Diagnostics of Insulation Condition and Risk Evaluation of Electrical Machines Employed in Mining Application

Medium voltage machines are extensively employed in power generation and industrial applications. In general, they are very reliable with an expected lifetime in the order of 30 to 50 years depending on service class. However, when a machine fails, sometimes unexpectedly, production disruption and downtimes can be very costly. About 50% of failures are related with loss of dielectric strength of the electrical insulation. Insulation deterioration is caused by the combination of thermal, mechanical, electrical and environmental stresses. Timely detection of insulation condition can be done mainly with off-line partial discharges monitoring and dielectric losses monitoring. This paper reviews the current issues involved in the diagnostics of insulation condition for an effective risk evaluation of electrical machines, highlighting the most relevant topics regarding mining application, where environmental conditions and feeding with power converters states more severe stresses than normal power applications. Based on the possible risk of phase to ground and phase-to-phase insulation failures, it is recommended a proper design, quality assurance and testing during manufacturing for providing valuable baseline data for proper assessment and trending of insulation condition of medium voltage machines during their lifecycle.