The many benefits of variable speed drives (VSD) in electric-submersible pumping systems (ESP) have led to exponential growth in the use of these devices in production fields handling high fluid output levels. The use of VSDs causes some difficulties when connected to the electrical power system,due to the fact that static power converters produce non-linear loads, affecting the natural sine shape of alternating current, introducing hamonic currents into the electric power network that could cause interference in the communication circuits and damage the equipment installe don the network.

Specially designed trnasformers calles phase shift transformers can help to mitigate the effect of speed drives when connected to the network, by helping to reduce the harmonics reaching the electrical netwrok, depending on the number of pulses of the VDS. This harmonic distortion may be mitigated by incresing the number of rectifying sections used in the VDS; for instamce, a 12 pulse converter has 2 rectifiers sections that are 30 out of phase, an 18 pulse converter has 3 rectifiers witha phase shift of 20 anda 24 pulse converter has 4 rectifiers that are 15 out of phase. Therefore, the larger the number of pulses, the smaller the trigger distance between waves, resulting ina shorter distance between wave crests and thus in lower harmonic distortion.

It is important to take into account that, the hicher the number of pulses, the more complex the system becomes and the cost of the required equipment may be considerable higher.