Energy and Power Engineering, 2013, 5, 1478-1483
doi:10.4236/epe.2013.54B280 Published Online July 2013 (http://www.scirp.org/journal/epe)
Study of Lightning Damage Risk Assessment Method for
Power Gr id
Xiaolan Li1, Jiah on g Chen2, Chun Zhao2, Shanqiang Gu2
1China Electric Power Research Institute, Wuhan 430074, China
2State Grid Electric Power Research Institute, Wuhan 430074, China
Received 2013
ABSTRACT
Based on the idea of risk evaluation, the existing lightning damage risk assessment methods are reviewed and summa-
rized in this paper. And the power grid lightning damage risk assessment system is established on the basis of lightning
flashover risk evaluation methodology for transmission lines, and adopts the improved Analytic Hierarchy Process as
the core algorithm. It can comprehensively evaluate the risk for transmission lines of regional grid, various sections of a
line and each tower of the section, considering much more impact factors, including the running time of line,
importance of grades, equipment damage, and the success rate of lightning stroke reclosing and so on. According to the
calculation results of the risk assessment of the analytic hierarchy process and lightning flashover risk evaluation, the
principles and methods of grade classification for power grid lightning damage risk map are studied, and give typical
examples in the paper. It can describe the lightn ing withstand ing ability much more scientifically and prov ide important
references for the manage department of power system.
Keywords: Power Grid; Lightning Damage Risk Assessment; Analytic Hierarchy Process; Lightning Stroke Trip-out
Rate; Power Supply Reliability; Transmission Line
1. Introduction
For the increasingly huge power system day by day, each
lightning trip out of transmission line make the power
grid a strong perturbation, and may also cause damage to
the insulators an d other equipments. The imp ulse voltage
wave formed after the lightning flash, and operation over-
voltage of reclosing can pose a serious threat to the sys-
tem equipment components, which transmit into trans-
former substation along the line [1, 2]. Lightning damage
risk assessment of power grid is a quantitative assessment
of influence and damage possibility for the lightning
stroke to the power grid [3]. In terms of high-voltage grid,
lightning damage risk assessment should pay much more
attention to the transmission line [4-6]. The lightning
damage risk assessment can be divided into 3 following
respects in accordance with the scope of the assessment.
Lightning stroke risk assessment of every transmission
line in regional power grid, of every transmission line
section in the whole line, of each tower in a transmission
line section, can d etermine which line, which section and
which tower has the higher risk and need to pay special
attention in the operation.
Grid lightning damage risk assessment results reflect
the relative lightning damage risk strength and degree of
the objects, and have relativities. Lightning damage risk
assessment results of transmission lines can offer impor-
tant reference basis for the management department in
lightnin g protecti on Operation and m a i nt e nance.
2. Existing Lightning Damage Risk
Assessment Research of Power Grid
Currently, the grid lightning damage risk assessment
methods are of three kinds:
a) Calculation of lightning trip-out rate;
b) Power grid lightning hazard distribution map;
c) Tran smission lines lightning flashover risk assessment
technology.
2.1. Calculation of Lightning Trip-out Rate
The calculation of lightning trip-out rate is a traditional
calculation method for the transmission lin e lightning trip
out times. Ligh tning trip -out rate is a simula ted calcula tion
result according to the ligh tning activities, co n crete tower
geometric size, insulation arrangement, and the topography
features, and the results can accurately reflect the lightn-
ing withstanding ability of the tower. The lightning trip-
out rate of a transmission line or a section line is the
average result and reflect the average lightning withstand
level of a transmission line or a section line.

X. L. LI ET AL. 1479
2.2. Power Grid Lightning Hazard Distribution
Map
Power grid lightning hazard distribution map is a graph
characterization of grid lightning damage distribution
characteristics, based on the long-term detection data of
lightning location system, to determine the lightning
dangerous current range according to the insulation level
of power system. And the cloud-to-ground flash density
of dangerous current can be statistic by the grid method.
