Assessment of impact of impurities in epoxy - anhydride vacuum impregnation (vi) resin system

Epoxy-anhydride based resin system is widely used as an impregnant for the high voltage rotating electrical machines. The present paper brings out the significance and key role played by the quality control parameters in assessing the cumulative effect of various kinds of impurities present in the raw materials of VI resin. An experimental study was carried out on vacuum impregnating (VI) resin systems of three brands to demonstrate the effectiveness of the quality control test parameters for assessing the cumulative impact of impurities on the tank life and degree of penetration of VI resin into the insulation. Effect of resin to hardener ratio, humidity and accelerator on the reactivity of VI resin system has also been determined. The results of experimental study demonstrate that the normal quality control tests i.e. viscosity and reactivity are essential for assessing consistency of the quality of the incoming materials from an approved source. However, these tests are not sufficient for evaluation and screening of VI resin systems of different brands. The rate of rise of the viscosity at a given temperature of the sample from a new source in comparison to approved sample is also to be determined for assessing their relative storageability (tank life) which is an important aspect for cost effective utilization of the materials. Further, the investigation reveal that the temperature of measurement of 60°C and the composition of resin & hardener mix of ratio of 100:100 are relatively more sensitive to detect the impact of impurities in comparison to the temperature measurement of 70 °C and the ratio 100:120 and preferred for assessing the impact of impurities present in fresh resin and hardener. The hardener is relatively more sensitative to the humidity than the resin for increasing reactivity of VI resin system.