Q8

 

Speed of Alternators and Motors with different loads

There are two identical alternators having individual prime mover as shown in the figure. They are connected to a common bus and operating parallel but catering different KW loads.

There are also two identical induction motors connected to the same common bus as shown. These motors are running with unequal loads. Load on one motor is more as compared to other.

In this condition

Speed (RPM) of both Motors can be same or different? Why?

Speed (RPM) of both Alternators can be same or different? Why?

Answer

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Quiz is a mental exercise to enhance reasoning power in the subject. Hence personal attempt for reply is expected before jumping to answer. Answer given here is just for confirmation.

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Answer

Motors

Motors are running with different loads. Motor slip is proportional to its load. So slip of both motors may be different. Running speed of motor is synchronous speed minus slip speed. Hence motor running with more loads has more slip and lower speed as compared to motor running at less load.

 Alternators

Alternators are running in parallel hence they are in synchronism. Therefore speed of both alternators may be same. However as they are sharing unequal active power, their power angle with respect to bus may be different. Alternator sharing more power has larger power angle compare to that sharing less power.