Alexandre Piantini

University of São Paulo piantini@iee.usp.br

Lightning-Induced Voltages on Overhead Power Distribution Lines

April 6rh – 8th, 2016 Cartagena de Indias,

Colombia

OUTLINE

Introduction Validation of Coupling Models Characteristics of Lightning-Induced Voltages Protective Measures (shield wires, arresters) Priority Issues in Lightning Research Final Remarks

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

INTRODUCTION - INDIRECT STROKES

Courtesy: Prof. S. Yokoyama Magnitudes << than those of the surges related to direct strokes, but the

phenomenon is much more frequent à greater no. flashovers (≤ 15 kV).

I = 54 kA; tf = 3.2 µs; b = 0.11; hc = 600 m; h = 10 m; Rg = 200 Ω; ρ = 0 Ωm All parameters referred to the FS system

x

450 m 450 m

70 m

VALIDATION OF COUPLING MODELS

Surge arresters

450 m

(ERM)

Scale model (USP)

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.

Extended Rusck Model – ERM

SCALE MODEL

Measurement: USP (Scale Model)

I = 70 kA

Top view (urban line)

tf = 2 µs

All parameters referred to the FS system

VALIDATION OF COUPLING MODELS

Calculation: LIOV-EMTP (Nucci et al.)

model

Agrawal et al. (1980) and its equivalent formulations - Rachidi (1993) and

Taylor et al. (1965)

-  Magnitude, front time, and propagation velocity of the stroke current

-  Distance between line and 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

CHARACTERISTICS OF LIVs

Shorter durations in comparison with the overvoltages caused by direct strokes.

Top view (urban line), d = 20m, hb = 5 m Top view (urban line), d = 20m, hb = 15 m

SCALE MODEL

Measurement: USP (Scale Model)

I = 50 kA

tf = 2 µs

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 = 50 kA; tf = 3 µs; b = 0.3; ρ = 1000 Ω.m

hg = 11 m

10 m

Rg

300 m 300 m 300 m

50 m

SHIELD WIRE – ground resistance

ERM

x

I = 50 kA; tf = 3 µs; b = 0.3; ρ = 1000 Ω.m

hg = 11 m

10 m

Rg

300 m 300 m 300 m

50 m

SHIELD WIRE – ground resistance

x

d = 61 m

Mast

SURGE ARRESTERS

USP

Measured Induced Voltages

x

1:50 scale model

SURGE ARRESTERS - spacing

I = 38 kA; tf = 3.2 µs; b = 0.11; hc = 600 m; h = 10 m; gapless S.A.; ρ = 0 Ωm; Rg = 50 Ω

x

I = 38 kA

70 m

300 m

162 kV

67 kV

125 kV

600 m

x

Despite the existence of reliable models for the analysis of lightning transients, the application of such models for assessing the probability that a particular event detected by a LLS could lead to a power outage is still a challenging issue. LIVs depend on many parameters and are particularly affected by the stroke location and current magnitude and waveshape. It is essential to continue efforts to develop more reliable power equip. models, improve the performance of LLS and ↓ the uncertainties in the estimation of the stroke location and current parameters.

PRIORITY ISSUES IN LIGHTNING RESEARCH

Measurements of lightning current parameters (FS and SS) in different locations; ↑ accuracy in the estimation of lightning locations and current parameters from remote EM field meas.; models for positive lightning flashes; better characterization of lightning transients; more accurate models to represent the behavior of power equipment subject to lightning surges.

PRIORITY RESEARCH TOPICS

LIV on overhead lines depend on many parameters, which may combine in an infinite variety of ways;

validity of models, characs. of LIV and their dependence on important parameters involved in the ind. mechanism;

examples illustrating the mitigating effects of a multi-grounded shield wire and line arresters;

analyses involved simulations using a reliable model and both reduced and full-scale experiments;

priority issues in lightning research.

FINAL REMARKS

MUCHAS GRACIAS POR SU ATENCIÓN!

April 6rh – 8th, 2016 Cartagena de Indias,

Colombia