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Brief guide on what are AC Line Reactors & when is it used

The Line Reactors are also called as Line Chokes or InductorsLine reactors are electromagnetic devices which consist of a steel core electrical grade laminations and copper inductor coils. The coil forms a magnetic field as current flows through it, which limits the rate of rise of current. 

Reactors are classified as Line (Input) Reactors and Load (Output) reactors. Line Reactors – connected between AC Line Source and the input of a Variable Frequency Drive (VFD) and protects the drive from tripping nuisance and damages. 

Load Reactors on the other hand are used at the load side of a VFD to protect motors if the wiring distance between the VFD and motor is very long (over 100 feet).


Recap the difference between AC Line Reactors, AC Load Reactors & DC Line/Link Chokes in VFD

  • AC Line reactor – installed before the VFD, protects the drive
  • AC Load reactor – installed after the VFD, protects the motor
  • DC Link reactor – inserted into the DC link of a drive


A Reactor at the Input to reduce Harmonics

with no reactors

WITH NO REACTOR – the three phase input current may contain as much as 85% or more total harmonic distortion.


with ac line reactor

WITH AC LINE REACTOR – the peaks of the line current are reduced and somewhat broadened out.

*Image source: Rockwell Automation


When to Install a Line Reactor?

  • Filter out spikes of current, transient and surges from input power in order to protect the drive from damage
  • Require compliance with IEEE 519 standards on Harmonic distortions in Power systems
  • To add Line Impedance to the AC circuit
  • To reduce the burden on upstream electrical components

line reactor


Single Phase & 3-Phase Line Reactors

3-phase Line Reactor is a set of three (3) separated winding coils in one assembly. It is connected in the supply line such that all line current flows through the reactor. A single-phase reactor on the other hand has one (1) coil winding


What is Impedance?

Line reactors are classified by their percent impedance (denoted as IZ%) which is the voltage drop due to impedance at the rated current expressed as a percent of rated voltage

  • 2% Impedance – Line Reactors are usually sufficient to absorb power line spikes and motor current surges. They prevent nuisance tripping of drives or circuit breakers in most applications.  
  • 4% impedance – Line Reactors are best for reducing harmonic currents and frequencies. Use them when you must comply with IEEE 519.
  • When higher line disturbances are present 5% impedance reactors may be needed.
  • Higher impedance reactor can be used to reduce harmonics even further when the aim is to diminish noise from the motor or to extend motor life


Explore EMIS Line Reactors Product Range


Benefits of Line Reactors:

  • Reduction of main harmonics levels to ~35%
  • Impedance at 2%, 3%,4%,5%
  • Protection of motor drive electronics
  • Limitations of inrush Currents
  • Prevention from nuisance tripping caused by power line voltage spikes
  • Low Ripple
  • Increased System Performance and Reliability
  • Improves power factor
  • Mitigates voltage distortion
  • Custom built line reactors are available on Customer request



Line Reactors For VFD Drive Applications – HVAC Equipment

In the HVAC industry energy efficiency is very important and is considered key for achieving energy savings and lower operation costs. With the increased use of Variable frequency drives as the standard control system in HVAC installations for precision speed control of motors driving pumps, chillers, fans and compressors. With the use of VFDs comes the problem of harmonic distortions that can affect sensitive electronic equipment sharing the AC power supply. Line/Load reactors become an economical alternative to remove high frequency harmonic distortions and to protect sensitive equipment.


Other Industry Applications for Line Reactors

When a line reactor is added to the equipment, it safeguards the electronic equipment from input power disruptions. Sometimes these disruptions may potentially damage the whole drive. These are the most typical applications where line reactors are extensively used to protect the equipment.

  1. Motor Drives 
  2. Power Quality
  3. Automotives
  4. Factory Automation
  5. Construction and Infrastructure

Line reactors sometimes have to be made specifically according to motor power capacity & ratings, EMIS INDIA is capable of designing and manufacturing customised Line/Load Reactors/Chokes according to the customer requirement.


How can a three phase line reactor be used for single phase applications?

Three phase line reactors can be used for single phase applications by connecting each of the two supply conductors through an outside coil and leaving the centre coil disconnected as shown below.


Line Reactors Connection Diagram for VFD Applications

line reactor circuit diagram