Electrician Theory ||DC Machine Important Points - 05||

Electrician Theory ||DC Machine Important Points - 05||

Author -Er. R.Kumar R.Kumar

Sunday, March 29, 20204 minute read

 

1. The shaft torque in the dc motor is lower than the armature torque due to iron, friction and windage losses.

2. Before the field pole or armature core was saturated. The torque of the dc series motor is proportional to the square of the armature current.

3. Pole shoes are used to keep the magnetic flux evenly around the armature.

4. Brushes of metal graphite are used in generators using welding.

5. The hold on the four-point starter is connected by a parallel resistance to the hold on coil supply.

6. DC series motor should not start without load.

7. The conductor of the armature widening is soldered on the riser of the commutator.

DC Machine

8.​ Brushes are made of carbon and graphite for general use.​

9. In order to keep the starting current in the dc motor in range it is necessary to apply the starting resistance.

9.​ The two-point starter, used to start the series motor, reduces the starting current at the time of starting.

11.​ The presence of graphite inside the brushes acts as a lubricating action.

12. Back EMF in dc motor is less than the supply voltage.

13. ​The speed of dc series motor is inversely proportional to load torque.

14. While changing the brushes, brushes of the same grade and same size should be applied.

15.​ The armature voltage drop is proportional to the product of the I2R.

16. The dc series motor is used for traction use.

17.  ​The field windings in the separately excited generator source is Separately added.

18. While testing insulation, a suitable time for testing should be given until the meter pointer becomes stable.

19. A 6 pole D.C. Wound generator whose armature is wave wound. If the armature is rewound for lap winding, then the emf generated will be reduced three times.

20. By adding resistance in the series of the field of the dc shunt generator, the voltage of the generator will be reduced because the exciting current of the field winding of the generator also decreases due to resistance.

21. The emf produced at the running stage in the dc motor is opposed to the supplied voltage.

22. The output power from an electric motor is derived by coupling on the shaft.

23. The dc generator works on the principle of Faraday's electromagnetic induction.

24. A four-pole D.C. shunt generator is giving 200 ampere current and the generator is a lap wound, then the parallel path per current will be 50 amperes.

25.​ When measuring the armature resistance from a shunt type oh meter, it should be checked that the meter is giving zero reading when the meter is shortened.

26. According to Fleming's left-hand rule, the thumb indicates the direction of rotation of the conductor.

27. The dc series motor must be directly coupled to the load.

28. The shunt field is formed by thin wires and a large number of turns, due to which its resistance is high.

29. 3 Three point starter has two parallel paths.

30. Series fields are added to the armature series.