High-Power Transformer Differential Relay
The character and scheme of differential protection of high-power transformers are analysed. This kind of relay is constituted by active filters, integrated operational amplifier, CMOS circuit etc. The operating time approaches to 10 ms. The protection consists of percentage, 2nd, 5th harmonic restraint, differential cut-off, broken wire interlocking. This relay is both an interphase fault, turn-to-turn, single earth fault protection and an overvoltage protection. The pick-up current is 0.1 I_(non) of the transformer.