Page 702 - Basic Electrical Engineering

case the motor is overloaded, current drawn will increase beyond the rated
capacity, the overload relay contact will open, the contactor coil will get de-
energised and, as a consequence, the motor will get disconnected from the

supply.

8.14.2 Manual Star–Delta Starter

Fig. 8.16 Shows a manual star–delta starter where the switch S is placed in
start position to connect the stator winding terminals A , B , C in star and
2
2
2
connecting the other ends of the windings, i.e., A , B and C to the supply.
1
1
1
The motor will start running with the stator windings star connected and with
full supply voltage applied to them. Once the motor picks up speed, the
switch is placed in run position and the stator windings will get connected in

delta and the same supply voltage applied to them. This way the current
drawn by the motor from the supply lines during starting is reduced to one-

third the value of the current that would have flown if the windings were
delta connected during starting period.

Figure 8.16 Manual star–delta starter

This can be understood from the following calculations.