1. Detailed Study on Gas Insulated Substation (GIS)
Guided by:
Prof. Samyak Shah
Nirma University, Ahmedabad
Prepared by:
Panara Shanni (15bee161)
Rathod Bharat (15bee169)

2. Outline of Presentation
 Introduction to Substation
 Limitations of Air Insulated Substation
 Need of Gas Insulated Substation
 Assembly of GIS
 SF6 Circuit Breaker
 Layout of GIS
 GIS Cable
 Gas Insulated Transformer
 GIS failure statistics
 Main Drawbacks of GIS
 Underground GIS
 Advancement in GIS Technology
 GIS in Gujarat, India
 Conclusion
 References

3. Substation

4. Limitations of Air Insulated Substation
 Large dimensions due to statutory clearances and poor dielectric strength of
air
 Insulation deteriorations with ambient conditions and susceptibility to
pollutants
 More space required
 Effect of atmosphere
 Life of steel structures degrades
 Regular maintenance required
 Reliability is less
 Large planning and time execution
 Life

5. Need of Gas Insulated Substation
 Non-availability of sufficient space
 Difficult atmospheric and seismic condition at site
 Urban site
 High altitudes
 Limitations of AIS
 In this type of switchgear, all the necessary components of switchgear can be
assembled in very limited space. GIS is a kind of metal enclosed switchgear.
 Where all the equipment are placed in a gas insulated metal enclosure. Mostly
as a insulating gas a sulphur hexafluoride(SF6) gas is used.

6. Properties of SF6 Gas
 Electronegative gas
 Insulation properties are 3 times higher than that of air
 Life-time
 Non-toxic, Colourless and heavier than air
 Non-inflammable and chemically stable
 Almost water insoluble
 Density is 6.15 kg/m3 at atmospheric condition

7. History of GIS
 In operation from
1965 until 2013
 48 years of reliable
operation!
 The first 110 kV GIS in the world
 Location: Indoor Substation Recklinghausen Germany

8. Development in GIS

9. Types of GIS
 Isolated phase GIS
 Integrates 3 phase GIS
 Hybrid GIS system
 Compact GIS
 Highly integrated GIS system

10. Surrounding Conditions Overview
 GIS perfectly match all surrounding conditions
 Air pollution
 Saline contamination
 Altitude above sea level
 Underground installation
 Multi-storey installation
 GIS have minor environmental impact
 Low visual impact
 Low electromagnetic disturbances

11. 1.Busbar
2.Disconnector
3.Maintenance Earthing Switch
4.Current Transformer
5.Circuit Breaker
6.Current Transformer
7.Maintenance Earthing Switch
8.Disconnector
9.Earthing Switch
10.Voltage Transformer
11.Bushing

12. SF6 Circuit Breaker

13. Advantages of SF6 Circuit Breaker over
Conventional Circuit Breaker
 Electrical clearance is very much reduced
 Noiseless operation
 Performance is not affected due to variations in atmospheric condition
 No over voltage problem
 No reduction in dielectric strength
 Less maintenance
 Low cost

14. Disadvantages of SF6 Circuit Breaker
 SF6 gas is suffocating to some extent
 Entrance of moisture in Gas tank is very harmful
 Cleaning of internal parts
 Periodic maintenance under clean and dry environment
 Requirement of special facilities for transportation
 For future extension, installation is not easy
 Greenhouse gas
 High mechanical energy required due to puffer design

15. Types of SF6 Circuit Breaker
 Single interrupter SF6 CB applied for up to 245 KV(220 KV) system
 Two interrupter SF6 CB applied for up to 420 KV(400 KV) system
 Four interrupter SF6 CB applied for up to 800 KV(715 KV) system

16. Features of GIS
 Compact Design
 Safety
 Superior Reliability
 Elimination of periodic maintenance
 Installation & transportation

17. Components of Gas-Insulated Substation
 Electrical bus bars
 Electrical isolators or disconnectors
 Circuit breakers
 Current transformers
 Voltage transformers
 Earth switches
 Surge arresters or lightning arresters

18. Electrical isolators or Disconnectors
 Disconnectors or isolators are used for electrical isolation of circuit
parts.
 Disconnect switches can be three pole, group- operated or single
pole operated.
 They are slow acting and operating at off load.

19. Circuit Breakers
 Under short circuit conditions , however the current may reach
tens of thousands of amperes at a power factor as low as 0.1.
 It is duty of a circuit breaker to interrupt such currents as soon as
possible to avoid equipment damage.

20. Current Transformers
 In the single phase enclosed core of CT is located outside the enclosure
inside for three phase.
 Gas compartment to reduce access of moisture and to suppress gas-
tight bushing for secondary connections.
 CT current rating is 120% of rated primary current.

21. Voltage Transformers
 Variable location on feeder and bus bars.
 Integrated disconnecting facility for GIS and power cable testing without
dismantling and gas handling.

