When static Volt–VAr control helps and when it does not: Operational and planning lessons from a weak radial distribution feeder

Long radial distribution feeders are increasingly exposed to sustained undervoltage as electrification-driven load growth outpaces reinforcement. Static inverter Volt–VAr curves are attractive because they can be deployed through existing controller settings, but standard curves may be too conservative for electrically weak feeders. This paper evaluates the operational and planning value of feeder-specific static Volt–VAr settings under data conditions commonly available to distribution system operators: sparse voltage measurements, hourly feeder-level inputs, and offline parameter updates. The study applies the slope-selection procedure developed in [ 1 ] to a predefined BESS Volt–VAr curve and evaluates the resulting setting through quasi-static time-series power flow for a real 22 kV radial feeder in Northern Norway. During the constructed 168 h high-load/no-generation stress period, the model-based, condition-matched comparison produced 153 h within the adopted target band with the full feeder-specific setting, compared with 8 h under the IEEE 1547-type setting and 1 h without BESS Volt–VAr support. An independent 2025 operating period was used for quantitative comparison with field measurements. The model reproduced the average voltage and voltage-band occupancy, while the disagreement in hourly variation limits its use to comparative screening rather than point-by-point prediction. The transferred feeder-specific setting produced 0 h outside the target band, compared with 16 h under the IEEE-type curve and 55 h without BESS Volt–VAr support. Higher-resolution measurements from the BESS and hydropower plant were used separately to examine interaction between the two local controllers. Under the 59% industrial-growth stress scenario, 4 MVAr was the smallest tested reactive-power rating that kept all 168 hourly voltages at or above the lower limit of the adopted target band after feeder-specific slope selection. The results provide a practical DSO screening procedure: test static tuning first, then identify whether the remaining limitation is curve setting, VAr headroom, or interaction between independently controlled assets.