Differential Protection:
The bus-bar is fed by a generator and supplies load to two lines. Secondaries of CT in the generator lead, in line 1 & 2 are all connected in parallel. The protective relay is connected across this parallel connection. When a fault occurs, the fault current upsets the balance and produces a differential current to operate a relay.
Fault Bus Protection:
The metal supporting structure or fault bus is earthed through a CT. A relay is connected across the secondary of this CT.
