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Adjustable-speed ac drive systems (ASD) have come to maturity since their introduction over 15 years ago. It is estimated that over 100 000 units are now in use. At the present time, the available industry standards do not provide sufficient guidance to the user. Most of the currently available standards were developed for uses other than ASD. Also, some proposed standards are being developed but have not progressed as rapidly as originally planned. A simplified discussion of the principles of ASD, their different types, and major components is provided. A brief evaluation of the applicability of the available industry standards, particularly to larger ASD, is presented to assist the user. A review of the proposed standards is also presented to keep the user abreast of developments in this area.