Voltage Sag Event Energy Impact Calculator — Estimate Energy Lost During Sags
Model how much energy a load may fail to receive during repeated voltage-sag events. Choose how the load responds to voltage so the calculation does not silently assume one behavior for every type of equipment.
Sag event inputs
Why a voltage sag is not automatically an energy calculation
A sag is fundamentally a voltage disturbance. To translate it into energy impact, you need an assumption about how the connected load's real power changes during that disturbance.
Constant-impedance model
For an idealized resistive or constant-impedance load, real power varies approximately with the square of voltage.
Constant-current model
For a load that maintains roughly constant current over the event, power varies approximately in proportion to voltage.
Constant-power model
A control system may attempt to maintain real power as voltage changes. Under that simplified model, there is little direct energy reduction even though equipment stress or interruption risk can still exist.
Worked example
For a 100 kW load at 400 V dropping to 280 V for 0.25 seconds, the energy impact under a constant-impedance model is much larger than under a constant-power model because power scales with voltage squared in the first case.
Important limitation
A short voltage sag can cause a process interruption even when the lost electrical energy is tiny. This calculator does not monetize downtime, scrap, restart or equipment trips.
Frequently asked questions
Can a voltage sag cause zero modeled energy loss?
Yes. Under the constant-power model, the direct real-energy reduction is approximately zero.
Does this measure voltage quality?
No. It only converts an entered sag event into an energy-impact scenario.
Can I model multiple events?
Yes. Enter events per day and operating days per year.