51. Induction motor can run at synchronous speed ? True or false? Explain .
No, if the speed of induction motor is Ns then the relative speed between the rotating flux and the rotor will be zero and so no torque is produced.
52. An induction motor is generally analogous to ?
It is analogous to a winding rotating transformer with its secondary circuit closed’
.
53. Can the starting torque of of a slip ring induction motor being increased?
Yes. It can be increased by adding resistances to the rotor.
54. What would happen if a 3 phase induction motor is switched on with one phase disconnected?
The motor is likely to burn .
55. What happens if the air gap flux density in an induction motor increases?
The increase in air gap flux increases iron loss and hence efficiency decreases.
56. State the advantages of skewing?
It reduces humming and hence quite running of motor is achieved. It reduces magnetic locking of the stator and rotor.
67 State the condition at which the starting torque developed in a slip-ring induction motor is maximum.
When R2=X2
68 What are the effects of increasing rotor resistance on starting current and starting torque?
The additional external resistance reduces the rotor current and hence the current drawn from the supply.
It improves the starting torque developed by improving the power factor in high proportion to the decrease in rotor current.
68 What is slip of an induction motor?
The slip speed expressed as the ratio of synchronous speed is defined as slip.
Percentage slip S=Ns-N/Ns*i00
69 How the magnitude of rotor emf is related to the slip in an I M?
Rotor circuit emf per phase E2r=SE2
70 How the frequency of rotor emf is related to the slip in an I M?
Frequency of rotor emf/current fr=Sfs
No, if the speed of induction motor is Ns then the relative speed between the rotating flux and the rotor will be zero and so no torque is produced.
52. An induction motor is generally analogous to ?
It is analogous to a winding rotating transformer with its secondary circuit closed’
.
53. Can the starting torque of of a slip ring induction motor being increased?
Yes. It can be increased by adding resistances to the rotor.
54. What would happen if a 3 phase induction motor is switched on with one phase disconnected?
The motor is likely to burn .
55. What happens if the air gap flux density in an induction motor increases?
The increase in air gap flux increases iron loss and hence efficiency decreases.
56. State the advantages of skewing?
It reduces humming and hence quite running of motor is achieved. It reduces magnetic locking of the stator and rotor.
67 State the condition at which the starting torque developed in a slip-ring induction motor is maximum.
When R2=X2
68 What are the effects of increasing rotor resistance on starting current and starting torque?
The additional external resistance reduces the rotor current and hence the current drawn from the supply.
It improves the starting torque developed by improving the power factor in high proportion to the decrease in rotor current.
68 What is slip of an induction motor?
The slip speed expressed as the ratio of synchronous speed is defined as slip.
Percentage slip S=Ns-N/Ns*i00
69 How the magnitude of rotor emf is related to the slip in an I M?
Rotor circuit emf per phase E2r=SE2
70 How the frequency of rotor emf is related to the slip in an I M?
Frequency of rotor emf/current fr=Sfs
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