WBUT University > Electrical Engineering > Sem 5

Marks: 5M

Year: May 2010

On-load tap changers (or circuit tap changers), permit tap changing and hence voltage regulation with the transformer on-load. Tap changing is usually done on the HV(High voltage) winding for two reasons:

1. Because the currents are lower, the tap changer contacts, leads, etc., can be smaller.
2. As the HV winding is wound outside the LV(Low voltage) winding, it is easier to get the tapping connections out to the tap changer.

An on-load tap-changer(oltc) gear comprises two major components, the tap selector and the diverter switch.

The tap selector selects the tapping and its electrical contacts are designed to carry the rated current of the transformer but not to make or/and break this current.

The diverter switch, however, needs to be designed to carry, make and break the load current in circuits previously selected by the tap selector.

During the operation of diverter switch the transition resistors bridge the tap in use and the tap next to be used, thereby limiting the circulating current due to the inter-tap voltage