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Air Core Shunt Reactors

Trench is a supplier of specialized electrical products and a recognized world leader in the design and manufacture of dry type air-core reactors for all utility and industrial applications. Trench air-core reactors range from small kvar units for applications such as capacitor bank inrush limiting or distribution system short circuit current reduction, to large power reactors for a number of applications, such as shunt reactors that may be over 100 MVAr per coil.

Traditionally shunt reactors are manufactured in oil immersed design. However in recent years Trench has been able to gradually extend the range for dry type air-core shunt reactors up to 500 kV operation voltage and posses a long list of references for projects all over the world. This technology offers significant technical advantages and with the maintenance free design, customers benefit from lower total cost of ownership over the complete lifecycle.


Up to

kV operation voltage

for Trench high voltage air-core shunt reactors

Air-core dry-type reactors for reactive power compensation are installed for system voltages up to 500 kV.

General features

Shunt reactors are used to compensate for capacitive reactive power generated by lightly loaded transmission lines or underground cables. They can either be connected to the tertiary of the power transformer or directly to the line. Available up to 500kV.


As the name implies, shunt reactors are connected in a parallel (shunt) configuration to compensate for capacitive reactive power of transmission and distribution thereby to keep the operating voltages within admissible levels.

Two main applications of shunt reactors can be identified:

  • reactors that are required permanently in service for stability reasons (especially on long transmission lines), or
  • reactors that are needed for voltage control in a meshed system and are switched in only during light load conditions, when there is an excess of capacitive reactive power.


  • Tertiary connected shunt reactors
  • Shunt reactors directly connected to high voltage
  • Switching of shunt reactors
  • WYE connected shunt reactors with the neutral grounded through a neutral reactor

More information about the different types of connection can be found in the attached product brochure.



  • No environmental concern, no oil collection system required
  • No fire hazard, no fire deluge system
  • Minimal efforts and maintenance costs
  • Less civil work, lower weight
  • Easy to handle and transport
  • Simplicity of insulation to ground [self-healing]
  • Simple protection scheme
  • No risk of bushing failures
  • No excessive magnetizing inrush current, no iron core
  • Lower investment cost
  • Affordable cost for spare units [single phase unit only)
  • Shorter lead time
  • Cold start capability [no need to pre-heat oil prior to energization during low ambient temperatures)
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