Answer / kanth

1.we can store dc only with batteries
so it is easy to give the control ckt continuous
supply .we cant store ac by any device
2. we can use ac also ,but there batrtery is must through
inverter only we can have ac from battery
bur for controlling purpose most of us preferred dc

Answer / prabhu gnanasekaran

There is specific reasons for using for using DC supply as
control circuit.
All controll units like( Realys, ok
TRIP CIRCUIT,ALARM,indication lamps and other units are
designed for DC supply. The are meters and control cicuits
for AC source also

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