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IEC/TR 60894 1st Edition, March 1, 1987
Complete Document
Superseded By: IEC 60034-27-3
Guide for a Test Procedure for the Measurement of Loss Tangent of Coils and Bars for Machine Windings
Includes all amendments and changes through Corrigendum 1, July 1987
Additional Comments: BILINGUAL * W/D S/S BY IEC 60034-27-3
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The characteristics of an insulation system can be evaluated in terms of dielectric strength, insulation resistance, dielectric loss, etc.

This report is applicable to a method of measuring dielectric loss properties of the insulation system of the slot portions of new coils or bars for rotating electrical machines having rated voltage UN of 5 kV and above.

The test is applicable to form wound coils or bars in which the insulation is cured before the winding is inserted in the stator.

For tests on post-impregnated machines, see Appendix A.


The uniformity of manufacture is judged to some extent by measurement of the dielectric loss tangent as a function of voltage and by statistical evaluation of the test results.

For a known insulation system, the following properties can be assessed:

 - a low loss tangent at low voltage (0.2 UN) indicates a high degree of molecular crosslinking of the bonding medium (degree of resin cure),

 - the magnitude of delta tan delta by increase of voltage gives some indication of the void content  of the insulation.