JPH0865885A - Neutral point ground fault detection and protection device - Google Patents

Abstract

PURPOSE: To make it possible to cut off only a fault section when a ground fault takes place in a bus line, by connecting a current transformer to each neutral point of a transformer, and using a selective-breaking protective relay put in series in an annular circuit and connected to a transformer on a secondary side and a ground-fault detecting common relay, in which a small annular circuit is constituted. CONSTITUTION: A current transformer 6 is connected to each neutral point of a transformer 1. A plurality of selective breaking protective relays 31 and 32 are connected to the transformer 1 on a secondary side to protect an overall circuit. The protective relays 31 and 32 are connected in series annularly in an annular current circuit to carry a ground-fault current or an unbalanced current. In addition, a ground-fault detecting common relay 10 is connected to the annular current circuit 7 in a way that each annular circuit for the protective relays 31 and 32 are separately formed. As a result, when a fault in bus line takes place, only a power-supply circuit related to a defective bank can be cut off, and in this way, reliability in ground-fault protective system can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a neutral grounding type three-phase four
The present invention relates to a neutral point ground fault detection protection device in a wire type power supply circuit.

[0002]

2. Description of the Related Art A conventional neutral point ground fault detection and protection device in a three-phase four-wire parallel operation circuit connects neutral points of a plurality of transformers to each other and connects the connection points to a ground fault detection transformer. It is grounded via a current transformer and the ground fault current flowing in the current transformer for ground fault detection is detected by a ground fault relay. However, in such a parallel operation state, when the ground fault occurs, the ground fault current flows through the neutral point of both transformers, so not only the fault point cannot be selected, but also the power failure of both circuits occurs. The system is completely out of power and the reliability of the system is significantly reduced. Also,
In the conventional technology, a method of connecting a ground fault interruption relay to the neutral point of each transformer and connecting a common alarm relay between the connection point of this ground fault interruption relay and the grounding point is also adopted. However, the ground fault accident current flows through the transformer on the side of the accident bus when the transformer is operating independently, and the relay operation is limited to the bank on the accident side. In parallel operation of transformers, the ground fault accident current is not limited to the relay operation by flowing through the transformer on the accident bus side, and the neutral point shunt current due to the unbalanced load of the three-phase, four-wire type load is between the transformers. As a result, the relay on the side of a healthy line also operates and a total power failure occurs. Of course, in order to distinguish between the independent operation of the transformer and the parallel operation of the transformer, a circuit equipped with a single-parallel changeover switch or a busbar breaker is also used, but the circuit is complicated. Therefore, there is a problem that the cost and the reliability are lowered, and a neutral point ground fault detection and protection device that is simpler and has high reliability has been desired.

[0003]

SUMMARY OF THE INVENTION According to the present invention, at the time of a bus accident, only a power supply line of a bank which is directly related to the accident is selected and cut off, and a cross current due to imbalance is circulated between the current transformers. Providing a neutral point ground fault detection and protection device that can detect the faulty line by combining the operations of the common relay for breaking, prevent unnecessary operation of the ground fault protection relay, and improve the reliability of the ground fault protection system. Is intended.

[0004]

The neutral point ground fault detection and protection device of the present invention is connected to a current transformer connected to each neutral point of a plurality of transformers and a secondary side of the current transformer. For selective earthing protection, an annular current circuit that connects the selective interruption protective relays in series annularly, and a ground fault detection that forms an annular small circuit with each of the selective interruption protective relays connected to the annular current circuit It is characterized by having a common relay. Claim 2
The neutral point ground fault detection and protection device described in 1., the trip coil of the busbar connection breaker for parallel operation, which is energized with the operation of the common relay for ground fault detection and the protection relay for both selective interruptions as an AND condition, Main change 2 which is provided for each transformer and is activated on the condition that the common relay for ground fault detection operates, the operation of the protective relay for selective breaking for its own transformer side, and the non-operation of other protective relay for selective breaking. It is characterized in that it is provided with a trip coil of a secondary circuit breaker.

[0005]

In the neutral point ground fault detection and protection device of the present invention,
Connect a current transformer to the neutral point of each of the transformers, connect a protective relay for selective breaking to the secondary side of the current transformer, and connect the protective relay for selective breaking to the loop current circuit in series and loop. A common relay for ground fault detection is connected to the ring current circuit to form a ring small circuit with each of the protection relays for selective interruption. Further, the neutral point ground fault detection and protection device according to claim 2 energizes the operation of the common relay for ground fault detection and the protection relay for both selective cutoffs as an AND condition, and the trip coil of the main transformer secondary breaker. Is provided for each transformer, and it is activated on the condition that the common relay for ground fault detection operates, the operation of the protective relay for selective interruption with respect to its own transformer side, and the non-operation of other protective relay for selective interruption. It has a feature.

