PORCELAIN VERSUS POLYMER INSULATORS ------ A CHANGING ERA IN TRANSMSSION LINESSYNOPSIS :In the country and worldwide transmission lines passes through transverse areas having different situations like environmental and pollution levels. Over the years environmental challenges are appearing cum acting very fast, in particular increase in pollution levels and have become a global phenomenon. With increase in pollution levels frequent transient faults appear, which finally lands to permanent ie breakdown of transmission line. This breakdown sometimes leads to collapse of grid. Breakdowns are inconvenient to everyone and great loss to nation /society. Never the less a threat to security system.

With liberalisation of electrical market, individual clients will have a right to choose companies who provide quality service. Current prime minister of India has given such statements from time to time.Over the years engineers and scientists have made efforts to meet such threats and to overcome such situation porcelain insulators are being replaced by polymer ones. Which are appearing to be superior to porcelain and demand is on increase by virtue of its proven inactive use.In this article, an effort has been made to understand difference between the two and agency would decide the type of insulators to be deployed for ensuring long life of transmission line with respect to rate of rise of pollution in country.Pollution level in IndiaIndia is one out of the top 10 most polluted countries in the world. This is due to the developments taking place. Regardless of wealth, pollution has become uncontrollable. Environmental monitoring regulations and protections acts are not matching with pace of development. On one hand industry is developing and on other hand modern techniques are giving birth to newer chemicals, emissions etc besides urbanisation.As per THE ATLANTIC magazine, pollution rise in India is as under:

POLLUTION LEVELS IN TRANSMISSION LINESPollution problem in transmission system starts when pollutants existing in air settle in the surface of insulator. In other words pollution degrades electrical properties of insulators. CPRI/CEA & world level affected utilities have conducted studies on pollution levels from time to time. Pollution on insulators appear in following ways;Bird droppings.Brick kilns {refer photo} , thermal plantsIndustry discharge chemicals/fly ash, Agricultural ash/ burning, wild fire etcMineral handling processSalt due to coastal areasCement industry, oil refineries etcCommercial and domestic vehicles (railway yards, highway crossings etc )Level of deposit on insulators also depends upon wind speed and direction. It also depends upon the area /locality from source of pollution. Clouds & fog during winters acts as a catalyst to create flashovers.MEASUREMENT OF DEPOSITS ON INSULATORSDeposits on insulators are measured and in technical terms is called as ESDD ( equllient salt deposit density ) { refer photo }.Pollution levels has been categorised as under;LEVEL ESDD (mg/sq.cm)LIGHT 0.03 ------ 0.06MEDIUM 0.06 ----- 0.20HEAVY 0.20 ---- 0.60VERY HEAVY > 0.60From time to time with increase in pollution levels insulation distance have been designed as underSYSTEM VOLTS ( KV ) MIN, CREEP DISTANCE ( mm ) MODERATE POLLUTION HEAVY POLLUTION72.5 1100 1700125 1850 2800145 2250 3400245 3800 5600420 6480 9660

Also insulators are designed and used as under:POLLUTION LEVEL MIN. CREEP DISTANCE. ( mm/kv --- phase to phase )LIGHT 16MEDIUM 20HEAVY 25V. HEAVY 31Now the time have come/coming that to ensure long trouble free life of insulators/ transmission Line, it will have to be designed for 36 kv/mm. GOI is putting up all efforts to control pollution levels but due to deforestation and urbanisation, it is increasing day by day as evident from the graph above Pollution mapping is continuous type of job and need to review after every 2/3 years for awareness towards technological and society angle. Also stringent enforcement of laws. REPLAEMENT OVER THE TIMEWith passage of time conventional type porcelain insulators are being replaced by polymers and are giving better performance in polluted areas, In our country it has been developed and under use for the last 8 to10 years and in large scale for the last 5 to 6 years. Worldwide are in use for the last 25 years. IN our country their performance in long run is yet to be established and particularly in areas where temperature falls below (-) 10 degrees.COMPARISON BETWEEN POLYMERS AND PORCELAINCOMPARISON OF POLYMER VS PORCELAIN INSULATORS

GENERAL COMPARISON

FactorCERAMICS ( PORCELAIN ) POLYMER

Weight Heavy ,approx. weight of 400kv string is 135 kgs Lighter and offer an equal cum better strength. Approx. wt of 400kv string is about 20 kgs

