VTdrive What is VFD Line Reactor0 pages

WHAT IS A LINE REACTOR?

A 3-phase Line Reactor is a set of three (3) coils (also known as windings,

chokes or inductors) in one assembly. It is a series device, which means it is

connected in the supply line such that all line current flows through the reactor,

as shown below.

Transformer

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Line Reactor (XJ

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Line Current

Loads

Line Reactors are current-limiting devices and oppose rapid changes in current because of their

impedance. They hold down any spikes of current and limit any peak currents. This resistance to change

is measured in ohms as the Line Reactor's AC impedance (XL) and is calculated as follows:

XL = 2 TT f L (ohms), where:

f = frequency

harmonic frequency examples:

Harmonic (60 Hz) Frequency (Hz)

5th 300

7th 420

11th 660

L = reactor inductancein henries (H), millihenries (mH) — H x 10-3, microhenries (uH)

-Hx10-6

By inspection of the XL formula, the Line Reactor is directly proportional to the frequency (f) and the

inductance (L). That is, if the impedance of a Line Reactor is 10 ohms at 60 Hz, then at the 5th harmonic

(300 Hz) the impedance is 50 ohms. If the inductance (L) is increased, then the impedance will increase

proportionally.

This increase in Line Reactor impedance will reduce the current in the line. The higher the frequency

(Hertz), the lower the current. A Line Reactor's DC resistance (R-ohms) is very low by design so that the

power losses (watts-l2R) are low.