Line reactors are commonly used in adjustable speed drive
applications to improve power quality.
They are connected in series with the input terminals of the drive to
serve multiple functions.
1) Suppress voltage transients, protect
thyristors,
2) Increase effective input impedance resulting
in lower drive input harmonic current distortion and system voltage distortion,
reduce true rms current, improve total (true) power factor.
5% effective impedance (at full
load) yields about 35% THD-I, 3% impedance at full load results in about 45%
THD-i. Note: a drive system with a 5% impedance line reactor, operating at 60%
of reactor current rating will look like a 3% impedance reactor.
3) Reduce
voltage notching upstream of the line reactor. Reactor serves (along with
upstream impedance, ie: transformer) as part of a voltage divider network where
the notch voltage is distributed proportionately across the two impedances. To
solve voltage notching, the line reactor must be connected at the input
terminals of the SCR converter (ie: DC drive) that is producing the voltage
notches.
