A reactor made for variable frequency drives (VFDs) is nothing more than a coil of wire wound around the core of laminated steel. The desirable characteristic of a reactor is the inductance which means the opposition to a rapid change in the flow of the current. VFD is the equipment which draws current from the power line in sharp pulses that leads to the flow of the harmonic current.
The reason behind drawing current in sharp pulses is that input diodes conduct current only at the peak of the voltage waveform so that the capacitors remain fully charged. This is why you need line reactors to smooth the current flowing to VFDs and reduce harmonics.
Line Reactors made for VFDs are available as either AC reactors or DC reactors, also known as link chokes. So, it is important that you know the merits and drawbacks of the AC line reactors and DC line reactors before making a selection between the two. So, let’s take a quick look.
AC Line Reactors
Merits:
- AC line reactors enhance the reliability of variable frequency drive and allow facilities to comply with utility standards.
- They provide protection to VFDs Diode Bridge against voltage transients or spikes caused by the lighting surge or power factor capacitor switching.
Drawbacks:
- While AC line reactors protect VFD Diode Bridge, they also cause a voltage drop to the VFD because of a condition called Overlap of Diode Conduction. This voltage drop can result in nuisance tripping on under-voltage or power loss when a VFD is installed on a power line that dips in voltage.
- They are costly when compared with DC line reactors for the same impedance for smoothing the harmonics current.
DC Line Reactors
Merits:
- Just like AC line reactors, DC line reactors also increase the reliability of VFD and help to remain compliant with utility standards.
- Unlike AC line reactors, they don’t cause any voltage drop to the VFD and suitable for the cases where VFD is installed on a power line that dips in voltage.
- They are comparatively cheaper than AC line reactors.
Drawback:
- The only drawback that DC line reactors come with is that they don’t provide any protection to the VFDs Diode Bridge against the possible voltage transients or spikes caused by surges in lighting or power factor capacitor switching.
Knowing about these merits and drawbacks of AC and DC line reactors will help you decide which of the line reactors is suitable to install for a particular application. So, it is imperative to carefully comprehend all the above points for coming up with the most suitable option.