0195136047.pdf

574 ROTATING MACHINES

• Solid-state control (variable-terminal-voltage control, variable-frequency control, rotor-
  resistance control for wound-rotor motors, injecting voltage into rotor circuit of wound-rotor
  motors) usually discussed under power-semiconductor controlled drives (see Section 16.1).
  Figure 13.2.10 lists various ac motors as well as techniques for their speed and torque control.

Starting Methods for Polyphase Induction Motors

When high starting torques are required, a wound-rotor induction motor, with external resistances

inserted in its rotor circuits, can be used. The starting current can be reduced and high values of

starting torque per ampere of starting current can be obtained withrotor-resistance starting.The

external resistances are generally cut out in steps as the machine runs up to speed.

Induction

motors

Synchronous

motors

Multispeed

winding

control

Wound

rotor

Squirrel

cage Hysteresis

Adjustable

frequency

Adjustable

voltage

Synchronous

generator

Voltage

regulator

Induction

Impedance generator

Electronic

SCR-commutator

motor

Electronic

magnetic

SCR

Salient

pole Reluctance

In-line

control

(stator)

Figure 13.2.10Ac motors and techniques for their speed and torque control.