The Variable Speed Drive is becoming more common with ESP installations as the understanding of VSD technology with downhole ESP applications improves. The advantage of a VSD is that it increases the optimum operating range of any ESP.

The disadvantage is that in order to change the frequency VSD’s manipulate incoming power through a series of ultra high speed switching which can create disturbances in the power system both to the ESP and back onto the power grid or gen-set. These disturbances are known as harmonics. It is impossible to determine the level of harmonics with standard electrical instrumentation. A power spectrometer is required and is normally set up on a well for a few days to get an idea of the harmonic being generated.

It is surprising how much work can go into the evaluation of downhole equipment and the reservoir, but rarely is the power supply reviewed. Often great gains in run life can be made in this area.