IRIS POWER

Dissipation Factor Testing – Standards Up-date: IEC 60034-27-3

Published Jan 4th, 2017 Howard Sedding

IEC 60034-27-3:2015, “Rotating electrical machines – Part 27-3: Dielectric dissipation factor measurement on stator winding insulation of rotating electrical machines” was published by the International Electrotechnical Commission in late 2015. Dissipation Factor (quantitatively similar to Tanδ or power factor) testing has long been used as a means to measure the quality of the electrical insulation in stator coils and bars rated 3.3 kV and above. A variation of the dissipation factor (DF) test is called the DF “tip-up” test (also called the power factor tip-up or Δtanδ test). The tip-up test is a measure of void content within the ground wall insulation – it is essentially an indirect partial test. In North America, tip-up is measured by measuring the DF at a high voltage (often rated line-to- ground voltage) and subtracting from it the DF at relatively low voltage (25% of rated line-to-ground). In Europe, tip-up is usually defined as the difference in DF when tested at two voltages that differ by 20% of the rated phase-to-phase voltage.

The new standard describes how to perform the test on stator bars and coils, and for the first time in an international standard, presents maximum values for DF and DF tip-up. The standard describes the bridge and power factor methods for measuring DF that have been used for many decades. Both the European and the North American definitions of tip-up are accommodated within the new document. In addition, it also includes the modern digital method of measuring DF such as we use in the PDTech DeltaMaxx™.

The establishment of the maximum values for DF and tip-up was controversial. During the creation of 60034-27-3, most end-users on the working group took the view that the limits were very easy to meet, and would not ensure that the groundwall was well impregnated. Some machine manufacturers took the view that the proposed limits were too conservative, and some well-made coils and bars would fail the test. As is inevitable with international standards, the resulting standard is a compromise that probably satisfies no-one.

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