Post on 03-Jan-2016
FINAL EXAM WILL BE
WEDNESDAY APRIL 29FROM 10:00AM – 12:00PM
IN THIS ROOM
DISREGARD THE SATURDAY DATE ON THE FINAL EXAM MATRIX
Ideal Transformers
nN
N
V
V
1
2
1
2
ˆ
ˆ
dt
dNv
dt
dNv
2211 and
2211 iviv nN
N
V
V
I
I
1
2
1
2
2
1
ˆ
ˆ
ˆ
ˆ
Ideal TransformersExample: Redraw the diagram below twice as a single electric circuit, the first time reflected to the high-voltage circuit, and the second time reflected to the low-voltage circuit.
Ideal Transformers
Reflected to the high-voltage circuit:
Ideal Transformers
Reflected to the low-voltage circuit:
Real TransformersMust account for:
• Resistance in the winding conductors• Power (I2R) losses
• Leakage reactance• Flux produced by one winding that does
not link the other
• Energy to magnetize core• Alignment of magnetic domains in core
steel
• Electrical losses in core• Hysteresis and eddy currents
Real Transformers
Polyphase Induction Motors
Polyphase Induction MotorsStator circuit produces a rotating magnetic field.
http://www.ece.umn.edu/users/riaz/animations/spacevectors.html
Polyphase Induction Motors
A voltage is induced across the rotor bars by transformer action (Faraday’s Law).
This is possible because the rotor turns slightly (3%-5%) slower than the rotating stator field.
The speed differential between the stator field and the rotor is the slip.
NO SLIP NO TRANSFORMER ACTION NO TORQUE
Polyphase Induction MotorsSpeed-Torque Curves
Polyphase Induction MotorsSpeed-Torque Curves
Polyphase Induction MotorsPower Flow / Losses