Causes and treatment of faults in differential protection device of microcomputer transformer in substation

1 Overview

Differential protection is the main electrical protection to ensure the normal operation of transformers in substations. When a short circuit occurs in the electrical part surrounded by the current transformers on both sides of the transformer, the protection will quickly operate without delay to cut off the fault. If the differential protection device fails to operate due to the fault when the transformer fails, it may cause varying degrees of damage to the transformer or even burn it out, which will greatly affect the safe and stable operation of the power system. Conversely, if the differential protection device malfunctions due to the fault, it will cause abnormal shutdown of the transformer, affect the power generation and supply of the power system, and even cause system oscillation, which is very unfavorable to the power generation and supply operation of the power system. Therefore, when the differential protection device of the microcomputer transformer fails, the cause should be quickly found and handled. This article discusses the cause and treatment of the differential protection device of the microcomputer transformer in the substation.

2 Failure of differential protection device

When the differential protection device fails to operate, it is very harmful to safe operation, because when an accident occurs in the equipment, the failure of the differential protection device may cause the equipment to burn out. The cause of the fault should be preliminarily determined and necessary elimination should be carried out according to the accident message and the action of the protection device. Because the busbar wiring methods of various transformers are different, the fault handling methods are also different. Here we only introduce the general situation.

2.1 General reasons for the failure of differential protection device to operate

(1) The function hard pressure plate of the differential protection device is not put into operation or the SV soft pressure plate is not put into operation;

(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) The TA line is broken and the differential protection device is locked;

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

2.2 Inspection and handling of failure of differential protection device to operate

2.2.1 The function hard pressure plate of differential protection is not put into operation

If the function hard pressure plate of the differential protection device is not put into operation, the on-duty personnel should verify that there is no abnormal voltage between the function pressure plate and the ground and both ends (or check that the differential protection input quantity changes from 0 to 1) before it can be put into operation; if the SV soft pressure plate is not put into operation, check whether the switch SV within the differential protection range is put into operation (especially pay attention to the internal bridge connection).

2.2.2 The setting of the differential protection device is incorrect

If the setting of the differential protection device is incorrect, the duty personnel should first withdraw all the outlet hard pressure plates (or GOOSE outlet soft pressure plates) of the tripped transformer in the device, and then check and modify the setting in the differential protection device with the setting list issued by the dispatcher (first check the setting area code of the protection device, then check the setting, and modify the incorrect setting if any error is found). After the setting in the differential protection device is checked, the duty personnel should verify that there is no abnormal voltage between the outlet pressure plate and the ground and both ends, and then put in the outlet hard pressure plate (or put in the GOOSE outlet 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 duty personnel should first use an external meter to check whether there is voltage at the input 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 duty personnel should give up the test of 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 hard pressure plate at the outlet of the differential protection device disappears, the duty personnel should first use an external meter to measure the voltage between the two ends of the outlet hard pressure plate to the ground. If there is no voltage between the two ends to the ground, then it should be considered whether the terminal of the outlet pressure plate is loose and not in contact.

2.2.5 TA line break lockout differential protection device

If the TA line break lockout differential protection device, the duty personnel 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 notified immediately to adjust the operation mode and the maintenance personnel should be notified to come to the station immediately for processing.