Determination of Temperature Rise of Energized Transformers by the Resistance Change Method

The problems of measurement of networks which remain energized by ac power during measurement are discussed. Particular attention is given to methods which permit continuous measurement with the aim of recording directly temperature rise as determined by the change of resistance. Deflection methods, as well as potentiometric and bridge methods, are treated, and their relative advantages in accuracy, convenience, cost, and complexity are considered. Results of heat runs on a 1/2-hp split-phase motor, a 3 kVA single-phase loaded transformer, and a 100-kVA three- phase transformer are included.