Overhaul of propulsion motors onboard G.O. Sars

Customer: Havforskningsinstituttet
Date: February 2012

The research vessel G.O. Sars is owned by Havforskningsinstituttet and the University of Bergen. The ship was launched in 2003, and is the third research vessel carrying the same name. The ship’s DC propulsion motors showed very low insulation values and repeated attempts of cleaning with chemicals and soap/water resulted in little change.
It was decided that the motors should be upgraded to increase the lifetime, and Karsten Moholt got the job. The most efficient way to improve the stator insulation is to VPI-paint (Vacuum, Pressure, Impregnation) the windings.
VPI-painting is an acknowledged and much used method for increasing the lifetime of high voltage machines. The paint is applied to the coil windings in a vacuum tank, so that the paint will be sucked into all cracks and cavities. Afterwards an exterior preassure is applied in order to force the paint further in. The paint seals microscopic cracks, and thus increases the dielectric strength in the insulation. This decreases the risk of discharges within the windings. The paint also gives the winding increased mechanical strength.
The motors were very large, and could therefore not be lifted ashore. They had to be dismantled onboard, which is a laborious process. The windings were extracted one by one and sent to Karsten Moholt's workshop for processing. After cleaning, reinsulating and VPI-painting the windings were sent back to G.O. Sars for reassembly.
This is the largest DC project Karsten Moholt has ever performed out in the field. All testing was done in cooperation with DNV.