Analysis of current transformer abnormalities and accident handling
Due to the secondary circuit of a current transformer being close to a short-circuit state during normal operation, it is generally considered silent. However, faults in current transformers often accompany noise and other phenomena. When the secondary circuit suddenly opens, a high induced potential is generated in the secondary coil, with peak values reaching thousands of volts or more, posing a threat to the lives of personnel working on the secondary circuit and the safety of equipment. Moreover, high voltage may cause arcing and ignition. Simultaneously, due to the sharp increase in magnetic flux within the iron core, it reaches a highly saturated state. The iron core experiences severe heat loss and heating, which may damage the secondary winding of the rheometer. At this time, the increase in magnetic flux density causes non-sinusoidal waves, leading to extremely uneven vibration of the silicon steel sheets and thus generating significant noise.
- Handling of current transformers in an open circuit
If the operating personnel discover such a fault, they should maintain the load unchanged, disable the protection device that may malfunction, and notify relevant personnel to eliminate it promptly.
II. Handling of secondary circuit disconnection (open circuit) of current transformer
- Anomalous phenomenon
(1) The ammeter reading drops to zero, the readings of the active and reactive power meters decrease or fluctuate, and the watt-hour meter slows down or stops.
(2) Differential disconnection light indicator alarm.
(3) The current transformer emits abnormal noise, or it becomes hot, emits smoke, or the secondary terminal wire end discharges or sparks.
(4) The relay protection device fails to operate or operates incorrectly (this phenomenon is only observed during fault investigation after a bypass trip caused by incorrect or failed tripping of the circuit breaker).
- Exception handling
(1) Immediately report the fault phenomenon to the relevant dispatcher.
(2) Based on the phenomenon, determine whether the open circuit of the current transformer belongs to the measurement circuit or the protection circuit. Before handling, consider disabling the protection that may cause false operation.
(3) When inspecting the secondary circuit of a current transformer, it is necessary to stand on an insulating mat, pay attention to personal safety, and use qualified insulating tools.
(4) When a fire is caused by an open circuit in the secondary circuit of a current transformer, the power supply should be cut off first, and then a dry asbestos cloth or a dry fire extinguisher can be used to extinguish the fire.
III. Current transformer body fault
If a current transformer experiences any of the following faults, it should be immediately taken out of service for maintenance:
(1) There is an abnormal noise, overheating, and accompanied by smoke and a burning odor from the interior.
(2) Severe oil leakage, porcelain damage, or electrical discharge.
(3) Fuel spray ignition or gumming phenomenon.
(4) The elongation of the metal expander significantly exceeds the specified value at ambient temperature.