Calculating Real Utility Demand to Prevent Voltage Sag and Air Pressure Losses
Calculate real utility demand using empirical millisecond-level coincidence vectors to size low-impedance feeders and local buffers, preventing voltage sags and air loss.
Supply Bus Sag
Meaning
Transient root-mean-square voltage drops between ten and ninety percent of nominal supply voltage lasting from half a cycle to one minute represent common power quality disturbances in industrial electrical distribution systems. Heavy load switching, motor starting, or remote transmission faults pull excess current through system source impedances. Electrical facility managers analyze supply bus sag events to prevent automated production line stoppages and sensitive controller resets.
Permanent voltage reductions and total blackouts fall outside the sag definition.
Disturbance Mechanism
High magnitude current surges create transient voltage drops across upstream transformers and line impedances. Sag depth depends on the fault location, source short-circuit capacity, and transformer vector group configurations. Power quality monitors record supply bus sag duration and voltage depth across critical facility distribution panels.
Installing sensitive variable frequency drives without line reactors causes drive undervoltage tripping during routine line sags.
Facility Impact
Undervoltage conditions cause contactors to drop out and sensitive programmable logic controllers to reset unexpectedly. Automated assembly processes halt mid-cycle, requiring manual clearing and equipment re-zeroing. Unmitigated sags cause significant operational downtime and lost batch production.
Mitigation Standard
Dynamic voltage restorers and active power conditioners inject series voltage to maintain bus levels during utility sags. Tap-changing transformers adjust voltage levels across longer duration low-voltage events. Facility design standards mandate ride-through capability for essential automated loads.