Insulation resistance measurements versus temperature made on aged stator bars and coils

The rule "insulation resistance halving for a 10 degC increase in temperature for rotating machine insulation" has been widely used in the industry. The rule was established based on testing of some insulation systems during the late 1950s. IEEE standard 43-2000 also provides a chart of the insulation resistance temperature coefficient versus temperature for correction of insulation resistance obtained at various temperatures based on this rule. However, it is unclear if this rule fits modern insulation systems. This paper presents laboratory tests on individual modern stator bars and coils to investigate insulation resistance versus temperature. The test results show that there is considerable discrepancy in the insulation resistance versus temperature characteristics between modern stator bars and old stator bars.