Power grid lightning hazard distribution map first describe
the lightning hazard risk distribution characteristics in
graphically intuitive reaction. However, the values of
dangerous lightning current range in this technology are
concluded from the calculation results of the typical
tower, so it can’t fully consider the differences of the
configuration, insulation and topography characteristics
of each tower in the line, and the result presents the
macroscopic characteristics.
2.3. Transmission Lines Lightning Flashover
Risk Assessment Technology
Transmission lines lightning flashover risk assessment
technology based on differentiation lightning protection
technology considers the differences of lightning
activities, the transmission line structure, topography
characteristics, calculates the lightning trip-out rate of
each tower by the lightning protection calculation. The
lightning stroke flashover risk of each tower can be
divided into four grades of A, B, C, D according to the
evaluation criteria. This technology can describe the base
tower lightning level of risk and characteristics more
accurately. The lightning stroke flashover risk grades of
line segments and the whole line are calculated by the
average lightning trip-out rate. For multiple lines of
lightning damage risk assessment, only the lightning
trip-out rate as the evaluation index, also can’t
comprehensively and scientifically quantify impact and
the loss of lightning stroke to the power grid, due to the
differences of the various lines nature.
2.4. Analysis of Existing Research
From the analysis above, the lightning trip-out rate is a
very important indicator of the lightning stroke flashover
risk evaluation, Power grid lightning hazard distribution
map can reflect the macro mine disaster risk distribution
characteristics of the regional grid, and the transmission
lines lightning flashover risk assessment technology
evaluate the lightning damage risk level and features of
each tower accurately.
For the regional grid transmission lines, as well as
many other complex factors impact lightning risk,
include the running time of the line, the reliability, the
importance level, the loss of lightning stroke to the line,
and so on. These factors are not carefully considered in
the studies above. In the lightning damage risk assess-
ment of each line segment, the average lightning trip-out
rate value used to assess the lightning stroke flashover
risk grade is an average of quantitative assessment
method, and also need to explore a more method that can
accurately reflect the strength of the degree of risk of
lightni ng damag e assessm en t .
In the lightning stoke flashover evaluation of each
tower in a transmission line, the characteristics in terms
of run time, reliability, and importance level are
consistent. The transmission lines lightning flashover risk
assessment technology can get the accurate lightning
trip-out rate of each tower. Using this technology to
assess the grade of each base tower in a line is scientific
and rational.
3. Research on Technology of Lightning
Disaster Risk Assessment for Power
System
3.1. The Analytic Hierarchy Process
Analytic Hierarchy Process (Analytic Hierarchy Process,
AHP) is a decision-making method proposed in the
1970s. It is an effective way that can transmit a semi-
qualitative, semi-quantitative problem into quantitative
which posed of many factors interrelated, mutual
restraint complicated and often a lack of quantitative data.
It makes the variety of factors hierarchical, drills more
kinds of associated factors, and provides a quantitative
basis for the development of the analysis and prediction.
First of all, the problems should be organized, and a
hierarchical structure model can be formed in the
application of AHP. In this model, the complex problem
is decomposed into the parts of elements. These elements
form into a number of levels according to their attributes
and relationships. The element on a hierarchy is regarded
as the predominant criterion to the relevant elements of
the next level.
These levels can be divided into three categories:
 The highest layer: this layer has only one element. It
is generally the target or desired result of the analysis,
and is also known as the target layer.
 The middle layer: this layer contains intermediate
links to achieve the goal, it may be composed of several
levels, including the criteria and sub-criteria need to be
considered. Therefore, it is also known as the criterion
layer.
 The lowest layer: this layer includes a variety of
measures and decision-making solutions to realize the
goals, and also called the measure layer or the program
layer.
AHP in decision-making has a wide range of
applications, mainly used to determine the comprehensive

X. L. LI ET AL.
1480
evaluation of the weight coefficient. Matrix operations
are the main mathematical tools in AHP.
