Reduction of overvoltages on ESP systems [electrical submersible pumps]

The use of electrical submersible pumps (ESP) located in sub sea wells is one of the artificial lift techniques which make the economic exploitation of marginal oil fields possible. However because of the long lengths of cables involved and where variable speed drives are used, the motors are subjected to large and repetitive overvoltages. These are believed to contribute over a period of time to motor failure. Measurements of the transient overvoltages occurring due to the switching of the variable speed drive have been taken on the Texaco Captain WPP Installation. Time domain simulations have been set up to predict motor overvoltages for the different cable lengths and motor sizes. This paper presents the measured waveshapes and compares them to simulations. Time domain modelling of the various components are discussed. The connection of RC-dampers to the ESP system to reduce the damaging overvoltages impressed on the terminals of the motors are also presented.