1. Comparison of AIS and GIS Grid Station Muhammad Ali Ashraf Management Associate (Electrical) CPP Project

2. CONTENT 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

3. Overview of CPP Project
Objective of CPP:
Natural Gas shortfall for plant
Power Export to national grid
Providing steam to existing plant
Plant overview :
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

4. Components of Switchgear
Disconnector and Earthing Switch
Circuit Breaker
Current Transformer
Voltage Transformer
Make Proof Earthing Switch
Cable Termination

5. 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

6. Air Insulated Grid Station (AIS) :
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.

7. AIS Grid Station Layout

8. 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.

9. 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.

10. 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.

11. Properties of SF6 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.

12. Essential parts of GIS Grid

13. Advantages 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

14. 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.

15. Hybrid Grid Station

16. Space Comparison
Source : ABB

17. AIS vs GIS Grid Station

18. Maintenance AIS Maintenance Requirements GIS Maintenance Requirements
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

19. Cost Comparison

20. 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.

21. Thank you !