Page 232 - Electrical Equipment Handbook _ Troubleshooting and Maintenance

SYNCHRONOUS MACHINES

SYNCHRONOUS MACHINES 11.7

FIGURE 11.5 Open-circuit and short-circuit characteristics of a synchronous machine.

TORQUE TESTS

Some torque values are important for a synchronous machine. They include the following:
1. Locked-rotor torque: This is the torque developed when the rated voltage and frequency
are applied to the motor while the rotor is prevented from turning (Fig. 11.6).
2. Pull-out torque: This is the maximum possible torque developed and sustained at syn-
chronous speed for 1 min when the rated voltage and frequency are applied to the motor.
3. Pull-in torque: This is the maximum constant torque that the motor will develop as it
approaches the synchronous speed when the voltage and frequency are applied.
4. Pull-up torque: This is the minimum torque developed during start-up at speeds below
the synchronous speed when the rated voltage and frequency are applied to the motor.
5. Speed-torque characteristic: This is the variation of the torque developed by the motor
versus the speed when the excitation is not applied to the motor and the rated voltage
and frequency are applied to it.

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.