Operate Alternators, Generators. Test 16

If a cable length 100m, dia.1.25 mm has a resistance of 30 Ohm, what length cable of same material with dia.0.75 mm has a resistance of 25 Ohm?

The principle of an automatic voltage regulator (AVR) is to produce an excitation current proportional to _____

What would be the correct setting of the current relay for a three phase induction motor?

Can the speed of an asynchronous motor be regulated ?

Yes, if a thyristor regulator is used.
No, because the windings are not designed for that.
No, because speed can only be regulated by adjusting the voltage of the rotor winding.
Yes, using resistors in series with the stator winding.

Why is synchronization required when one alternator is to be paralelled with another?

The overall insulation resistance can go down if no synchronization is carried out.
If two unsynchronized generators are connected, both the diesel prime mover and the generator can be damaged.
Two generators which are not synchronized cannot be connected.
If not, the electrical net voltage may be out of phase after the generators have been connected.

The commutator of a DC generator is examined and is found to have a smooth appearance and a dark chocolate colour. What action would you take?

Change the brush springs.
Clean the commutator with emery cloth until the surface is bright and burnished copper.
Change the brushes.
None, this is hoe it should appear.

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