91. What is the phasor relation between induced emf and terminal voltage of a 3 phase synchronous motor?
The rotating magnetic field is initially established by the prime source of supply V. The main field then causes an emf e to get induced in the 3 phase winding. Hence when the machine operates as a synchronous motor the emf phasor always lags the terminal voltage phasor by the load1torque angle .
92 At what load angle is power developed in a synchronous motor becomes its maximum value ?
When its load angle is equal to the impedance angle .
93 What are V and inverted V curves of synchronous motor ?
The variation of magnitude of line current with respect to the field current is called V curve . The variation of power factor with respect to the field current is called inverted V curve.
94 What happens when the field current of a synchronous motor is increased beyond the normal value at constant input?
Increase in emf causes the motor to have reactive current in the leading direction. The additional leading reactive current causes the magnitude of line current, accompanied by the decrease in power factor.
95. Distinguish between synchronous phase modifier and synchronous condenser
A synchronous motor used to change the power factor or power factor in the supply lines is called synchronous phase modifier.
A synchronous motor operated at no load with over excitation condition to draw large leading reactive current and power is called a synchronous condenser.
96 How the synchronous motor can be used as s synchronous condenser?
Synchronous motor is operated on over excitation so as to draw leading reactive current and power from the supply lines. This compensates the lagging current and power requirement of the load making the system power factor to become unity. The motor does the job of capacitors and hence called as synchronous condenser.
97 What type of single phase induction motor would you use for the following applications?
(i) Ceiling fan
(ii) Wet grinder
Ceiling fan – capacitor start and run motor
Wet grinder – capacitor start motor
98 After servicing a single phase fan it was found to run in reverse direction. What could be the reason?
The connection to the starting/ auxiliary winding would have reversed.
99 What will be the direction of rotation of a shaded pole single phase induction motor?
The motor rotates in the direction specified by the unshaded to shaded region in the pole phase
100.What is the property of a single phase single winding induction motor?
It has zero starting torque
101.Which winding in a double cage induction motor has high resistance and low inductance?
Outer cage winding
The rotating magnetic field is initially established by the prime source of supply V. The main field then causes an emf e to get induced in the 3 phase winding. Hence when the machine operates as a synchronous motor the emf phasor always lags the terminal voltage phasor by the load1torque angle .
92 At what load angle is power developed in a synchronous motor becomes its maximum value ?
When its load angle is equal to the impedance angle .
93 What are V and inverted V curves of synchronous motor ?
The variation of magnitude of line current with respect to the field current is called V curve . The variation of power factor with respect to the field current is called inverted V curve.
94 What happens when the field current of a synchronous motor is increased beyond the normal value at constant input?
Increase in emf causes the motor to have reactive current in the leading direction. The additional leading reactive current causes the magnitude of line current, accompanied by the decrease in power factor.
95. Distinguish between synchronous phase modifier and synchronous condenser
A synchronous motor used to change the power factor or power factor in the supply lines is called synchronous phase modifier.
A synchronous motor operated at no load with over excitation condition to draw large leading reactive current and power is called a synchronous condenser.
96 How the synchronous motor can be used as s synchronous condenser?
Synchronous motor is operated on over excitation so as to draw leading reactive current and power from the supply lines. This compensates the lagging current and power requirement of the load making the system power factor to become unity. The motor does the job of capacitors and hence called as synchronous condenser.
97 What type of single phase induction motor would you use for the following applications?
(i) Ceiling fan
(ii) Wet grinder
Ceiling fan – capacitor start and run motor
Wet grinder – capacitor start motor
98 After servicing a single phase fan it was found to run in reverse direction. What could be the reason?
The connection to the starting/ auxiliary winding would have reversed.
99 What will be the direction of rotation of a shaded pole single phase induction motor?
The motor rotates in the direction specified by the unshaded to shaded region in the pole phase
100.What is the property of a single phase single winding induction motor?
It has zero starting torque
101.Which winding in a double cage induction motor has high resistance and low inductance?
Outer cage winding
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