Oil Immersed Current Transformer has the feature that direct measurement of current in high voltage system is not possible because of insulation problem of measuring instruments and it is also not possible to use current flowing through the system directly for protection purpose due to its high insulation problem. The Transformer is used to reduce the line current to a value which is suitable for measuring instruments relays etc and to isolate the measuring instruments, meters, relays etc. From high voltage side an installation. The Transformer can withstand operational voltage and over voltage in the network and withstand rated primary current in continuous operation without exceeding maximum allowed temperature rise. The Transformer is capable to sustain thermal and mechanical stresses developed due to system fault current and feeds current to external circuit with accuracy at specified primary currents. The Oil Immersed Current Transformer has rated primary current and the feature of short time withstands current.