In the process of repeatedly checking and practice of
AHP, scientists also proposed an improved the analytic
hierarchy process, taking advantage of the optimal
transmission matrix, naturally meeting the conformance
requirements, reducing the human subjective evaluation
results, and the evaluation results are more reasonable
and scientific. Currently, this method has been widely
used in the risk assessment.
The improved Analytic Hierarchy Process is used to
be the core algorithm to assess the risk of lightning
damage on the power grid in this paper.
3.2. Lightning Damage Risk Assessment of
Transmission Lines in the Regional
Power Grid
For a regional power grid transmission lines, following
three cases are considered in the lightning damage risk
assessment:
 Successful reclosing after the lightning trip out of
transmission line.
 Unsuccessful reclosing after the lightning trip out of
transmission line, successful forced energization.
 Forced en er g i zatio n and reclosing bo th unsuccessfu l
after the lightning trip out of transmission line.
In the first case, three factors of the running time of
transmission line, importance of grades and equipment
damage need to be considered three factors; in the case
of two and three, the power su pply reliability should also
be cons idered.
After considering these factors, the improved analytic
hierarchy process is used to the matrix analysis calculation,
and the relative risk of lightning damage values are
received, the higher the risk value, the higher the risk of
the section line.
In the risk assessment of lightning damage on the
power grid used the improved analytic hierarchy process,
the target layer is to assess the risk of lightning damage,
and get the risk value of lightning damage; the criterion
layer is to assess the factors considered in lightning
damage assessment, including power supply reliability,
running time, importance level and equipment damages;
the program layer is the objects of lightning damage risk
assessment, that is the transmission line.
The assessment model is shown in Figure 1 below. By
the improved analytic hierarchy process matrix operations,
considered the concrete characteristics of transmission
lines, the lightning damage risk assessment values can be
obtained.
Compared with lightning trip-out rate, lightning damage
risk assessment results through the improved analytic
hierarchy process are considered much more comprehensive
and scientific. For management decision-making depart-
ment, this appro ach also provides a quantitati ve b asis and
conditions for decision-making.
AHP applied in the power grid lightning damage risk
assessment is the first of its kind, and there is no
reference currently. The study in this paper is a kind of
tentative exploration based the research on the lighting
stroke flashover risk assessment of transmission lines.
And the analytical results have a strong dependence due
to the accumulation of operating experience data. The
longer operating experience data accumulation time,
evaluating the results obtained will be more accurate.
Therefore, this approach still has to be continually
refined and improved for the support of management,
operation and maintenance depart ments.
3.3. Lightning Damage Risk Assessment of the
Sections in a Transmission Line
For the sections lightning damage risk assessment in a
transmission line, the improved AHP is also adopted to
the analytical calculation of risk evaluation, in order to
change the situation of using the average lightning trip-
out rate to evaluate the risk.
Figure 1. Lightning damage risk assessment of power grid in AHP.

X. L. LI ET AL. 1481
In the section assessment, the calculation is based on
the results of lightning stroke risk level of lightning
flashover risk evaluation method for transmission line,
such as the level of A, B, C, D. To statistic the
percentage of tower numbers of each level in a section
occupied the section tower numbers. Then the proportion
of A, B, C, and D will be obtained. Considering the
different coefficient of various grades to the lightning
damage risk assessment, the improved AHP will be used
to get the lightning damage risk assessment values of
each section, as shown in the Figure 2.
3.4. Lightning Damage Risk Assessment of Each
Tower in a Transmission Line
For the relative lightning flashover risk of each tower in
transmission line, the impact factors mainly include the
existing differences of lightning activities, topography,
structures and so on. Figure 3 describes the process of
lightning flashover risk Evaluation method of transmission
lines. And the lightning risk grade results by the lightning
flashover evaluation method of transmission lines can
represent the relative lightning disaster risk of each
tower.
