Proceedings of Undergraduate Research 2018, Bangi, Selangor, Malaysia, 2018

OPTIMAL DIMENSIONING OF CORONA RING IN HIGH VOLTAGE

INSULATOR STRING

DIMENSI OPTIMUM CINCIN KORONA DALAM RENTETAN PENEBAT VOLTAN TINGGI

Siti Saffiza Bahrol*, Syahirah Abdul Halim

Faculty of Engineering & Built Environment, National University of Malaysia

ABSTRACT

Every conductor used in high voltage electric transmission network is exposed and protected by the surrounding
air causes the conductivity of the electric current through the conductor to not occur perfectly. However, using
only insulation will also causes problems where corona discharges occurs due to air ionization (or any other
liquid) surrounding the electrical conductor, as a result of a strong electric field. Due to the high intensity of
electric field cause by corona discharges at an energized end at insulator string, it may cause a complete failure
for it to well-functioning. The main aim of this project is to design an optimal dimension of corona ring to
reduce electric field distribution at high voltage insulator string surface during normal operating condition.
Designing a corona ring with an insulator string is to reduce the effect of corona discharges as well as intensity
of electric field stress at the energized end at insulator string. The electric field analysis was done using
COMSOL Multiphysics, a finite element based software used to design the insulator string with corona ring
model by using Finite Element Method and MATLAB, a proprietary programming language software using its
implementation of algorithms program to determine the optimal configuration of the corona ring by using
Particle Swarm Optimization Method.

Keywords: Corona Discharge; High Voltage Insulator String; Corona Ring; Finite Element Method; Particle
Swarm Optimization Method

ABSTRAK

Setiap konduktor yang digunakan dalam rangkaian penghantaran elektrik voltan tinggi terdedah dan dilindungi
oleh udara di sekeliling menyebabkan kekonduksian arus elektrik melalui konduktor tidak berlaku dengan
sempurna. Walau bagaimanapun, hanya menggunakan penebat juga akan menyebabkan masalah di mana
nyahcas korona berlaku disebabkan pengionan udara (atau cecair lain) yang mengelilingi konduktor elektrik,
hasil daripada medan elektrik yang kuat. Disebabkan oleh tekanan intensiti yang tinggi dari medan elektrik
yang disebabkan oleh nyahcas korona pada konduktor elektrik pada hujung penebat, ia boleh menyebabkan
kegagalan penebat untuk berfungsi dengan baik. Tujuan utama projek ini adalah untuk merekabentuk dimensi
optimum cincin korona untuk mengurangkan pengagihan medan elektrik pada permukaan penebat voltan tinggi
semasa keadaan operasi biasa. Merekabentuk cincin korona dengan penebat adalah untuk mengurangkan kesan
nyahcas korona serta tekanan intensiti medan elektrik pada konduktor elektrik pada hujung penebat. Analisis
medan elektrik dilakukan menggunakan COMSOL Multiphysics, sebuah perisian berasaskan elemen terhingga
yang digunakan untuk merekabentuk model penebat voltan tinggi dengan cincin korona dengan menggunakan
Analisis Unsur Terhingga dan MATLAB, perisian bahasa pengaturcaraan proprietari menggunakan
pelaksanaan program algoritma untuk menentukan konfigurasi optimum cincin korona dengan menggunakan
Teknik Pengoptimuman Kerumusan Zarah.

Kata kunci: Nyahcas Corona; Penebat Voltan Tingg; Cincin Corona; Analisis Unsur Terhingga; Pengoptimum
Kerumusan Zarah

INTRODUCTION needs electricity to produce effective electricity

production. The supply of electricity needs to be
Electric is an important requirements for peoples to through three stages namely the generation of
use electrical and electronic in this modern days. electricity at power stations, transmission and
Life and daily activities are not smooth when there distribution of electricity to consumers. The
is a power supply system failure. The existence of generation of electricity at the power station will be
electrical energy has a high impact on human increased by voltage before being sent to the main
facilities in daily activities. The industrial sector entrance substation at the specified destination and

