A/B Flashcards
Motors function
Device that converts electrical power (energy) into mechanical power (energy)
What is an Inducting motor?
A machine that gets energy into the rotating part by mutual induction
Define Torque
Moment of force
Prony brake
Measures a motors torque.
More sophisticated alternate is a dynometer
Unit of measurement for torque
Newton meters - (Nm)
Torque formula
T = F X r
F - force in newtons (N)
r - radius in meters (m)
What is Efficiency?
The ratio of output energy (power) over input energy (power)
Induction motors 3 parts
Frame (enclosure)
Stator
Rotor
Induction motor frame includes
Cast steel frame
End brackets (frame)
Bearings in the end brackets
Junction box
Drip proof motors allow outside air too
-Enter one end of the motor
-Flow past the stator windings
-Flow between the stator and windings
-Exit the other end
3 Types of totally enclosed motors
Fan cooled (tefc)
Non ventilated (tenb)
Pipe ventilated (tepv)
Stator is comprised of?
stationary iron and winding
Stator core is constructed of
Thin silicon steel laminations to minimize Eddie current and hysteresis
Two types of Stator windings are
Lap windings
Concentric windings
Define a Rotor
Rotating part of an electrical machine is called a rotor.
What are 2 types of rotors
Squirel cage rotors and wound rotors
Squirrel cage rotors consist of
Aluminum or copper bars called rotor conductors or rotor bars
Slip speed
Difference between rotor speed and the synchronized speed of the stators magnetic speed
Wound rotor motor is identical to what?
The stator is identical to a SCIM stator.
wound rotor motors are less common than the squirrel cage because it needs more maintenance
What is the Slip speed %
Typically 2 - 5% of synchronized speed
Parts of a Rotors includes
laminated iron conductors and the shaft
Losses in an induction motor
Iron loses
Copper loses
Mechanical or electrical
Nema design A
The starting current in a stator is about ___ % of FLA
The starting torque in a rotor is about ____ % of full load torque.
The breakdown torque of a rotor is about ___ % of full load torque.
600%
150%
200%
Nema design B
The starting current in a stator is about ___ % of FLA
The starting torque in a rotor is about ____ % of full load torque.
The breakdown torque of a rotor is about ___ % of full load torque.
500%
150%
200%
Most common
Nema design C
The starting current in a stator is about ___ % of FLA
The starting torque in a rotor is about ____ % of full load torque.
The breakdown torque o
Is produced at the instant of ____
500%
225%
Start
Has double squirrel cage
Nema design D
The starting current in a stator is about ___ % of FLA
The starting torque in a rotor is about ____ % of full load torque.
The breakdown torque is produced at the instant of ____
400%
275%
Start
Canadian electrical code allows ___% in rush
300%
Slip is ___% the instant a motor is energized
100%
A variable frequency drive (VFD) ….
Achieve speed control in wound rotor motors
Speed control of a wound rotor motor is most suitable from….
0 r/min to full load speed
Main disadvantage of a wound-rotor motor is….
Greater cost and higher maintenance
When a rotor is built with thinner rotor bars what happens?
Rotor resistance increases
List 3 advantages of a wound rotor induction motor
High start torque
Low starting current
Variable speed
List 4 disadvantages of a wound rotor induction motor
High cost
Large frame
More maintenance
Low efficiency
Lap windings have coils with?
Varying pitch
A rotor spins in the same direction as the rotating magnetic field produced by the stator?
True
What are two major components of the stator?
Stationary iron
Windings
Main purpose of the rotor is to produce?
Torque
The stator rotating magnetic field (RMF) rotates at a?
Constant speed
How many windings does a 4 pole three phase induction motor have?
- (3x4)
Current listed on a motors nameplate is called?
Full load current
The speed listed on a motors nameplate is the?
Full load speed
What does an induction motor do?
It’s a machine that gets energy into the rotating part by mutual induction
The transfer of energy from the stator to the rotor is achieved by?
Mutual induction
What is the function of the motor frame?
To protect the winding’s and bearings
List 3 types of totally enclosed motors
Fan cooled
Non ventilated
Pipe ventilated
name 4 main parts of the stator
Laminated and slotted iron
The conductors
Conductors insulation
Protective sleeves and wedges for the slots
What is the function of the stator core?
It provides a high permeability path for magnetism
What is the function of the stator winding?
To generate a rotating magnetic field which creates torque
Name 2 Types of rotors
Squirrel cage
Wound rotor
The stator windings may be wound through the stator slot in two ways. What are they?
Lap windings
Concentric windings
What’s the function of the rotor?
Rotate and drive the motors output shaft to produce work
The squirrel cage rotor consists of aluminum or copper bars called?
Rotor conductors
Define rotor speed
It is the rotational speed of a rotor in an electric motor.
A wound rotor motor is?
The ideal induction motor. Combining the best starting characteristics. (High rotor resistance and low rotor inductance)
Wound rotor motors have several disadvantages such as
Higher cost
Larger frame
Extra maintenance
