Relay protection with transformer
Fuses may adequately protect small transformers, but larger ones require overcurrent protection using a relay and CB, as fuses do not have the required fault breaking capacity. Conventional earth fault protection using overcurrent elements fails to provide adequate protection for transformer windings. This applies particularly to a star-connected winding with an impedance-earthed neutral. For the high-impedance type, the residual current of three line current transformers is balanced against the output of a current transf. The restricted earth fault schemes described above depend entirely on the Kirchhoff principlethat the sum of the currents flowing into a conducting network is zero. Power transformer protection relaying (combined differential / REF, overfluxing, tank-earth and oil / gas) 1.
Read More
