POWER ELECTRONICS
Unit 5:
5.3. Torque - Speed Characteristics of Three Phase Induction Motor: - Play
Assumptions:
@ Constant Voltage and Constant Frequency
The characteristics is divided in to 3 main regions.
1. Motoring (Forward motoring) Region. (0 <= S <= 1)
2. Generating (Forward Regeneration) Region (S < 0) and
3. Braking (Reverse Plugging) Region. (S > 1)
1. Motoring (Forward motoring) Region. (0 <= S <= 1)
a. Here Motor runs as Motor (Electrical to Mechanical Energy)
b. Motor and Rotating magnetic field = Same direction.
c. as SLIP Increases, TORQUE Increases (While Flux AIR GAP is Constant)
d. The Torque, T = T(Max), at [S=S(Max)]
e. Then TORQUE decreases with increase in SLIP due to reduction of Air Gap flux.
2. Regeneration (Generating) Region. (S < 0)
Here Motor Speed (N) is > than Synchronous speed (Ns)
SLIP is Negative.
Power flows from Motor Shaft to motor circuit & the motor acts operates as a generator.
The motor returns Power to the Supply System.
3. Plugging or Braking Region. (S > 1)
The Motor rotates in the OPPOSITE direction of the Rotating Magnetic field, So Slip > 1.
Done by reversing the power supply terminals.
Hence the Machine is QUICKLY brought to the STOP and if the Supply is not disconnected, the MOTOR starts rotating in the Opposite Direction. (Called PLUGGING).
During Braking, the mechanical power is absorbed and dissipated as heat in the Rotor Conductors.
This method is mostly not recommended.
5.4. SPEED CONTROL METHODS OF INDUCTION MACHINE: - Play
5.4.1. STATOR VOLTAGE CONTROL - Play
5.4.4. Inverters for Variable Voltage & Frequency Control: - Play
