 8 are the same, so the difference is zero; however, when the output of the difference extractor 4 changes, the difference is zero. Since the output of the filter changes gradually due to the transient response of the filter itself, a difference occurs for a certain period of time, and this is level-detected and output. Incidentally, the overcurrent detector 3 shown in FIG. 1 may be of any configuration or type as long as the required detection sensitivity can be ensured. Further, although the above embodiment uses a secondary residual circuit of each phase current transformer, a tertiary zero-sequence shunt may be used to detect the zero-sequence current. FIG. 7 shows an example in which the device of the present invention is applied to a three-phase four-wire direct-to-ground distribution line. 11 is the neutral wire, 12
is the device according to the present invention, and the neutral line current I〓 _N is I〓 _N
=-(I〓 _R +I〓 _S +I〓 _T ), current transformer outputs I〓 ₁ and I〓 ₂ are the same as in the case of 3-phase 3-wire system, and as mentioned above, there is a ground fault. Accidents can be detected. As described in detail above, according to the present invention, by detecting overcurrent in the neutral point grounding circuit and detecting a change in the difference current between the zero-sequence current of the protected circuit and the neutral point grounding circuit current, Even if there is a residual current caused by the current, the structure is configured so that single-line ground fault faults can be accurately determined without being affected by the residual current. A highly sensitive and configurable direct ground system that can downsize the entire device and reduce costs by detecting zero-sequence current using the secondary residual circuit or tertiary zero-sequence shunt of a current transformer. A ground fault protection relay device can be provided.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the earth fault protection relay device according to the present invention, Fig. 2 is a vector diagram when there is no ground fault, Fig. 3 is a vector diagram when there is a ground fault, and Fig. 3 is a vector diagram when there is a ground fault. Fig. 4 is a block diagram showing a specific example of the difference detector in Fig. 1, Fig. 5 is a block diagram showing a specific example of the first change detector, and Fig. 6 explains the operation of Fig. 5. FIG. 7 is a configuration diagram showing another embodiment of the apparatus of the present invention. 1, 2...Current transformer, 3...Overcurrent detector, 4...
...Difference extractor, 5...Change detector, 6...
NOT circuit, 7...AND circuit, 8...fundamental wave passing filter, 9...difference extractor, 10...level detector.

Claims (1)

[Scope of Claims] 1. In a line selection ground fault protection relay device for a neutral point directly grounded multi-phase AC circuit, the neutral point grounding circuit current taken out from the current transformer of the neutral point grounding wire is predetermined. An overcurrent detector that outputs an overcurrent detection signal when the current exceeds the current value, and a secondary residual circuit or tertiary zero-phase shunt of each phase current transformer installed in the protected line are used to The residual current due to the load current is detected, and in the event of an accident, the zero-sequence current including the residual current is detected, and the zero-sequence current including this residual current and the neutral point grounding circuit current are input, and the vector difference between the two currents is extracted. An extractor and the output of the difference extractor are introduced into a fundamental wave passing filter, and when the level difference between the output of the fundamental wave passing filter and the difference extractor output exceeds a predetermined level, a signal is generated. and a change detector that outputs a change detector, and on the condition that there is no output signal from this change detector and an overcurrent detection signal from the overcurrent detector is received, it is determined that there is a line-to-ground fault in the protected line. A ground fault protection relay device comprising a determination circuit that outputs a signal.