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Proceedings of Undergraduate Research 2018, Bangi, Selangor, Malaysia, 2018

through the electricity transmission stage. due to the insulation material used and the resulting
Subsequently, the electricity delivered will be capacitance are not uniform causes the electrical
distributed to consumers during the electricity field magnitude on the insulation units near the end
distribution stage. These three stages are important of the insulation will increase (A. Rahimnejad &
in supplying electricity to consumers. If one of the M. Mirzaie, 2012).
stages failed or damaged, the electric supply fails to To reduce the magnitude of the electric
deliver to the consumers. field and improve the performance of high voltage
This study is related to the second stage in insulation strings by reducing the corona discharge,
supplying electricity which is the transmission of the corona ring is designed (B. M'hamdi et al.
electricity to consumers. In the transmission stage 2015). Therefore, the optimum corona ring design
of electricity, there are some main components is proposed to reduce the electric field magnitude
required during transmission of electrical energy on high voltage insulation. This also helps side
and each component has its own functionality to effects due to corona discharges that occur on the
prevent the occurrence of electricity transmission insulation thus helping to reduce the potential for
failure to consumers. Insulation is one of the major transmission failure of electricity to consumers. In
components required in high voltage electric power addition, to produce optimum corona ring design
transmission networks and also plays an important requires a high cost when conducting research and
role as the insulation path between live conductors testing if using a real prototype. Thus, computer
from electrical transmission and distribution equipped with relevant software is used to perform
towers. This high-voltage insulator helps separate the operating ability, simulation and corona ring
life conductors from one another and from utility performance in the early stages before proceeding
poles (Ammar al-Ghelani, 2016). Due to the flow with the actual prototype construction reduces the
of conductors exposed and resulting in flashover on cost of doing research and testing.
the surface of the insulation occurs, especially
when in wet or damp conditions, transmission of METHODOLOGY
electricity to consumers will fail and interfere with
the daily activities of the user. After collecting all relevant information / theories,
There are three main types of insulating the design for high voltage insulation and optimal
materials used in high voltage electric transmission corona ring can be built. The design of high voltage
systems i.e. glass, porcelain or polymer composite. insulator string and corona ring is built using
Electrical Utility has changed the polymer COMSOL Multiphysics and optimized by
composite material for some types of insulation MATLAB computer software by using the Finite
such as insulation center rods made of overhead Element Analysis and Particle Formula Optimizer
fiber plastic and outdoor weather shields made of alternately. The effects of high voltage insulation
silicon rubber as will be used in this study. Silicone geometry and corona rings on the electric field
rubber insulator or also knows as composite distribution will be studied and compared to reach
insulator having many advantages such as good the objective of designing corona rings with
performance when pollution occurs around it due to optimum dimensions to maximize the reduction
its hydrophobic composite properties. Besides that, electric field magnitude.
silicone rubber insulator is also lightweight, has
Modeling of insulator string using FEM
low installation costs, easy to operate and requires
little maintenance to ensure the insulator is in a
good condition (Hackam R. 1999). The two-dimensional (2D) axial symmetry model
However, every conductor used in high geometry of 230kV Silicone Rubber insulator
voltage electric transmission network is exposed string with corona ring (FIGURE 1) was designed
and protected by the surrounding air causes the by FEM software using electrostatic as an interface
conductivity of the electric current through the of the AC/DC module available in the software to
conductor to not occur perfectly. Using only solve the model. As stated by A. Rahimnejad and
insulation will also occur problems where corona M. Mirzae (2012), this FEM is the primary
discharges (light on conductors when high voltage) numerical calculation technique for calculating and
which occurs due to air ionization (or any other optimizing insulation performance under the
liquid) surrounding the electrical conductor, as a electromagnetic field. Due to these statements, this
result of a strong electric field (Suat İlhan & technique is to be used to design high voltage
Aydoğan Özdemir. 2011). Corona discharges
insulator string and corona rings in this study to
occurs producing sizzling noise, visual violet light,
achieve the main objective of reducing the electric
surrounding ozone gas conductor, radio frequency
interference, electrical energy loss and increasing field distribution over insulator string surface. The
electrical field magnitudes and failing power designed height of insulator string model is
supply transmission. The electrical field magnitude 2405mm with surrounding air around the insulator
and the voltage distributed over the insulation strap string was also drawn spherical around model to

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Proceedings of Undergraduate Research 2018, Bangi, Selangor, Malaysia, 2018

observe electric field distribution on the surface of height of corona ring which is the position of
the insulator’s sheds. corona ring from the center and from the bottom
The uniformity degree of voltage end of FRP rod respectively. However, the
distribution depends on insulator sheds capacitance, optimized value of these dimensions must reduce
the number of sheds which designed in this model the electric field distribution along the insulator
were 69 sheds overall consists of 35 outer sheds axis, which is located at the tip of first shed near to
and 34 inner sheds and corona ring dimensions (E. high voltage electrode of insulator string which is
Akbari & M. Mirzaie, 2012). Each domain was categorized as critical on insulator string. To avoid
assigned with its material properties and each any surface discharge, the maximum electric field
boundary in geometry was applied to relevant distribution on silicone rubber surface must be
interface conditions. At upper part of insulator equal or less than the breakdown strength of
string, the ground boundary condition was applied silicone rubber around 30.00kV/mm to
with zero electric potential while at the bottom part 40.00kV/mm and the maximum electric field
of insulator string was applied as a terminal source distribution on air domain must be equal or less
of 230kV electric potential. Also, the boundaries of than breakdown strength of air, 3.00kV/mm. Table
corona ring were applied as 230kV electric 2 below shows the different dimensions (in
potential and the remaining boundaries of geometry boundary range) of corona ring which was
were set as continuity. optimized to achieve the optimal dimensions of
According to B. M’hamdi et al. (2015), corona ring. To avoid impractical corona ring
there are no specific standards for the design and position in applications, the boundary ranges in this
position of corona ring. The designs were different study are chosen for the feasibility region of corona
from each manufacturer because they make their ring is;
own recommendations for the use of corona rings.
The optimization dimensions are the radius and

