Line reactors protect electric motors and variable frequency drives (VFDs) from harmful current and voltage surges. Reactors also effectively reduce power line distortion by adding impedance to the power system, also known as harmonics.
 
UNDERSTANDING REACTORS

A three-phase line reactor is essentially an inductor connected in series within a power system. Line reactors are simple electromagnetic devices, often referred to as 'inductors'. They are manufactured by designing and manufacturing coils with copper or aluminum windings and silicon wafers with air gaps. Line reactors are connected in series between the grid and variable-frequency drives (VFDs), while motor protection reactors are connected in series between the drives and electric motors.

The line reactor provides additional circuit inductance used to obtain the line resistance. Impedance, typically defined as resistance in ohms, is combined with the system voltage and line current passing through the reactor and expressed as a percentage (%). This percentage is used to define the impedance level for each line reactor rating.

Impedance serves to slow down the rate of current changes in the line. As the current passing through the reactor increases, the applied impedance percentage also increases. The reactor impedance percentage reaches its maximum value when the current passing through the reactor equals the nominal current of the load. As the current decreases, in other words, as the reactor falls below its full load current value, the applied impedance percentage will decrease proportionally. Therefore, it is vital that the reactor has sufficient physical size and that the conductor thicknesses are correctly selected; reactors manufactured larger or smaller than necessary create problems in terms of load current.
 
VFD (ENGINE DRIVER) PROTECTION AND HARMONIC REDUCTION

When a line reactor is connected to the input side of a variable frequency drive, the reactor impedance effectively smooths and slows down line voltage disturbances (surges and fluctuations). This helps prevent damage to the drive when voltage deviations occur and also prevents the drive from giving an overvoltage fault. Switching on and off of compensation capacitors and load current fluctuations cause disturbances in power systems.

Reactors also reduce harmonic currents drawn by the drive and help prevent voltage harmonics that could interfere with drive operation. Connecting a line reactor to the input of drives is an economical solution for drive protection and harmonic reduction in almost all drive applications.
 
IN CONCLUSION

Line reactors are crucial in stabilizing the current waveform and acting as an impedance between the grid and the drive. The reactor impedance protects the drive's input section and reduces the harmonic current drawn from the power system.