A novel solution for the reliable online partial discharge monitoring (olpd) of vsd-operated EX/ATEX HV motors

The majority of the larger (> 7.5 MW) high voltage (> 3.3 kV) motors in the oil and gas industry are operated through variable speed drives (VSDs). In order to maintain the availability of these critical machines, on-line condition monitoring (CM) technology is required. This paper describes a novel solution for reliable, on-line partial discharge (OLPD) CM of the HV stator winding insulation condition of VSD-operated HV motors. Inductive, tri-band sensors were used to provide a power frequency synchronization signal alongside the OLPD measurement signal. This enables phase resolved partial discharge (PRPD) patterns across the power cycle to be constructed, at all of the VSDs operating frequencies. The data acquisition technology utilises a 24-channel smart multiplexer with 6-channel synchronous data acquisition to enable pulse precedence measurements to be made between distributed sensors. The new OLPD monitoring solution has been trialed in a pilot project with an oil and gas operator in Norway where a 5.9 kV, 40 MW twin-winding VSD-operated EX-P motor was successfully monitored on-line for partial discharge activity. This was made possible through the active discrimination of the electromagnetic (e/m) noise from the VSD power electronics using precedence detection of synchronous signals detected from multiple sensor installations. A total of 18 sensors were utilized to monitor the complete twin-winding VSD and HV motor circuit in this project. The OLPD monitoring results reported show that only around 1 pulse in 1000 (0.1%) detected by the system was a PD pulse with the remaining 99.9% being e/m noise pulses caused by the VSDs power electronics switching.