Page 32 - Energize April 2021

TECHNICAL

Managing transmission voltages

in power systems

by Ricardo Carvalho Campos, André Lanza de Oliveira e Silva, Marcelo Ricardo de Moraes, Jari Kotiniitty and Tommi Keikko, GE Grid Solutions

During normal conditions, the operating voltages of transmission and distribution systems must be
maintained within very tight limits, typically, from 0,95 to 1,05 p.u. of the rated value. At low system

loading, operating voltages increase due to the capacitive nature of the grid. Shunt reactors are then
used to absorb this excess reactive power generated by the grid’s capacitances and thereby regulate the
operating voltages of transmission and distribution systems.

his document presents useful information on the Design of dry type air core shunt reactors
application and specification of shunt reactors Typically, dry type air core reactors for shunt application are
Tfor transmission and distribution power systems, designed using fiberglass encapsulated construction. The winding
describing how voltage control is achieved. It also provides consists of numerous insulated aluminium conductors, which are
a brief explanation of the design aspects and benefits of mechanically immobilised and encapsulated in epoxy impregnated
using dry type air core shunt reactors, including switching, fiberglass filaments, forming cylinders (or layers).
protection, and grounding. Depending on the reactor’s ratings, one or more cylinders
are connected in parallel between the aluminium spiders. The
Benefits of air core dry type shunt reactors individual cylinders are separated by vertically oriented fiberglass
Dry type air core shunt reactors are a very cost-effective spacers, forming cooling ducts for heat dissipation by means of
solution for reactive power compensation of transmission and air flow from the bottom to the top of winding. This construction
distribution systems. Their feasibility depends primarily on allows the use of compact coils even for high inductance, reducing
the combination of required voltage and power. Nowadays, installation footprint.
they can be installed in system voltages up to 500kV, being Medium voltage shunt reactors are typically designed with
connected directly to substation busbars, transmission line a single coil per phase. For high voltage applications, the shunt
endings or tertiary windings of large power transformers. reactors can be split into two or more coils in series per phase, in
order to meet insulation requirements (dielectric creepage length).
When the combination of power/voltage allows, the benefits Figure 1 shows a typical dry type air core reactor and its main
of using air-core dry type shunt reactors include: parts, which are normally included in the standard scope of supply.
• Very low maintenance requirements Other accessories may be part of the supply, upon demand and/
• Eco-design (environmentally friendly)
• No need for oil treatment systems or oil retention tanks
• Simple transportation
• Simple erection and commissioning
• Shorter lead times
• Simple protection requirements

Additionally, GE’s air core reactors offer further benefits,
including:
• Best-in-class materials and production process, resulting
in high quality and reliability of the equipment
• Conservative temperature rise and dielectric design for an
extended service life
• High mechanical strength to withstand elevated short-
circuit forces
• Surface treatment for protection against UV radiation and
pollution
• Customized space-saving solutions for installation in
compact areas Figure 1

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