21-02-2010, 07:35 AM
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INTRODUCTION
Composed of pipes that houses conductors in SF6
Invented in 1974
Both overhead & underground system
Drawbacks of XLPE lead to GIL
Most economic, environment friendly & maintenance free alternative
WHY GIL
Installation expense is less
XLPE needs extra cooling arrangement
Allowed conductors to be larger in cross-section
Construction of large capacity transmission link
SUPERIOR PROPERTIES OF SF6 GAS
High dielectric strength at lower cost
Regeneration capacity following a breakdown
Low pressure-increase following a breakdown
High load transfer capacity
INSTALLATION
Ground level
Elevated above ground
Below grade in an open or covered trench
Directly buried underground
Vertically in tunnels, shafts or towers
Suspended from existing substation structures
MAIN COMPONENTS
Conductors & enclosures
Insulators & particle traps
Plug in contacts
Aluminum bellows
Enclosure joints
HOW TO REDUCE THE COST OF GIL
Standardization of components
Optimization of pipeline
Introduction of N2
ADVANTAGES OF SF6-N2 MIXTURE
Less harm to atmosphere
Reduced cost for GIL
Useful for long distance power transmission
Insulating property is improved
H-GIL
Large capacity.
For long distance power transmission line.
Structure between that of GIL & XLPE.
Uses 3 sub-conductors.
Covered with solid dielectric polyethylene.
Insulated with SF6.
More flexible.
Withstands voltage same or more than GIL.
ADVANTAGES
High current carrying capacity
Limited working space
High efficiency
Low resistive & capacitive loss
Good appearance
No interference with communication circuits
No extra cooling is required
High reliability
DISADVANTAGES
Length of is each GIL section is limited.
Particle contamination lower the insulating reliability of GIL.
Breakdown of insulator.
Earthquake resistant design must be considered.
SF6 gas is harmful to ozone.
APPLICATIONS
Installation in tunnels
Ideal for environments that are sensitive to electro-magnetic fields.
Suitable for metropolitan areas where high energy rate is required.
Well suited for high power transmission.
CONCLUSION
One of the best transmission system in the world
Safe and reliable for more than 20 years
Researches are still going on to improve efficiency
