JPS5821489B2 - Protective relay device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to the occurrence of a ground fault in a power system consisting of power transmission and distribution lines that have a grounding transformer, power transmission and distribution lines that do not have a grounding transformer, and buses connected to these transmission and distribution lines. The present invention relates to a protective relay device that prevents a breaker of a power transmission/distribution line having a grounding transformer from being tripped unnecessarily by a short-circuit relay attached to the power transmission/distribution line.

FIG. 1 shows an example of the above power system and a protective relay device that protects this system.

Referring to FIG. 1, F3 is a power transmission line Fl having a grounding transformer G-Tr.

F2 is a transmission line without a grounding transformer, NGR is a grounding resistor connected to the neutral point of the grounding transformer G-Tr, B is a bus bar,
M-Tr is the main transformer, GPT is the grounding transformer, CT-8,
CT-G, C'r-1, CT-2 are current transformers, CB-8,
CB-G, CB-1, Cf3-2 are circuit breakers, 64 is a ground fault overvoltage relay that responds to the zero-sequence voltage derived from the grounding transformer GPT, and 51 NG is a ground fault overcurrent that responds to the current of the grounding resistor NGR. Relay 518 is an overcurrent relay provided on the secondary side of the main transformer M-Tr, 51-G, 51-
1.51-2 is an overcurrent relay that protects power transmission lines Fl'j F2 and F3 from short circuit, and 67-1.67-2 is a zero-sequence current from the residual circuit of current transformer CT-1゜CT-2. This is a ground fault direction relay that responds to the zero-sequence voltage derived from the ground transformer GPT.

FIG. 3 is an explanatory diagram of the breaker control sequence of the system of FIG. 1.

In FIG. 3, BP is a positive power supply bus, and BN is a negative power supply bus.

When a short circuit accident occurs in the power transmission line F3 having a grounding transformer, the high setting element 51H or the low setting element 51L of the overcurrent relay 51-G operates, and the circuit breaker CB-G is tripped.

When a short circuit fault occurs in the power transmission line F1, the overcurrent relay 51
-1 high setting element 51H, low setting element 51L is still operating and breaker CBI is tripped.

When a ground fault occurs in the power transmission line F1, the ground fault direction relay 67-1 operates and the breaker CB-1 is similarly tripped.

Similarly, if a failure occurs in transmission line F2, breaker CB
-2 is tripped.

If a ground fault occurs in the power transmission line F3 or bus B, which has a grounding transformer, the ground fault overvoltage relay 64 or the ground fault overcurrent relay 51 NG is activated.

After the time limit of the current GT, the breaker CB-8 on the secondary side of the main transformer MTr is tripped.

If a short circuit fault still occurs on bus B, main transformer M
The overcurrent relay 51S on the secondary side of the Tr operates and the breaker CB-8 is tripped after the timer 51ST has expired.

Power transmission line F1. F2. F3 overcurrent relay 51G.

An example of the operating time characteristics of 51-1.51-2 is as shown in Figure 2 A. When the input current is low and is equal to or higher than the bell IL, the time T
If the input current is higher than the high setting 2 level IH, it is configured to operate after the time TH, and the ground fault direction relay 67-1, 67-2 of the power transmission line is As shown, it is configured to operate after a certain period of time Ta2 if the input current is equal to or higher than the setting level I67.

3 Here, points to be noted regarding the power system shown in Fig. 1 and the protection of this system are listed below.

The grounding transformer GTr is an in-house power source for the substation, and its capacity is very small.

Therefore, the load current of the power transmission line F3 is also very small, and if a ground fault occurs in this power system 3, the ground resistance will always be NG.
A ground fault current flows through R.

However, since the low-voltage side of the grounding transformer G-Tr is connected in a delta manner, current caused by a ground fault on the low-voltage side of the grounding transformer G4''r will not flow to the high-voltage side.

The ground fault overcurrent relay 51NG, which responds to the current flowing through the ground resistance 41NGR, is a relay that provides backup protection in the event of a ground fault, and even if a ground fault occurs, the power transmission line F1. When the F2 ground fault direction relay 671.67-2 does not operate (i.e., when a ground fault occurs on the high voltage side of the power transmission line F3,
Or when the ground fault direction relays 67-1 and 67-2 malfunction), a trip command is given to the circuit breaker CB-8.

The reason why a ground fault direction relay is not installed on the power transmission line F3 is as follows.

In other words, if transmission line F3 is instantaneously tripped by a relay trip command in response to a ground fault on the high-voltage side of transmission line F3, this system becomes an ungrounded system, so there is no possibility of a ground fault occurring. It becomes unprotected and it becomes difficult to continue operation.

Since it is not desirable to immediately make the system ungrounded due to a ground fault, the earth fault overcurrent relay 51 (NG), which provides back-up protection, will be used to remove the ground fault on the transmission line F3. That's what I did.

As mentioned above, this power system can be protected using the conventional breaker control sequence shown in Figure 8.
Based on this sequence, conventional protective relay devices had the following problems.

It is necessary to set the low setting element 51L of the overcurrent relay 51-G attached to the power transmission line F3 so that it can reliably protect the low voltage side winding of the grounding transformer G-Tr from short-circuit accidents. -The capacity of the Tr is only enough to cover the power supply capacity within the substation, and the capacity is very small.

Since the impedance of this useless grounding transformer G-Tr is large, even if the grounding transformer G-Tr low voltage side winding short-circuits, a large current does not flow, and the setting value IL of the low setting element 51L becomes a small value.

