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Reactors Percent Impedance: 3% or 5% Line and load reactors are classified by their percent impedance (denoted as percent IZ or %IZ), which is the voltage drop due to impedance, at the rated current, expressed as a percent of rated voltage. The most common line reactors have either 3% or 5% impedance.

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.

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.

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.

3% impedance reactors are typically sufficient to absorb power line spikes and motor current surges. They will prevent nuisance tripping of drives or circuit breakers in most applications. 5% impedance reactors are best for reducing harmonic currents and frequencies.

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.

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.

A line reactor (also called an input reactor) is installed before the VFD and protects the drive, while a load reactor (also called an output reactor) is installed after the VFD and protects the motor.