24-Pulses Phase Shift Transformer

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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 harmonic currents into the electric power network that could cause interference in the communication circuits and damage the equipment installed on the network. Specially designed transformers called 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 network, depending on the number of pulses of the VSD. This harmonic distortion may be mitigated by increasing the number of rectifying sections used in the VSD; for instance, a 12 pulse converter has 2 rectifiers sections that are 30° out of phase, an 18 pulse converter has 3 rectifiers with a phase shift of 20° and a 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 in a shorter distance between wave crests and thus in lower harmonic distortion. It is important to take into account that, the higher the number of pulses, the more complex the system becomes and therefore the cost of the required equipment will be considerably higher.