- Shunt Reactor Definition: A shunt reactor is defined as an electrical device that absorbs reactive power in power systems.
- Reactance Calculation: The reactance of a shunt reactor can be calculated as it is nearly equal to its impedance.
- V-I Characteristics: The V-I characteristics of a shunt reactor are linear due to the use of a gapped core.
- Three-Phase Measurement: In three-phase shunt reactors, measure reactance by applying three-phase voltage and calculating the average current.
- Zero Sequence Reactance: Zero sequence reactance is measured by shorting the reactor’s terminals, applying single-phase voltage, and multiplying the result by three.
Two key factors must be considered when measuring the reactance of a shunt reactor.
- The reactance of a shunt reactor is nearly equal to its impedance because the resistive component is negligible.
- The V-I characteristics of the shunt reactor is almost linear under operating range of applied voltage. This is because, gapped core is used in the shunt reactor to prevent magnetic saturation of the core within normal operational range.
The simple formula of impedance in ohm is
Where, V is voltage in volt and I is current in ampere.
But in the case of shunt reactor, impedance Z = reactance X.
Hence, here
Where, V is applied voltage across the winding of the reactor and I is the corresponding current through it.
As the V-I characteristic of the reactor is linear, reactance of the reactor winding remains fixed for any applied voltage below the maximum rated value.
In the case of reactance measurement of three phase shunt reactor, we use sinusoidal three phase supply voltage of power frequency (50 Hz) as test voltage. We connect three supply phases to three terminals of the reactor winding as shown. Before that we should make sure that the neutral terminal of the winding is properly earthed.
After turning on the supply, measure the current flowing through each phase of the winding using a sensitive clip-on meter. Calculate the average current per phase by summing the three-phase currents and dividing by three. This average current is used to determine the reactance of the three-phase shunt reactor.
For three phase reactors with magnetic iron path for zero sequence flux, zero sequence reactance may be measured as follows,
In this method, short the three terminals of the reactor and apply a single-phase supply between the common phase terminal and the neutral terminal. Measure the current through the common path, then divide the applied single-phase voltage by this current. Multiply the result by three to obtain the zero sequence reactance per phase.
