Voltage Regulation Assessment of a D-STATCOM on the IEEE 13- Bus Feeder

Abstract

Voltage sag along radial medium-voltage distribution feeders worsens as load grows, and utilities increasingly rely on Distribution Static Synchronous Compensators (D-STATCOMs) for fast, continuously adjustable reactive power support. However, many published D-STATCOM studies compare a compensated feeder only against an uncompensated one, without directly contrasting the STATCOM's dynamic behavior against a conventional fixed capacitor of the same MVAr rating. This study models the IEEE 13-Node Distribution Test Feeder as a balanced positive-sequence equivalent, solved with the backward/forward sweep load-flow method, and compares three reactive power compensation strategies — no compensation, a fixed capacitor, and a droop-controlled D-STATCOM, both rated at 1.5 MVAr — across ten feeder loading levels (10–100% of rated load, in 10% steps) at all eight of the feeder's load-carrying buses. Results show the two devices perform identically once loading exceeds their shared rating, but below that point their behavior diverges sharply: at 10% load, the fixed capacitor overvoltages the bus to 1.0333 pu and, counter-intuitively, increases total feeder real-power loss more than fifteen-fold above the uncompensated case (18.575 kW vs. 1.150 kW, concentrated in the trunk branches carrying the excess reactive current), whereas the D-STATCOM holds the bus at exactly 1.0000 pu while keeping losses at or below the uncompensated baseline at every loading level tested. A full siting sweep across all eight load buses shows both the loss-reduction benefit and the crossover load level are sitedependent: Bus 671, the feeder's main junction, achieves the largest loss reduction (28.3%) and the earliest crossover (60% load), while Bus 634, isolated behind the feeder's step-down transformer, achieves only 1.7% loss reduction and never saturates its 1.5 MVAr rating even at full load. The uncompensated worst-case sag of 0.9178 pu is consistent with sag magnitudes (0.9081–0.9131 pu) reported for real Indian distribution feeders in prior studies. An independent Newton-Raphson implementation reproduced all backward/forward sweep results to within 5×10?? pu, cross-validating the solver implementation itself (though not the balanced-equivalent modeling assumption against the feeder's official unbalanced specification).

KEYWORDS: D-STATCOM; voltage regulation; reactive power compensation; IEEE 13-bus feeder; power loss; backward/forward sweep