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Abstract—Lightning surges represent, as a rule, a major cause

of momentary and sustained outages on overhead power lines.

They may result from direct hits or induction by nearby strokes.

Although the magnitudes of the transients associated with direct

strokes are usually much higher than those induced by nearby

strokes, the latter are much more frequent and of more concern to

overhead distribution systems with rated voltage 15 kV and less.

In this paper, discussions are provided on the basic characteristics

of the lightning-induced voltages, their dependence on various

parameters involved in the induction mechanism, and the

effectiveness of the main protective measures. Some priority

issues in lightning research are also indicated.

Index Terms— electromagnetic induction, lightning, lightning-

induced voltages, overvoltage protection, power distribution lines.

I. INTRODUCTION

IGHTNING transients have usually an important impact

on the power quality of distribution systems. The

understanding of the characteristics of the overvoltages

induced by nearby strokes and their dependence on the several

parameters involved in the induction mechanism is essential

for the decision-making process about the most suitable

protection measure that could be adopted for a particular

power distribution network.

In the next sections the subject of lightning-induced

overvoltages on overhead power distribution lines is discussed

considering the following aspects: coupling models, voltage

characteristics and their dependence on various parameters,

and effectivenesses of the main protective measures. Finally,

some priority issues in lightning research are indicated.

II. VALIDATION OF COUPLING MODELS

Various coupling models have been proposed for the

analysis of the response of transmission lines excited by

external electromagnetic fields, as e.g. the Agrawal et al. [1]

and the Rusck [2] ones. As demonstrated by Cooray [3] and

Michishita and Ishii [4], for the case of an electromagnetic

field radiated by a lightning channel perpendicular to the

ground plane, these models are equivalent and lead to identical

results. Since the validity of any model should be verified,

Manuscript received March 2, 2016.

A. Piantini is with the Institute of Energy and Environment, University of

São Paulo, São Paulo, Brazil (phone: + 55 11 3091-2580; email:

piantini@iee.usp.br).

whenever possible, by means of comparisons with reliable

experimental results, a scale model system was developed and

implemented with this purpose [5]-[8]. This unique facility

enabled tests to be performed under controlled conditions; data

obtained from the simulation of a wide variety of situations

were used to confirm the validity of the Agrawal et al. model

[1] and the Extended Rusck Model (ERM) [8], [9], as well as

for the analysis of the lightning electromagnetic pulse response

of complex electric power networks [6], [10], [11].

For illustration, comparisons between measured and

calculated induced voltage waveforms on a three-phase line

with either a shield wire 1 m below the phase conductors

(h = 10 m; hg = 9 m) and grounded every 450 m (ground

resistance Rg equal to zero) or surge arresters installed on all

phases every 450 m (Rg = 200 Ω) are presented in Fig. 1. The

detailed simulation conditions can be found in [8].

(a)

(b)

Fig. 1. Measured (scale model) and calculated (ERM) phase-to-ground

induced voltages at the point closest to the stroke location on a line with a

shield wire or surge arresters. Perfectly conducting ground. (Voltage and time

scales referred to the full-scale system.) Simulation details can be found in

[8]. a) line with a shield wire b) line with surge arresters

Lightning-Induced Voltages on Overhead Power

Distribution Lines

Alexandre Piantini, Senior Member, IEEE

L

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As mentioned in [8], the ERM is an extension of the Rusck

model in the sense that it allows to take into account situations

of practical interest such as the case of a line with various

sections of different directions, the presences of a multi-

grounded neutral or shield wire, and equipment such as

insulators, transformers, and surge arresters. The incidence of

lightning flashes to nearby elevated objects and the occurrence

of upward leaders can also be considered, as well as the effect

of the soil parameters. All the calculation results presented in

the next sections were obtained using the ERM.

III. CHARACTERISTICS OF LIGHTNING-INDUCED VOLTAGES

The induced voltage magnitudes and waveshapes depend on

many lightning parameters and are substantially affected by the

soil characteristics, the relative position of the line and the

stroke location, the observation point, and the network

configuration.

Despite their large variations, lightning-induced voltages are

characterized by shorter durations in comparison with

overvoltages associated with direct strokes. Examples of

measured induced voltages on two parallel 2.7 km long non-

energized conductors – one with and the other without surge

arresters - can be found in [12]. The conductors are distant 6 m

from each other and their height above ground is about 10 m.

