Three Phase Motors Flashcards
What are the three main three phase motors?
Squirrel Cage
Wound Rotor
Synchronous
What are the characteristics of a squirrel cage induction motor?
Small
Rugged
Very good speed regulation
What are the 4 main parts of a three phase motor?
Stator
Rotor
Frame with end shields
Bearings
What is the stator?
Stationary part that consists of the windings to connected to power
Pressed in laminated core
What is the rotating part?
Connected to the Load
Consists of rotor bars welded to 2 end rings to form a squirrel cage
has fins welded to it for air circulation
a steel shaft with key way is welded through its center
What is the frame?
Consists of all connections
Built for the environment
What are the bearings?
To reduce rotation friction
What are the three main types of bearings?
Ball
Roller
Sleeve
What is synchronous speed?
The speed of the rotating magnetic field in the stator
How is synchronous speed determined?
Determined by the supply voltage frequency and the number of poles of the motor
What is the formula for synchronous speed?
120 x F/ # of poles
What are the rpms of a 2, 4, and 6 pole motor?
2 Pole- 3600 rpm
4 Pole- 1800 rpm
6 Pole- 1200 rpm
What is slip?
Slip is the difference between synchronous speed and rotor speed
How is slip represented?
As a percentage
What percentage should slip be less then?
5%
What is the formula for %slip?
SS- rotor speed/ SS x 100
What are the three types of motor starters?
Manual
Magnetic
VFD
What is a motor starter?
A three phase contractor and an overload relay combined
What is the top half of a motor starter?
The three phase contact
What is the bottom half a motor starter?
The three phase overload relay
What are 4 uses for motor starters?
Start motors
stop motors
reverse motors
protect motors
What are the two main types of diagrams?
Wiring
Schematic
What is a wiring diagram?
Shows actual location of all components and wiring
What is a schematic diagram?
Shows the logic of the circuit without actual location of components and wiring. (AKA- Ladder or elementary diagram)
What are the five rules of a schematic diagram?
1.) Only one load per line
2.) Pilot device (control) is wired before the load
3.) You must number the rungs from top to bottom
4.) You must contact Reference
5.) You must wire reference (Top to Bottom, Left to right)
How do you wire a motor for high voltage?
Series connection
How do you wire a motor for low voltage?
Parallel connection
What are the components of a SCIM rotor?
Windings
What is the power source supplying the SCIM connected to?
Stator
What type of bearing uses oil as its method of lubrication?
Sleeve bearing
What is the speed at which the magnetic field travels in the stator called?
Synchronous Speed
What determines the speed at which the magnetic field travels in the stator?
Poles and Frequency
What happens when the rotor of SCIM turns at the same speed at which the magnetic field travels in the stator?
No torque is developed
When the SCIM is running at full load what is the current compared to the start current?
It is lower
What is the power factor of a 3 phase SCIM operating unloaded?
Very Poor
The interaction between between rotor magnetic field and stator magnetic field has a direct impact on the SCIMs what?
Torque
