TABLE OF CONTENTS Excellent text books are already available dealing with the design theory and operation of power transformers. (1 ) This chapter therefore concentrates on highlighting certain important aspects of:
Voltage selection Calculation of transformer voltage ratio, specification of insulation levels, examples of voltage regulation, rating, tap ranges and impedance calculations.
Thermal aspects Specification of temperature rise and ambient conditions. Some comments are made on constructional features of different types of transformer in common use together with the purpose and selection of accessories. A review of the relevant IEC Standards and summary of the parameters to be specified by the user when detailing a transformer for a particular application are given.
The phasor diagram for a single phase transformer with a 1:1 turns ratio supplying an inductive load of power factor cos ? 2 is shown in Fig. 14.1. The transformer no-load current, I 0 consists of the physically inseparable magnetizing current and core loss components. The primary magnetizing current, I m is lagging the primary induced emf, E 1 by 90 . The primary core loss component, I c consists of hysteresis and eddy current components. The hysteresis loss is proportional to the frequency of operation and the peak flux density while the eddy current loss is a function of the frequency, rms flux density and the thinness of the core laminations. Normally the magnetizing current is much larger than...
