An on-load tap-changer is an indispensable operating equipment for the regulation of power transformers in energy supplying networks. The importance of on-load tap-changers has steadily increased over the years. Today, in Germany and other industrialized countries, almost all generator-type transformers and power transformers are equipped with on-load tap-changers. In developing countries, too, the energy supply demands more and more regulated power transformers. Generally, it can be said that an increase in the density and links of a network corresponds with an increase in the need for regulating transformers.

Today, the on-load tap-changer is surely not one of the central educational topics at colleges and universities. In everyday business, communication between tap-changer manufacturers and users reveal uncertainties which can easily result in costly misunderstandings. This situation gave rise to the decision to provide comprehensive answers to frequently asked questions, starting from the very basis and dealing with the techniques as well as the particularities of on-load tap-changers.