Ans. The motor will achieve dangerously high speed and may destroy itself.
Q.2. What happens if the direction of current at the terminals of a series motor is reversed?
Ans. It does not reverse the direction of rotation of motor because current flows through the armature in the same direction as through the field.
Q.3. What is the function of interpoles and how are interpole windings connected?
Ans. Interpoles are small poles placed in between the main poles. Their function is to assist commutation by producing the auxiliary or commutating flux. Consequently, brush sparking is practically eliminated. Interpole windings are connected in series with the armature windings.
Q.4. In rewinding the armature of a d.c. motor, progressive connections are changed to retrogressive ones. Will it affect the operation in any way?
Ans. Yes. Now, the armature will rotate in the opposite direction.
Q.5. Why does a d.c. motor sometime spark on light load?
Ans. Due to the presence of paint spray, chemical, oil or grease etc. on commutator.
Q.6. When is the armature of a d.c. motor likely to get over-heated?
Ans. 1. When motor is over-loaded.
2. When it is installed at a place having restricted ventilation.
3. When armature winding is shorted.
Q.7. What causes are responsible for over-heating of commutator in a d.c. motor?
Ans. It could be due either to the brushes being off neutral or being under excessive spring pressure. Accordingly, brushes should be adjusted properly and the spring pressure should be reduced but not to the point where sparking is introduced.
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