22. Earth Switches
 Slow operating earthing switch are used for protection purpose.
 When work is being done in the substation, but are operated only when it is
certain that the high-voltage system is not energized.
 The fast closing earthing switch can close against full voltage and short circuit
power.
 The high speed earthing switch is achieved by means of a spring-closing device.

23. Rated voltage
(kV)
72.5 145 170 245/300
Breaking current
(kA)
40 40 40/50 50
Rated current (A) 1,600/ 2,500 2,000/ 3,150 2,000/ 3,150/
4,000
4,000/ 5,000
Phase per
enclosure
3 3 3, 1 1
Breakers per pole 1 1 1 1
Mechanical
endurance
M2 M2 M2 M2
Operating
mechanism
Spring Spring Pneumatic,
Hydraulic,
Spring
Hydraulic, Spring
Comparison of different GIS systems

24. Customer Benefits
 Reduces cubicle space by >35%
 Suitable for highly polluted environment
 Safe operation behind close door
 Ease of installation & sealed for life
 Peace of mind with almost zero maintenance
 Productivity maximization
 No fire risk

25. GIS Configurations for Busbar arrangements
 Single busbar
 Double busbar
 Single busbar with transfer bus
 Double busbar with double circuit breaker
 One and a half circuit breaker scheme
 Ring busbar

26. Layout of GIS

27. https://www.youtube.com/watch?v=jD3lWTxArOM

28. GIS Cable

29. Gas Insulated Transformer (GIT)

30. Comparison between Oil-Immersed and
Gas-Insulated Transformer
Parameters to be
compared
Oil-Immersed
Transformer
Gas Insulated
Transformer
Insulation/Cooling Insulating oil SF6 Gas
Solid insulation material Oil impregnated paper,
Pressboard
PET film, PPS film,
Aramide paper, Press
board
Conservator Necessary Unnecessary

31. Advantages of Gas-Insulated Transformer
 Non-flammability
 Tank-explosion Prevention
 Compactness
 Easy installation
 Easy inspection and maintenance work
 Environmentally Friendly

32. GIS Failure Statistics

33. Main Drawbacks of GIS
 High cost compared to conventional substation(AIS)
 Excessive damage in case of internal fault
 Diagnosis of internal fault and rectifying takes very long time (high outage
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

34. Space requirement

35. Very Fast Transient Overvoltages (VFTO)
 Very Fast Transient Over Voltages (VFTO) are caused by disconnector
switching operations within a Gas Insulated Substation.
 The very fast transient overvoltages contains very high frequency
components in the order of several 10's of MHz and may cause high
frequency oscillations in the transformer windings, leading to possible
overstressing of the transformer insulation.
 For certain switching conditions where GIS disconnectors are operated
following circuit breaker operation it is possible to generate VFTO, which act
as travelling waves and propagate within and external to the GIS. The source
of these overvoltages is due to the re-strikes or pre-strikes during
disconnector opening or closing operations.
 The maximum magnitude of the restrike voltage is 2.0 pu.

36.  This value is largely dependent upon the level of trapped charge on the GIS
busbar existing at the time of the restrike.
 The amplitude of trapped charge is strongly influenced by the asymmetry of
the intercontact breakdown voltage occurring on the fixed and moving
contacts of the disconnector. This is dependent upon the dimensional
differences between the contacts. Trapped charge is also influenced by the
operating speed of the disconnector during its opening cycle.

37. LCC Calculation
 LCC is the Life Cycle Cost of the substation.
 Where,
LCC = Life Cycle Cost
IC = Investment Cost
FC = Fixed annual cost
VC = Variable cost
n = substation planned lifetime
p = Interest rate

38. Cost Comparison
Cost Parameters Air Insulated
Substation
Gas Insulated
Substation
Substation Cost 5,376,000 5,376,000
Cost of prime per sqm. 500 500
Prime Lot Cost 2,500,000 2,000,000
Investment Cost 7,876,000 7,376,000
Operational Cost 1,125,000 1,000,000
Income 820,120 945,120
Sales Revenue 1,945,120 1,945,120
ROIC 10.41% 12.81%

40. Comparative conclusion
 The choice between GIS substation and AIS depends largely on the advantages
versus disadvantages of the two equipments. GIS being compact is the
obvious choice of many utilities because of its many technological advantages
over AIS.
 And though most industry are getting conscious about global warming issues,
until such time SF6 is banned, like those chlorofluorocarbons (CFCs) before for
being identified as greenhouse gas, it is still worthy investment for a utility
upgrade.
 When it comes to financial aspect of an investment, overall performance
measure, suggest GIS has significantly edges AIS.

41. Use of Modern Subterranean Substations
 For more than 40 years proven gas-insulated switchgear (GIS) has helped to
secure efficient energy supply. It is suitable for various urban or industrial
settings, e.g.
• Vicinity of public buildings
• Subway stations
• Plazas or parking lots
• Stadiums, parks or recreation areas
• Historic or religious places
• Offshore wind parks or oil platforms
• Hydropower stations
 Furthermore, the adaptation to different design-concepts, e.g.
• Underground substation
• Semi-underground substation
• On-top building provides additional architectural flexibility.


