Power protection

 The purpose of fuse fail signal in abb make rel670 distance protection relay to block the all impedance based protection when this signal is high.Its means when the fuse failure signal high Zone-1,Zone-2,Zone-3,Zone -4 tripping of line are block.

  Knee point voltage of current transformer secondary side, the value of voltage at which when the applied across current transformer secondary side   is increased by 10 percent, causes the exciting current to increase by 50 percent.

 Goose in numerical relay used to share the signal between two numerical relay at comman network.

 There is no zero sequence current in delta winding line of transformer.so for protect star delta three phase  Transformers from external fault zero sequence current compansation must we used in differential protection scheme (87T).