Alexandre Piantini University of São Paulo Lightning Transients in Medium- Voltage Power Distribution Lines V Russian Conference on Lightning Protection 17 th – 19 th May, 2016 Saint Petersburg

OUTLINE INTRODUCTION LIGHTNING OVERVOLTAGES IN MV NETWORKS Direct strokes Indirect strokes INFLUENCE OF VARIOUS PARAMETERS ON THE LIVs LIGHTNING PROTECTION OF MV NETWORKS Shield wire Surge arresters CONCLUSIONS

Lightning: - equipment damages and failures - damages to customer electronic devices - voltage sags - supply interruptions Widespread use + growing dependence on the continuous operation of sensitive electronic equipment  increasing awareness of the importance of mitigating such effects  to evaluate the lightning overvoltages and the effectivenesses of the protective measures INTRODUCTION

5.1 km U = f (I, t f, R g, x g, x, V x t,...) MV range! DIRECT STROKES

INDIRECT STROKES Courtesy: Prof. S. Yokoyama Magnitudes << than those of the surges related to direct strokes, but the phenomenon is much more frequent  greater no. flashovers (≤ 15 kV).

- Magnitude, front time, and propagation velocity of the stroke current - Distance between the line and the lightning strike point - Upward leader / elevated object - Line configuration (horizontal or vertical, rural or urban) - Conductors’ heights, presence of a shield wire or neutral conductor - Observation point - Position of the stroke channel relative to the line - Soil resistivity and ground resistance - Grounding / surge arresters’ spacing - Surge arrester V/I characteristic MAIN PARAMETERS Shorter durations in comparison with the overvoltages caused by direct strokes.

SCALE MODEL Measurement: USP (Scale Model) I = 34 kAI = 50 kA Top view - 1:50 scale model (USP) t f = 2  s Calculation: LIOV-EMTP (Nucci et al.) All parameters referred to the FS system VALIDATION OF COUPLING MODELS (ERM) Agrawal et al. (1980) and its equivalent formulations - Rachidi (1993), Taylor et al. (1965) Extended Rusck Model – ERM (1997) Model of the stroke channel The induction mechanism and the problems related to LIV on distrib. lines have been studied for a long time and various models and codes have been proposed for LIV calculations.

1:50 SCALE MODEL (USP)

1) Measured 2) Chowdhuri 3) Liew-Mar "Stroke Current" INDUCED VOLTAGES (Scale Model) d = 1.4 m 14 m (ERM) Line: single-phase, matched “channel”

INDUCED VOLTAGES (Scale Model) "Stroke Current" d = 1.4 m 14 m (ERM) Voltage (V)

1) t c = 250  s 2) t c = 50  s 3) t c = 25  s (1) (2) (3) t f = 3  s t c = 50  s Stroke current waveshape (t f, t c ) d = 50 m 1.8 km 50 kA 25 kA 0 t f t c  = 500  m  = 0  m

Distance line - stroke location (d) d 1.8 km I = 50 kA t f = 3  s 1 2 t c = 50  s 3 1) d = 20 m 2) d = 50 m 1) d = 20 m 2) d = 50 m 3) d = 200 m  = 0  m  = 500  m

1)  = 1000  m1)  = 1000  m 2)  = 500  m 1)  = 1000  m 2)  = 500  m 3)  = 0  m Soil resistivity (  ) 50 m 1.8 km I = 50 kA tftf 1 2 t c = 50  s 3 t f = 3  s t f = 1  s x = 0

I = 50 kA t f = 3  s t c = 50  s x = 1000 m x = 150 m  = 500  m Soil resistivity (  ) x = 0 m x = 500 m x = 0 m x = 0 x = 250 m x = 500 m x = 1000 m x = 500 mx = 1000 m  = 0  m

Top view (urban line), d = 20 m, h b = 5 m Top view (urban line), d = 20 m, h b = 15 m SCALE MODEL Measurement: USP (Scale Model) I = 50 kA t f = 2  s All parameters referred to the FS system Nearby Buildings

PROTECTIVE MEASURES Increasing CFO Shield wire Surge arresters Direct strokes Indirect strokes X MV lines: measures against short interruptions and voltage sags stemmed from lightning:

