Calculate the synchronous speed of a 10-pole three-phase machine connected to a 50 Hz supply.

1. The generator characteristic shown in Figure 9.28 is for a

 

(a) shunt machine

(b) series machine

(c) differentially compounded machine

(d) cumulatively compounded machine

2.The speed of a DC motor can be increased by

(a) reducing the brush pressure

(b) weakening the field strength

(c) strengthening the field

(d) reducing the armature voltage

3.The direction of rotation of a DC shunt motor can be reversed by

(a) reversing the polarity of the DC supply

(b) reversing the connections of both the armature and the field

(c) changing to a series field

(d) reversing either the armature or the field connections

4. Show by a series of MMF vector diagrams how a ‘rotating’ field is produced by

a spaced three-phase winding such as in an induction motor.

5.Calculate the synchronous speed of a 10-pole three-phase machine connected to

a 50 Hz supply.

6.If the synchronous speed of a three-phase machine connected to a 50 Hz supply

is 750 r/min, how many poles has it?

7. What frequency is applied to a four-pole three-phase stator with a synchronous

speed of 1800 r/min?

 

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