Shunt Reactors Selection Guide
LED drivers, UPS units and XLPE cable runs can push a facility capacitive; for shunt reactor selection, the cause and the reactive energy limit matter.
This guide explains what to look for when choosing products in the Shunt Reactors category.
Why a facility shifts to capacitive
LED lighting drivers, UPS units, equipment containing semiconductor power electronics and XLPE cable runs create a capacitive effect on the grid. The problem often appears during the hours when production stops: at night and on weekends the inductive loads drop out, the UPS and lighting keep running, and the meter records capacitive reactive energy even when all the capacitor steps are switched off. At this point, adding capacitors makes the situation worse; the excess can only be balanced by a component that draws inductive power.
The reactive energy charge applies when the ratio of reactive energy to active energy exceeds the limit in the tariff. According to the practice published by the designated supply company, the limit for facilities with an installed capacity below 50 kVA is 33% inductive and 20% capacitive; for larger installed capacities it is 20% inductive and 15% capacitive. The ratios are set by the procedures and principles for tariff implementation and may change; confirm the current value that applies to your facility with your distribution company.
How reactor power is determined
The reactor is chosen not by estimate but according to the measured capacitive reactive power. With the capacitor steps switched off and the facility at its lowest load, the capacitive kVAr read phase by phase from a network analyzer or from the display of the reactive power relay gives the power to be compensated. The kVArh total on the bill is not enough on its own; it does not show at which hour or on which phase the capacitive consumption occurs.
- If the capacitive power varies during the day, plan several steps instead of one large reactor. An oversized reactor that stays in circuit all the time would bring the facility close to the inductive limit this time.
- The reactive power control relay that will manage the steps must include shunt reactor among its connectable step types. For some of the three-phase relays in this store, single-, two- and three-phase shunt reactor steps are stated as a product feature.
Current and connection in single-phase and three-phase reactors
- Single-Phase Shunt Reactors: rated for 230 V and connected between phase and neutral.
- Three-Phase Shunt Reactors: rated for 400 V and connected to the three phases.
Step components are chosen according to the reactor's rated current. In the Entes table, 21.74 A is given for the 230 V 5 kVAr single-phase ENT.SRS1 model and 28.9 A for the 400 V 20 kVAr three-phase ENT.SRS3 model. The fuse, contactor and cable cross-section are determined according to this current and the manufacturer's connection diagram; to compare cross-sections you can use the cable current carrying capacity calculation tool.
The difference between a contactor step and SVC
In a contactor system each reactor is either fully in circuit or out of circuit; balancing is limited to the precision the step increments allow. In SVC, the reactors are fed through an inductive load driver and the inductive power drawn is adjusted to the need; the specifications of some of the drivers in this store state switching in between 0% and 100% and response without delay. Entes defines SVC for facilities with rapidly changing and unbalanced loads.
According to Entes data, a driver is designed to drive three single-phase shunt reactors at full load, and all of the standard-series single-phase reactors are compatible with SVC. The 1.66 kVAr, 3.33 kVAr, 6.67 kVAr and 10 kVAr single-phase reactors given for SVC are used in groups of three and are listed under SVC Shunt Reactors.
The difference between a shunt reactor and a harmonic filter reactor
Both are coils, but their roles are different. A shunt reactor is connected in parallel to the grid on its own and balances capacitive reactive power. Harmonic Filter Reactors, on the other hand, are connected in series with the capacitor; their purpose is to protect the capacitor step from harmonic currents and resonance, and they do not remove capacitive excess. The two products are not interchangeable.
Brands in this category
- Tibcon: single-phase and three-phase shunt reactors with the TBSR code; the product name states the power and phase configuration.
- Entes: ENT.SRS1 (230 V single-phase) and ENT.SRS3 (400 V three-phase) standard series. The model whose name states several power ratings (0.3/0.4/0.5 kVAr) is given in the manufacturer's table with three separate power and current values.
Ordering notes
Reactors are sold per piece; if you are building three-phase compensation with single-phase reactors, enter a separate quantity for each phase. Some of the products are listed as made to order; for these, the lead time is confirmed before the order. You can reach a product directly by typing manufacturer codes such as TBSR5409 or ENT.SRS3 400/20 into the site search.
Comparison and selection table
| Selection Criterion | Small Step Shunt Reactor (0.5 – 5 kVAr) | Medium Three-Phase Shunt Reactor (7.5 – 25 kVAr) | SVC-Driven Stepless Shunt Reactor |
|---|---|---|---|
| Primary Function | Absorbs excess capacitive reactive power from LED drivers & long cables | Balances off-peak/weekend leading power factor penalties | Driven from 0% to 100% by a thyristor SVC controller for exact cosφ = 1 |
| Connection Method | Switched in parallel across 400 V bus via contactor step | Triggered by inductive reactor output of PFC controller | Phases wired to thyristor SVC power module outputs |
| Construction & Safety | Built-in NC thermal switch (trips contactor on overheating) | Low-loss silicon steel core, vacuum-impregnated windings | Low acoustic noise, thermal cutout switch, 400 V 50 Hz |
| Key Distinction | Size according to no-load/nighttime capacitive kVAr reading | Do not confuse with series harmonic filter reactors | Match reactor kVAr rating to the SVC driver capacity |
Frequently asked questions
When is a shunt reactor needed?
It is needed when the facility supplies capacitive reactive energy even with all the capacitor steps switched off, and the capacitive ratio is approaching or exceeding the limit during the billing period. This is mostly seen in businesses with LED lighting, UPS units and long cable runs whose load drops at night and on weekends. Adding capacitors makes the problem worse; capacitive excess can only be balanced by a component that draws inductive power.
How is shunt reactor power calculated?
The input to the calculation is measurement. With the capacitors switched off and the load at its lowest level, the capacitive kVAr for each phase is read from the analyzer or from the display of the reactive power relay. The reactor steps are chosen large enough to cover this value but not so large that they carry the facility to the inductive limit. If the capacitive power changes with the hour, a plan made of several steps is used instead of a single reactor. Final sizing should be done according to the project and manufacturer data.
How is a shunt reactor connected?
A shunt reactor is connected in parallel to the grid: the single-phase 230 V model between phase and neutral, the three-phase 400 V model to the three phases. In automatic compensation, each reactor is connected to the grid through its own fuse and contactor, and one step output of the reactive power control relay drives the contactor coil; in an SVC system, the inductive load driver takes the place of the contactor. For the connection diagram, fuse and cable cross-section, the manufacturer's installation instructions are the basis.
Can my existing reactive power control relay manage a shunt reactor step?
Not every relay can. Relays designed only for capacitor steps do not recognize a reactor step. The relay's technical data must list single-phase or three-phase shunt reactor among the connectable step types; if SVC is to be installed, the relay must also support the driver output (TCR). For the three-phase reactive power control relays in this store, this information appears in the connectable step types and SVC compatibility lines of the product features.
What is the capacitive reactive energy limit?
According to the tariff practice published by the designated supply company, for facilities with an installed capacity below 50 kVA, the capacitive reactive energy supplied to the system must not exceed 20% of the active energy, and the inductive reactive energy drawn must not exceed 33%; for larger installed capacities the limit is 15% capacitive and 20% inductive. The reactive energy tariff does not apply to residential, lighting and single-phase subscribers. The ratios may change with tariff regulations; confirm the current limit that applies to your facility with your distribution company.