Page 701 - Basic Electrical Engineering
P. 701
Figure 8.15 DOL starting of three-phase induction motors: (a) direct connections to supply through a
switch but without any overload or short-circuit protection; (b) push-button-operated DOL starter with
overload and short-circuit protection
When the start push button is pressed the contactor coil, M gets energized
as the coil gets connected to R-phase and B-phase. The main contacts as well
as the auxiliary contacts m and m will close. The motor will get full supply
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and start rotating. Since the auxiliary contact m , is closed, pressure on the
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start push button can be released and the contactor will continue to remain
energized. Indicating lamp will get supply through contact m , and will glow,
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showing that the motor is running. To switch off the motor the stop push
button is to be pressed which will de-energize the contactor coil thereby
opening its contacts and making power supply to the motor disconnected. In
