Observation

 

1. State one application of a direct on-line starter.

5(a): A majority of the candidates were unable to recognize the different components of a direct current (d.c.) generator.
5(b): Many of the candidates displayed a lack of understanding when it came to identifying the functions of the various parts of a direct current (d.c.) generator.
5(c): A majority of the candidates did not include the required tools for dismantling a direct current (d.c.) generator in their list.
5(d): Several candidates were unable to accurately outline the steps involved in rewinding a motor.
5(e): Many candidates lacked a clear understanding of the difference between an AC and DC motor.

Expected response:
(a)

W:	yoke
X:	main pole
Y:	main field/coil
Z:	commutator

 

(b)

FUNCTION OF LABELED PARTS

 

W:     houses all the parts of the generator or provides mechanical protection to the parts
X:      holds the main field/coils                                                                                           
Y:      produces the magnetic field                                                                                       
Z:      draws unidirectional current from the rotating armature coils or it converts a.c. to d.c.      

 

(C) (i)      TOOLS NEEDED TO DISMANTLE THE GENERATOR

 

1. Extractor
2. Set of spanners
3. Combination plier
4. Mallet
5. Allen key/Wrenche
6. Screw driver
7. Hammer
8. Hand glove

   (ii) STEPS IN THE PROCEDURE IN DISMANTLING A GENERATOR

 

1. Take data from name plate
2. Mark both front and back covers
3. Loose bolts and nuts
4. Tap the shaft from one end with mallet/wood
5. Remove front and back shields

(D) (i)      WHAT HAPPENS WHEN THE PART LABELED Y IS BURNT

1. The generator will not function/start

(ii) STEPS IN THE PROCEDURE OF REWINDING A MOTOR

1. Take data from name plates
2. Strip the burnt coil
3. Wash the slots
4. Count/check the number of turns in each coil
5. Insulate the slots and insert the coils
6. Connect the coils
7. Test the coil
8. Bind the coil
9. Varnish/bake/dry the coil
10. Test run the motor

(e) (i)  DIFFERENCES BETWEEN AN A.C. MOTOR AND A D.C. MOTOR

a.c. motor	d.c. motor
uses rotor as rotating part uses a.c. current uses slip-ring has three input terminals magnet field rotates Armature is stationary	uses armature uses d.c. current uses armature has two input terminals magnet field is stationary armature rotates

(ii)  APPLICATION OF A DIRECT ON-LINE STARTER

1. Used on a smaller a.c. electric motor
2. Water pumps
3. Conveyor belts
4. Exhaust fans
5. Used in compressors
6. Used in blowers