Heating induction motors

Due to excessive starting and braking heat losses it is not advisable to switch an induction motor ON and OFF frequently. The number of starts and stops a motor is capable of performing will depend upon its working conditions such as type of switching, braking and load demand etc. and can be determined from... 

Figure 14-6. Typical squirrel cage induction motor performance curves. (Used by permission Bell, C. J., and Hester L. R. Heating/Piping/Air Conditioning, p. 51, Dec. 1981. Penton Media, Inc. All rights reserved.)...

Figure 6.89 Longitudinal section drawing of a flameproof cage induction motor, with an annular-shaped air-to-air heat exchanger.

Externally mounted fans on the shaft or in the heat exchangers should be made of a material that cannot produce a spark if the blades happen to touch their surrounding metalwork. See also sub-section 5.1.8 for further comments on the construction of induction motors. 

K. In addition to the miniaturization of the rotating machinery, reliable and long-life operation for these coolers is dependent upon the fabrication of a high-effectiveness, compact heat exchanger and the development of a small high-speed, low-voltage ac induction motor with reasonable efficiency. 

Some induction heating furnaces must operate at frequencies higher than the supply frequency. Formerly, rotating motor alternator frequency converters were used. Now the avadabdity of high speed, high power sdicon controlled rectifiers for use in frequency converters has made rotary converters obsolete. Modem units operate at higher efficiency, cost less, require less factory space, and coordinate readdy with process controls (2). 

Noise protection is needed to protect against RFI/EMI problems caused by mobile and stationary radio, television, and handheld walkie-talkies radio-controlled overhead cranes radar induction heating systems static discharge high-speed power-switching elements high-AC current conductors large solenoids and relays transformers AC and DC motors welders and even... 

---