Standards special-purpose motors

Special-purpose motors such as increased safety motors, flame-proof or explosion-proof motoi s must be checked for gaps, clearances and creepage distances of all the mating parts forming flame paths. The construction of these motors must follow lEC 60079 as noted in the list of standards. 

As with the motor driver, the steam turbine must be matched to the compressor. Also, a turbine rating of 110% of the maximum power required by the compressor should be specified. This should be at the compressor s normal speed point. The turbine speed should include a maximum continuous speed 105% of the normal compressor speed. API Standards 611 and 612 cover general purpose and special purpose steam turbines 7, 8]. 

NEMA also classifies electric motors by appUcation as general-purpose, definite-purpose, or special-purpose. A general-purpose motor is an indnction motor which has a continuous rating, service factor, and temperature rise in accordance with NEMA standards. General-purpose motors are built in quantity in standard ratings with standard operating characteristics and mechanical construction for a wide variety of common appUcations. 

Tbe use of special motors was more relevant until the 1980s. when solid-state technology was still in its infancy and wa.s not so widely applied. With the advent of static drives, as discus.sed in Sections 6.2-6.4, the use of standard motors is gradually becoming more common for all these applications. The drive it.self can alter the supply parameters to the required level to make a standard motor operate and perform within desired parameters, besides conserving energy. The purpose of describing a few of these applications is only to indicate their non-standard features, where a standard motor with normal controls may not be able to perform the required duties. 

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