UZ Series Tap-changers Technical guide

Overview

On-load tap-changer (OLTC)
The UZ types of on-load tap-changers operates according to the selector switch principle, that is, the tap selector and diverter switch functions are combined in one. The tap-changer is built-up by using single-phase units, each identical, mounted in the openings on the rear of the compartment. Each singlephase unit consists of an epoxy-resin moulding, a selector switch, transition resistors and, in most cases, a change-over selector.
The UZ types of tap-changers are mounted on the outside of the transformer tank. All of the equipment necessary to operate the tap-changer is contained in a single compartment, with the motor-drive mechanism attached to the outside. Because the UZ types are designed for mounting on the outside of the transformer tank installation procedures are simplified and the overall size of the transformer tank can be reduced.

Standard tanks are designed for the UZ types. The standard tanks have a number of standard flanges to get great flexibility for accessories. Standard accessories are pressure relay and oil valve, and a great number of extra accessories can be ordered. See Figs. 09 and 10.

As a design option, the UZ types can be supplied without the tank. This gives the transformer manufacturer the flexibility to design the tap-changer tank as an integral part of the transformer tank.

The oil should be of class II according to IEC60296, 2012-02.