Download Comparison of AIS and GIS Grid Station

Comparison of AIS and GIS Grid
Station
Muhammad Ali Ashraf
Management Associate (Electrical)
CPP Project
CONTENT
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FFBL Coal Power Plant Project Overview
Grid Station Overview
Conventional substations (AIS)
Limitations of AIS
Introduction to GIS
Properties of SF6
GIS assembly
Advantages of GIS
Drawbacks of GIS
Hybrid Grid Station
Area and Cost Comparison
Recommendation
Overview of CPP Project
Objective of CPP:
 Natural Gas shortfall for plant
 Power Export to national grid
 Providing steam to existing plant
Plant overview :
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2x250 T/hr, 92 Bar & 515⁰C Boilers
3x16 MW STG’s at 60Hz
1x55MW STG’s at 50 Hz for Power Export
Establishment of 132KV Indoor AIS/GIS Grid Station
for Power Export
Components of Switchgear
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Disconnector and Earthing Switch
Circuit Breaker
Current Transformer
Voltage Transformer
Disconnector and Earthing Switch
Voltage Transformer
Make Proof Earthing Switch
Cable Termination
Grid Station Overview:
• An Assembly of apparatus installed to provide the Ties, Transformation, Switching
and Protection of Transmission and Distribution systems.
• The Switchyard/Grid delivers power generated at the Power Plant to the Electrical
grid
1.Primary power lines
2.Ground wire
3.Overhead lines
4.Voltage Transformer
5.Disconnect switch
6.Circuit breaker
7.Current transformer
8.Lightning arrester
9.Main transformer
10.Control building
11.Security fence
12.Secondary power lines
Air Insulated Grid Station (AIS) :
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Air used as a dielectric for phase to ground Insulation.
Normally used for outdoor substations.
In very few cases used for indoor substations.
Easy to expand (in case that space is not an issue)
Excellent overview, simple handling and easy access.
AIS Grid Station Layout
Limitations of AIS
• Large dimensions due to clearance requirement and poor
dielectric strength of air.
• Insulation deterioration with ambient conditions and
susceptibility to pollutants.
• Large space requirement.
• Life of steel structures degrades.
• Large planning & execution time.
• Regular maintenance of the substation required.
Gas Insulated Grid Station (GIS)
• Various
Grid
Station
equipment are housed in a
metal Enclosed module in
a ground metallic housing.
• Metal Enclosed module
filled with
pressurized
Sulphur
Hexaflouride
(SF6)
• Compact, multi-component
assembly.
Gas Insulated Grid Station Overview
• Sulphur Hexaflouride (SF6)
gas used as the primary
insulating and extinguishing
arc medium.
• SF6 gas has superior
dielectric properties, used at
moderate pressure for phase
to phase and phase to
ground insulation.
• Preferred for voltage rating
of 66 kV, 132 kV, 220 kV
and 500 kV and above.
Properties of SF6
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Non-toxic, very stable chemically.
Lifetime – Very long (800 to 3200 years).
Insulating properties 3-times that of air.
Colorless & heavier than air.
Almost water insoluble.
Non inflammable.
Essential parts of GIS Grid
Advantages
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Compact assembly, less space compared to AIS Grid Station.
More reliable compared to Air Insulated Grid.
Number of outages due to the fault are less.
Maintenance Free, Protection from pollution.
Reduced Installation time.
Full protection against contact with live parts.
Explosion-proof and Fire-proof Installation
Drawbacks
• High cost compared to conventional Grid Station(AIS).
• Excessive damage in case of internal fault.
• High outage time, Diagnosis of internal fault and rectifying
takes very long time
• SF6 gas pressure must be monitored in each compartment.
• Reduction in the pressure of the SF6 gas in any
module results in flash over and faults.
• SF6 causes ozone depletion and global warming.
Hybrid Grid Station
Space Comparison
Source : ABB
AIS vs GIS Grid Station
Maintenance
AIS Maintenance Requirements
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Insulators and Disconnect contacts must be cleaned regularly
Operating mechanisms must be checked and maintained
All equipment exposed to weather conditions
Maintenance for AIS Grid station is relatively easier than GIS.
Fault Troubleshooting easier because of visual indications.
GIS Maintenance Requirements
– Arrangement of switchgear will play a significant role in how
maintenance will be carried out
– Considerable dismantling may be required if a main element fails
– Major failure of a component may require manufacturer assistance.
– Manufacturer supervision will be required for the 20 year full overhaul
Cost Comparison
Recommendation
Technically, both AIS and GIS substation types are considered
acceptable for the requirements of FFBL CPP Power Export
Project.
• Cost : Equipment Cost of GIS will be greater than AIS
• Size : For AIS, Area required will be larger than GIS
• Operational Flexibility: AIS offers more scope for easier
maintenance with GIS currently having long term
maintenance (after 20 yrs) restricted to servicing by the
original supplier. AIS also offers more scope in terms of
operational flexibility due to the larger compound resulting
in greater space available for change if required.
Thank you !