Evaluation of the performance of the impregnating resin of high voltage electrical machine when exposed to raw natural gas

Future high-speed electrical motor technology will utilise wellstream hydrocarbon gas as cooling medium. Such integrated motor-compressors are currently under qualification for use on the sea floor in the North Sea. A vital part of the insulation system is the resin used to impregnate the motor windings and the resins ability to withstand chemical aging caused by the components inside the wellstream gas. The purpose of the resin in such a machine is to give mechanical support to the winding and to fill all gaps and voids inside the mainwall insulation, which consists of a mica paper tape. Various types of epoxy resins were exposed to an environment consisting of hydrocarbon gas, condensate and a mixture of water and monoethylene glycol (MEG). The specimens were built by casting the resin into a mould and curing it in an oven according to the procedure recommended by the resin manufacturers. According to the tests, the epoxy novolac and bisphenol A epoxy resin with BCl₃ accelerator were able to withstand their tensile strength and e-modulus during the exposure far better than the bisphenol F epoxy resin. The influence of an accelerator in an epoxy anhydride resin system was detected. Resins accelerated with zinc naphthenate provided the highest modulus before the tests, but were not able to retain it during the exposure. Resins accelerated with BCl₃ seemed to tolerate the environment better. The tensile strength of the resin was also dependent upon the amount of BCl₃ accelerator used.