JPS6013420A - Ground-fault protecting device of power distribution system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention prevents malfunctions due to circulating current due to third harmonics generated when multiple transformers whose neutral points are grounded are operated in parallel. The present invention relates to a ground fault protection device for a power distribution system.

[Technical background of the invention]

FIG. 1 shows an example of the configuration of a power distribution system in which a plurality of transformers are operated in parallel. In the figure, 1 and 2 are two transformers with a triangular connection on the primary side and a star connection on the secondary side, and the primary side is connected to a power transmission line (not shown) via an interrupter 3.4. In addition, the secondary side is connected to the distribution buses 8 and 9 to which a load group (not shown) is connected via the bus-bar connection breaker 7 via the circuit breakers 5 and 6, so that parallel operation is possible. There is. Further, the secondary sides of each of the transformers 1 and 20 are grounded, and ground fault overcurrent relays 12.13 are respectively installed in the ground circuits via instrument current transformers 10.11.

FIG. 2 shows an example of the configuration of a conventional ground fault protection circuit in the power distribution system shown in FIG. In the figure, P and N are control power supply buses. Further, 12a and 13a are the normally open contacts of the ground fault overcurrent relay 12 and 13 to which the barge operation switch 14 and 15 are connected in parallel, and the auxiliary normally closed contacts 3b and 4b of the circuit breaker 3 and 4 are connected in parallel. 3 and 4 tripping coils ?a and 4a are provided between the control power supply buses P and N via series connection, respectively.

Even in such a configuration, during normal times, the busbar connection breaker 7
With the opening of the transformer, each transformer is operated independently. If a ground fault occurs on either one of the transformers 1 or 2 in such a state, the ground fault overcurrent relay 12 or 13 installed in the ground circuit of the transformer operates.

When the contact 12a or 13h closes, the tripping coil 3
By energizing a or 4a, the breaker 3 or 4 is tripped to provide accident protection.

On the other hand, in the case of single-unit operation for uninterruptible switching (for transformer inspection, maintenance, or load reduction), the power supply to the load is switched to one of the transformers to stop operation in an uninterrupted state. When performing switching), from the above-mentioned individual operation state, first the busbar connection j to the interrupter 7 are closed, and then the breaker 3 or 4 of the transformer 1 or 2 to be stopped is opened.

[Problems with background technology]

In this case, transformers 1 and 2 will be operated in parallel from when the busbar connection breaker 7 is closed until the breaker 3 or 4 of either transformer 1 or 2 is opened. A closed circuit is formed on the secondary side through the neutral point.

As a result, the third harmonic that exists in a single phase between the primary side triangular winding heel of the transformer is paralleled, and the transformer 1,
A circulating current flows through the neutral point of 2, and as a result, the magnitude of this circulating current causes the ground fault overcurrent relay 12, 13 installed in the grounding circuit to malfunction. In particular, in systems where the transformer neutral point is directly connected to ground, if the transformers are operated in parallel for longer than the operating time of the ground fault overcurrent relay installed at the neutral point, there is a risk that the ground fault overcurrent relay will malfunction. However, due to the malfunction of the ground fault overcurrent relays 12 and 1.9, the circuit breakers 3 and 4 of each transformer 1 and 2 were disconnected, resulting in a total power outage. [Purpose of the present invention] The present invention was made to solve the above-mentioned problems, and its purpose is to solve the problem of disconnection due to the malfunction of the earth fault overcurrent relay due to the circulating current that occurs when multiple transformers are operated in parallel. An object of the present invention is to provide a ground fault protection device for a power distribution system that can reliably prevent tripping of a device.

[Summary of the invention]

In order to achieve the above object, the present invention provides a grounding circuit for a plurality of transformers in which the neutral point is grounded and the secondary side is interconnected with a busbar connection disconnector to enable parallel operation. A ground fault overcurrent relay is installed in each of the distribution systems, and in the ground fault protection device for the distribution system, which trips the breaker of the transformer by the operation of the relay, the The transformer is equipped with a fault overvoltage relay, and is characterized in that when the busbar communication breaker is in a closed state, the breaker of the transformer is tripped on the condition that both the ground fault overvoltage relay and the ground fault overcurrent relay operate.

[Embodiments of the invention]

Hereinafter, an embodiment of the present invention shown in the drawings will be described.

