How to Prevent Current Transformer Burning up?

Cause of current transformer burning up

•  Secondary open circuit of the current transformer produces high voltage to burn out the current transformer.
• Long-term use of the current transformer makes the insulation aging, local breakdown or discharge occurs and overvoltage is thereof produced, thus burning out the current transformer.
• The aluminum contact surface of current transformer’s primary connection is seriously oxidized, which results in large contact resistance. The contact resistance gives out heats and burns out the current transformer.
• Long-term overload operation makes the current transformer to give out heat, it is thereof burned out.

Problems existing in the special transformer, user breaker and wiring

• Generally, both the 10kV vacuum breaker and SF6 breaker have the over-current protection and overload protection, they can trip correctly when there’s an interphase short circuit or overload, overvoltage is solved by the equipped Zinc Oxide arrester. All current transformers for metering user high voltage of our special transformer are installed between the disconnecting switch and breaker, therefore, once the current transformer gets wrong and the breaker and arrester are unable to remove fault, the upper breaker trips to eliminate the fault and expand the power failure coverage, the current transformer will be burned out at the same time due to delayed removal of faults.
• When the single-phase grounding happens at the user side and the breaker doesn’t trip, we have to cut off the branches of a same common line gradually to find a ground point, as a result, the common line will be powered off and the power outage range increases.
• Insulation of the lighting arrester at the user side becomes aging, so it can’t effectively prevent the overvoltage.

Countermeasures

• Add a watchdog breaker and avoid the power failure of whole feeder line caused by faults on branches, particularly, ensure that the branch breaker can trip correctly in case of single-phase grounding at the user side.
• Connect the metering current transformer downstream the breaker, so as to guarantee that the breaker and lightning arrester operate correctly to remove faults when the transformer breaks down.
• Strengthen the flashing test for user’s high voltage metering current transformer and lightning arrester (it shall not be more than 4 years according to regulations), find out the aging degree of current transformer and lightning arrester insulation as early as possible, replace timely to avoid power failure caused by burning out of metering current transformer.
• Clean the user primary device regularly to reduce the occurrence of flashover, avoid insulation reduction.