Oil Filled Current Transformers

Oil Filled current transformers in high voltage applications are still the preferred ones due to cost advantages and easy availability of the technology. They are available in live and dead tank versions depending on the customers requirements. In measuring and protection applications they can be manufactured in single or multi-core as well as multi-tap designs. Tap changing can also be on primary or secondary, however due to convenience of low current and low voltage, secondary tap changing is now a days the preferred trend.

Construction

Secondary winding is made first over the toroid with thermal isolation. Insulation of the secondary winding is done in accordance with high voltage requirements. Primary is finally wound over the insulated coil. Surface of the coil is made uni-potential with special tapes. Number of such uni-potential layer depend upon the system voltage. Such layers will relieve the coil from voltage stresses. Secondary leads are brought to the terminal box through the insulator. The complete coil assembly is then placed in the tank and gently slipped inside the vacuum heating and drying ovens to completely dehydrate the equipment and ensure long operating life.

All Current transformers have special identification number given right from stage one. This will enable us to trace the fault up to root level in case of failures and thus implement the preventive action.

TESTING

Current transformers are tested in fully equipped testing lab for all routine tests as per IS : 2705, I IEC6004-part 1or other relevant standard as specified by the customer. The CTs are also tested at CPRI for various rating from time to time in approved labs for design validation.