1 Overview
Differential protection is the main protection to ensure the normal operation of the transformer in the substation. When the electrical part surrounded by the current transformer on each side of the transformer has a short circuit fault, the protection acts quickly without delay to remove the fault. If the transformer fails, the differential protection device refuses to operate due to the fault, which may cause different degrees of damage to the transformer, or even burn out, and will greatly affect the safe and stable operation of the power system. On the contrary, the malfunction of the differential protection device due to the fault will cause the abnormal outage of the transformer, affect the power supply of the power system, and even cause system oscillation, which is very unfavorable to the power system. Therefore, when the fault of the differential protection device of the microcomputer transformer occurs, the cause should be quickly found and dealt with. This paper discusses the causes and treatment of the fault of the differential protection device of the microcomputer transformer in the substation.
2 Differential protection device rejection
When the differential protection device refuses to operate, it is very harmful to safe operation, because when the equipment has an accident, the differential protection device refuses to operate, which may cause the equipment to burn out. The cause of the failure should be preliminarily determined and necessary elimination should be carried out quickly according to the accident report and the operation of the protection device. Due to the different wiring methods of the busbar where various types of transformers are located, the methods of fault handling are also different. Here is only the general situation.
2.1 General reasons for the refusal of differential protection devices
(1) The differential protection device function hard plate is not put in or the SV soft plate is not put in;
(2) The setting value of the differential protection device is incorrect.
(3) Differential protection device power switch trip;
(4) The differential protection device outlet hard plate positive power supply disappears;
(5) TA disconnection locking differential protection device;
(6) Differential protection device power board failure.
2.2 Inspection and treatment of differential protection device rejection
2.2.1 Differential Protection Hard Plate Not Available
If the functional hard plate of the differential protection device is not put in, the duty personnel should verify that there is no abnormal voltage on the ground and at both ends of the functional pressure plate (or check that the input amount of the differential protection is changed from 0 to 1) before putting it in; if the SV soft pressure plate is not put in, check whether the switch SV within the differential protection range is put in (especially the inner bridge wiring).
2.2.2 differential protection device setting error
If the setting value of the differential protection device is incorrect, the staff on duty should first exit all the outlet hard pressure plates (or GOOSE outlet soft pressure plates) of the transformer running in the device, and then be able to check and modify the setting value of the differential protection device with the setting order issued by the dispatcher (first check the setting area code of the protection device, then check the setting value, find any errors, and modify the wrong setting value). After the setting value of the differential protection device is checked correctly, the staff on duty should check the ground and both ends of the outlet pressure plate for no abnormal voltage, and then put it into the outlet hard pressure plate (or put it into the GOOSE outlet soft pressure plate).
2.2.3 differential protection device power switch trip
If the power switch of the differential protection device is tripped, the duty officer should first use an external meter to check whether there is a voltage at the inlet terminal of the power switch of the differential protection device. If there is a voltage and the voltage value is within the qualified range, the air switch should be considered. If there is a short circuit between the differential protection device, the duty officer should give up the power switch of the differential protection device.
2.2.4 differential protection device outlet hard plate positive power supply disappears
If the positive power supply of the outlet hard plate of the differential protection device disappears, the duty personnel should first measure the voltage to the ground at both ends of the outlet hard plate with an external meter, and find that there is no voltage to the ground at both ends. Then they should consider whether the outlet pressure plate terminals are loose and not in contact.
2.2.5 TA disconnection locking differential protection device
If the TA disconnects the locking differential protection device, the duty personnel shall notify the relevant professionals to deal with it.
2.2.6 differential protection device power board fault
If the power board of the differential protection device fails, it should be reported immediately to adjust the operation mode and notify the maintenance personnel to arrive at the station immediately.
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