Power transformers equipped with on-load tapchangers
(OLTCs) have been the main components
of electrical networks and industrial applications for
nearly 90 years. OLTCs enable voltage regulation
and/or phase shifting by varying the transformer
ratio under load without interruption.
From the start of tap-changer development, two
switching principles have been used for load transfer
operation – the high-speed resistor-type OLTCs and
the reactor-type OLTCs.
Over the decades both principles have been developed
into reliable transformer components which
are available in a broad range of current and voltage
applications. These components cover the needs of
today’s network and industrial process transformers
and ensure optimal system and process control [1].
The majority of resistor-type OLTCs are installed inside
the transformer tank (in-tank OLTCs) whereas
the reactor-type OLTCs are in a separate compartment
which is normally welded to the transformer
tank (fig. 1).
This paper mainly refers to OLTCs immersed in transformer
mineral oil. The use of other insulating fluids
or gas insulation requires the approval of the OLTC
manufacturer and may lead to a different OLTC design,
as shown in chapter 4.2.2