I = 36 kA; t f = 3.1  s; b = 0.11; hc = 600 m; h = 10 m; hg = 9 m; Rg = 0  m x 450 m 70 m Shield wire (ERM) 1:50 scale model, USP SHIELD WIRE - INDIRECT STROKES

Shield wire height x I = 24.9 kA; t f = 3.5  s;  = 0 .m h g = 7 m h g = 11 m 10 m R g = 50  450 m 70 m 1:50 scale model, USP

Shield wire – relative position h g = 9 m 10 m x 750 m R g = 0  70 m I = 24.9 kA; t f = 3.5  s;  = 0 .m 1:50 scale model, USP

I = 50 kA; t f = 3  s; b = 0.3;  = 1000 .m h g = 11 m 10 m RgRg 300 m 50 m SHIELD WIRE – ground resistance ERM x

I = 50 kA; t f = 3  s; b = 0.3;  = 1000 .m h g = 11 m 10 m RgRg 300 m 50 m SHIELD WIRE – ground resistance x

1:50 scale model Current through the surge arrester (calculated) 1.4 m (70 m) I = 1.32 A x Measured and calculated voltages 1.4 m (70 m) X t (  s) I (A) m Surge arrester Rg = 0  Reference line mr cr mt ct Rg = 0  Test line (23.8 kA) t (  s) U (kV) SURGE ARRESTERS - INDIRECT STROKES

1:50 scale model Decomposition (ct = U s.a. + U d.c. ) U s.a. U lead R = 0  1.4 m (70 m) I = 2.97 A (53.5 kA) x t (  s) U (kV) Measured and calculated voltages 10 m U s.a. U lead URUR U (kV) t (  s) ct SURGE ARRESTERS - INDIRECT STROKES mt ct I = 1.32 A (23.8 kA) mr cr

I = 54 kA; t f = 3.2  s; b = 0.11; hc = 600 m; h = 10 m; Rg = 200  m All parameters referred to the FS system x 450 m 70 m LINE WITH SURGE ARRESTERS Surge arresters 450 m (ERM) 1:50 scale model, USP Extended Rusck Model – ERM

1:50 scale model I = 38 kA; t f = 3.2  s; b = 0.11; hc = 600 m; h = 10 m; gapless S.A. Surge arresters – ground resistance 162 kV 95 kV 600 m x x I = 38 kA t f = 3.2  s 70 m 31 kV 1:50 scale model, USP

x SURGE ARRESTERS - spacing I = 38 kA; t f = 3.2  s; b = 0.11; hc = 600 m; h = 10 m; gapless S.A.;  = 0  m; Rg = 50  x I = 38 kA 70 m 300 m 162 kV 67 kV 125 kV 600 m

148 m 174 m 75 m 75 m I = 34 kA t f = 2  s s e = 148 m; s d = 174 m s e = s d = 75 m 1:50 scale model SURGE ARRESTERS - spacing

50 m x I = 40 kA; t f = 2  s; t t = 80  s; b = 0.5 h g = 11 m 10 m 50  CURRENT TO GROUND 1000 m IgIg Current (kA)

Overvoltages produced by both direct and indirect strokes  voltage sags, supply interrups. and degradation of the power quality indices; U depend on several parameters related to the return stroke current, soil, and network configuration; Line height, stroke current magnitude and front time, distance line-l.s.p., soil resistivity: significantly affect U; Finite length of the stroke channel, stroke current wavetail: minor influence on U. CONCLUSIONS

DIRECT STROKES: Protecting is difficult because of the high surge currents, steep rates of rise, and large energy content in lightning flashes. To virtually eliminate flashovers: Arresters (on every pole and every phase) + Shield Wire CONCLUSIONS { Arresters  protect the insulation from backflashover Shield Wire  divert most of the current to the ground (arresters are not subject to much energy input)

INDIRECT STROKES: A shield wire may reduce the overvoltages regardless of its position with respect to the phase conductors. Effectiveness decreases with the increase of x g and R g. Line arresters can be effective in reducing the no. of flashovers provided that the arrester spacing is not too large. CONCLUSIONS

Благодарим за внимание! THANK YOU FOR YOUR ATTENTION! V Russian Conference on Lightning Protection 17 th – 19 th May, 2016 Saint Petersburg