42. Underground GIS

43. Equipments used in Underground GIS
 Transformers
 Gas-insulated high-voltage switchgear (GIS)
 Medium-voltage switchgear
 Automation
 Protection and control systems
 Auxiliary equipment for station services
 AC and DC distribution boards
 Batteries
 Ventilation and air-conditioning systems
 Fire protection systems

44. Benefits of Underground GIS
 Due to the inherent safety and compact layout of a insulated substation, it is
the best solution for substations which are to be built in restricted
underground spaces.
 Gas insulated substations are particularly suitable for underground
construction beneath public buildings.

45. On-top building (Haymarket, Sydney, Australia)

46. Commissioning of GIS
 The outer surfaces of epoxy insulating tubes of the poles are to be wiped
out with a clean and dry cloth.
 The wiring and connections of the auxiliary circuit are to be carefully
examined.
 DC voltage should be checked to see whether it is suitable for coil and
motor or not (if equipped).
 The opening-closing coils are to be operated 15-20 times and the accuracy
of the relay circuit is to be checked before energizing the circuit breaker.
The circuit breaker is to be mounted with two MI2 bolts through its
anchoring shoes. It should not move during operation.
 No excessive load should be exerted to the poles and if possible flexible
cables should be used.

47.  The incoming and outgoing contacts must have clean surfaces and their
contact resistance should be as low as possible.
 When connecting the circuit breaker to protection system and auxiliary
supply, the cable cross sections should be according to the table given. The
circuit breaker must be grounded through at least 16 mm steel tape (by
cable shoe).
 After all, the following procedure must be performed:
• Open the isolator of circuit breaker
• Prepare the circuit breaker for closing operation by driving mechanism
• Close the isolator or circuit breaker firmly
• Send the closing signal to the circuit breaker

48. Advancement in GIS Technology
(For Further Space reduction)
 Gas Insulated Transformer (GIT) Instead of Oil Immersed Transformer (OIT).
 SMART GIS -Integration of Electronic CT’s & PT’s
 Combined Earthing Switch & Disconnector

49. Combined Disconnector/Earthing Switch
 The DSES incorporates the two functions of a disconnector and a
maintenance earthing switch as a result saving the space in GIS.
 This is achieved by a sliding contact characterized by three defined positions:
• Disconnector open / Earthing switch closed
• Disconnector closed / Earthing switch open
• Disconnector open / Earthing switch open

50.  The use of one moving contact for the disconnector and the earthing switch
inhibits simultaneous closed position of both switches.
 Combined disconnector and earthing switch is mounted at the front, and acts
via bevel gears and an insulating shaft on the three parallel contact pins.
 Depending on the direction of movement the contact act as disconnector or
earthing switch(maintenance earthing switch).
 By means of a crank handle, manual operation of the combined disconnector
and earthing switch is also possible.

51. Smart GIS - Integration of Electronic CT’s & PT’s

52.  The Combined sensors are the Rogowski coil for current measurement and
the capacitive divider for voltage measurement.
 A combined current and voltage sensor has been developed to replace the
conventional current and voltage transformers in GIS.
 The capacitive ring, which acts as a voltage sensor, also has a linear
characteristic and is very simple in terms of the insulation
 Advanced CT’s without a magnetic core (Rogowski coil) & Capacitive sensor
have been developed to save space and reduce the cost of GIS. The output
signal is at a low level, so it is immediately converted by an enclosure
mounted device to a digital signal.

53. Testing of GIS
 Polarity test
 Insulation test
 Pressure measurement test
 Tan-δ test of CT/CVT/Transformer
 Enclosure monitoring test
 Grounding test
 Testing of GIS must be perfomed as per the standards techniques and
conditions.

54. GISinGujarat,India
GIS in Gujarat, India

55.  The two substations will be located at Betul in Madhya Pradesh and Navsari in
Gujarat. Both substations will be completely manufactured in India, making
this Power Grid´s first ´Make in India´ 400 kV GIS.
 The Power Transmission & Distribution business of L&T Construction has
executed and commissioned two benchmark projects in the country. The first
being India’s first 765 kV Gas Insulated Substation in Pune and other is first of its
kind 765 kV transmission line on EPC basis in Rajasthan.

56. Application of GIS
 Power transmission
 Integration of renewable power generation units to the grid
 Railways

57. Conclusion
 GIS are necessary for EHV & UHV and some important areas to be studied
include more conservative designs better particle control & improved gas
handling & decomposition product management techniques Achieving &
maintaining high levels of availability requires a more integrated approach to
quality control by both users and manufactures.

58. References
➢ Ieeexplore.ieee.org › Gas Insulated Substations
➢ www.slideshare.in
➢ new.abb.com/substations/gis-substations
➢ https://www.scribd.com/doc/98800555/Gas-Insulated-Substation-Report
➢ https://www.youtube.com/watch?v=jD3lWTxArOM
➢ IEC 60480:2004 Guidelines for the checking and treatment of sulphur
hexafluoride (SF6) taken from electrical equipment and specification for its re-
use