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Choose the INCORRECT statement with respect to synchronous machines.


1. The rotating air gap field and the rotor in the machine rotate at the same speed.
2. The power factor of the machine is always closer to 0.9 lag at any condition.
3. It runs at a constant speed at steady state when it is connected to fixed supply with variable load.
4. The rotor poles are excited by a DC current, and its stator windings are connected to an AC supply.

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Correct Answer - Option 2 : The power factor of the machine is always closer to 0.9 lag at any condition.

CONCEPT:

The power factor of synchronous machine under various conditions is given below

pf ALTERNATOR MOTOR

unity

Purely cross magnetizing

purely cross magnetizing
Zero PF lag purely demagnetizing purely magnetizing
Zero PF lead purely magnetizing purely demagnetizing
0.8 lag partly demagnetizing+partly cross magnetizing purely magnetizing+purely cross magnetizing
0.8 lead partly magnetizing+partly cross magnetizing partly demagnetizing+partly cross magnetizing

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