High voltage insulation testing

Date: February 2012
Location: Gullfaks A

The electric condition monitoring department of Karsten Moholt has been hired to run high voltage insulation tests on all the high voltage motors located at Statoil's rig Gullfaks A. The purpose was to identify the winding condition of the motors. This process is usually conducted every fourth year to ensure that the stators are in a good condition. The different types of motors that were tested on the rig were:

  • Exhaust fan motors
  • Ballast pump motors
  • Sea water pump motors
  • Main sea water pump motors
  • Cargo oil pump motors
  • Air compressor motors
  • Feed water pump motors
  • Process cooling pump motors
  • Crude circulation pump motors
  • Air conditioning fan motors
  • Booster pump motors

 All together there were 30 motors to be tested. In average it takes a day to run the test on one motor, so the work lasted about a month, distributed over two periods of two weeks each. On three of the motors there were measured values outside the recommended limits. One of the cargo oil pump motors got partial discharge (PD) values of 21.0 and 37.5 nC at line voltage, which are above limit values. This motor could be put back into operation, but was recommended for overhauling.
 
One of the process cooling pump motors got a PD value of 60 nC at line voltage and a polarization index (PI) of 0.20. Both values are outside recommended limits. Based on the results of the test, the risk of breakdown was considered to be high, and the motor should be taken out of operation as soon as possible.
 
The crude circulation pump got a PI of 1.91 and an insulation resistance (IR) of 0.065 GΩ. Based on the low values and the fact that the motor had not been in use since 1997, Karsten Moholt recommended that also this motor should be overhauled