SU42186A1 - Device for protection of three-phase generators with ungrounded neutral from earth faults - Google Patents

Description

The proposed device is designed to automatically turn off the generator or to give a signal when a stator winding closes to the housing (ground). The difference between the proposed device and the known ones is that the sinus wattmeter relays are connected to the interfacial voltage and the zero sequence current so that during ground faults, the relay actuation power is determined by the equation:

 - navy

where ip-tqv. in the current winding of the relay, bmf - interfacial voltage at the terminals of the secondary winding of the voltage transformer.

In addition, the device uses a partitioned grounding resistor, for alternately shutting off sections of which serve as voltage relays.

The drawing shows a circuit diagram of the proposed device.

Wattemeter relays 4, responsive to power

W7 / sin9

adventure current windings to (414)

current transformers 1, forming a zero-sequence current filter; and voltage windings, to voltage transformer 2, for an interphase voltage.

Artificial grounding of the generator is performed using partitioned grounding resistor 10 connected to the secondary circuit of the grounding reactive coil 3.

The device uses a blocking using the overvoltage relay 6, the undervoltage relay 8 and the time relay 7, which achieves an increase in the earth fault current when short to earth on a certain part of the generator turns.

When ground faults are in the protected zone (between current transformers 1 and the generator zero, if the generator windings are connected in a star), a fault current ground fault current (transformed value) determined by the value of grounding resistance and coefficient flows in the secondary circuit of current transformers 1 transformations of current transformers.

The voltage between the intact phases remains almost constant and forms with the current damaged

phase angle of 90 °. The voltage between the damaged and non-damaged phase may vary in magnitude and direction within certain limits. When grounding on any of the generator phases, one of the three watt-meter relays will react to power

 .VMF

and the other two relays will respond to power

IF-0.5 ip

The blocking action is as follows. Under normal conditions, grounding resistance 10 is fully on; during ground faults, voltage boost relay 6 is activated and switches on time relay 7. Depending on the voltage value at the terminals of the grounding coil S or the current flowing through the grounding coil, and therefore depending on what part the stator winding is short-circuited to earth, the minimum voltage relay 8 is activated, including the grounding resistance sections in such a way as to ensure the required ground fault current. It should be noted that the contacts of the relay 7 and 5 must be designed to break and turn on the current circuit in the secondary winding of the reactive coil 3 and therefore, in the practical implementation of the device, they can be replaced by automatics driven by the corresponding relays.

The device does not limit the number of grounding resistance levels (the drawing shows a diagram with four grounding resistance levels).

Time of operation of time relay 7 must be greater than the time of operation of minimum voltage relay 8.

The time relay 9 shown in the drawing is assigned to open the secondary circuit of the earthing jet coil 5 during a long circuit to earth and thereby to stop the flow of the ground current through the fault site.

According to the author's calculation, using a similar scheme for switching on wattmeter relays, a significant reduction in the percentage of unprotected turns is achieved.

The subject matter of the invention.

Claims (2)

1. A device for protection of three-phase non-grounded neutral generators against earth faults, consisting of three sinus power direction relays, in which the current coils are fed by a ground fault current from three parallel-connected current transformers, characterized in that the relay voltage windings are turned on, For example, through a voltage transformer 2, between different phases of the generator to be protected, in order to reduce the percentage of unprotected turns. 2. In the device of claim 1, the use of a partitioned grounding resistor, for alternately shutting off sections of which serve as voltage relays.