3
4 1

5
2

FIGURE 1. 2D asymmetry of Silicone Rubber insulator string with corona ring (circle) model

TABLE 1. Material properties of insulator string components

Relative permittivity,
Domain Components Material Conductivity, σ (Sm-1)
εr
1 Corona ring
High voltage Aluminum 1 3.774x104
2
electrode
Sheds of insulator
3 Silicone rubber 4.3 1x10-18
string
Fiberglass
4 Insulator rod 7.2 1x10-18
Reinforced Plastics
5 - Air 1 0

TABLE 2. Initial dimensions of Corona Ring and range of boundary dimensions to optimization
Dimensions Radius(mm) Height(mm)
Initial value 185.00 131.15
Lower boundary 155.00 101.15
Upper boundary 205.00 151.15

Optimization dimensions using PSO that has been reached is known as Pbest,
(Local/Particle Best). Whereas, Gbest (Global
In Particle Swarm Optimization method, each Best) is obtained by the best comparison of Pbest
particle tracks its coordinates in the problem particles that have been identified based on the
surface associated with the best solution (output)

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Proceedings of Undergraduate Research 2018, Bangi, Selangor, Malaysia, 2018

minimum output value which is in this study, the electric field distribution value. The flowchart of
value of the output to be achieved is the minimum PSO Method is shown in FIGURE 2.

Start

Declare PSO parameters

Generate first swarm

Evaluate the fitness of all

particles

Record Pbest fitness of all Update the

particles velocity and
position of
Find Gbest particle particles

Swarm met the No

termination criteria?

Yes

End

FIGURE 2. Flowchart of Particle Swarm Optimization Method

RESULTS

FIGURE 3 shows the electric field distribution the maximum electric field magnitude was
around 230kV potential energy at energized end occurred comparing both magnitudes after applying
insulator string surface (a) without corona ring, (b) a corona ring in FIGURE 4. Discontinuity of the
applying corona ring with initial value of electric field between insulator’s outer and inner
dimensions and (c) applying corona ring with sheds domain was observed due to difference in
optimum dimensions which were optimized using permittivity value of materials at 2D cut line which
PSO techniques in this study during normal were assigned at outer sheds line. Masoud Jowkar
operation. The electric field magnitude around et. Al (2011) mentioned that in electric field
insulator string surface is high but reducing after distribution, the electric field magnitude is high at
applying a corona ring to insulator string. This the energized end at insulator string and reduces
shows that applying a corona ring can reduce the exponentially along the insulator length.
electric field distribution along the insulator string TABLE 3 presents the electric field
surface as well as reducing corona discharges and magnitude at the tip of first shed near to high
its effect during the discharges. The lowest electric voltage electrode of insulator string obtained from
field magnitude among the maximum electric field insulator string without corona ring, with initial
magnitude of electric field distribution of FIGURE dimensions of corona ring and with optimized
3 electric field distribution at insulator string dimensions of corona ring. From TABLE 3, it can
surface was recorded from FIGURE 3b, be seen that after the PSO optimization yield lower
7.40kV/mm. After the implementation of PSO minimum electric field magnitude than the initial
algorithm in the model, the results shows that there dimensions of corona ring which the percentage of
was a reduction of maximum electric field reduction from electric field magnitude at the tip of
magnitude from insulator string applying with the first shed near the energized end increase from
initial dimensions and after the optimization. This 28.2726% by initial dimensions to 39.9060% by
result also shows that the electric field distribution optimized dimensions of corona ring.
also depends on the dimensions of the corona ring.
FIGURE 4 shows the electric field
distribution along the insulator outer sheds for as
same application in FIGURE 3. Minor reduction on

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Proceedings of Undergraduate Research 2018, Bangi, Selangor, Malaysia, 2018

(a) (b)

(c)
FIGURE 3. Electric field distribution along 230kV insulator string surface (a) without corona ring, (b) applying corona ring
with initial value of dimensions and (c) applying corona ring with optimum parameters

(a) (b)

(c)
FIGURE 4. Electric field distribution along outer sheds surface (a) without corona ring, (b) applying corona ring with initial
value of dimensions and (c) applying corona ring with optimum parameters

TABLE 3. Electrical and insulation data of insulator.

