Assignment 7
What two factors determine the synchronous speed of a squirrel cage induction motor?
1. Frequency
2.Number of poles
Is a start winding required for a squirrel cage induction motor?
No
Are the two windings of each phase in a 230/460V squirrel cage induction motor connected in a series or parrallel for operation at 480V?
Series
What should the normal electrical ohase displacement be between the interconnected stator coils of a SCIM?
120°
Does a squirrel cage induction motor require the use of capacitors for phase displacement?
No
What type of material is used for squirrel cage rotor bars
Non-Ferrous metal (typically copper or aluminum)
What is the minimum number of terminal leads required for connection of a single configuration, single voltage 575 V rated squirrel cage induction motor?
Three
What is the minimum number of terminal leads required for connection of a single configuration, dual voltage 230/460 V rated squirrel cage induction motor?
Nine
To reverse a squirrel cage, induction motor, which wiring connections are interchanged?
L1 & L3 typically(Or any two line leads)
The voltages and current are developed in the rotor bars of a squirrel cage motor by what process or action?
Electromagnetic induction
What is the synchronous magnetic field speed of a 10 pole squirrel cage induction motor operating at 60 Hz?
720 RPM
In a 6 pole, squirrel cage, induction motor, how many electrical degrees are there between the phases?
120 electrical degrees
in an eight pole, squirrel cage, induction motor, how many mechanical degrees are there between the 'A' phase coils of the stater?
45 degrees
how is the efficiency of a squirrel cage induction motor normally calculated?
Efficiency = input W/output W x 100
As the load increases on a squirrel cage induction motor, does both power factor and torque improve or decline?
Improve
What would be the lead identification numbers for the 'A' phase coils of a 9 lead, dual voltage squirrel cage induction motor?
T1, T4, T7
What is meant by the term single phasing in relation to a squirrel cage induction motor?
Open line or open phase
List three applications of squirrel cage induction motors.
Mixers, grinders presses, feeders, augers, fans, blowers, pumps, mills, compressors
List two to 'V' type rotor bar design in squirrel cage induction motors.
1. Lowest percent slip difference
2. Excellent speed regulation(Constant speed applications)
List two advantages to ‘A’ type rotor bar design in squirrel-cage induction motors.
1. Highest starting torque
2. Lowest starting current
List three advantages of squirrel-cage induction motors.
1. No Brushes, No Slip rings, No Capacitors, No resister bank,
2. No DC Voltage Required, Rugged Design, Embedded rotor Bars
3. Power Factor and Torque improves as load is added
A 5 HP, four-pole squirrel-cage induction motor rotates at 1742 rpm during full load
condition and 1788 rpm at no load condition on a 60 Hz system. Calculate the speed
regulation of the motor.
2.6%
Calculate the percent slip of the following squirrel-cage induction motor. 1725 RPM 60Hz
4.167%
Squrriel-cage induction motor components
1. Eye hook / Lifting eye / Lifting hook
2. Frame / enclosure / case
3. Stator pole piece / pole core
4. Stator field winding
5. Bearing
6. Shaft
7. End plate / Bell end
8. Squirrel cage rotor assembly
9. Base
10. Terminal Box
11. Bearing
12. Cooling Fan