Causes and solutions of faults of microcomputer transformer differential protection devices in substations

1 Overview

Differential protection is the main electrical protection that ensures the normal operation of the substation transformer. When a short-circuit fault occurs in the electrical part surrounded by the current transformer on each side of the transformer, this protection will act quickly to remove the fault without delay. If the transformer fails and the differential protection device refuses to operate due to the fault, it may cause varying degrees of damage to the transformer, or even burn it out, which will also greatly affect the safe and stable operation of the power system. Conversely, if the differential protection device malfunctions due to a fault, it will cause abnormal outage of the transformer, affect the power generation and supply of the power system, and even cause system oscillation, which is very detrimental to the power generation and power supply operation of the power system. Therefore, when a fault occurs in the microcomputer transformer differential protection device, the cause should be quickly found and dealt with. This article discusses the causes and treatments of microcomputer transformer differential protection device failures in substations.

2 The differential protection device refuses to operate

When the differential protection device refuses to operate, it is very harmful to safe operation, because when an equipment accident occurs, the differential protection device refuses to operate, which may cause the equipment to be burned. The cause of the fault should be preliminarily determined and necessary elimination based on the accident message and the action of the protection device. Since the busbar wiring methods of various types of transformers are different, the fault handling methods are also different. Here we only introduce the general situation.

2.1 Common reasons why the differential protection device refuses to operate

(1) The functional hard pressure plate of the differential protection device is not engaged or the SV soft pressure plate is not engaged;

(2) The setting value of the differential protection device is incorrect;

(3) The power switch of the differential protection device trips;

(4) The positive power supply of the hard pressure plate at the outlet of the differential protection device disappears;

(5) TA disconnection locks the differential protection device;

(6) The power board of the differential protection device fails.

2.2 Inspection and treatment of differential protection device refusal to operate

2.2.1 The differential protection function hard pressure plate is not put in place

If the differential protection device function hard pressure plate is not put in, the person on duty should verify It can only be put into operation after proving that there is no abnormal voltage between the ground and both ends of the functional pressure plate (or checking that the differential protection input value changes from 0 to 1). If the SV soft pressure plate is not put into use, check whether the switch SV within the differential protection range is turned on (especially pay attention to the inner bridge wiring).

2.2.2 The setting value of the differential protection device is incorrect.

If the setting value of the differential protection device is incorrect, the personnel on duty should first remove all the outlet hard pressure plates (or GOOSE export soft pressure plates) of the transformer in mid-jump operation of the device, and only then can the setting value and dispatch of the differential protection device be issued. Check and modify the setting sheet (first check the setting area code of the protection device, and then check the setting. If any errors are found, modify the wrong setting). After the setting of the differential protection device is correct, the personnel on duty should check that there is no abnormal voltage between the outlet pressure plate and the ground and both ends, and then put in the export hard pressure plate (or put in the GOOSE export soft pressure plate).

2.2.3 The power switch of the differential protection device trips

If the power switch of the differential protection device trips, the person on duty should first use an external meter to check whether there is voltage at the incoming terminal of the power switch of the differential protection device. If there is voltage and the voltage value is within the qualified range, it should be considered that there is a short circuit between the air switch and the differential protection device, and the person on duty should give up trying to close the power switch of the differential protection device.

2.2.4 The positive power supply of the hard pressure plate at the outlet of the differential protection device disappears

If the positive power supply of the outlet hard pressure plate of the differential protection device disappears, the person on duty should first use an external meter to measure the voltage at both ends of the outlet hard pressure plate to ground. If it is found that there is no voltage at both ends to ground, then it should be considered whether the outlet pressure plate terminals are loose and not in contact.

2.2.5 TA disconnection locking differential protection device

If it is a TA disconnection locking differential protection device, the person on duty should notify relevant professionals to handle it.

2.2.6 Failure of the power board of the differential protection device

If the power board of the differential protection device fails, the dispatcher should be immediately reported to adjust the operating mode, and the maintenance personnel should be notified to arrive at the station immediately for processing.