4. Establishment of Grid Lightning Damage
Risk Assessment System
Based on the lightning flashover risk assessment of
transmission lines, the improved AHP is taken as the
core algorithm method, and the relative lightning damage
risk assessment of the lines in regional grid, the sections
of a line, and the towers of a section is researched
in-depth in this pap er, as shown in the Figure 4. The gr id
lightning damage risk assessment system from the grid to
the transmission line to the line segment to specific base
tower is established. And this establishment provides
more intuitive, convenient decisions for the management
decision-making department. According to the assess-
ment results, they can decide which line; segment and
tower should be paid more attention in the lightning pro-
tection operation and mainten a nce.
Figure 2. Lightning damage risk assessment method of line sections in AHP.
Lightning detection
data of lightning
location sy s t em
Geographical
information of the
line
Statistics of lightning
parameters for the
line
Appointing the
statistical time period
Comput ati o n of
lightning flashover
rate of each tower
and the whole line
Detailed data of each
tower inc l u d i n g
configuration,
insulation, terrain, etc.
Evaluation Risk grade
reference
Lightning flashove r
risk grade of each
tower and the whole
line
Figure 3. Process of lightning flashover risk Evaluation method of transmission lines.

X. L. LI ET AL.
1482
5. Power Grid Lightning Damage Risk Map
Draw
The power grid lightning damage risk map in this paper
based on the AHP method is different with that based on
the lightning parameters statistics.
The power grid lightning damage risk map based on
the lightning parameters statistics is concluded by the
lightning detection data of lightning location system,
considering the cloud to ground flash density distribution
of lightning current of the back flashover and shielding
failure lightning withstanding level, and it reflects a ma-
cro characteristics of lightning damage risk in the re-
gional power grid.
The power grid lightning damage risk map based on
the analytic hierarchy process results is divide into risk
distribution maps of the regional grid lines, sections of a
line, and towers of a section.
The lightning damage risk map of the regional grid
lines is ranked in descending order according to the
calculation values, and used different colors to represent
different risk level of lightning damage, as shown in
Figure 5.
The lightning damage risk map of line sections also
uses different colors to represent the lightning with
standing ability of each section, according to the section
risk assessment values. Compared with the cloud to
ground flash density distribution map, the lightning
damage risk of section is caused b y lightning activ ities or
any other factors (topogr aphy, tower structure and so on)
can be clearly distinguished. And it has higher degree of
agreement with the existing lightning fault records, as
shown in Figure 6.
Figure 4. Process of the grid lightning damage risk assess-
ment system.
Figure 5. Lightning damage risk map of regional grid lines.
The lightning damage risk map of the towers is drawn
by the calculation results of lighting trip-out rate, and the
dot-line figure can describe the relative strength of
lightning damage risk in these towers, as shown in the
Figure 7.
6. Conclusions
1) According to the risk assessment concepts and
theories, the existing lightning damage risk assessment
methods are reviewed and summarized.
(a) Lightning damage risk distribution of s e c tions
(b) Cloud to ground flash density distr ibution of sections
Figure 6. Lightning damage risk map and cloud to ground
flash density distribution of line sections.
050100 150 200 250300 350
0.0
0.4
0.8
1.2
1.6
Shielding failure flashover rate/(1/100km.year)
Tower Number
Grade D
Grade C
Grade B
Grade A
Figure 7. Lightning damage risk map of the towers in a line.

X. L. LI ET AL. 1483
2) Adopting the improved Analytic Hierarchy Process
as the core algorithm, the power grid lightning damage
risk assessment system is established on the basis of
lightning flashover risk evaluation methodology for
transmission lines. It realized the assessment for
transmission lines of regional grid, various sections of a
line and each tower of the section.
3) Based on the calculation results of the risk
assessment of the analytic hierarchy process and
lightning flashover risk evaluation, the principles and
methods of grade classification for power grid lightning
damage risk map are studied, and give typical examples
in the paper. It can describe the lightning withstanding
ability much more scientifically.
7. Acknowledgements
This work w as su pported by Eleventh-Five Year Science
and Technology Program of State Grid Corporation of
China under Grant SG0881. And the research process
was completed in lightning protection technology
research division of Wuhan NARI limited company of
State Grid Electric Power Research Institute.
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