AC Input Reactors

If the supply is very low impedance the AC reactor will be required to limit current into the inverter; particularly the input rectifiers and capacitors. A low impedance supply is one where, when the inverter is running at full load, the voltage drop measured at the input terminals is one percent or less. If the short circuit current of the supply is 200 times greater than the full load input current of the inverter, the supply impedance is low. A low impedance supply will cause high currents to flow in the input rectifies and DC link capacitors, and may cause overheating.

If the supply is subject to transients, voltage peaks etc. The AC reactor will reduce these and protect the inverter from damage. Voltage surges and transients can be caused by power switching, lighting strikes, or badly regulated supplies. In an industrial installation, transients may be caused by old DC drives, welding equipment, load switching, and especially power factor correction equipment. The inverter is protected from transients internally, but where frequent transients of high energy are expected, an input AC reactor will limit the magnitude and energy adsorbed by the inverter.