- Shunt Reactor Definition: A shunt reactor is defined as an electrical device used in high voltage power systems to stabilize voltage during load changes.
- Voltage Stabilization: It controls dynamic overvoltage and provides capacitive reactive power compensation in systems above 400kV.
- Impedance Types: Shunt reactors come in gapped core or magnetically shielded air core types to maintain constant impedance and avoid harmonic currents.
- Loss Measurement Methods: Losses are measured at lower voltages for high voltage reactors and scaled up; the bridge method is preferred due to the low power factor.
- Operating Conditions: Must handle continuous voltage without overheating, ensuring it operates within safe temperature limits.
What is Shunt Reactor
A shunt reactor is an inductive device connected in high-voltage power transmission systems to absorb surplus charging vars and hold the voltage down when the load is light. A fixed-rating reactor stays on the transmission line all the time, or it is switched in and out as the load changes.
A three-phase shunt reactor is often connected to a 400 kV or higher electrical bus system to absorb line-charging reactive power and to limit the dynamic overvoltage that follows load rejection. The same function is also used on many lower extra-high-voltage circuits; 400 kV is a common Indian EHV example, not the only voltage.
The shunt reactor must handle the highest continuous operating voltage of the system, often 420 kV on a 400 kV network, without exceeding the purchaser’s IEC 60076-6 temperature-rise limits during normal power-frequency variations. A 150°C top-spot figure appears on some thermometer scales and specifications; it is not a single universal hotspot limit.
The shunt reactor should be a gapped-core type or a magnetically shielded air-core type. Both designs keep the impedance nearly constant, which limits harmonic current when the system voltage rises.
Core loss is a large part of shunt-reactor loss in service, so the magnetic circuit is designed to keep that loss down.
Measurement of Losses in Shunt Reactor
Measure shunt-reactor losses at rated voltage and frequency when the test plant can do so. For a high-voltage reactor, a lower test voltage is often used and the measured loss is then referred to rated current. IEC 60076-6 requires that referred result at rated current, rated frequency and the reference temperature; a simple I-squared scale is only an approximation.
The power factor of a shunt reactor is very low, so a conventional wattmeter reading is a poor loss measurement. A bridge method is the usual choice.
The test does not split the losses among the parts of the reactor. To avoid a large temperature correction, take the measurement when the average winding temperature equals the agreed reference temperature.
