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Electrical Machines One Liner For Competitive Examinations: Part 1

Electrical Machines One Liner For Competitive Examinations: Part 1

This Blog on Electrical Machines One Liner For Competitive Examinations: Part 1 is a series which starts today and it will deal with some of the most important one-liners on Electrical machines.

1.The simplest way to shift load from one d.c. shunt generator running in parallel with another is to adjust their field rheostats.

2.The commutation process in a d.c. generator basically involves the reversal of current in an armature coil as it crosses MNA.

3.In a clockwise-rotating loaded d.c. generator, brushes have to be shifted clockwise.

4.CRGO Steel is used in the core of transformer to reduce Hysteresis loss.

5. The short circuit test on a transformer is conducted to obtain copper losses.

6. Two parallel shunt generators will divide the total load equally in proportion to their kilowatt output ratings only when they have the same rated voltage and voltage regulation.

7.A d.c. motor can be looked upon as d.c. generator with the power flow reversed.

8. As the load is increased, the speed of a d.c. shunt motor reduces slightly (though it can be considered as constant speed motor).

9. Under-compound generators DO NOT need equalizers for satisfactory parallel operation

10.The Eb/V ratio of a d.c. motor is an indication of it’s efficiency.

11. The main function of interpoles is to minimize sparking between the brushes and the commutator when the d.c. machine is loaded.

12. Unlike a shunt motor, it is difficult for a series motor to stall under heavy loading because it develops high overload torque.

13.The V-curves of a synchronous motor show relationship between d.c. field current and a.c. armature current.

14. Lap winding is suitable for high current, low voltage d.c. generators.

15. If the field of a synchronous motor is under-excited, the power factor will be lagging.

16.The d.c. armature winding in which coil sides are a pole pitch apart is called full-pitch winding.

17.In small d.c. machines, armature slots are sometimes not made axial but are skewed. Though skewing makes winding a little more difficult, yet it results in a quieter operation with a slight decrease in losses.

18. The angle between the synchronously-rotating stator flux and rotor poles of a synchronous motor is called torque angle.

19. If the field circuit of a loaded shunt motor is suddenly opened then the circuit breaker or fuse will open the circuit before too much damage is done to the motor.

20. A synchronous motor running with normal excitation adjusts to load increases essentially by the increase in its armature current.

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