HV HV/MV G G G MV/LV MV Grid +10% G LV Grid Asym +10% 253.0 V 248.4 V 243.8 V 239.2 V 234.6 V 230.0 V 225.4 V 220.8 V 216.2 V 211.6 V 207.0 V 3% U -10% m -10% HV/MV HV G MV-Regulation Transformer G 5% of Intervals/Week -15% (a) G MV/LV ∑ +10% U 3% 4% 4% 6% As ym -10% -15% (b) HV/MV G G ∑ ym 3% As 6% As 8% -10% HV LV-Regulation Transformer +10% Asym 3% 6% Asy G MV/LV 3% LV DG 2% MV DG 2% HV/MV 5% MV Voltage Drop at Lines 2% MV/LV Transformer 6% LV Voltage Drop at Lines ym 253.0 V 3% LV DG 12% 248.4 V 2% MV DG 243.8 V 9% 2% HV/MV 239.2 V 234.6 V 5% MV Voltage 230.0 V Drop at Lines 225.4 V 2% MV/LV Transformer 220.8 V 9% 15% 216.2 V 6% LV Voltage 211.6 V Drop at Lines 207.0 V 5% of Intervals/Week DG with Curtailment and VVC G G Flexible Loads +10% +10% m Asy U -10% -10% -15% Asy m 5% of Intervals/Week 253.0 V 3% LV DG 248.4 V 243.8 V 2% MV DG 2% HV/MV 239.2 V 234.6 V 5% MV Voltage 230.0 V Drop at Lines 225.4 V 2% MV/LV Transformer 220.8 V 216.2 V 6% LV Voltage 211.6 V Drop at Lines 207.0 V (c) figure 5. Voltage regulation bands with (a) only OLTC at the primary substation, (b) MV and LV inline autotransformers, and (c) using flexibility from generators (red and blue) and consumers (clear green). Color bands: yellow and brown indicate raising margins in LV and MV lines, respectively; dark green and blue indicate voltage drops in LV and MV lines, respectively; margins at the substations are indicated in white. The asymmetry of loads among phases (asym) requires the preservation of part of the voltage band. may/june 2017 ieee power & energy magazine 35