61
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What is a criterion for selecting numbers of
equalizing rings in the DC Generator?
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|
The numbers of equalizing rings in the DC Generator is =
Numbers of armature conductors / Numbers of pair of poles
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62
|
What is meaning of winding has been developed for
100% equalization connection?
|
|
If all the armature conductors are connected to the equalizer rings,
it is called as 100% equalization connection.
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63
|
Why the equalizing connection is not used in the
wave wound machines?
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Equalization connection
- The equalizing connection is not used in the wave winding because
there are two parallel paths in the wave winding resulting no unbalance of
current in that path.
- If there is inequality of flux, they will affect each
parallel path equally.
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64
|
What is happened when two DC shunt Generator is connected parallel with incorrect polarity?
|
|
When two DC Generators are paralleled with incorrect polarity, short
circuit occurs. This will damages brushes and commutator and tripping of the
Generators.
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65
|
What is meaning of ‘floating’ condition in the two
parallel operated DC shunt Generator?
|
|
Floating
- When two Generators are paralleled with each other, the induced emfs
of the both Generators are same.
- This will result the current cannot be flow
between them. This condition is known as ‘floating condition’.
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66
|
How one Generator is taken out of
service in the two parallel operated DC shunt Generator?
|
|
Two parallel DC shunt generator
- The field of the DC Generator which is taken out of service is
weakened and that of the other Generator is increased till the ammeter of the
Generator shows zero.
- The circuit breaker and the switch are open thus
removing the DC Generator out of service.
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67
|
Which Generator delivers more current than that of
other one if the DC shunt Generator A has more drooping characteristics than
that of DC shunt Generator B?
|
|
The DC shunt Generator A delivers less current than that of DC shunt
Generator B.
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68
|
The parallel operation of two compound Generators is
possible or not? Why?
|
|
The parallel operation of the two compound Generators is unstable for
constant load condition.
- Let it is assumed that compound Generator A carries slightly higher
load than that of compound Generator B due to some reason.
- Due to current
passing through series field winding of compound Generator A, its field
strengthens resulting raises the generated emf. The Generator A takes even
more load.
- The load on the Generator B drop as the system load is constant.
Therefore the generated emf of the compound Generator B reduces result
further drop in load.
- This process is cumulative resulting Generator A will
take entire load and Generator B acts as a motor.
- The circuit breaker of one
Generator will open. This will result the parallel operation of the Generator
stop.
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69
|
What is magnetizing characteristic of the DC
Generator?
|
|
The magnetizing characteristics of the DC Generator show the relation
between no load armature emf and field current.
|
70
|
Which type of DC Generator does not requires
equalizing ring for Parallel operation?
|
|
Under compound DC Generator
|
71
|
Which characteristic of DC Generator helps to decide
stability for a particular application?
|
|
External characteristics of DC Generator : Terminal voltage ( V )
versus load current ( I )
|
72
|
Explain : ‘The open circuit characteristics of the
self excited Generator is straight line at low value of flux density.’
|
|
Open circuit characteristic
- The reluctance of the iron path is negligible at low value of flux
density resulting the total reluctance is only air gap reluctance which is
constant.
- Therefore the generated emf is directly proportional to field
current at low value of flux density.
|
73
|
‘ The generated emf is directly proportional to
field current ’ comment on above statement
|
|
Generated emf – Field current
- The generated emf is directly proportional to the field current is
true only for low value of flux density.
- The value of permeability is small
at high value of flux density therefore the reluctance of the iron path
becomes appreciable.
- Due to above reason the relation between generated emf
and field current is not straight line.
|
74
|
Is there any emf is generated at zero field current
in the self excited DC Generator?
|
|
Some emf is always generated at zero field current in the self excited
DC Generator due to residual magnetism
of poles.
|
75
|
Which parameter greatly affects the initial slope of
the generated emf – field current?
|
|
Air – gap width
|
76
|
Explain the term : Critical resistance
|
|
Critical resistance
- The slope of the open circuit characteristics of the DC shunt
Generator is called as critical resistance.
|
77
|
Describe the condition of building up DC Shunt
Generator.
|
|
Condition of building up DC Shunt Generator
- There must be some residual magnetism in the poles.
- The shunt field
coil should be correctly connected to armature coil. The shunt filed
resistance should be less than the critical resistance if it is excited an
open circuit.
|
78
|
How to obtain driving torque in the DC Generator?
|
|
The driving torque is nothing but prime mover therefore it is diesel
engine, steam turbine or water turbine.
|
79
|
What is direction of rotor and electromagnetic
torque in the case of ( a ) Generator ( b ) Motor ?
|
|
Generator
- The direction of rotor and electromagnetic torque are in the opposite
direction.
Motor
- The direction of the rotor and electromagnetic torque are in the same
direction.
|
80
|
Why the electromagnetic torque in the ( a )
Generator is opposite to that of the rotor direction. ( b ) Motor is same as
that of direction of the rotor?
|
|
Generator
- The field flux in the Generator concentrated at the trailing pole tips
whereas it weaken at leading pole tips so the generated electromagnetic
torque is opposite direction to that of the direction of the rotor.
Motor
- The field flux in the motor concentrated at the leading pole tips
whereas it weaken at trailing pole tips so the generated electromagnetic
torque is same direction as that of the direction of the rotor.
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