Electric Field at tip Reduction Electric

Radius of Corona Height of Corona
Model of the first shed Field from without
Ring (mm) Ring (mm)
(kV/mm) Corona Ring(%)
Without Corona Ring - - 0.4255 -
Initial Corona Ring 185.0000 131.1500 0.3052 28.2726
PSO optimized 188.8491 121.7659 0.2557 39.9060

DISCUSSION model using FEM and the materials and conditions

of each component are taken into account. To
To understand the effect of difference dimensions overcome the results, as many as 20 iterations
of corona ring applied to 230kV insulator string, an calculation of optimization by MATLAB had been
attempt was done by designing a 2-D asymmetric

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Proceedings of Undergraduate Research 2018, Bangi, Selangor, Malaysia, 2018

done and the program loop running for maximum Insulator Type And Corona Ring On
10 times to get the best optimized value of Voltage Distribution Over 230KV
dimension corona ring with minimum value of Insulator String Using 3D FEM.
electric field distribution. International Journal of Engineering
Sciences & Emerging Technologies,
CONCLUSION Volume 3, Issue 1, pp: 1-8 © IJESET,
ISSN: 2231-6604.
According to the results, electric field distribution
over insulator string with applying a corona ring Hackam R (1999). Outdoor HV Composite
depends on the position (parameters) of corona ring Polymeric Insulators. IEEE Trans Dielect
from the energized end at insulator string. It is wise Electr Insul 1999;6:557–85.
to choose the suitable materials and its
characteristic to use in simulation since it will give Suat İlhan & Aydoğan Özdemir (2011). Effects Of
difference in electric field distribution result. By Corona Ring Design On Electric Field
optimizing the dimensions of corona ring, the Intensity And Potential Distribution Along
electric field intensity around the insulator string An Insulator String. Electrical
surface successfully reduced while maintaining its Engineering Department, Faculty of
physical properties. The lowest concentration of the Electrical and Electronics, Istanbul
electric field around insulator string surface can be Technical University, 34469, Maslak,
achieved as well as the life span of the insulator Istanbul, Turkey
string.
M. R. Al Rashidi and M. E. El-Hawary (2009). A
REFERENCES
Survey Of Particle Swarm Optimization
Applications In Electric Power Systems.
IEEE Trans. Evolutionary Computation,
Ammar Al-Ghelani, Wayne Rowe, Yongxiang Li,
Vol. 13, No. 4, pp. 913– 918, 2009.
Khoi Loon Wong. 2016. Stress Control
Methods On A High Voltage Insulator: A
Review. 1st International conference on Kalaiselvi Aramugam (2015). Insulator String
enerfy and power, ICEP2016, 14-16 Design Optimization Using Non-Linear
December 2016, RMIT University, Optimization Techniques. Comsol
Melbourne, Australia Conference, Asia Pasific University,
Electrical, Malaysia.
A.Rahimnejad, M. Mirzaie. 2012. Optimal Corona
Ring Selection For 230KV Ceramic I- Masoud Jowkar, Ahmad Gholami. 2011. Corona
String Insualtor Using 3D Simulation. Ring Designation for 400kV AC
International Journal of Scientidic & Transmission Line with Composite
Engineering Research Volume 3, Issue 3, Insulators by FEM. International
July-2012, ISSN 2229-5518 Power System Conference

B.Marungsri, W.Onhantuek, A.Oonsivilai and T.

Kulworawanichpong (2009). Analysis of *Siti Saffiza binti Bahrol
Electric Field and Potential Distributions Department of Electrical, Electronic and System
along Surface of Silicone Rubber Engineering,
Insulators under various Contamination Faculty of Engineering & Built Environment,
Conditions Using Finite Element Method Universiti Kebangsaan Malaysia, Malaysia
World. Academy of Science, Engineering
and Technology 53 2009. Syahirah Abdul Halim
Department of Electrical, Electronic and System
B. M’Hamdi, M. Teguar and A. Mekhaldi. 2015. Engineering,
Optimal Design of Corona Ring on HV Faculty of Engineering & Built Environment,
Composite Insulator Using PSO Approach Universiti Kebangsaan Malaysia, Malaysia
with Dynamic Population Size.
Laboratoire de Recherche en *Corresponding author; email:
Electrotechnique Ecole Nationale saffizabahrol@gmail.com
Polytechnique, 10 Avenue Hassen Badi,
B.P. 182 El-Harrach, 16200, Algiers,
Algeria.

Ebrahim Akbari, Mohammad Mirzanie (2012).

Investigating The Effects Of Disc

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