Preventive measures against burning of current transformers

　　 It is necessary for users and power supply companies to prevent and reduce the re-burning of user current transformers.

　　1. Reasons for burning of current transformers

　　(1) The current transformer is opened for the second time, which generates high voltage and burns out the current transformer.

　　(2) The service life of the current transformer is too long, and the insulation is aging, and part of the breakdown or discharge occurs, resulting in overvoltage, causing the current transformer to heat and burn out.

　　(3) The contact surface of the current transformer connected to the aluminum row at a time is too oxidized, the contact resistance is too large, and the current transformer burns out due to heat.

　　 (4) The user has a long time of overload operation, which causes the current transformer to heat up and burn out.

　　2, there is a problem with the circuit breaker and wiring of the dedicated transformer user

　　(1) Generally, 10kV vacuum circuit breakers and SF6 circuit breakers are equipped with overcurrent and overload protection. The circuit breaker can trip correctly when there is a phase-to-phase short circuit and overload, and the overvoltage is removed by the installed zinc oxide arrester.

　　(2) When a single-phase grounding occurs on the user side, because the circuit breaker does not trip, it is necessary to pull the offline branches of a common line one by one in order to find the grounding point, which will also cause the common line to be disabled and increase the power outage.

　　 (3) The insulation of the lightning arrester on the user side is aging and cannot effectively prevent overvoltage.

　　 3. Adopt countermeasures

　　 (1) Install watchdog circuit breakers to prevent branch faults from power outages of the entire feeder, especially to ensure that the branch circuit breakers can reliably trip when the power side is single-phase grounded.

　　 (2) Connect the metering current transformer to the back of the circuit breaker to ensure that the circuit breaker and arrester operate correctly when the metering current transformer is faulty.

　　(3) Strengthen users’ high-voltage measurement current transformer and arrester high-voltage insulation test (the regulations do not exceed 4 years), find the insulation aging degree of the measurement current transformer and the arrester as soon as possible, and replace it in time to prevent the occurrence of a burnout of the measurement current transformer and cause a power outage.

　　(4) Regularly clean the user’s equipment once to reduce pollution flashover and prevent insulation degradation.