Question { ABB, 8548 }

Differentiate between power relay and reverse power relay?

Answer

Power Relay will operate when the power is more than the set irrespective of the direction where as reverse power relay will operate when the power is transferring the opposite direction...

Question { Alstom, 47105 }

What is the purpose of SOTF being used inspite of distance
Protection given?

Answer

SOTF is known as Switch On T Fault as the name suggest it will act when there is fault on the line when closing. Here you asked the question of why we use even Distance protection is there. In distance if the fault is in Zone 2 as per distance protection it will operate only after predetrmined time normally 0.3 or 0.5 Seconds for Zone 2 but this type of faults has to be removed instantaneously but in this condition as Distance Zone Fails SOTF which clear the fault instantaneously. This fault mostly occur while restoring the line after maintenance if earth switch not open at other end of line normally this will be in Zone 2 of distance as Zone 1 will cover only for 80% of line so in this case SOTF will act faster than distance.

Question { KPTCL, 3835 }

what is broken conductor indication

Answer

If suddenly current in one phase of the line falls then there me and fault that particular phase got opened this will be detected by broken conductor protection by measuring the ratio of negative and positive sequence currents. in simple it is open circuit fault