01․ Which of the following motors has negative speed regulation?
In differential compound motors flux will reduce as load increases because series flux opposes shunt field flux. This will increase speed. Therefore it has negative speed regulation which means speed will increase due to increase in load.
02․ Field weakening control method is used for the _________ ?
By reducing of field current, flux will also reduce. As speed is inversely proportional to flux, so this method can be used for only above rated speed.
03․ Armature resistance control method is used for the _______ ?
In armature circuit resistance method armature resistance is increased. As a result the back emf decreases. As the speed is directly proportional to back emf speed will also decrease. Therefore this method is only used for below rated speed.
04․ Armature reaction effect is more in which of the following methods?
In field weakening method we are reducing the working flux to increase the speed. Therefore effect of armature flux on main field flux or armature flux will increase in case of field weakening method.
05․ Field weakening method is also called as-----------?
Field flux conrtol method is a constant power drive. In this method speed is controlled by varying the field current. Power remains constant for a given speed range.
06․ Armature resistance control method is also called as-----------?
Armature resistance control is constant torque drive. The motor shaft torque become constant given over a speed range.
07․ If terminal voltage of one 1000 rpm shunt motor is reduced to half the speed of the motor will be
If voltage is reduced to half then flux will also be reduced to half because the current flowing through the shunt field is also halved. So speed will remain same.
08․ Diverters are used only in
Diverters are used only in series motors for speed control, these are not used in shunt motors. Since, shunt field winding resistance is very high, if we connect a diverter across shunt field winding, total current will flow through the diverter and almost short circuit the shunt field winding. This will increase the motor speed to a very high value. Therefore diverters are not used in shunt motors.
09․ Which of the following starter is sufficient to start the DC series motor ?
2 point starter is enough to start the dc series motor. Since armature and field winding are in series. No requirement of 3 or 4 point starter.
10․ Which of the following represents the rotating losses of machine?
Eddy current and hysteresis losses are the iron losses of a machine. Frictional and windage losses are due to rotation of the machine.