The topic mainly deals about different methods of high power Underground transmission systems currently implemented across the world as well as about the modern GIL systems. It also explain about the advantages, construction and features of GIL (Gas Insulated Transmission Lines) by highlighting its future scope as well.

1. SEMINAR ON
UNDERGROUND TRANSMISSION
LINES FOR HIGH POWER AC AND
DC TRANSMISSION
DONE BY
VISHNU ARAVIND
S7 EEE
UEANEEE030

2. CONTENTS
• Underground cables
• Why Underground cables
• Underground Power Transmission Systems
• Types of Underground Electric Transmission
Cables
• Gas Insulated Transmission Lines
• Basic layout of GIL
• Main Components
• Installation Of GIL
• Technical Data of GIL
2UEC,Vallivattom 13-Feb-17

3. • Advantages Of GIL
• Dis advantages Of GIL
• Applications
• References
3UEC,Vallivattom 13-Feb-17

4. UNDERGROUND
CABLES
• An underground cable consists of one or more
conductors covered with some suitable insulating
material and surrounded by a protecting cover .
• The cable is laid underground for the transmission of
electric power.
4UEC,Vallivattom 13-Feb-17

5. Why Underground
cables ?
The underground system of Electrical distribution and
transmission of power is increasingly being adopted in
modern countries, although it is costly system of
distribution as compared to over head system. It ensures
the continuity of supply apart rom the following features
• It ensures non-interrupted continuity of supply
• Its maintenance is less
• It has a long life
• Its appearance is good
• It eliminates hazards of electrocution due to breakage
of over head conductors.
5UEC,Vallivattom 13-Feb-17

6. UNDERGROUND POWER
TRANSMISSION SYSTEMS
• New York City- no overhead since 1890’s
• Singapore- 100% underground
• Netherland-Distribution occurs 100% underground
• Denmark- Replaced six 132 KV OH lines with two new
400KV underground cables
• France- Due to frequent storms 25% of OH cables are
transferred to underground cables.
6UEC,Vallivattom 13-Feb-17

7. Types of Underground
Electric Transmission Cables
The common types of underground cable construction
include:
 High-pressure, fluid-filled pipe (HPFF)
 High-pressure, gas-filled pipe (HPGF)
 Self-contained fluid-filled (SCFF)
 Solid cable, cross-linked polyethylene (XLPE)
7UEC,Vallivattom 13-Feb-17

8. 1. High-Pressure, Fluid-Filled Pipe-Type Cable
• It consists of a steel pipe that contains three high-
voltage conductors.
• Each conductor is made of copper or aluminum;
insulated with high-quality, oil-impregnated kraft paper
insulation; and covered with metal shielding (usually
lead)
• Three conductors are surrounded by a dielectric oil at
200psi act as insulator.
• The fluid is usually static and removes heat by
conduction.
Disadvantage:
• Maintenance issues and
possible contamination of surrou
nding soils and groundwater due to
leaking oil.
8UEC,Vallivattom 13-Feb-17

9. 2.High-Pressure, Gas-Filled Pipe-Type Cable
• Its a variation of the HPFF pipe-type, Instead of a
dielectric oil, pressurized nitrogen gas is used to
insulate the conductors.
• The conductors’ insulation is about 20 percent
thicker than the insulation in fluid-filled pipes.
• In case of a leak or break in the cable system, the
nitrogen gas is easier to deal with than the
dielectric oil in the surrounding environment.
Disadvantage:
• Nitrogen gas is less effective than dielectric fluids
at suppressing electrical discharges and cooling.
9UEC,Vallivattom 13-Feb-17

10. 3.Self-Contained, Fluid-Filled Pipe-Type
• It is used for underwater transmission construction
• The conductors are hollow and filled with an
insulating fluid that is pressurized to 25 to 50 psi.
• The three cables are independent of each other.
They are not placed together in a pipe.
Disadvantages:
• This type of construction reduces the risk of a total
failure, but the construction costs are much higher
than the single pipe used to construct the HPFF or
HPGF systems.
10UEC,Vallivattom 13-Feb-17

11. 4. Solid Cable, Cross-Linked Polyethylene
• It is the standard for underground electric transmission
lines less than 200 kV
• It requires little maintenance.
• It requires three separate cables, similar to the three
conductors required for aboveground transmission lines
11UEC,Vallivattom 13-Feb-17

12. • Each cable consists of a copper or aluminum
conductor and a semi-conducting shield at its core.
12UEC,Vallivattom 13-Feb-17

13. GAS INSULATED
TRANSMISSION LINES
• Gas Insulated Line invented in 1965 by Massachusetts
Institute of Technology
• GIL consists Aluminum conductor surrounded by mixture of
N2 and SF6 inside the enclosure.
• GIL system first installation in Black Forest as long ago as
1975 of about 4km. length.
• GIL system can be used both in above & below ground
13UEC,Vallivattom 13-Feb-17

14. BASIC LAYOUT OF GIL
14UEC,Vallivattom 13-Feb-17

15. MAIN COMPONENTS
• Conductors and
enclosures
• Post Insulators
• Particle traps
• Insulating gas
15UEC,Vallivattom 13-Feb-17

16. INSTALLATION OF GIL
1. Aboveground Installation
• GIL are unaffected by high
ambient temperatures,
intensive solar radiation or
severe atmospheric
pollution.
• High transmission power can
be achieved with
aboveground installation.
• Corrosion protection is not
required.
16UEC,Vallivattom 13-Feb-17

17. 2. Tunnel Installation
• With this method of
installation the land above the
tunnel can be fully restored to
agricultural use.
• The system stays accessible for
easy inspection and high
transmission capacity is
ensured.
3. Vertical Installation
• Top solution especially for
cavern hydropower plants.
• GIL systems pose no fire risk,
they can be installed in a
tunnel
17UEC,Vallivattom 13-Feb-17

18. 4. Direct burial Installation
• These systems are coated
with a continuous
polyethylene to safeguard
corrosion resistant
Aluminum alloy.
• The land can be returned
to agricultural use with
very minor restrictions.
18UEC,Vallivattom 13-Feb-17

19. TECHNICAL DATA OF GIL
19UEC,Vallivattom 13-Feb-17

20. ADVANTAGES OF GIL
• High transmission capacity
• Low capacitance
• Low transmission losses
• High reliability
• High operational safety (no fire risk, no external impact
in case of internal failures).
• No practical ageing of components
• Very low external magnetic field
• No interference with the communication systems
20UEC,Vallivattom 13-Feb-17

21. DISADVANTAGES OF GIL
• Length of 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.
21UEC,Vallivattom 13-Feb-17

22. 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.
22UEC,Vallivattom 13-Feb-17

23. REFERENCES
• Koch H.,Kumar A., Christl N., Lei X., Povh D.,
Retzmann D., Advanced Technologies for Power
Transmission and Distribution – Benefits and Impact of
Innovations, Siemens Brochure, 2010
• Giebel G., Nielson H., Hurley B., Bigger transmission
distance with lower load factors: the European dilemma,
Modern Power System, 10/2005.
• Benato R., Fellin L, Marzenta D., Paolucci A., Gas-
Insulated Transmission Lines: excellent performance
and low environmental impact, Vol.1 pp. 385–405,
Napoli, Italia, 12.–18. May 2000.
23UEC,Vallivattom 13-Feb-17

24. THANK YOU
24UEC,Vallivattom 13-Feb-17