Assignment 9
What are the three basic types of three-phase motors?
1. Squirrel-Cage Induction Motor
2. Wound Rotor Induction Motor
3. Synchronous Motor
Are the potential wiring configurations used in the stators of squirrel-cage induction motors,
wound-rotor induction motors and synchronous motors unique or common to all 3 types?
Common to all three types
What is the formula for synchronous speed?
Synchronous speed = 120 x F / # of poles
Shall a synchronous motor be started with DC connected to the rotor?
No
What is the purpose of the amortisseur winding in a synchronous motor?
An amortisseur winding is provide for starting because the synchronous motor is not self-
starting without this feature.
Is the excitation current of a synchronous motor AC or DC?
DC
What are the minimum number of slip rings required for a synchronous motor?
Two
What are the terminal leads connected to the slip rings on a synchronous motor labeled?
F1 (+) and F2 (-)
How is the DC field excitation controlled in a synchronous motor?
To control the DC field excitation, a field rheostat is used to vary the current in the field
circuit.
How can the power factor of a synchronous motor be varied?
The amount of power factor correction is varied by the amount of excitation current in the
rotor
When is a synchronous motor considered a synchronous condenser?
Under No-load condition, over-excited DC field and used for power factor correction (all
three conditions must be true for a synchronous condenser)
How can a synchronous condenser be made to have a leading power factor?
Over-excite the DC field
Are the rotor’s field windings connected in series or parallel in a synchronous motor?
Series
Do changes in the amount of excitation current affect the running speed of a synchronous
condenser?
No
What type of AC machine is used for power factor correction?
Synchronous Condenser
What detrimental condition causes reduced voltage and increased current flow to the stator
windings of any three-phase motor?
Single Phasing
List the two types of rotor assemblies found in synchronous motors.
1. Cylindrical
2. Salient Pole
List three applications of synchronous machines.
1. Power factor correction, voltage regulator, precise constant speed,
2. slow-speed motors, crushers, grinding mills, belt conveyors
3. rolling mills, plasma/laser cutters, fans, pumps, compressors
List the five components of a salient-pole rotor assembly.
1. Shaft
2. Slip rings
3. Salient Field Poles
4. Field Windings
5. Amortisseur Windings
Synchronous motor components
1. Armortisseur Winding
2. Salient Field Poles & Salient Field Windings
3. Slip Rings
4. Shaft
5. Air Gap
6. Frame / Housing / Case
7. Stator Field Windings
8. Terminal Box
9. Brushes & Brush Holders
10. Base