JPS60207416A - Low voltage ground-fault protecting device - 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 is particularly applicable to systems in which two transformers can be operated individually or in parallel, thereby eliminating malfunctions regardless of the operation mode of the transformers and ensuring that the ground level is maintained. The present invention relates to a low voltage ground fault protection device capable of providing protection.

[Technical background of the invention and its problems] Conventionally, there has been a system in which two transformers can operate independently or in parallel by switching off the secondary circuit breaker and the busbar connection circuit breaker. In order to detect ground faults, it is possible to directly ground a current transformer (hereinafter referred to as CT) through the neutral point of the transformer, and install a ground fault relay on the secondary side of this CT. It is being done. By changing the configuration of CT depending on the operating mode of the transformer,
Two types of ground fault protection devices are used.

In other words, in a system where transformers are operated in parallel at all times or where transformer banks are switched by performing instantaneous parallel operation, each CT@ A ground fault protection device is applied. In addition, in systems where transformers are never operated in parallel, that is, systems that operate independently, a ground fault protection device is applied that protects each transformer's neutral point grounding wire by providing an individual CT. There is.

As described above, ground fault protection devices are used depending on the operating mode of the transformer, and the reason for this is as follows. First, in the former ground fault protection device,
Even if the transformers are operated in parallel, the ground relay will not malfunction because the N current will not flow to the grounding point except due to ground fault fault current. If a ground fault occurs in one of the systems,
Since the ground fault current returns from the fault point to the ground point, the two ground fault relays operate, tripping the secondary circuit breakers of each transformer, resulting in a total power outage for the system.

Furthermore, at this time, it is difficult to determine the system in which the ground fault has occurred.

In addition, with the latter type of ground fault protection device, if transformers are never operated in parallel, the ground fault fault current will return from the fault point to the neutral point of the transformer on the fault side through the grounding point. Since only the ground fault relay in the system on which the fault occurred operates and only the secondary circuit breaker of the transformer in that system is tripped, the system does not experience a total power outage, and it is possible to clearly determine which system is the faulty system. be able to. However, if transformers are operated in parallel in a system to which this earth fault protection device is applied, 2
The ground fault relay malfunctions even though no ground fault has occurred because a neutral phase circuit forms between the neutral points of the transformer and the unbalanced current of the load flows. Such malfunctions also occur when instantaneous parallel operation is performed to switch the transformer system without interruption for the negative section.

For the above reasons, conventionally, after determining the system operation mode, the former or the latter ground fault protection device is selected. However, if the operating mode of the transformer has not been determined or has been changed, the applicable ground fault protection device cannot be determined or must be changed. In this case, since the grounding work for the transformer neutral point is normally class 2 grounding work, the grounding wire must be thick and cannot be easily separated from the ground, so this change should be made. is actually extremely difficult.

[Object of the Invention] The present invention has been made to solve the above-mentioned problems, and its purpose is to improve the operation mode of the transformers in a system where the transformers can be operated individually or in parallel. To provide a low-voltage ground protection device that can reliably provide ground fault protection regardless of the operating mode even in undetermined cases, eliminate malfunctions, and minimize the range of power outage in the event of a ground fault accident. be.

[Summary of the Invention] In order to achieve the above object, in the present invention, two transformers perform independent operation or parallel operation by turning off the respective secondary circuit breakers and busbar connection circuit breakers. In systems where it is possible to connect the low-voltage side neutral points of each of the above transformers to the common connection of their respective neutral point grounding wires and directly grounding them, each of the above neutral point grounding wires is provided with a ground fault detection current transformer,
The ground fault relays connected to the secondary sides of each of these current transformers, the secondary circuit breakers of each transformer, and the busbar connection circuit breaker are in the "on" state, that is, the transformers are in parallel operation. a state detector that operates when detecting the current transformer; and when the state detector operates, the above-mentioned rated relays are connected in series and connected in parallel with both ends of the secondary side of each of the current transformers to form a closed circuit; The connection configuration between each of the above-mentioned faulty electric devices and the secondary side of each current transformer is such that when the above-mentioned detector is inoperative, each of the above-mentioned rated relays is connected to the secondary side of each current transformer to form a closed circuit. DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention shown in the drawings will be described.

FIG. 1 is a single-line connection diagram showing an example of a system configuration in which the low voltage ground protection device according to the present invention is applied.

