Rotating electrical machines. Part 18-31. Functional evaluation of insulation systems. Test procedures for form-wound windings. Thermal evaluation and classification of insulation systems used in rotating machines

2Scope / Description

This standard applies to rotating electrical machines and establishes requirements for heat-resistant test methods for classifying insulation systems in indirectly cooled AC or DC rotating electrical machines with conductor windings. The performance of the test system is compared with that of a reference insulation system with specified operating characteristics. The test methods described in this standard are intended to compare the thermal conductivity of the housing insulation between the conductor(s) and the housing and, where specified, the coil or core design of the interturn insulation. The test shall not simulate operational mechanical loads experienced by the fastening of the winding head parts or supports. It does not include an assessment of thermomechanical wear resulting from expansion and contraction of insulation during temperature cycles. IEC 60034-18-1 specifies general requirements for hot-endurance tests of insulation systems used in rotating electrical machines. The specifications of IEC 60034-18-1 should be followed unless otherwise specified in IEC 60034-18-31. The heat class for an insulation system refers to the maximum permissible temperature of its hotspot. The average temperature measured during operation shall not exceed the permissible temperature values in accordance with IEC 60034-1. Note: 1. Large machines, particularly synchronized generators, may require special test methods for evaluating thermal performance that are not included in this section. 2 Recommended parameters for diagnostic tests may be used in accordance with IEC 60034-18-42 for rated windings with type II insulation systems for use in converters.