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Line Reactors are rated by % impedance, voltage, and current. However, they are sized by % impedance, voltage, and motor horsepower. The motor horsepower determines the necessary current rating for the Line Reactor.

Line reactors are electromagnetic devices used as inductors to protect variable frequency drives (VFDs) and other devices from electrical disturbances such as voltage spikes, surges, and transients. Line reactors can limit your current flow and harmful harmonics from the drive.

There are generally two types of line reactors used with VFDs; AC & DC. When a reactor is installed between the power system and the VFD, it is known as an AC line reactor. When a DC reactor is inserted into the DC link of a drive, it is known as a DC link reactor.

If you wish to calculate the value yourself, the following example may be helpful. If a 3% reactor was required for a 100 amp 480 volt drive, a 100 amp or larger current rating would be required. The drive impedance would be: Z=V/I or 480/100 = 4.8 ohms.

%Z = [(Voltage Drop x 100)/Applied Voltage] x ?3. Reactors can be applied to the line and load side of a VFD, each with numerous benefits.

The greater the current through the reactor, the greater the percentage of applied impedance will be. If a reactor is said to have an impedance rating of 3% or 5%, that means the reactor will apply that specified percent of impedance when the current flowing through the reactor is at the rated current of the device.

A 3% reactor is enough to provide line buffering and a 5% reactor would be a better choice for harmonic mitigation if no link choke is present. Output reactors, when used, are generally around 3%. This % rating is relative to the load or drive where the reactor impedance is a % of the drive impedance at full load.