Induction motor PP Flashcards
What does the rotor consist of?
squirrel cage or wound rotor
How does an induction motor operate?
virtue of currents induced from the stator field into the rotor
What is an induction motor?
AC voltages are induced in the rotor by the rotating magnetic field of the stator. Induction in the motor is similar to the induction between the primary and secondary windings of a transformer.
What is the most common induction motor?
squirrel cage winding. The winding is made up of heavy copper bars connected to two end metal rings made of copper or brass.
How is a wound rotor constructed
coils placed in the rotor slots
Stator construction?
laminated ring shaped core is bolted to the motor frame. Coils are placed in the slot, (to form a single phase or three phase winding) slots are closed by a wedge.
Squirrel cage rotor construction?
laminated iron core with slots, metal bars are molded into the slots, two rings short circuit the bars, bars are slanted to reduce noise.
What are single phase motors commonly used for?
air conditioners, refrigerators, pumps and fans
What do split phase motors use to induce a starting torque?
inductance, capacitance, or resistance
A resistance start induction run motor works by?
having the start and run windings out of phase with each other, due to the start winding having more resistance
In a RSIR the starting torque is produced by?
-strength of the magnetic field of the stator
-strength of the magnetic field of the rotor
-The phase angle difference between current in the start winding and current in the run winding (maximum torque is achieved when these two currents are 90degrees out of phase with each other)
In a RSIR the current?
lags the voltage by a large angle
In a RSIR the main winding?
Has high inductance and low resistance
In a RSIR the start winding?
has low inductance and high resistance, lags the voltage by a smaller angle
In a CSIR ?
the stator consists of the main (run) winding and the start winding, the start winding is in parallel to the run winding and is at a right angle to it.
How is the start winding at a right angle to the run winding in a CSIR?
obtained by connecting the auxiliary winding in series with a capacitor and starting switch. When the motor is energized, the starting switch is closed. This places the capacitor in series with the auxiliary winding.
When full speed is obtained in a CSIR the__?
centrifugal device cuts out the start winding. the motor then operates as a single phase induction motor.
3 characteristics of CSCR motors?
high starting torque
low starting current
highest cost
What are CSCR used for?
hard starting loads, compressors and pumps
3 thing about PSC?
primarily a fan and blower motor
poor starting torque
very low motor cost
How does a PSC operate&constructed?
capacitor in the “capacitor winding” provides a phase shift for starting
optimizes running characteristics
no centrifugal switch
Universal motor?
runs on AC or DC.
commutator and brushes
generally found in portable power tools
lower HP size
very high starting torque
higher torque on DC
higher the rpm, lower the torque
The magnetic field intensity is directly proportional to?
the number of turns
the size of the core.
the permeability of the core
What makes a conductor have opposition to current flow?
material
csa
length
ambient temperature
Why do we wrap a conductor into a coil?
If we wind that conductor into a coil the magnetic fields surrounding each
portion of straight conductor combine or add together to create a stronger or
substantial magnetic field. The magnetic field surrounding this coil or solenoid
can be compared to the magnetic field surrounding a permanent magnet. They
both have North and South poles.
what is inductance?
the opposition to change of a current in a circuit
Inductance is the ___ of the ___?
physical characteristic of the coil
Unit for inductance?
Henry
Symbol for inductance?
L
What three things are needed for generating electromotive force?
-current carrying conductor
-a magnetic field
-relative motion between the conductor and the magnetic field
What is Lenz Law
When there is a electromotive force generated, there is an electromotive force induced in each coil; which is slightly less than the applied emf and 180 Degrees out of phase with the applied emf. This “counter emf” oppose the current that its created.
What are the two oppositions to current flow in a coil?
Resistance and Inductive reactance
What are the characteristics that determine Inductive reactance?
number of turns
size of the core
permeability of the core
and frequency
Symbol for inductive reactance
XL
Unit for the XL is?
Ohm
What is the combination of resistance and inductive reactance (or total opposition to current in an inductive circuit) is called?
Impedance
What is the symbol for impedance?
Z
What is the unit for impedance?
Ohm
what is inductance?
Is the property of an electrical device that tends to oppose a change in current.
What is the capacitor made of?
two conducting plates separated by a non conducting material.
What characteristics are the capacitor dependent on?
-the area of the plates
-the distance of the plates
the dielectric constant of the material between the plates
