As the legislation surrounding the efficiency of electric motors continues to tighten, the volume of variable speed drives (VSDs) in service increases. Brian Park, service centre manager for Sulzer Glasgow, looks at the advancing technology and the maintenance processes that need to keep pace. Often specified by the motor manufacturer as part of the original installation – or retrofitted to improve efficiency – the drive contains both hardware and software that is designed to work with a motor in a specific application. So, what happens if the drive ceases to operate? Inverters, variable frequency drives (VFD) and VSDs are all effectively achieving the same goal, to control the speed and torque of an AC motor by varying the frequency and voltage of the motor supply. In modern applications they can interpret a range of input signals and vary the motor output according to the predefined software that is installed. In this way drives are capable of making significant energy savings by matching the motor output to the demands of the process. The increased implementation of drives has also been fuelled by the latest European energy efficiency regulations for electric moto...