Considerations for the Protection of Adjustable Speed Drive Installations

As the use of adjustable speed drives increases in popularity, additional considerations must be made for adjustable speed drive assemblies. For medium- and high-voltage applications, some of these considerations are as follows:•Thermal protection of the motor being driven.•Decreased levels of fault current at the motor level.•Presence of unconventional multi-legged transformers to feed the drive.•Introduction of harmonic currents and voltages. This paper addresses how to protect an adjustable speed drive installation by breaking the application down into specific components: motor, drive, input mechanism, and feeder. The paper provides a brief background on the advantages and classifications of adjustable speed drives, followed by an overview of considerations for protecting adjustable speed drive feeders at different voltage levels. A real-world adjustable feed drive application fed from a high-voltage source is analyzed. Best design practices for selecting protection parameters are also shared.