Adjustable Speed Drive
TA device that is used to control the speed of an AC motor by varying the frequency of the voltage supplied to it. These are also known as variable frequency drives, adjustable frequency drives and other, similar, names.
Source: API Recommended Practice 14FZ, Recommended Practice for Design, Installation, and Maintenance of Electrical Systems for Fixed and Floating Offshore Petroleum Facilities for Unclassified and Class I, Zone 0, Zone 1, and Zone 2 Locations, Second Edition, May 2013. Global Standards