[0006]

EXAMPLE An example of the present invention will be described below. In FIG. 1, a current transformer 6 is connected to each neutral point of the transformer 1,
A current measuring device for a relay that detects a ground fault current or an unbalanced current and protects the circuit. K represents the polarity of the primary side and k represents the polarity of the secondary side. Protective relays for selective interruption 31, 32
Is a relay connected to the secondary circuit of the current transformer 6 to detect a ground fault current or an unbalanced current and protect the circuit. The ring current circuit 7 is a circuit in which the protective relays 31 and 32 for selective breaking are connected in series in a ring shape, and a ground fault current or an unbalanced current flows in a ring shape. The ground fault detection common relay 10 is connected to the ring current circuit 7, and constitutes a ring small circuit so as to bisect the ring with each of the selective breaking protection relays 31 and 32. Is a relay that protects the circuit by detecting the ground fault current and unbalanced current flowing in each of the. Main change secondary circuit breaker 2
Reference numerals 1 and 22 are switches connected to the secondary side of the transformer 1 to open and close the secondary circuit. Further, the busbar circuit breaker 3 is a switch that is connected to the load side of the main variable secondary circuit breakers 21 and 22 and switches the load side to a single state or an array state via the protective device 4.

FIG. 2 is a circuit diagram showing an embodiment of the neutral point ground fault detection and protection device described in claim 2. The a-contact 31a of the protective relay 31 for selective interruption and the b-contact 32b of the protective relay 32 for selective interruption are respectively the common relay 1 for ground fault detection.
0 a contact 10a connected in series, and a contact 31
The a and b contacts 31b are connected in parallel with each other. Further, the a-contact 21a is a contact that is turned on when the main-changed secondary circuit breaker 21 is turned on, and is connected in series to the b-contact 32b.
The external coil 41 is a coil for disconnecting the secondary bus breaker 21 and is connected in series to the a contact 21a. Further, the a-contact 22a is a contact that is turned on when the main variable secondary circuit breaker 22 is turned on, and is connected in series to the a-contact 32a. The external coil 42 is used as the secondary busbar breaker 2
2 is a coil for tripping, and is connected in series to the a contact 22a. Further, the a-contact 3a is the busbar connection breaker 3
Is a contact which is turned on when the power is turned on and is connected in series to the a contact 32a. The external coil 51 is a coil for disconnecting the busbar circuit breaker, is connected in series to the a contact 3a, and the other ends of the external coils 41, 42, 51 are connected to the control power source N, and the a contact 10a. One is connected to the control power supply P.

That is, the external coil 41 for tripping the main change secondary circuit breaker 21 through the b contact 32b which is closed from the connection point of the a contact 31a and the a contact 32a when the No. 2 bank accident selection relay is inoperative. Connected to the control power supply N via. Furthermore, from the connection point of the a contact 10a and the a contact 31a,
It is connected to the control power supply N via an external coil 42 which trips the main changeable secondary circuit breaker 22 via a b contact 31b and an a contact 32a which are closed when the relay for bank number accident selection does not operate.

In the circuit thus constructed, the common relay 10 for ground fault detection does not operate because the current flows back between the secondary current transformers in the neutral cross current due to the unbalanced load during parallel operation. Therefore, no trip signal is output to each breaker. Next, in the case of a ground fault on one side of the bus during parallel operation, if, for example, Bank 1 fails, the ground fault current returns from the ground point to both transformers, so the secondary current of the current transformer does not flow back, as if Operate all relays in a way that divides into two. And the trip current is a
Bus contact breaker 3 passing through contacts 10a, 31a, 32a
To trip. However, since the accident continues on the No. 1 bus, the main change secondary circuit breaker 21 on the accident circuit side trips when the operating relay on the sound side is restored and the b-contact 10b is closed. A fully coordinated system
It can be configured with two current transformers and a fixed control circuit.

[0010]

According to the present invention, it is possible to eliminate an accident by shutting off only the accident classification without causing a total power failure in a bus-line ground fault in a three-phase four-wire circuit.
It is possible to avoid a malfunction due to a cross current of an unbalanced load.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a neutral point ground fault detection and protection device according to an embodiment of the present invention.

FIG. 2 is an explanatory view showing the operation of FIG.

[Explanation of symbols]

 6 Current transformer 7 Annular current circuit 10 Common relay for ground fault detection 10 31, 32 Protection relay for selective interruption

Claims (2)

[Claims] 1. A current transformer connected to a neutral point of each of the plurality of transformers, a protection relay for selective interruption connected to the secondary side of these current transformers, and protection for selective interruption thereof. A neutral circuit comprising a ring current circuit for connecting the relays in a series loop, and a common relay for ground fault detection which is connected to the ring current circuit and forms a ring small circuit with each of the protection relays for selective interruption. Point-to-ground fault detection and protection device. 2. A trip coil of a busbar connection breaker for parallel operation, which is energized under the condition of the operations of the common relay for ground fault detection and the protective relay for both selective cutoffs, and each transformer is provided. , Operation of the common relay for ground fault detection,
And a trip coil of a main variable secondary breaker which is energized on the condition that an operation of a protective relay for selective interruption with respect to its own transformer side and a non-operation of another protective relay for selective interruption are performed. The neutral point ground fault detection and protection device according to Item 1.