Which option is INCORRECT in relation to the applications of synchronous motors?

Question

Question

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SSC JE Electrical 10 Oct 2023 Shift 2 Official Paper-I

They are used in power house and substation in parallel to the bus bar to improve the power factors.
They are used to regulate the voltage at the end of transmission line.
They are used in factories having a large number of induction motors operated at leading power factor.
They are used in large loads where constant speed is required.

Answer 1

The correct answer is option 3.

Synchronous Motors

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Synchronous motors are inherently not self-starting. They require some external means to bring their speed close to synchronous speed before they are synchronized. The speed of operation is in synchronism with the supply frequency and hence for constant supply frequency, they behave as constant speed motors irrespective of load condition.
A synchronous motor can be used to compensate for voltage drop in a constant voltage transmission line by acting as a synchronous condenser. When the system voltage drops, the motor can be over-excited to generate reactive power, which helps to maintain the system voltage at the desired level.
Over-excited synchronous motors draw leading currents and hence act as synchronous condensers. So, they are used to improve the power factor and to improve the voltage regulation.
Synchronous motor finds applications where operating speed is less (around 500 rpm) and high power is required. For low power output below 40 kW in the medium speed range, the size, weight, and cost of the corresponding three-phase induction motor are very high.