Can a Single Reactor Be Applied To Multiple Motor Drives?
Usually not! This application note describes the only situation in which a reactor may be used at the input to multiple VFDs, and advises against this configuration for DC Motor Drives. Use of a single reactor to supply multiple motor drives is not recommended except in the specific circumstance described within this article.
Multiple AC variable frequency drives may be supplied through a single reactor only if the drives always run simultaneously. If the VFDs are started and stopped independently, they should each have their own input reactor.
The benefit provided by the reactor derives from its effective impedance, which is proportional to load current through the reactor. This relationship is illustrated by the formula:
% Impedance= ((I*2*pi*ƒ*L*v3)/V) *100
I is fundamental load current, actual or motor load in Amperes
ƒ is frequency in Hertz
L is reactor's per coil inductance in Henry (1 mH=0.001)
V is the line to line voltage in Volts
If the effective impedance becomes too low, the reactor will not provide the expected protection, If load current is relatively small, the effective impedance may become too low. The current that is demanded by multiple drives from a single source is likely to exhibit a great variation if the VFDs do not run simultaneously. This wide range of load current through a single reactor will result in a reduction of the benefits derived from the reactor.
Caution: Never use a single reactor to supply multiple DC Motor drives. It is likely that the drives will interfere with each other (crosstalk) unless they each have their own input reactor, This situation may also occur when more than one DC drive is on a single isolation transformer.
When using DC motor drives, apply a 3% impedance reactor to the power input of each drive to reduce the "notching" of the supply voltage that may cause interference with other loads sharing the same supply.