• Lowndes, Robert
• Balcombe, R.
• Cotton, Ian
• Dunsby, L.
• Twomey, B.
• Gardner, R.
• Peesapati, V.

Abstract

Premature failures of stator insulation account for a<br/>large percentage of repairs of marine generator systems. The<br/>failure mechanisms of such faults have been presented in many<br/>parts of the literature. Partial discharge activity, thermal<br/>degradation, thermal cycling, harmonics and transients are some<br/>examples of such failure mechanisms. Whilst there has been an<br/>insight into the failure mechanisms, there is still no definite<br/>answer to how these defects manifest in the first place. Most of<br/>the failures that have been identified within literature are on end<br/>windings, especially slot ends. Some failure mechanisms have also<br/>been linked with thermal cycling. Frequent and rigorous<br/>stop/start cycles stress coils by inducing mechanical forces<br/>between elements of the coil and housing owing to differential<br/>thermal expansion. This differential expansion is dependent on<br/>the rate of rise of temperature and also the different coefficients<br/>of thermal expansion of the materials. The present paper will<br/>evaluate the thermal degradation of insulation systems used on<br/>marine generators using Finite Element Analysis (FEA) methods.<br/>On board temperature measurements of stator coils during a<br/>high speed run are used as one of the parameters within the FEA<br/>simulations, to investigate if there is any risk of differential<br/>thermal expansions during such an operational cycle. Different<br/>ramp rates are also analyzed within the FEA simulations to<br/>understand the effect of uneven thermal expansions and the risk<br/>of material degradation of the insulation in coils on marine<br/>systems. A brief review of the standards available for thermal<br/>cycling and testing are also presented within the paper.

Topics

• impedance spectroscopy
• simulation
• thermal expansion
• defect
• finite element analysis