DC Machine Interpole MCQ || DC Machine Interpole Question and Answers

1. The function of interpoles in DC machine is to:

1. Reduce field winding heating
2. Reduce losses
3. Compensate for airgap variation
4. Improve commutation

Explanation:

• Interpoles are similar to the main field poles and located on the yoke between the main field poles.
• They have windings in series with the armature winding.
• The inter poles are tapering in shape i.e. having a broad base and less pole shoe area to reduce the extra air gap flux under the trailing pole tip
• The air gap under inter poles is more than the air gap under the main field poles to avoid the saturation

Interpoles in DC machine has basically two functions:

• Automatic neutralization of cross magnetization due to armature reaction.
• To counter and cancel reactance voltage in the coil undergoing commutation.

2. The narrow poles placed in between the main poles of a DC machine are called ______

1. Intrapole
2. Interpole
3. Small Pole
4. Large Pole

Explanation:

No-load characteristics: It is also known as magnetic characteristics or open-circuit characteristics (O.C.C.). It shows the relation between the no-load generated emf in the armature (Eo ) and the field current (i.e., exciting current) If, at a specified speed.

3. Direct current machines are attached with inter-poles in order to

1. Increases the starting torque
2. Improve commutation under loaded conditions
3. Increase running torque
4. Decrease windage loss

Explanation:

• Interpoles are similar to the main field poles and located on the yoke between the main field poles.
• They have windings in series with the armature winding.
• The inter poles are tapering in shape i.e. having a broad base and less pole shoe area to reduce the extra air gap flux under the trailing pole tip
• The air gap under inter poles is more than the air gap under the main field poles to avoid the saturation

Interpoles in DC machine functions:

• Automatic neutralization of cross magnetization due to armature reaction
• To counter and cancel reactance voltage in the coil undergoing commutation
• Direct current machines are attached with inter-poles in order to Improve commutation under loaded conditions.

4. Interpoles are located on the yoke between the ____.

1. Main field Pole
2. Armature Winding
3. Stator
4. Rotor

Explanation:

• Interpoles are similar to the main field poles and located on the yoke between the main field poles.
• They have windings in series with the armature winding.
• The inter poles are tapering in shape i.e. having a broad base and less pole shoe area to reduce the extra air gap flux under the trailing pole tip
• The air gap under inter poles is more than the air gap under the main field poles to avoid the saturation

5.  In series Motor Interpole winding is connected in ______ with the armature circuit.

1. Series
2. Parallel
3. Series Parallel
4. Any of the above

Explanation:

To improve the power factor of a series motor, the cross-flux which is mainly responsible for armature reactance must be canceled out by a compensating winding connected in series with the armature circuit.

6. Interpoles or Compoles are:-

1. Fixed in the yoke and spaced in between the main poles
2. Placed to balance the armature core
3. Both (1) and (2)
4. Neither (1) nor (2)

Answer: 1. Fixed in the yoke and spaced in between the main poles

Explanation:

• Interpoles or compoles are similar to the main field poles and located on the yoke between the main field poles.
• They have windings in series with the armature winding.
• The inter poles are tapering in shape i.e. having a broad base and less pole shoe area to reduce the extra air gap flux under the trailing pole tip
• The air gap under inter poles is more than the air gap under the main field poles to avoid the saturation

7.  The interpoles can be used effectively in ____

1. DC Motor only
2. DC Generator Only
3. Both Motor and Generator
4. None of the above

Answer: 3. Both Motor and Generator

Explanation:

The interpoles can be used equally effectively in motors as well as in 3 generators. When the mode of operation of the machine changes from motor to generator, the currents in the armature and the interpoles are reversed in direction. Therefore, their voltage effects cancel each other out.

8. There must be enough _____ in the interpoles so that they do not become saturated.

1. Copper
2. Nickel
3. Iron
4. Cobalt

Explanation:

Care must be taken to see that there is enough iron in the interpoles so that they do not become saturated at any load current or (armature current).

The interpole MMF must be sufficient to neutralize the cross-magnetizing armature MMF in the interpolar region and enough more to furnish the flux density required for the rotational voltage in the short-circuited armature coil to cancel the reactance voltage.

9. The inter-pole winding consists of:

1. Large number of turns of thin wire
2. Large number of turns of thick wire
3. Small number of turns of thick wire
4. Small number of turns of thin wire

Answer: 3. Small number of turns of thick wire

Explanation:

Interpoles are connected in series with the armature through brushes. Since inter-pole windings carry armature current (high current) it must have a higher cross-section area and few turns to ensure low resistance and low losses.

10. Air gaps under interpoles are kept ____ than that under the main poles.

1. Maximum
2. Larger
3. Smaller
4. Minimum

Explanation:

• In order to avoid saturation in the inter poles, air gaps under these poles are kept longer than the main poles.
• The inter poles cause demagnetization at the trailing pole tip, magnetization at the leading pole tip there by the air gap flux distribution nearly becomes a flat-topped wave.

11. Field strength of interpoles is _____ to the load current.

1. Directly Proportional
2. Indirectly Proportional
3. Same
4. Half

Explanation:

• The inter-pole winding is connected in series with the armature winding because the inter-pole must produce flux that is directly proportional to the armature current.
• Field strength of interpoles is directly proportional to the load current.
• The armature flux in the commutating zone which tends to shift the magnetic neutral axis is neutralized by an appropriate component of inter-pole flux.

12. In a generator, interpoles must have the ______ as the next upcoming pole.

1. Same Polarity
2. Different Polarity
3. Same Current
4. Same voltage

Explanation:

In the case of a generator, the neutral plane is shifted in the direction of the rotation. Therefore, conductors undergoing commutation have the same polarity of voltage as the pole they just left. To neutralize this voltage, the interpole must have opposite flux which also is the flux of the next coming pole.

Hence In a generator, interpoles must have the same polarity as the next upcoming pole.

13. In a motor, interpoles must have the _____ as the previous main pole.

1. Same Polarity
2. Different Polarity
3. Same Current
4. Same voltage

Explanation:

In a motor, the neutral plane shifts opposite to the direction of the rotation, and conductors undergoing commutation have the same flux as the pole has. Therefore, the interpole must have the same polarity as the previous main pole.

14. The field produced by the inter pole winding should be ____

1. Very Strong
2. Very weak
3. Neither week nor strong
4. Either week or strong

Answer: 3. Neither week nor strong

Explanation:

The field produced by the inter pole winding should be neither too weak nor too strong. Weak field results in under commutation accompanied by arcing and a strong field into over commutation with arcing in the reverse direction. Therefore, the value of ampere-turns per pair of interpoles must be selected judiciously.

15. The flux produced by the Interpoles winding is ______

1. Very Small
2. Very Large
3. No Flux is produced
4. None of the above