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.

AC reactors are placed in series with the incoming AC power line. An advantage they provide is some protection from voltage transients created by power factor capacitor switching and lightning surges because they are installed before the VFD. A disadvantage they cause is a voltage drop to the VFD due to a condition called Overlap of Diode Conduction. This can be a problem when the VFD is installed on a power line that dips in voltage. If the voltage dips low, and the AC reactor drops some voltage, the drive might nuisance trip on an Under Voltage or Power Loss fault trip. For example a 5% impedance...

When shopping for a reactor we generally look to see how much the reactor will reduce the damaging harmonics. A VFD with no reactor could produce 60-130% harmonic current distortion on the power line.* Reactors are commonly sold in values of percent impedance with 1.5%, 3%, and 5% being standard values sold. Ideally, 5%-6% overall impedance will yield the best cost vs. effect. Installing greater than 6-7% impedance has little beneficial affect on harmonic reduction with a major disadvantage of excessive losses. That leaves the question do we buy a AC or DC reactor? The best solution to balance...

Headquarters Address: 6F, Xinfeng Building B, Yangguang Industrial Zone, Xili Town, Nanshan District,Shenzhen, China. Factory Address: 3F&4F, Xihe Industrial Zone, TangTou Load, Shiyan Town, Baoan District, Shenzhen,China.