AC Reactor

AC Reactor

A ac reactor, also known as line reactor or choke, is a coil of wire that acts as resistance to current flow.ac reactor When inserted between the VFD and power system, it limits current overcurrent, reduces harmonic distortion, prevents voltage spikes, minimizes notching, and improves line impedance. It is also used to help prevent the high-order harmonics generated by electrical equipment from polluting the power system and protect the drive and other equipment from damaging effects of current transients.

There are two primary types of ac reactor: DC and AC. When an ac reactor is installed on the DC bus of a variable frequency drive, it is known as a DC reactor. When an ac reactor is installed between the power system and the VFD, it is known as an AC reactor.

Both AC and DC reactors are designed to reduce current transients/surges that occur through the rectifier. The difference between the two is that an AC reactor has a copper winding and a control winding wrapped around a single-phase iron core while a DC reactor has only the DC control winding wound on a single-phase iron core. The DC circuit of a DC reactor is much simpler than the AC circuit of an AC reactor as the inductance of the copper winding is proportional to the amount of current flowing through the core, and the control winding is simply a DC current that causes saturates of the core.

An ac reactor is rated by the ohms of inductance it offers at a certain frequency at a specified current. The higher the ohms of inductance, the greater the resistance it provides to current flow. Generally, the inductance must be less than 3% of the rated current. This is because the higher the inductance, the more it restricts the flow of current and may cause overcurrent, leading to damage or failure.

During initial startup, many electric motors draw several times their full-load current as they begin to turn. This high inrush current can create voltage sags or trip breakers in other equipment and cause notching in power distribution systems. A reactor can be added in series to increase the reactance and reduce this inrush current.

A ac reactor can be tapped to change the reactance value to match different loads or power system characteristics. This feature allows the reactor to be "tuned" to match the load or power system requirements without modifying the drive itself.

When a voltage spike or surge occurs, the drive will hog current to recharge its capacitor bank quickly. This results in short bursts of current that are disruptive to the power system, causing voltage drops and distortion of the power voltage waveform. A ac reactor can be installed to limit these short bursts of current, reducing the impact on the power system and helping to protect the drive from power system faults.

Tags:reactor installation | series reactor | shunt reactor | smoothing reactor