Characteristics of Load Ratio Control Circuits For Changing Transformer Ratio Under Load

The influence of saturation phenomena in series reactors on the circuit performance of load ratio control equipment is discussed. It is shown that unless care is exercised in the design of these reactors, gross distortion may be introduced into the circuit, resulting in obtaining across the reactor voltage peaks which on the one hand may endanger the insulation, and on the other hand greatly increase the rupturing duty on the circuit breaking devices. Formulas are developed which show what proportion of line voltage is absorbed by a series reactor subject to magnetic saturation. It is shown that this voltage can be expressed in terms of the reactive constants of which the circuit is composed, and that it is independent of the current or voltage wave form. Numerical solutions are given in the shape of curves, assuming that the magnetic circuit of the reactor is made up of typical transformer steel. The great influence of a small air gap in the magnetic circuit in reducing these voltages is shown.