Measuring Transformer Winding Temperatures Continuously with the Transformer Carrying Load

Conventional test methods are not sufficiently accurate for the measurement of heating transients in transformer windings when high or rapidly changing temperatures are involved. For resistance measurements made after shutdown, the accuracy is increased by improved methods of evaluation which may be based on a cooling curve or on a single test point. These calculations are somewhat laborious, and are limited in accuracy and usage. For this reason, suitable connections are described for testing winding temperatures with d-c bridges throughout any load cycle, with or without the application of a-c line voltage. This technique applies to the factory test of single or polyphase transformers and will measure the temperatures in two or more windings simultaneously. Test results of temperature transients obtained by this new method are included in curve form.