In the figure, the main circuit system connects the output of power supply 1 to transformer 4.5 via disconnectors 2 and 3 on the No. 1 and Nα2 sides, respectively.
The voltage is transformed to low voltage, and further transformed, and supplied to the load side 8.9 from the pressure transformer secondary breaker 6.7, and the Nα1 side load 8 and the Nα2 side load 9 are connected by a busbar connection breaker 10. It is configured.

On the other hand, the low-voltage side neutral point of the Nα1 transformer 4 and the low-voltage side neutral point of the No. 2 pressure gauge 5 are commonly connected to the ground 13 by neutral point grounding WA11°12, respectively. Furthermore, each of the neutral point grounding wires 11.12 is provided with a CT 14.15 for detecting a ground fault, and dischargers 16.17 for protecting the CT secondary open are connected to both ends of the secondary side thereof. . Furthermore, the above CT14
．． Ground fault relays 18 and 19 are connected to the secondary sides of 15, respectively, under the condition that transformers 4 and 5 are operated in parallel, that is, auxiliary contacts 5a and 7a of transformer secondary circuit breakers 6 and 7. Auxiliary contacts 20a+, 20a2゜20b of CT secondary side circuit switching relay 20 as a state detector that is excited when auxiliary contact 10a of busbar connection breaker 10 is closed 1. '
20b2 to form a closed circuit depending on the operating state of the transformer 4.5.

That is, first, when the transformers 4 and 5 are operated in parallel, the contact 20
a 1.20a 2 is closed, contact 20bt.

20b2 opens, transformer 4.
The ground fault current at the time of a ground fault accident during parallel operation in 5.
The ground fault currents detected at 14.15 are combined on the CT secondary side and flowed in series into two ground fault relays 18.19 to detect a ground fault. Also, when the transformer 4.5 is operating independently, the contacts 20a 1 and 20a 2 are open, and the contacts 201
)t.

2C1b2 closed, two ground T8 relays 18.19
is connected to the secondary side of each CT14.15 to form a closed circuit, and a part of this closed circuit is connected to the secondary side of each CT14.15.
Because it is shared with the secondary side, in the event of a ground fault accident when transformer 4゜5 is operating independently, the ground fault current for each separated system will flow into the corresponding ground fault relay 18 or 19. This is used to detect ground faults.

FIG. 2 shows an example of the configuration of a control circuit for the transformer secondary side circuit breakers 6, 7. In the figure, 21H, 22
H is an operator switch 21 for turning on the secondary side circuit breakers 6.7 of the No. 1 and Nα2 transformers, respectively;
Similarly, 22 is an operation cut-off switch for each exception. Further, 23.24 is an auxiliary relay that is operated by closing the auxiliary contacts 18a and 19a of the ground relay 18.19, respectively, and the breaker 6.7 is tripped by the auxiliary contacts 23a s and 24a 1, respectively. and the same auxiliary contact 23
The drive signal is outputted to the alarm circuit 25.26 by a2.24a2. In addition, P and N are control power supply busbars, H is a circuit breaker and disconnect terminal, respectively, and COM is a common terminal.

Next, the operation of this configuration will be described.

First, Fig. 3 shows an equivalent connection between the secondary side of CT 14.15 for ground fault detection and ground fault relay 18.19 when transformer 4.5 is in parallel operation in Fig. 1. The equivalent circuit when a ground fault occurs in this case is as shown in FIG. Therefore, to explain Fig. 4, if a - line grounding fault occurs at point F in the diagram, - line grounding current IF will pass from the grounding point 13 through the grounding relays 19 and 18, and will flow to each power supply side by 1F/2. Divided into and circulated. The magnitude of the negative line ground current at this time is determined by the transformer secondary side phase voltages E1 to E2, the impedance of the ground fault point F at the time of a ground fault, and the magnitude of the resistance value of the ground point 13.

In this manner, when the transformers 4 and 5 are operated in parallel, both ground fault relays 18 and 19 are automatically connected in series, so that the same ground fault current flows. This allows each rated relay 1
8. When 19 is operated, contact 23a1 is activated as shown in FIG.
．． By closing 24a1, the transformer secondary circuit breakers 6.7 on the No. 1, No. 2, and No. 2 sides are tripped to protect the system, and at the same time, contact 2382.24 is connected to the alarm circuit 25°26.
When 82 is closed, a drive signal is output.

