2.1
QUESTONS AND ANSWERS ON SINGLE-PHASE MOTORS
Q1. HOW WOULD YOU REVERSE THE DIRECTION of rotaion of a capacitor start- induction-run motor
Ans. BY reversing either the running or starting-winding leads where they are connected to the lines. Both must not be reversed.
Q2. In which direction does a shaded pole turn?
Ans. Itrens from the unshaded to the shaded pole (Fig. 31-55)
Q3. Can such a motor be reversed?
Ans3. Normally ,such motors are not reversible because that would involve mechanical dismantling And re-assembly. However,special motors are made having two rotors on a common shaft, each having one stator assembly for rotation in opposite direction.
Q4. What is universal motor?
Ans. It is built like a series d.c. Motor with the difference that both it's stator and anmature are laminated. They can be used either on d.c. Or a.c. Supply although the speed and power are greater on direct current. They cannot be satisfactorily made to run at less than about 2000 r.p.m.
Q.5 How cana universalmoter?
Ans By reversing either the field leads or armature leads but not both.
Q6. How can we reverse the direction of rotation of repulsion,repulsion-induction and repulsion-start-induction-run motors?
Ans. By shifting the brush positions by about 15• electrical.
Q7. How can we reverse the rotation of a 1-phase,split-phase motor?
Ans. By veversing the leads to either the running or starter winding (fig. 31-56) but not both.
Q8. What could be the reasons if a repulsion induction motor fails to start?
Ans. Any one of the following
(I) no supply voltage (ii) low voltage (iii) excessive overload (iv) the bearing lining may be stuck or frozen to shaft (v) armature lining may be rubbing (vi) brush yoke may be incorrectly located (vii) brush spacing may be wrong.
Q9. What could by the reasons if a sprit-phase motor foils to start and hurns loud by
Ans. It could be due to the starting winding-being open or grounded or burnt ac.
Q10. What could be he reasons if a split phase motor runs too slow?
Ans. Any one of the following factors could be responsible : (i) wrong supply voltage and frequency (ii) overload (iii) grounded starting and running windings (iv) short-circuited or open winding in field circuit.