DC & AC additional

Exciter switch

The switch in the prime mover that provides power to the exciter during starting, which supplies the initial field current to the generator or motor.

Excitation current

The current to the motor's field winding that is adjusted by varying the exciter control knob in a Synchronous Motor, which can change the motor's speed or power factor.

Armature resistance

A factor that does not decrease the terminal voltage of a Separately Excited DC Shunt Generator and usually has a negligible effect on the terminal voltage.

DC Shunt Generator

(i) When the load increases, terminal voltage increases. (ii) When the load increases, armature current increases. (iii) When the load increases, power generated increases.

Degree of compounding

The degree of compounding of a DC Compound Generator is said to be "flat compounded" when the series and shunt field fluxes produce a constant terminal voltage regardless of the load variations.

Over-compounding

The ideal condition for long-distance transmission of power via cables or bus bars where the generator is over-compounded.

Differential compounding

When the flux created by the series field opposes that of the shunt field in a generator.

Odd number of poles

False. DC motors cannot have an odd number of poles.

Odd number of parallel paths

True. DC motors can have an odd number of parallel paths in their armature windings.

Odd number of conductors

False. DC motors cannot have an odd number of conductors in their armature windings.

DC motors classification

False. DC motors are not classified as self-excited or separately excited.

Changing rotation of a DC motor

True. To change the rotation of a DC motor, you can change the connection of the field or the armature, but not both.

Counter EMF

True. The smaller the load of a motor, the smaller its counter EMF (back EMF).

Flux of a shunt motor

True. In a shunt motor, if the field circuit resistance is not changed, the flux of the motor remains relatively constant.

Torque and flux relationship

False. In a motor, as the flux increases, the torque typically does not increase.

Speed and flux relationship

False. In a motor, as the flux increases, the speed typically does not increase.

Speed at full-load

True. In a DC motor, the speed at full-load is generally less than the speed at no-load.

Counter EMF at standstill

True. In a DC generator, the counter EMF at standstill is equal to the terminal voltage. If a DC motor has no load, its armature current is zero.

Speed regulation

False. For constant speed applications, a lower speed regulation is not better.

DC motor excitation

False. DC motors cannot be self-excited or separately excited, just like DC generators.

Armature current with no load

True. If a DC motor has no load, its armature current is very close to zero.

Speed regulation

True. For constant speed applications, a lower speed regulation is better.

Armature current and torque relationship

True. The smaller the armature current in a motor, the smaller the torque produced.

Starting current

True. The starting current of a motor is typically higher than its running current.

Starting torque

False. In a motor, the starting torque is usually not higher than the running torque.

Flux and speed relationship

False. As the flux increases in a motor, the speed typically does not decrease.

Counter EMF and terminal voltage

True. In a motor, the counter EMF may be greater than the terminal voltage.

Counter EMF and terminal voltage

False. In a motor, the counter EMF is not always less than the terminal voltage.

Starter resistance and starting current

True. In a motor, the higher the starter resistance, the higher the starting current.

Load and speed relationship

True. As the load of a motor increases, its speed typically decreases.

Torque conversion

True. 1 N-m of torque is greater than 1 ft-lb of torque.

Speed conversion

True. 1 rps (revolution per second) is the same as 60 rpm (revolutions per minute) of speed.