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%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.

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.

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.

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.

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.

L =XL/(2¶FL) Where L is inductance in Henrys, XL is inductive reactance or impedance in Ohms and F is the frequency. In general Frequency will be the line frequency for both input and output reactors. Your drive distributor should be able to help you size a reactor for use with a 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.