Page 42 - Energize August 2021

TECHNICAL

Open-core power voltage

transformer delivers 333 kVA

Information from Končar

ower voltage transformers (PVTs) are special Additionally, they are used as a backup option for temporary supply for local
hybrid instrument transformers which consumers during substation construction.
Pincorporate features of a single-phase Končar PVT is a line-to-ground connected single-phase transformer which can be
inductive voltage instrument transformer with that of used as a single unit or in a three-phase bank to power loads. The single-phase units
a distribution power transformer to offer a compact, are used for direct transformation of power from high, transmission level voltages
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reliable power source. of up to 550 kV (1800 kV BIL) to low voltage according to customer requirements
Via that direct energy transfer, the distribution grid (typically between 120 V and 1000 V). With that in mind, the rated power of such
is bypassed entirely. This eliminates the necessity for units spans from 10 to 333 kVA single-phase or 1 MVA three-phase. An example
the intermediate transformation of power, consequently of such a unit, used for auxiliary supply in a substation is given in Figure 1.
removing the related costs of primary and secondary Končar PVTs are unique in design due to their open core, the main
equipment as well as the costs of the corresponding characteristic being that the main flux is partially closed through the non-magnetic
infrastructure. material, meaning that an air gap is inherently present in the main magnetic
Therefore, the main application of such circuit. The main flux path is dictated by the flux-directing yoke, which forces the
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transformers is power supply of auxiliary systems flux path towards the immediate vicinity of the main core limb. PVTs enclosures
and services within a substation or remote industrial consist of the base assembly, insulator, heat sink, bellows and bellows cover.
consumers (communication towers and antennae, The design allows PVTs to achieve minimal oil volume. The active part of the
mines, pump stations). Furthermore, PVTs can transformer is located inside the insulator. As per client request, external insulation
be one of the most economical solutions for rural can be either porcelain or composite. Porcelain insulators are made of the highest
electrification. They can act as a reliable power source quality C130 aluminous porcelain, while the composite insulators are made from a
to allow rural communities access to electricity. glass-fibre reinforced resin tube with silicone rubber sheds.

Figure 1: PVT in substation application

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