Fragile AbilityHighly fragile to shock & vibrations Not fragile to shocks

Packing and transportRisky and expensive Easy and economical

InstallationRisky & expensive & more labour is required Very easy and economical

HandlingDifficult and handle with care Easy

Maintenance cost Being fragile in nature, hence maintenance cost moderately high Low as compared to porcelain

Vandalism ( stone pelting/ gun shots )More susceptible Highly resistant

Breakages & secondary damage Highly fragile -10-15% breakage are reported during transportation ,storage and installation Flexible, highly resistant to breakage. But susceptible to cuts and scratches

TECHNICAL

Mechanical failure Reduces in life span and separation due to pins getting eroded Single piece. Hence no such problems

Resistance to flashovers and puncturesComparatively Low. But can sustain maximum 2 to 3 flashovers, then require replacementHigh. But if once flashover takes place, to be replaced immediately

Anti tracking and erosion resistance Low tracking resistanceExcellent tracking resistance avoids erosions or tracking of the housing materials

Dielectric strengthReduces with ageExcellent insulation performance

Contamination and pollution affected less affected

HydrophobicityNon hydrophobicity, as porcelain surface forms water films on the surface making easy path leading to flashovers .Hydrophobicity properties of silicon rubber provide better behaviour and resists wetting by forming beads of water without the need of washing or greasing even in humid or polluted climates. Hence low failure rate combined with low overall operating and maintenance costs

Self cleaning qualitydirt, sand salt & snow are easily attracted but gets cleaned during rainsYes. due to hydrophobicity recovery characteristics

Tensile strengthGood Excellent due to crimping technology

MaintenanceNeeds maintenance like cleaning ,washing and greasingNo maintenance. Difficult to work on insulator due to dimension limitations

Performance in snowBetter

Comparatively poor, develops cracks with passage of time t

DesignDesign flexibility is limited. Requires larger and heavier towers for installation and more space insulator design allows for adaptations to suit specific needs such as creep distance .results in space saving and lower cost

Manufacturing process long manufacturing process leading to long delivery schedule ,manufacturing process causes pollution and health riskPollution free, safe and less process time. Hence short delivery periods

Safety Susceptible to explosion & breakages, due to high fragile properties.Provide high level of safety, superior flexibility and strength. Not susceptible to explosion.

OTHERS

part replacementPossiblenot possible

shelf lifeExcellentdevelops fungus/algae

susceptible to reptiles/rats (Storage)Nilvery easy and eats away

Life Expectancy> 25 Years in Non-Polluted areasYet to established in Long Run.

RemarksThe comparison of polymers with glass insulators is more or less same. Only glass insulators have property/tendency of shattering down due to any problem arising which increases possibility of cross flash over.

VOLTAGE DISTRIBUTION AND DESIGN FLEXIBILITY (refer photographs)One of another major advantage of polymers is that voltage distribution is uniform all along length of string, hence no chance of flash over /overshoot ie it does not exist.Other advantage of polymers is of its flexibility in design/shape. It can be given any type of shape to obtain creep distance and suiting to customer requirement.

LIMITATIONS OF POLYMERSEating by rats etc during storage {refer photo}Notching by birdsIn the event of damage, whole string requires replacement. Whereas in porcelain replacement of damaged /broken insulators is possible. (Refer photo above) Bad storage {refer photo}. Due to bad storage petticoat has a tendency to shear. Polymers have also tendency to develop ALGAE, FUNGUS & LITCHENS. This is bluish cum green cum yellowish type deposit on petticoats. This reduces ph value, lowers hydrophobicity and decolourisation .Finally develops dry bands meaning thereby brittleness.Hence polymer requires testing / inspection from time to time, particularly when stored in open. Periodical cleaning will retain its properties ie prolong shelf life.Power grid and other transmission utilities has changed porcelains to polymers since 201112. There is Drastic fall in transient faults . Latest example that in this year winter season (nov. 2014 --- jan. 2015). This increased system security and reliability. K r suri Gen Mgr ( retd ) powergrid Consultant to Sterlite power grid ventures ltdREFRENCES1 CEA report on insulators, nov 20082 The Atlantic, face book, Air pollution map, june 11,20143 Aging of polymer insulators, university of engg. and technology, taxila, Pakistan4 Ceramic and non-Ceramic insulators, article A00038, university of firat.5 Various IEEE Papers Remarks: The views expressed are purely of Individual and nothing to do with manufacturer or utility.