On the other hand, for example, if a ground fault occurs at 11 points on the power transmission line F1, a ground fault current INOR flows from the neutral point resistance NGR of the grounding transformer G-Tr to the fault point f.

The ground fault current lNOR is also applied to the overcurrent relay 51-G of the power transmission line F3, and in some cases, the ground fault current lNOR is higher than the low setting value IL of the overcurrent relay 51-G. In this case, the overcurrent relay 51-G of the power transmission line F3 is activated due to a ground fault of the power transmission line F1, causing the inconvenience that the circuit breaker CB-G is tripped unnecessarily.

As a method for solving this inconvenience, the following two methods can be considered.

1. A directional overcurrent relay having directionality is provided in place of the overcurrent relay 51-G.

2. Operating time T of ground fault direction relay 67-1 of power transmission line F1
Lower setting element 51-G of overcurrent relay 51-G than 6□
The operation time TL of L is made sufficiently slow.

However, the above method 1.0 requires high cost equipment.
2. Delaying the operation time of the overcurrent relay 51-G by the method described above delays the removal time of the short-circuit fault in the low voltage side winding of the grounding transformer G"Tr.
There was a problem that there was a risk that the material would be burned out and the original purpose of protection would be lost.

This invention was made in view of the above problems, and provides a protective relay device that prevents a power transmission line with a grounding transformer from being mistripped due to a ground fault in a power transmission line without a grounding transformer, without increasing the price. The purpose is to make suggestions.

The present invention will be explained below with reference to the drawings.

FIG. 4 is a sequence explanatory diagram showing an example of a breaker control sequence according to the present invention.

The difference from the control sequence in Figure 3 is that the grounding transformer G
The operation condition of the ground fault overvoltage relay 64 or the ground fault overcurrent relay 51NG that responds to a ground fault that occurs in this power system is the operation of the low setting element 51L of the overcurrent relay 51-G of the power transmission line F3 having a Tr. The point is that it is configured so that it is invalidated.

According to this sequence, if a ground fault occurs in the system, the ground fault overvoltage relay 64 or the ground fault overcurrent relay 5 is immediately activated.
1 NG causes transmission line F with grounding transformer G-Tr
The overcurrent relay 51-G of No. 3 is locked.For example, the problem of the conventional protective relay device is that the circuit breaker CB-G of the power transmission line F3 is tripped unnecessarily due to a ground fault of the power transmission line F1. This can be solved with 5 devices.

By the way, in order to achieve the purpose of this application with the trip sequence circuit shown in FIG.
It is necessary for the ground fault overvoltage relay 64 and the ground fault overcurrent relay 51 NG to operate earlier than the G low setting element 51L operates, but in general, the voltage rises faster than the current, so the ground fault overvoltage There is no problem because relay 64 operates faster than the low setting element of overcurrent relay 51-G to lock the trip circuit.

As shown in FIG. 2, it still takes a considerable time TL for the low setting element of the overcurrent relay 51-G to operate.
During this time, the ground fault overcurrent relay operates.

As described above, the protective relay device according to the present invention can be used in a power system having a power transmission and distribution line having a grounding transformer and a power transmission and distribution line not having a grounding transformer. Since the overcurrent relay of the power transmission/distribution line with a grounding transformer is locked by the operation of the ground fault fault detection relay that responds to It is possible to prevent a breaker for a power transmission/distribution line from being mistakenly tripped.

[Brief explanation of drawings]

Figure 1 is a single-line connection diagram of a power system that includes power transmission and distribution lines with grounding transformers, power transmission and distribution lines without grounding transformers, and busbars to which these power transmission and distribution lines connect, as well as the protection that protects this power system. Connection diagram showing an example of a relay device, 2nd
The figure is a characteristic explanatory diagram showing an example of the operating time characteristics of the overcurrent relay and ground fault direction relay shown in Fig. 1, and Fig. 3 is a sequence explanatory diagram showing an example of the breaker control sequence of the conventional protective relay device. FIG. 4 is a sequence explanatory diagram showing an example of a breaker control sequence of the protective relay device according to the present invention. In the figure, Fl and F2 are transmission and distribution lines without a grounding transformer, F3 is a transmission and distribution line with a grounding transformer, B is a busbar, and G
4:'r is the grounding transformer, NGR is the grounding resistance of the grounding transformer G4'r, 51 NG is the ground fault overcurrent relay, 51-G is the overcurrent relay, 67-'f. 67-2 is a ground fault direction relay, and 64 is a ground fault overvoltage relay. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A protective relay that protects a power system that has a first power transmission and distribution line that has a grounding transformer, a second power transmission and distribution line that does not have a grounding transformer, and a bus bar connected to these power transmission and distribution lines. In the electrical equipment, an overcurrent relay that trips the first power transmission and distribution line when the current in the first power transmission and distribution line reaches a predetermined value, and that responds faster than the overcurrent relay to a ground fault that occurs in the power system. 1. A protective relay device comprising a ground fault detection relay, the operation of the ground fault detection relay locking the operation of the overcurrent relay. 2. The protective relay device according to claim 1, wherein the ground fault fault detection relay is a ground fault overvoltage relay that responds to a zero-sequence voltage derived from the bus bar. 3. The protective relay system according to claim 1, wherein the earth fault detection relay is an earth fault overcurrent relay that responds to the neutral point current of a grounding transformer.