01․ Which of the following is/are the advantages of carbon brush over the copper brush?
Advantages of carbon brush over the copper brushes are as follows:
- They are not hard as copper brushes.
- They are self lubricating in nature which ensure excellent mechanical conditions with rotating commutator.
- In case of any sparking they will be less damaged than copper brushes.
02․ The size of inter poles is small as compared to main poles. What is the reason?
Inter poles are small poles and they are tapered in shape, intentionally designed with larger air gap than the main pole, so as not to get saturated when the load current flows through the inter polar windings.
03․ The functions of inter poles are
Interpoles serves two functions
1. It produce a counter emf in the coil undergoing commutation because of its opposite polarity and nullify the reactance voltage produced during commutation. This will improve the commutation.
2. It reduces the cross magnetization effect of armature reaction and impoves commutation.
04․ Which of the following statements is/are correct ?
Compensating winding will act under the pole to reduce armature flux and demagnetizing effect of armature reaction.
Inter pole winding will act in inter polar region to improve commutation where compensating can't work.
05․ In DC machine shape of main field flux distribution is?
The main field flux distribution is flat tapped or trapezoidal in shape.
06․ In DC machine shape of armature MMF wave is?
The shape of armature MMF is triangular in nature and directed towards brush axis.
07․ In DC machines shape of net flux density is?
In DC machine the net flux density due to armature reaction is peaky in nature.
08․ In DC machines internal characteristics are plotted between
To know the application the characteristics should be known. It is basically variation of terminal voltage with load. Characteristics are divided in to
1. No load 2. load.
Load characteristics are again divided in to 1. Internal characteristics (Eg vs Ia)
2. External characteristics (Vt vs load current)
09․ Series generators are used in which of the following applications?
Series generators have rising voltage characteristics, which are not at all suitable for ordinary power supplies but they are used as boosters in dc distribution or transmission to compensate the voltage drop.
10․ Which of the following generators are used in arc welding?
To limit the welding current which resembles short circuit, DC differential compound generators are used.
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