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A three-phase cylindrical rotor synchronous generator has a synchronous reactance Xs and a negligible armature resistance. The magnitude of per phase terminal voltage is VA and the magnitude of per phase induced emf is EA. Considering the following two statements, P and Q, P: For any three-phase balanced leading load connected across the terminals of this synchronous generator, VA is always more than EA Q: For any three-phase balanced lagging load connected across the terminals of this synchronous generator, VA is always less than EA Which of the following options is correct?

A three-phase cylindrical rotor synchronous generator has a synchronous reactance Xs and a negligible armature resistance. The magnitude of per phase terminal voltage is VA and the magnitude of per phase induced emf is EA. Considering the following two statements, P and Q, P: For any three-phase balanced leading load connected across the terminals of this synchronous generator, VA is always more than EA Q: For any three-phase balanced lagging load connected across the terminals of this synchronous generator, VA is always less than EA Which of the following options is correct? Correct Answer P is false and Q is true

Given that the cylindrical synchronous generator with

Synchronous reactance = XS and

Armature resistance = Ra = 0

Now, the simplified circuit of the synchronous generator looks like as shown below

[ alt="F1 U.B Madhu 09.05.20 D28" src="//storage.googleapis.com/tb-img/production/20/05/F1_U.B_Madhu_09.05.20_D28.png" style="width: 193px; height: 91px;">

Case 1: The load is lagging in nature.

The corresponding phasor diagram is

[ alt="F1 U.B Madhu 09.05.20 D29" src="//storage.googleapis.com/tb-img/production/20/05/F1_U.B_Madhu_09.05.20_D29.png" style="width: 174px; height: 160px;">

⇒ |V| < |E|

Case 2: The load is leading in nature.

The corresponding phasor diagram is shown below.

[ alt="F1 U.B Madhu 09.05.20 D30" src="//storage.googleapis.com/tb-img/production/20/05/F1_U.B_Madhu_09.05.20_D30.png" style="width: 184px; height: 122px;">

⇒ |V| > |E|

  • A cylindrical rotor synchronous generator (with Ra = 0) has always positive voltage regulation for lagging p.f. loads i.e. EA > VA
  • Whereas it has positive, zero, and negative regulation for leading loads i.e. all cases EA > VA, EA = VA, and EA < VA are possible.

 

Therefore, statement P is False, and Q is True.

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