Basic Electricity 2, WASSCE (PC), 2016

Question 4

 

  1. A four pole three-phase induction motor operates from a supply of frequency 50 Hz.  Calculate the synchronous speed.
  1. (i) state three methods of starting a three-pole inductor motor.
  2. state one application for each of the following single-phase induction motors:
      1. universal;
      2. capacitor start. 

 

Observation

 

 

(b)(i)   Methods of starting a 3 phase inductions motor 
             (i) Star – delta
             (ii) Auto transformer
             (iii) Direct on line 
             (iv)  Rotor resistance starter                                  
                                                                                            
(b)(ii) Application of single phase motors
            (i)        Universal motor        -   Vacuum cleaner
                                                        -   Food mixers
                                                            -    Domestic sewing machine
                                                        -   Portable drills
            (ii)       Capacitor start          -    Ceiling fan

  • Compressors
  • Refrigerators
  • Air conditioners

                                                                                                                                                                                                    
The first part was well attempted by candidates but they could not provide correct answers for the other part.