2. SWITCHYARD:
Switchyard will exist at a generating station to
coordinate the exchange of power between the
generators and the transmission lines.
PURPOSE & NECESSITY OF SWITCHYARD
Generatedpowertobeevacuatedtoloadcentersforconsumption.
Generatingstationsarefarfromloadcenters.
Theprocessof
Generation Transmission Consumption/Load center
(in22kV) (in400kV) (in230V)
4. Limitation of AIS
Large dimensions due to statutory clearances
and poor dielectric strength of air.
Wastage of space.
Life of steel structures degrades.
Seismic instability.
Large planning & execution time.
Regular maintenance of the substation
required.
5. Gas Insulated Switchgear
Gas Insulated Switchgear (GIS), where the
conductors and equipments are insulated by
pressurized sulphur hexafluoride gas(SF6).
I. Outdoor GIS (without screen house)
II. Indoor GIS (with screen house)
7. Merits of GIS
The space occupied by switch gear is greatly
reduced.
Totally unaffected by atmospheric conditions.
Provides high operational reliability.
Easier to install in difficult site conditions.
Installation time is lesser than air insulated
switchgear.
8. TECHNICAL PARAMETERS OF GIS
Make: Xian XD Electric switchgear Co.,Ltd
System nominal voltage: 400kV
Maximum working voltage: 550kV
Rated current: 4000A
Rated frequency: 50Hz
Rated short-circuit breaking current: 63kA for 1sec
Rated peak withstand current: 170kA
Rated control voltage: 220V DC
SF6 Gas pressure at 20°C: 0.5Mpa (Breaker chamber)
0.4Mpa (other gas chamber)
12. In this two buses are provided.
These two buses are inter-connected by three circuit
breakers.
They are designated as 1-52 CB, 2-52 CB, and 3-52 CB.
Line - 1 is connected in between 1-52 CB & 2-52 CB.
Line - 2 is connected in between 3-52 CB & 2-52 CB.
Line-1 having two feeding paths i.e.
A. Via bus-1 & 1-52 CB
B. Via bus-2, 3-52CB & 2-52CB
Line-2 having two feeding paths i.e.
A. Via bus-2 & 3-52 CB
B. Via bus-1, 1-52CB & 2-52CB
For interrupting line-1 the 1-52CB and 2-52CB is to be
tripped.
For interrupting line-2 the 3-52CB and 2-52CB is to be
tripped.
13. For any problem in line-1 or line-2 along with main breaker, the
tie breaker (2-52 CB) must trip.
Normally in all types of busbar configurations one breaker is
sufficient for one feeder.
Here two feeders are controlled by three breakers.
So these two feeders controlled by three circuit breakers 1-52
CB,2-52CB & 3-52CB.
It is called one & half breaker system.
The bay between bus-1 & line-1 is called main bay for feeder-1.
The bay between line-1 & line-2 is called tie bay for feeder-1 &
2.
The bay between bus-2 & line-2 is called main bay for feeder-2.
In this system full dia means 2 feeders controlled by 3 CBs.
Half dia means 1 feeder controlled by 2 CBs.
14. GIS EQUIPMENT
• Bus bar
• Circuit breaker
• Disconnecting switch
• Earthing switch
• Current transformer
• Voltage transformer
• SF6 to air termination
• Lightning arrestor
• Capacitance voltage transformer
• Wave trap
Outdoor
equipments
20. Properties of SF6
• Non-toxic, very stable chemically.
• Insulating properties is 3-times more than air.
• Colorless & heavier than air.
• Density is 5 times more than air.
• Non inflammable.
21. Compactness of GIS
• Saving of land depending upon voltage level.
• Land required is 10-20% of AIS.
25. Impact of insulating medium on size of the
switchyard
Voltage Level Bay Width AIS Bay Width GIS
132KV 12m 1m
220KV 18m 2m
400KV 27m 3.6m
765KV 51.5m 6.5m
26. ERECTION AND COMMISSIONING
Switchgear assemblies are split into optimized
shipping units for easy transport.
Quick installation is facilitated because of easy to
handle factory assembled modular units.
Need of special tools for erection is very less.
Take less time to check all switching devices and
control circuits.
All flanges are double checked for tightness.
All tests are performed in accordance with IEC
standards.
30. Step3: Install the current transformer
on the circuit-breakers
Step4: Assemble the disconnectors and
earthing switches on to the current
transformer.
43. Life Cycle & Cost of GIS
Life cycle of GIS is about 50 years, where as for AIS life
cycle is 25 years.
Approximate cost per bay for 400 KV of GIS & AIS is as
follows:
GIS 7-8 crores
AIS 4-5 crores.
Hence initial cost of GIS is approximately
1.5-1.7 times that of AIS.
When all merits over the life cycle of GIS is considered
then GIS becomes techno-economic feasible than AIS.
44. Demerits 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).
Reduction in the pressure of the SF6 gas in
any module results in flash over and faults.
SF6 causes ozone depletion and global
warming.
45. CONCLUSION
Excellent adoptability due to low space
requirement and high dielectric strength of SF6
gas.
Short erection and commissioning time.
Safety to operators
less requirement of maintenance.
Initial cost of GIS is higher than AIS, but when all
merits and life cycle cost of GIS is considered the
GIS becomes techno-economic feasible than AIS.