Do You Really Need An Ac Line Reactor On The Inverter Input?

If your facility experiences random overvoltage trips, or if your transformer capacity is over 10 times larger than the drive rating, installing an ac reactor for inverter setups is mandatory.

An ac input reactor acts as a sacrificial shield. It blocks line-side transient voltage surges, reduces harmonic current distortion by up to 50%, and prevents premature bridge rectifier failure.

3 Symptoms Your System Needs an AC Reactors

1. Frequent Overvoltage Faults

Do your drives trip during utility capacitor switching? High-peak transient voltages pass directly into the DC bus. Adding an ac reactors block on the line side absorbs these voltage spikes safely.

2. Transformer Mismatch

When a small drive connects to a large utility transformer, the low line impedance allows massive fault currents. Adding artificial impedance is the most cost-effective way to balance this network.

3. Harmonic Interference

• Screen flicker on nearby monitoring equipment

• Unexplained overheating in distribution panels

• Nuisance tripping of thermal relays

Real-World Comparison: Input vs. Output Protection

Different issues require different hardware placement. Use this quick reference to select the correct defense:

• AC Input Reactor (Line Side): Protects the drive from the grid. It dampens line-side harmonics and stabilizes incoming voltage.

• AC Output Reactor (Load Side): Protects the motor from the drive. An ac output reactor mitigates high dV/dt voltage spikes caused by long motor cables.

Common Installation Questions

Can I skip the input reactor if I have a built-in DC choke?

While a DC choke reduces harmonics effectively, it does not offer the same level of transient surge protection for the input rectifier diodes as a line-side reactor does.

What impedance rating is ideal?

A 3% impedance reactor is standard for most industrial sites, balancing excellent surge protection with minimal voltage drop.