Three phase and poly induction Flashcards
Advantages of three phase circuit
Power does not pulsate power to load constant Power distribution 3/4 less copper better operating characteristics smaller,lighter, more efficent
Where is phase voltage and line voltage measured in three phase
Phase voltage is from netural to line, line is line to line
What are main types and parts of induction motors. also which is most common
Rotor and stator, squirrel cage and wound rotor. Squirrel is most common
Why is the squrirell most common
Simple, rugged,low maintenance, good operating characteristics.
What is the syncronus speed ?
The speed of the rotating magnetic field of the stator.
how does synchronous speed affect rest of the motor.
It rotates sweeping bars on the rotor. this cause induced current and creates a magnetic field in rotor.
How do the magnetic feilds react with each other.
They react by producing torque, which accelerates the motor
What affect would slower rotor have on motor
greater relative motion with stator rotating feild and rotor conductors, more current and higher frequency.
What does rotor frequency depend on
Slip
What does rotor frequency determine
Rotor power factor and torque produced
What is powerfactor of rotor
phase angle between rotor resistance and rotor reactance
What determines the torque of the motor
The strength of the magnetic feilds and phase angle between them
What does industial setting pay for with power
The apparent power. VA
What are the different characteristics of double squirrel cage motor
High starting torque, two sets of rotor bars, outer have high resistance with low inductance. inner have high inductance with low resistance
What does a wound rotor motor behave like
The stator acts like primary, rotor acts as secondary. so like a transformer
What is different about wound rotor
slip rings and brushes connected to external resistance on shaft.
Name differnt characterisitcs of wound rotor motor
Stator similar to squirrel
High external resistance connected rotor, resulting in increased power factor and torque
resistance cuts out as speed increases
Increased mechanical load means higher induced current in stator and rotor
expensive, hard install, high maintence.