Fig. 2 shows the voltages induced simultaneously on the

conductors by a lightning flash which hit a tree located 61 m

from the closer one. The distance between the measuring point

and the nearest surge arrester was about 30 m.

Fig. 2. Phase-to-ground voltages induced simultaneously on two conductors

(measuring points in front of each other). Lightning strike point was a tree

61 m far from the conductor with surge arresters. Adapted from [12].

In comparison with a line located in a rural area, an urban

line is characterized not only by a higher density of

transformers and surge arresters but also by many laterals and

the presence of structures and buildings in its vicinity.

Regarding the line configuration, the induced voltages are

affected not only by the presence of the laterals but also by the

conditions of their terminations. If the laterals are long,

matched or ended by surge arresters, the induced voltages tend

to decrease. As shown in [11], the shorter the distance between

the observation point and the nearest lateral, the larger the

voltage reduction. On the other hand, if the laterals are

relatively short and terminated by an open circuit, the induced

voltages may increase as the distance between the observation

point and the nearest lateral diminishes [11].

Nearby buildings cause two opposite effects: firstly, they

attract lightning to closer distances in comparison to the case

of a line in open ground and therefore the overvoltages may

reach high magnitudes; secondly, they shield the line and

reduce the lightning electromagnetic field, and this leads to a

reduction on the induced voltages. For a fixed distance

between the line and the stroke location, the higher the

buildings, the lower the voltage magnitudes. For illustration

and considering the test configuration shown in Fig. 3, Fig. 4

compares two phase-to-ground induced voltages measured at

the transformer of the main feeder located 20 m from the

lightning strike point, for buildings' heights of 5 m and 15 m.

The experiments were performed on a scale model [13].

Because of the presence of laterals, shorter distances

between surge arresters, and shorter distances between line and

stroke location, lightning-induced voltages on urban lines tend

to present stronger oscillations in relation to those induced on

lines located in rural areas.

Fig. 3. Top view of the test configuration (scale model) relative to the

presence of buildings in the vicinity of the line. Distance of 20 m between

main feeder and stroke location. Triangles and circles represent transformers

and surge arresters, respectively, while squares and rectangles denote blocks

with buildings 5 m high. "M" corresponds to the measuring point. All

dimensions in meters. Adapted from [13].

Fig. 4. Measured induced voltages on an urban line configuration for

buildings' heights of 5 m (Fig. 3a) and 15 m. Stroke current of 50 kA with

front time of 2 μs. Distance of 20 m between line and stroke location. All

parameters values referred to the full-scale system. Adapted from [13].

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IV. PROTECTION MEASURES

One alternative to reduce the frequency of flashovers

associated with indirect strokes is to increase the critical

flashover overvoltage (CFO) of the line structures. However, a

consequence would be that surges with higher magnitudes

would then travel over long distances, thus increasing the

stresses on line equipment.

Other options involve the use of a shield wire or the

application of surge arresters. An evaluation of the

effectivenesses of these alternatives in mitigating overvoltages

associated with both direct and indirect strokes is done in [14].

The use of a shield wire in conjunction with arresters on every

pole and every phase is effective against direct strokes and

theoretically eliminates flashovers, but in any case a cost-

benefit analysis of the possible solutions should be performed.

In this section the effect of shield wires and surge arresters

in reducing lightning-induced voltages are discussed. In the

simulations, performed using the ERM, the line, with phase

conductors at the height h = 10 m, and the shield wire 1 m

above the middle phase (hg = 11 m), is assumed to be 2 km

long and lossless. The diameter of all the conductors is 1 cm,

and the inductance of the down conductor is 1 μH/m. In [15],

Rachidi et al. demonstrate that when the line length does not

exceed a certain critical value (typically 2 km), the surge

propagation along it is not appreciably affected by the finite

ground conductivity as long as the conductivity is not lower

than about 0.001 S/m.

A. Use of a Shield Wire

Due to its coupling with the phase conductors, a shield wire

reduces the amplitudes of voltages induced from external

electromagnetic fields regardless of its position with respect to

the phase conductors. However, the greater the coupling, the

more significant the voltage reduction.

Besides its height, the effectiveness of a shield wire depends

on the combination of several parameters such as the

grounding spacing (xg), the ground resistance (Rg), the soil

resistivity (ρ), the stroke current front time (tf), and the relative

position of the stroke channel with respect to the grounding

points. An analysis of the influence of these parameters, based

on computer simulations and test results obtained from scale

model experiments, was carried out in [16] considering typical

configurations of a rural distribution line and perfectly

conducting soil. In [17] the analysis has been extended to the

case of a finite ground conductivity.