FIG. 3 shows an example of the configuration of a power distribution system to which the present invention is applied, and the same parts as in FIG. In FIG. 3, a ground fault overvoltage relay 17 is installed on the power distribution bus 9 in FIG. 1, which operates by detecting the zero-sequence voltage of the bus through an instrument transformer 16.

Moreover, FIG. 4 shows an example of the configuration 6 of the ground fault protection circuit of the present invention, and the same parts as in FIG. 2 are given the same reference numerals and the explanation thereof will be omitted. In Fig. 4, auxiliary normally closed contacts 7.1, 7b2 of the busbar connection breaker 7 are provided in series with the contacts 12g, 1.9a in Fig. 2, and in parallel with these contacts 76+, 7b2. A series circuit of the auxiliary normally open contacts 7aj, 7m2 and the normally open contacts J7, 1.17a2 of the earth fault overvoltage relay 17 is provided.

In this configuration, first, when the busbar connection breaker 7 is open, its auxiliary normally closed contacts 7bl 17b2 and the contacts 12a of the ground fault overcurrent relays 12.13.

13&, the tripping coils 3h and 4m of the circuit breaker 3.4 of each transformer 1 and 2 are energized, respectively, and when the busbar connection circuit breaker 7 is closed, its auxiliary normally closed contact 7b1 is energized. ”b2 and the contact 171L1.17a2 of the ground fault overvoltage relay 17 and the ground fault overcurrent relay 12.1
3 contact 12a.

The tripping coils 3m and 4a of the circuit breakers 3 and 4 of the transformers 1 and 2 are energized, respectively, according to the AND condition of 1.9 &.

Therefore, if a ground fault occurs when the two transformers 1 and 2 are operating independently due to the bus breaker 7 opening, the ground fault installed in the ground circuit of the transformer or 2 on the accident side If the fault overcurrent relay 12 or 13 is activated by the ground fault current, its contacts 12aV or 1,? a is closed, the tripping coil 3a''! or 4a is energized, and the breaker 3 or 4 is tripped.

On the other hand, the above-mentioned uninterruptible switching, etc., bus bar connection breaker 7
When closed and two transformers 1 and 2 operate in parallel,
As described above, a circulating current of the third harmonic component flows through the neutral point. This causes the ground fault overcurrent relays 12 and 13 installed in the ground circuit to operate, closing their contacts 12a and 13a. However, in this case, the circulating current is a single-phase current that flows in each of the three phases with the same mode and value, so that no zero-phase voltage is generated. Therefore, the ground fault overvoltage relay 17 does not operate and its contacts 17a.

Since 17a2 is open, the tripping coil 3a
and 4a are not energized and the circuit breakers 3 and 4 are not tripped. In addition, if a ground fault occurs during the above-mentioned parallel operation, the resulting zero-sequence voltage is detected and the ground fault overvoltage relay 17 operates, so that the contact 1
By closing 7a1゜1732, υ tripping coil 3m, 4
By energizing the circuit breaker a, the circuit breakers 3 and 4 are tripped.

As mentioned above, the neutral point is grounded, and the grounding circuits of the two transformers 1 and 2, which are configured to be operated in parallel by connecting the secondary sides to the busbar connection breaker 7, are connected to the ground. In a ground fault protection device for a distribution system in which a fault overcurrent relay 12.13 is installed and the operation of the relay trips the circuit breaker 3, 4 of the transformer, the zero phase of the distribution buses 8, 9 of the distribution system is provided. A ground fault overvoltage relay 17 that operates by detecting voltage is provided, and the ground fault overvoltage relay 17 and the ground fault overcurrent relay 12 and 13 are both operated when the busbar communication breaker 7 is in a closed state. The circuit breaker 3 and 4 of the transformer 1.2 are configured to be tripped.

9- Therefore, it is possible to prevent the tripping of the circuit breaker 3゜4 due to the malfunction of the ground fault overcurrent relay 12, 13 due to the circulating current that occurs when the transformers 1 and 2 are operated in parallel due to uninterruptible switching, etc., and prevent ground fault accidents. It becomes possible to reliably protect the power distribution system by tripping the circuit breakers 3 and 4 only occasionally.

It should be noted that the present invention is not limited to the above embodiments, but can also be implemented as follows.

FIG. 5 shows an example of the configuration of a power distribution system according to another embodiment of the present invention, and the same parts as in FIG. Fig. 5 shows an auxiliary normally closed contact 7a that closes when the busbar connection breaker 2 is closed as shown in Fig. 6.
The main contact 18a of the electromagnetic contactor 18 is excited by
18b.

