Behavior of machine insulation systems subjected to accelerated thermal aging test

TLDR

Accelerated aging tests are widely used on motor and generator insulation systems to simulate long‑term deterioration in a short time, identify designs with longer life, and support qualification of new systems. After each thermal cycle the insulation system is exposed to mechanical stress, moisture, and voltage, its condition is non‑destructively assessed by measuring dissipation factor, insulation resistance, and partial discharge, and end‑of‑life is determined by AC and impulse voltage tests. The study demonstrates that two VPI machine test insulation systems of thermal class F, subjected to three repeated thermal overstress cycles, exhibit changes in electrical and dielectric properties that support qualification through comparative evaluation.

Abstract

Accelerated aging tests have been extensively used on motor and generator insulation systems to simulate in a short time period the deterioration mechanisms occurring during normal operation of many years, to identify insulation system designs with longer life time and to support the qualification of a new system. The contribution presents results from extensive investigations on the behavior of two VPI machine test insulation systems (reference and candidate) with thermal class F (155°C), which were subjected to three thermal overstresses in repeated cycles. After each thermal cycle the insulation system is subjected to mechanical stress, moisture, and voltage. In order to check the condition of the insulation systems in a non-destructive manner several properties of insulation like dissipation factor, insulation resistance and partial discharge quantities were measured after each thermal cycle. After that the end of life of the insulation systems were checked with ac voltage and impulse voltage. The results support the qualification by comparative evaluation and they indicate, how the changes in electrical and dielectric properties of insulation take place during the accelerated aging test.