In order to illustrate the effect of the shield wire, Fig. 5

presents phase-to-ground and phase-to-shield wire induced

voltages corresponding to different values of the ground

resistance. In the calculations, the stroke current was assumed

to have a triangular waveshape with amplitude I = 50 kA,

tf = 3 μs, time to half-value of 50 μs, and propagation velocity

(vf) equal to 30 % of that of light in free space (c). As shown in

Fig. 5a, in the absence of the shield wire the magnitude of the

induced voltage would be 500 kV.

It can readily be seen from Fig. 5 that the dependence of the

phase-to-shield wire voltages with the ground resistance is

more significant than that of the phase-to-ground voltages. In

addition, the phase-to-ground voltages increase with Rg, while

the phase-to-shield wire or phase-to-neutral voltages have the

opposite behavior. As shown in [17], the influence of the

ground resistance on both voltages is more pronounced when

the stroke location is in front of a grounding point.

The results presented in Fig. 5 are an indication that a shield

wire can substantially reduce the magnitudes of lightning-

induced voltages between the terminals of power equipment.

(a)

(b)

Fig. 5. Phase-to-ground and phase-to-shield wire lightning-induced voltages

at the point closest to the stroke location for different values of the ground

resistance. Stroke location equidistant from the closest grounding points.

I = 50 kA; tf = 3 μs; vf = 0.3 c; d = 50 m; h = 10 m; hg = 11 m; xg = 300 m;

ρ = 1000 Ωm. a) phase-to-ground b) phase-to-shield wire

B. Application of Surge Arresters

The installation of line arresters on all phases of MV

distribution systems can be effective in reducing the

magnitudes of the lightning-induced voltages provided that the

arresters' spacing is not too large.

An example that illustrates the influence of the distance

between adjacent arresters is depicted in Fig. 6, relevant to

experiments performed on a scale model simulating a 1.4 km

long 15 kV distribution line. The MO surge arrester protective

level was about 34 kV (for an impulse current of 5 kA, 8/20 μs

waveshape). Additional test details are described in [14]. In

Fig. 6, all the quantities are referred to the full-scale system by

applying the corresponding scale factors.

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Fig. 6. Measured induced voltages on lines with and without surge arresters,

at the point closest to the stroke location, for arresters' spacings of 300 m and

600 m. Lightning strike point 70 m from the line and equidistant from two

sets of arresters. I = 38 kA; tf = 3.2 μs; vf = 0.11 c; Rg = 50 Ω.

As shown in [14], the greater the value of the ground

resistance or the stroke current steepness, the smaller the effect

of the surge arresters. Therefore, depending on the line

configuration, surges induced by subsequent strokes may reach

higher magnitudes than those associated with the first one [8].

V. PRIORITY ISSUES IN LIGHTNING RESEARCH

Despite the existence of reliable models for the analysis of

lightning transients, the application of such models for

establishing the probability that a particular lightning event

detected by a location system could lead to a power outage is

still a challenging issue. This is due mainly to the fact that

overvoltages induced by nearby strokes depend on many

parameters and are particularly affected by the stroke location

and current magnitude and waveshape. Although important

progress has been made in the last years, it is essential to

continue efforts to develop more reliable power equipment

models, improve the performance of lightning location systems

(LLS) and diminish the uncertainties in the estimation of the

stroke location and current parameters. Therefore, priority

research topics should include:

- additional measurements of lightning current parameters

(first and subsequent strokes) in different locations;

- improvement of the accuracy in the estimation of lightning

locations and current parameters (peak values and front

times) from remote electromagnetic field measurements;

- development of models for positive lightning flashes;

- better characterization of lightning transients;

- development of more accurate models to represent the

behavior of power equipment subject to lightning surges.

VI. CONCLUSION

Lightning-induced voltages on overhead distribution lines

depend on many parameters, which may combine in an infinite

variety of ways. This paper presented some discussions on the

characteristics of such transients and their dependence on

some important parameters involved in the induction

mechanism. Examples illustrating the mitigation effects of a

multi-grounded shield wire and line arresters were presented.

The analyses involved simulations using a reliable model and

experiments performed on either a full or reduced-scale

system. Some priority issues in lightning research were

indicated.

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