Voltage regulation by changing transformer tappings on-load

The extension of electricity supply systems from simple systems serving small towns and communities to the large complex and inter-connected grid systems of today, together with the requirement to maintain a reasonably constant supply voltage at the consumer's terminals, has necessitated the provision of means for varying the voltage ratio of a transformer whilst the transformer is still supplying load. This Paper reviews the requirement of on-load tap changing equipments as regards designs for different applications and contains some remarks on operation and maintenance.