GB333148A - Improvements in and relating to static electric transformers - Google Patents

Abstract

333,148. Ferranti, S. Z. de, Whibley, J. H., and Ferranti, Ltd. Jan. 31, 1929. Transformers.-A transformer adapted for supplying the voltage coils of a number of meters under test comprises a number of secondary windings arranged on a common core having a crosssection sufficiently large to ensure that secondary and primary voltages are nearly in phase and carrying a single primary winding. Provision may be made for maintaining the windings at a constant temperature in order to avoid variations in the voltage and phase relationships between the primary and secondary windings. The secondary windings 20 are in the form of a stranded conductor, each strand 21 being insulated and forming one secondary. Adjustment of transformation ratio and phase displacement is effected by combined adjustment of magnetic leakage (effected by means of a magnetic shunt 23a or an adjustable air-gap in the core) and a variable resistance 22a in the primary circuit. To render the transformer characteristics independent of external temperature changes the crosssections of primary and secondary windings are such as to introduce neglible errors over a range of from 10-30‹ C. Meters under test are arranged as shown in Fig. 4, with their current coils 26 in series, their voltage coils 24 being connected one to each secondary winding. This arrangement enables the usual isolating link between the current and voltage coils to be dispensed with. An arrangement of polyphase meters under test is also described. According to the Provisional Specification, the transformer may be wound with " Eureka" or like wire having a neglible temperature coefficient, and it may be oil-immersed and provided with heatadding or heat-abstracting means.