1. The function of interpoles in DC machine is to:
Reduce field winding heating
Reduce losses
Compensate for airgap variation
Improve commutation
Answer: 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 ______
Intrapole
Interpole
Small Pole
Large Pole
Answer: 2. Interpole
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
Increases the starting torque
Improve commutation under loaded conditions
Increase running torque
Decrease windage loss
Answer: 2. Improve commutation under loaded conditions
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 ____.
Main field Pole
Armature Winding
Stator
Rotor
Answer: 1. Main field Pole
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.
Series
Parallel
Series Parallel
Any of the above
Answer: 1. Series
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:-
Fixed in the yoke and spaced in between the main poles
Placed to balance the armature core
Both (1) and (2)
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 ____
DC Motor only
DC Generator Only
Both Motor and Generator
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.
Copper
Nickel
Iron
Cobalt
Answer: 3. Iron
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:
Large number of turns of thin wire
Large number of turns of thick wire
Small number of turns of thick wire
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.
Maximum
Larger
Smaller
Minimum
Answer: 2. Larger
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.
Directly Proportional
Indirectly Proportional
Same
Half
Answer:1. Directly Proportional
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.
Same Polarity
Different Polarity
Same Current
Same voltage
Answer: 1. Same Polarity
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.
Same Polarity
Different Polarity
Same Current
Same voltage
Answer: 1. Same Polarity
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 ____
Very Strong
Very weak
Neither week nor strong
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 ______
Very Small
Very Large
No Flux is produced
None of the above
Answer: 2. Very Large
Explanation:
Interpoles are connected in series with the armature winding so that they carry full armature current, as shown in Fig. As the load on the machine is increased, the current passing through the interpoles also increases, hence the flux produced by the interpoles is very large.
Consequently, the large voltage is induced in the conductor that opposes the voltage due to the neutral plane shift and the net result is that they neutralize each other.
