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Fig. shows two alternators with identical speed / load characteristics connected in parallel. The circulating current under no-load condition is

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  • Two identical alternators have impedances Z1 and Z2 connected in parallel produces, E1 & E2 as their individual induced emf’s.
  • If no load is connected between the alternators, the circulating current will flow in the circuit as given by 
  • Here, impedances are different also it should be noted that E1 & E2 are in phase relative to the external circuit but are in direct phase opposition in the local circuit, when it is in parallel.

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More Alternator Parallel Operation Questions

Q1.To operate two alternators in parallel, which of their quantities must be same? 
Q2.Choose one of the following which is not a necessary condition for the parallel operation of two alternators.
Q3.Which of the following is a necessary condition for the operation of two alternators in parallel?
Q4.Synchroscope is used to check _________.
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Q7.To operate two alternators in parallel, the _______must be matched for them.
Q8.Two generating units rated for 250 MW and 400 MW have governor speed regulations of 6% and 6.4%, respectively, from no load to full load. Both the generating units are operating in parallel to share a load of 500 MW. Assuming free governor action, the load shared in MW, by the 250 MW generating unit is _________. (round off to nearest integer)
Q9.Fig. shows two alternators with identical speed / load characteristics connected in parallel. The circulating current under no-load condition is

More Alternator and Synchronous Motors Questions

Q1.Which statements about voltage drop in an alternator are correct? I. The voltage drop due to armature resistance (IaRa) is in phase with the armature current (Ia). II. At unity power factor, the voltage drop IaRa directly subtracts from the generated EMF (E). III. For a leading power factor load, IaRa contributes to an increase in terminal voltage (V). IV. Armature resistance has no effect on voltage regulation.
Q2.Why are salient pole rotors NOT used in turbo alternators?
Q3.Compared to the MMF method, the EMF method is ___________.
Q4.Which application is a common use of synchronous motors? 
Q5.Under constant mechanical load, changing the excitation of a synchronous motor affects which of the following? I. Power factor II. Armature current magnitude III. Speed of the motor IV. Real power output 
Q6.In an alternator, if the load power factor changes from lagging to leading, the armature reaction effect shifts from:
Q7.Which statements about the maximum power output of a cylindrical rotor synchronous generator are correct? I. Maximum power output occurs when the load angle (δ) is 90°. II. Maximum power is proportional to the square of the terminal voltage (V). III. Over-excitation increases the generator’s maximum power capability. IV. Maximum power is independent of the synchronous reactance (Xs).
Q8.Stray load losses in synchronous motors are caused by __________. 
Q9.In a synchronous motor, If the load angle exceeds 90°, then the motor will: 
Q10.Why are short-pitch windings preferred in alternators despite their lower induced EMF per coil?
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Q1.If a 6-pole induction motor operates on a 60 Hz supply, its synchronous speed is _____________.
Q2.How are the segments of the commutator insulated from each other?
Q3.Which statements about voltage drop in an alternator are correct? I. The voltage drop due to armature resistance (IaRa) is in phase with the armature current (Ia). II. At unity power factor, the voltage drop IaRa directly subtracts from the generated EMF (E). III. For a leading power factor load, IaRa contributes to an increase in terminal voltage (V). IV. Armature resistance has no effect on voltage regulation.
Q4.What does the flux created by the load current in the primary winding, which links only with the primary winding, represent?
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Q6.Why are salient pole rotors NOT used in turbo alternators?
Q7.In the equivalent circuit without core losses, the magnetising branch consists of __________. 
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