VTdrive Comparison Between AC Reactor and DC Link Choke0 pages

Comparison Between AC Reactor and DC Link Choke

Typical VFD Line Current: No Reactor
A reactor designed for Variable Frequency Drives (VFD’s) is typically nothing more than a coil
of wire wrapped around a laminated steel core. The characteristic of the reactor that we
desire is inductance, “the opposition to a rapid change in current flow”. VFD’s draw current
from the power line in sharp pulses, causing harmonic current to flow. The current is drawn
in sharp pulses because the input diodes only conduct current at the peak of the voltage
waveform to keep the capacitors fully charged.

It is this feature that allows reactors to smooth the current flow to VFD’s and reduce
harmonics.

Typical VFD Line Current: 3% Reactor
Additionally, smoothing the current flow limits the high peak current pulses from abusing the
capacitor bank inside the VFD. Thereby extending the life span of the drive, and improving
the drive’s True Power Factor.

Reactors for VFD’s are sold as either AC reactors or DC reactors (also called link
chokes).

Both reactor types serve the same primary purpose, to smooth the current flow to

the VFD, and reduce damaging harmonics produced on the power line. However, there are
advantages and disadvantages to both AC & DC reactors.