Line reactors protect electric motors and variable frequency drives (VFDs) from harmful current and voltage spikes. Reactors also add impedance to the power system, also known as harmonics, effectively reducing power line distortion.

 

      UNDERSTANDING REACTORS

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      A three-phase line reactor is an inductor connected in series within a power system. Line Reactors are simple electromagnetic devices and are often referred to as 'inductors.' They are designed and produced with copper or aluminum wound coils and siliceous transformer sheets with air gaps. Line reactors are connected in series between the grid and variable frequency drives (VFD), and motor protection reactors are connected in series between the drives and the electric motor.

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

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      The impedance slows down the speed of current changes in the line. As the current flowing through the reactor increases, the percentage of impedance applied also increases. When the current flowing through the reactor is equal to the rated current of the load, the reactor impedance percentage has reached its maximum value. As the current decreases, in other words, as the full load of the reactor falls below the current value, the percentage of impedance applied will decrease proportionally. For this reason, the reactor must be of sufficient physical size so that the conductor thicknesses are selected correctly and that rectors produced larger or smaller than they should pose a problem regarding load current.

 

      VFD (MOTOR DRIVE) PROTECTION & HARMONIC REDUCTION

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       When a line reactor is connected to the input side of a variable-frequency drive, reactor impedance effectively smooths out and slows down line voltage distortions (spikes and surges). In this way, it helps to prevent damage to the drive when voltage deviations occur, and the drive is prevented from overvoltage failure.  Switching compensation capacitors on and off and load current fluctuations cause distortions in power systems.

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      Reactors also reduce the harmonic currents drawn by the drive and help block voltage harmonics, which can interfere with the drive's operation. Connecting a line reactor to the input of the drives is an economical solution for drive protection and harmonic reduction in almost all drive applications.

 

      AFTER ALL

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      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 input section of the drive and reduces the harmonic current drawn by the drive from the power system.