IEC/TS 60034-18-33:2010 describes procedures for evaluation of insulation systems by endurance testing where thermal and electrical stresses are applied simultaneously. The procedures are intended for insulation systems used in a.c. electrical machines using form-wound windings. The test procedures provide a comparison of performance between reference and candidate systems at combinations of voltage and temperature which have been used separately to assess quality in the past and which are chosen to produce failures within a suitable timescale and at stresses within practical limits. The outcome of the test on the candidate insulation system will indicate whether it is better or worse than the reference system with proven service experience. The main changes of this new edition with respect to the previous one are as follows:
- the requirement to investigate the nature of interactions between thermal and electrical stresses has been abandoned;
- the use of single stress acceleration factors has been removed;
- the selection of stress levels has been adjusted and the temperatures are now related to the thermal class temperature of the insulation system;
- the introduction of end-point criteria;
- a simplified method to display results.