Next, when the transformer 4.5 is in independent operation, the connection between the secondary side of the CT 14.15 for ground fault detection and the ground fault relay 18.19 is equivalently represented as shown in Fig. 5. N111
The equivalent corridor in the event of a ground level accident on the side busbar is shown in Figure 6. Therefore, to explain Fig. 6, if a line grounding fault occurs at point F in the diagram, the -line grounding current ■1 circulates from the grounding point 13 to the N111 side grounding relay 18 side, It does not flow to the relay 19 side. −Line ground current■.

The size of is determined in the same manner as above. In this way, when the transformer 4.5 is operated independently, the ground relay 18.
19 to N111 and the transformer 4.5 on the second side, respectively, the ground protection for each system will be shared.

- As mentioned above, by applying the low-voltage ground fault protection device of this configuration, the application of two types of ground fault protection devices was previously considered and applied selectively depending on the operating status of the transformer. can be used as a one-way ground fault protection device regardless of the operating mode of the transformer, and even if the operating mode of the transformer has not yet been determined, it is possible to divide the ground fault protection without any problems and clearly define the range. It is possible to provide ground fault protection, eliminate malfunctions, minimize the range of power outage in the event of a ground fault accident, and realize these at low cost.

In Fig. 1 above, the CT secondary circuit open protection discharge 116.17 is connected to both ends of the secondary side of CT14.15.
is the auxiliary contact 20a of the CT secondary circuit switching relay 20
1.2082 and 2. Obt.

It is not necessary if the mechanism 20b2 is switched by wrapping.

[Effects of the Invention] As explained above, according to the present invention, even if the operating mode of the transformer is undetermined, grounding protection can be reliably performed regardless of the operating mode, and malfunctions can be eliminated to prevent ground faults from occurring. It is possible to provide an inexpensive and extremely reliable low-voltage ground protection device that can minimize the range of power outages.

[Brief explanation of drawings]

FIG. 1 is a system configuration diagram showing an embodiment of the present invention, FIG. 2 is a configuration diagram showing the circuit breaker circuit breaker shown in FIG. 1, and FIG.
5 and 5 are circuit diagrams showing the connection between the ground relay and the CT secondary side when the transformers shown in FIG. 1 are operated in parallel and individually, respectively. 5 shows an equivalent circuit diagram when a ground accident occurs in the operating mode shown in FIG. 5 and FIG. 1...Power source, 2...NQ1 disconnector, 3...Se2 disconnector, 4...N111 transformer, 5...2nd transformer,
6...11111 Transformer secondary breaker, 7...-Nl
12 Transformer secondary breaker, 8...N11I side load, 9
...NQ2 side load, 1o...Bus bar connection breaker, 1
1.12... Neutral point grounding wire, 13... Grounding point, 14
... CT for ship 1 side ground level detection, 15... 11 Q2 side ground level detection CT, 16... Ship 1 side CT secondary open protection discharger, 17... IIQ2 side CT secondary open Protective discharger, 18...IIQI side grounding relay, 19...NQ2
Side ground relay, 2o...CT secondary circuit switching relay,
21H... No. 1 transformer secondary breaker operator switch,
21K...Same cut switch, 22H...N112 transformer secondary breaker operator switch, 22K...Same cut switch, 23.24...Auxiliary relay, 25.26...
Alarm circuit, P, N...control power bus, H...breaker input terminal, K...same disconnection terminal, COM...same common terminal. Applicant's agent Patent attorney Takehiko Suzuha

Claims (1)

[Claims] (1) In a system where two transformers are capable of individual operation or parallel operation of the transformers by turning off the respective secondary circuit breakers and bus line circuit breakers, the low voltage of each transformer is The side neutral point is directly grounded by commonly connecting each neutral point grounding wire, and a current transformer for ground fault detection provided on each neutral point grounding wire, and two current transformers of each of these current transformers are connected. a ground relay connected to the next side, a status detector that operates when it detects that the secondary side breaker of each of the transformers and the busbar connection breaker are in the "on"state; When operating, each of the rated relays is connected in series and connected in parallel with both ends of the secondary side of each of the current transformers to form a closed circuit,
Further, when the detector is inoperative, each of the fault relays is connected to the secondary side of each current transformer to form a closed circuit. A low voltage ground fault protection device comprising a connection switching means for switching. (2) Claim (1) characterized in that a current transformer secondary open protection discharger is connected to both ends of the secondary side of each current transformer.
Low voltage ground protection device as described in Section 1.