Directional Protection
Ring Main Protection with Directional Overcurrent Relays
A ring main feeds load from two directions, so a fault on one section can be fed from either side. Ordinary non-directional overcurrent rela...
Power System Protection
Buchholz Relay: Principle, Alarm, Trip — and Its Limitations
A transformer can develop a slow internal fault — a winding hot spot, a loose connection, insulation breaking down — long before it becomes ...
Distance Protection
Reactance Relay and the R–X Plane: Why Arc Resistance Does Not Fool It
A distance relay measures the impedance to the fault and trips if it falls inside its zone. The trouble is that a fault arc adds resistance,...
Induction Relay
Wattmeter-Type Induction Relay: Construction and IDMT Characteristic
The wattmeter-type induction relay is the classic overcurrent relay — the spinning-disc relay found in substations for decades before digita...