Reasons and solutions for faults in microcomputer transformer differential protection devices in substations

1 Overview

Differential protection is the main electrical protection that ensures the normal operation of substation transformers. In the event of a short circuit fault in the electrical part surrounded by current transformers on each side of the transformer, this protection will quickly act without delay to cut off the fault. If the differential protection device refuses to operate due to a fault in the transformer, it may cause varying degrees of damage to the transformer, even burning out, and greatly affect the safe and stable operation of the power system. Conversely, if the differential protection device malfunctions, it will cause abnormal shutdown of the transformer, affecting the power generation and supply of the power system, and even causing system oscillation, which is very unfavorable for the power generation and supply operation of the power system. Therefore, when a fault occurs in the microcomputer transformer differential protection device, the cause should be quickly identified and dealt with. This article discusses the causes and solutions of faults in microcomputer transformer differential protection devices in substations.

2. Differential protection device refuses to operate

When the differential protection device refuses to operate, it poses a great threat to safe operation, because in the event of an accident, the differential protection device may refuse to operate, which may cause the equipment to burn out. Based on the accident message and the action of the protection device, the cause of the fault should be preliminarily determined and necessary troubleshooting should be carried out. Due to the different busbar connection methods of various transformers, the methods of fault handling are also different. Here, only general situations are introduced.

2.1 General reasons for differential protection device refusal to operate

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

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

(3) Differential protection device power switch tripped;

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

(5) TA disconnection blocking differential protection device;

(6) Differential protection device power board malfunction.

2.2 Inspection and handling of differential protection device refusal to operate

2.2.1 Differential protection function hard pressing plate not activated

If the hard pressing plate of the differential protection device is not activated, the duty personnel should verify that there is no abnormal voltage between the pressing plate and the ground and both ends (or check that the differential protection input has changed from 0 to 1) before it can be activated; The SV soft pressure plate is not engaged. Check if the switch SV within the differential protection range is engaged (especially pay attention to the internal bridge wiring).

2.2.2 Incorrect setting of differential protection device setting

If there is an error in the setting of the differential protection device, the on duty personnel should first remove all the outlet hard pressure plates (or GOOSE outlet soft pressure plates) of the jumping operation transformer in the device, and then verify and modify the setting of the differential protection device with the setting list issued by the dispatch (first check the protection device setting area code, then verify the setting, and if any errors are found, modify the incorrect setting). After verifying that the setting of the differential protection device is correct, the on duty personnel should put the outlet hard pressure plate (or GOOSE outlet soft pressure plate) into operation after verifying that there is no abnormal voltage at the ground and both ends of the outlet pressure plate.

2.2.3 Differential protection device power switch tripping

If the power switch of the differential protection device trips, the on duty personnel should first use an external meter to check whether there is voltage at the incoming terminal of the differential protection device power switch. 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 on duty personnel should give up trying to close the differential protection device power switch.

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 duty personnel should first use an external meter to measure the voltage between the two ends of the outlet hard pressure plate and the ground. If it is found that there is no voltage between the two ends and the ground, then it should be considered whether the wiring terminal of the outlet pressure plate is loose and not in contact.

2.2.5TA Disconnected Locking Differential Protection Device

If the TA breaks and locks the differential protection device, the on duty personnel should notify the relevant professionals to handle it.

2.2.6 Differential protection device power board fault

If there is a fault in the power board of the differential protection device, the dispatch should be immediately reported to adjust the operation mode, and the maintenance personnel should be notified to arrive at the station immediately for handling.