A rotor-resistance starter for a three-phase wound-rotor induction motor

1. A rotor-resistance starter for a three-phase wound-rotor induction motor

 

(a) adds external resistance to the wound rotor via sliprings

(b) is connected in series with the machine stator

(c) can only be used in conjunction with a double-cage rotor

(d) applies only to DC motors

2. A large synchronous motor is often started by

(a) connecting it directly to the three-phase supply

(b) pushing the rotor in the required direction before connecting the supply

(c) running it up to speed using a ‘pony’ motor before energising the rotor

(d) first switching on the rotor supply then applying the stator voltage

3.A single-phase induction motor

(a) can only be used for loads rated at less than 0.5 kW

(b) will run in whichever direction the rotor is started

(c) must have a capacitor to start it

(d) must never have its frame connected to earth

4.A series motor can be used on AC or DC provided that

(a) the supply voltage never exceeds 250 V

(b) the load is low

(c) the field system is laminated

(d) only low-frequency AC supplies are used

5. A shaded-pole motor

(a) can only be used in situations protected from direct sunlight

(b) uses a three-phase supply and feeds very heavy loads

(c) must have a derating factor of 0.7 applied to it

(d) is fed from a single-phase AC supply and is usually of low ra

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