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ABI Improvement in Poll Perform by design Optimization

Improvement in Pollution Performance of Porcelain
Suspension Insulators by Design Optimization
SAKTHIVELU Subramanian, Debashis CHAKRABORTY, Gobinda PAHARI, Deepak CHERIAN, and
Grasim Industries Limited
(Unit: Aditya Birla Insulators)
Rishra, West Bengal, INDIA
Abstract— In order to address the pollution induced
flashover of transmission line outages, which is one of the most
important high voltage energy transmission problem, existing
anti-fog cap and pin type 160 kN disc insulator (suspension
insulator) has been taken for improving its performance in
artificial pollution test. The design of the existing porcelain
insulator has been optimized for important design parameters
such as form factor, creepage factor, ratio factor, and string
factor. A new specially designed insulator has been developed.
Both these, existing and new, insulators were type tested to
prove their general design conformity to IS 731. The pollution
performance was assessed by conducting salt-fog test on
400 kV single suspension string as per IEC 60507. The design
optimized porcelain insulators have shown 100% increase in
salinity withstand level in salt-fog test. The salinity level
achieved by the new design is 160 kg/m3, which is normally
obtained at a specific creepage distance of 31 mm/kV.
Keywords—Porcelain Insulator, Pollution Performance,
Creepage Distance, Form Factor, Flashover.
Insulator plays an important and critical role, in a power
system, to isolate among live parts and between live parts
and ground and rigidly or flexibly support electrical
conductors or equipment as mechanical protector. The
insulators are widely used at substations, transmission and
distribution network as well [1]. There are many shapes and
distinct styles or types of insulators with different sizes,
tensile strengths and performing properties with the aim to
withstand the worst conditions such as surge during lightning
and switching operations which will result in spiking of
voltage [2].
Porcelain as an insulating material has more than one
century of proven service history in terms of electrical,
mechanical, thermal and environmental stress withstanding
capability. The chemical stability of porcelain resists ageing
thus making it suitable for long term use [3]. The stable
chemical bonds of porcelain insulator, due to firing at high
temperature, imply satisfactory performance of porcelain
insulators under different environmental conditions such as
pressure, temperature, humidity, wind velocity etc., Hence,
porcelain insulators ensure successful, reliable and
uninterrupted operation of electrical power system.
In recent years, pollution induced flashover is the single
largest reason of transmission/distribution line outages, next
to lightning flashover [4] and has become one of the most
important high voltage energy transmission problem. Due to
rapid rise of transmission voltages and growth of polluting
industries, this problem has drawn more attention and many
studies have been carried out to understand the role of
different parameters on the flashover of polluted insulators
[5-7], several models have been developed to predict
flashover voltage of polluted insulators [8-10].
The major contributors to environmental pollution are
dust, dirt, industrial emissions, vehicular pollution, saline
deposits, desert salts etc. These contaminants, under damp
conditions interact with water, which then behaves as an
important pollutant vis-à-vis insulation capability [11]. The
pollution phenomenon is a most complex issue. The Electra
No. 64 document [12] describes the pollution flashover
process for ceramic insulation in detail.
Several improvements have taken place to tackle this issue
such as (a) modifications in design of porcelain insulators (b)
use of composite (polymer) insulators (c) coating of Room
Temperature Vulcanized (RTV) silicone rubber on porcelain
The improvements by modification of design of porcelain
insulators (profiles such as open, anti-fog, bell etc.) offer
superior performance under certain conditions to overcome the
pollution flashover issue. The selection of the optimum insulator
profile, based on site pollution severity/contamination severity,
is a key factor to get superior performance of porcelain
insulators in polluted areas.
Several countries have used composite insulators for high
voltage transmission lines for investigating their performance
and testing about their long term reliability. Based on field
experience, polymer insulators have a sizable number of
common failure modes, including: brittle fracture, surface
tracking and erosion of polymer sheds, chalking and crazing of
sheds which lead to increased contamination collection, arcing
and flashover, bonding failures and electrical breakdown along
the rod-shed interface, corona splitting of sheds and water
penetration which lead to electrical breakdown [13-15].
Additionally, exposure to heat, ultraviolet radiation, rain and
pollution will cause them to deteriorate over time. The longterm performance of the large population of polymer insulators
is a concern among power utilities.
The RTV silicone rubber coating for various types of
outdoor insulators suppressed the magnitude of leakage current
and increased the flashover voltage under various artificially simulated pollution [16]. However, the handling of RTV coated
insulators and assessment of coating adhesion to porcelain are
limiting factors.
This paper presents the achievement of improved
pollution performance of porcelain suspension (disc)
insulators, by modification of the design of porcelain