The Measurement of the Magnetization Characteristics of Large Power Transformers and Reactors through D.C. Excitation

Transformers and reactors used in the electric power transmission systems show non-linear magnetization characteristics, the exact knowledge of which is essential to the study of system transient operation. This paper describes a measurement method for these characteristics, based on D.C. EXCITATION. During such excitation, only applied voltage and absorbed current are measured and recorded, to be afterwards numerically processed. This measurement requires only a very small power, usually lower than 0.01 p.u. of the tested unit rated power; it is very accurate and makes it possible to obtain magnetization characteristics up to currents higher than the rated current. Theoretical bases on which the measurements are grounded, practical considerations on their performing and a set or relevant results on power high voltage transformers and reactors are afterwards exposed. More, it is possible by a d.c. excitation to measure magnetization characteristics which cannot be otherwise determined.