Sag Fighter™ Operation
The Sag Fighter™ is a series-connected, inverter-based, voltage compensation device with built-in surge suppression. The Sag Fighter™ consists of a three phase transformer with each of its secondary windings connected in series between the source (incoming line) and the load(s). Figure 1 shows a schematic of a single phase of the unit. Normally, the unit operates in a “bypass” mode with the primary of the transformer shorted electronically through SCR switches, so that load current flows through the secondary windings of the transformer. The ampere-turn balance is maintained through the primary SCR switches.
The Sag Fighter™ continuously monitors the input voltage waveform for any deviation (user selectable) from a balanced, three phase supply voltage. Upon sensing such a deviation (as would normally be caused by a voltage sag), the Sag Fighter™ engages, within 1/8th of a cycle, an inverter circuit to apply a compensating voltage to the primary windings of the series connected transformer. The compensating voltage is synthesized
with a magnitude, shape, and phase angle such that when it voltage is injected in series with the abnormal supply voltage, the resulting output voltage is a balanced, three phase voltage for the load(s). When a normal three phase supply voltage returns to the input of the Sag Fighter™, the inverter circuit is disengaged and the unit returns to its bypass mode.
It is important to note that the Sag Fighter™ operates differently than traditional voltage regulators in that it does not provide continuous, fine correction. Typically, the trigger point for the Sag Fighter™ is set around 90% of nominal voltage. This means that the unit will only start providing correction once the voltage drops below 90% and it will then correct the voltage back to ±5% of the nominal voltage.