18c and 18d (18a and 18c, 18b and 18d are interlocked, respectively) are inserted into the neutral point circuit of transformers 1 and 2, and the neutral point circuit is automatically activated according to the open/closed state of the busbar connection breaker 7. This changes the configuration. That is, when the busbar connection breaker 710- is open, the ground fault overcurrent relays 12 and 1.9 circuits are connected in parallel, and when the busbar connection breaker 710- is closed, the circuits are connected in series.

Note that the configuration of the earth fault protection circuit is the same as that shown in FIG. 2.

In this configuration, first, when the busbar connection breaker 7 is open, the main contacts 16th and 16c of the electromagnetic contactor 18 are open and the main contacts 16b and 16d are closed, so that the neutral point is connected to each transformer 1.
．． Each transformer 1, 2 is grounded, and the earth fault overcurrent relay 12.13 is also connected to the neutral point grounding circuit of each transformer 1, 2.
Two units of ground fault detection are being performed. On the other hand, when the busbar communication breaker 7 is closed, the electromagnetic contactor 18 is excited by its auxiliary normally open contact 7a, and its main contacts 16a, 16
c is closed and 16 b and 16 d are open, so the seventh
As shown in the figure, the neutral points of each transformer 1 and 2 are directly connected to each other, and there is one ground point. As a result, each fault overcurrent relay 12, 13 is removed from the circulation circuit and inserted into the neutral point circuit, and the above-mentioned malfunction caused by the circulation current can be eliminated.

In addition, in the case where the neutral point of the transformer in the low-voltage distribution system is directly connected to ground, the value of the zero-sequence voltage is 1/1 of the value when the transformer is not grounded.
Since the voltage is about 3, it would be a good idea to further boost the voltage using an auxiliary transformer or the like.

[Effects of the Invention] As explained above, according to the present invention, when a plurality of transformers are operated in parallel, the ground fault overcurrent relay installed in the ground circuit of the transformer and the ground fault relay that operates by detecting the zero-sequence voltage Since the transformer breaker is tripped on the condition that both overvoltage relays operate, the circuit breaker can be removed due to the malfunction of the overcurrent relay due to the circulating current that occurs when multiple transformers are operated in parallel. It is possible to provide a highly reliable ground fault protection circuit for a power distribution system that can protect the system by reliably preventing tripping of the power supply.

[Brief explanation of the drawing]

Figure 1 is a diagram showing a system configuration in which multiple transformers can be operated in parallel, Figure 2 is a diagram showing a conventional ground fault guarantee circuit,
3 and 4 are system configuration diagrams and circuit configuration diagrams showing one embodiment of the present invention, and FIGS. 5 to 7 are configuration diagrams showing other embodiments of the present invention. 1.2...Transformer, 3,4,5.6... Breaker,
7... Busbar connection breaker, 8, 9... Distribution busbar, 1
0.11...Instrument current transformer, 12.13...Ground fault overcurrent relay% 14.15...Push button operation switch, 1
6...Instrument transformer, 17...Ground fault overvoltage relay. 7 B...Magnetic contactor, 3b, 4b, 7a, 7a,
. 2a2 m7b1 . 7b2*12 & 113 &#
17a1 +17.2-...Contact point s l 8 m,
18b, 18e, 18d...main contacts. Applicant's agent Patent attorney Takehiko Suzue13

Claims (2)

[Claims] (1) The neutral point is grounded, and the secondary side is interconnected from the busbar connection disconnection arc to enable parallel operation. A grounding circuit is provided for each of the transformers to enable parallel operation, and the transformer is disconnected during operation. a ground fault overcurrent relay that trips the circuit breaker, and a ground fault overvoltage relay that operates by detecting the zero-sequence voltage of the secondary side system of the transformer, 1. A ground fault protection device for a power distribution system, characterized in that a breaker of a transformer is tripped on the condition that both a tonnage relay and a ground overcurrent relay operate. (2) The neutral point is grounded, the secondary side is connected to the busbar, and the grounding circuit of multiple transformers is connected to the interrupter to enable parallel operation. a ground fault overcurrent relay that trips the breaker of the transformer; and a ground fault overcurrent relay that is provided in the grounding circuit of each of the transformers and connects the neutral point of each transformer to the ground fault overcurrent relay on the condition that the bus connecting breaker is closed. A switching device for switching a circuit so as to be commonly connected to a ground path having a ground fault relay and to disconnect other ground fault overcurrent relays.