construction of a transmission line
TRANSCRIPT
Notes prepared by Er. Vibhor Mittal
Construction of a transmission line
A transmission system consists of associated transmission line and transmission station. A transmissionstation further consists of a substation and switching station (voltage coming to that station and goingfrom that station. It is classified as HV< 66kV, EHV=110/132/220/400kV and UHV>800/1200kV.
1. Statuary clearance: A mandatory requirement that is to be followed before construction of atransmission line. They will be approving after consent of the constituents of all the authorities(constituents), in this case Central Electricity Authority or CEA who has to approve the proposal.
2. Here, we require two points for construction of one transmission line that is a starting point andending point, we call it as dead points.
3. Starting point maybe a generation point or a substation.
4. While construction of a substation we require some extra land so that, this land may further beutilize for construction of a new bay.
NOTE: Augmentation is known as switchyard extension.
5. After that we have to go for the configuration of the circuit that are of three types that aresingle circuit, double circuit and multi-circuit. These days we prefer double circuit andmulti-circuit.
6. Statutory requirements related to following are necessary:
Airports
Mines
Forest
Hilly area
Marshy soil
Urban area
River crossing
Power-line
PTCC (power transmission coordination commission)
Notes prepared by Er. Vibhor Mittal
Gas pipeline
National highway
3 km
Figure of a river crossing
1 km
20 km radii
4 km radii Figurefor airport
8 km radii
NOTE: Truncated tower is used in this case (airport) which are of lower heights and have special iridiumcoating so that they can reflect the light ray so as to make the pilot of aircraft understand that here issomething with a good height. Also aviation signals are used for the same.
Notes prepared by Er. Vibhor Mittal
In case of railway crossing which is done 250m away, which is here tower falling distant.
NOTE: Life of normal tower is 50 year and river tower 150 year.
7. Tower foundation for the river tower is the strongest and costliest of all. Pit foundation as it isknown by the specialist civil agencies.
8. New concept is developed for the same is of anchor tower.
Anchor tower
Main tower
River Main tower
Anchor tower Figure for anchor tower
Another type of arrangement for the same type of construction is of mid stream location
Main
Tower
Mid stream towers Figure showing for mid stream
Developed by Power Grid Corp.
Main tower
Notes prepared by Er. Vibhor Mittal
NOTE: The above type of work is done during summer seasons where the work speed is moreand water levels are lower.
For the road minimum 12-15 meters ground clearance is required, for the slag and the span is of300 to 350 meters.
NOTE: Serve and route ailment is done before approaching the agency and final inspection isconducted for CEA and state regulatory bodies.
9. Then we proceed with the procurement of the maps or TOPO’s from Survey of India with indent(payment) made against each map. The maps are also of two types that are restricted andunrestricted maps. It is of two scales only that are 1:250000 and 1:50000. They are printed atBhopal and Dehradun.
10. Straight line joining starting and ending point is called BEE LINE or CROW FLY LINE.
dead end dead end
BEE LINE
A B
NOTE: 3 alternative lines is to be made with a comparison statement
11. Exercise of survey starts from here. First of all walkover survey is done, that means walkover theailment. This is done with help of GPS device with a tolerance of +/- 5 meters. We have toupdate the map here and there. Also, we have to visit the crossing points like that of a rivercrossing etc., from both the sides. Also railway crossings, highway crossing. There we make ourmarkings etc.
Notes prepared by Er. Vibhor Mittal
5 meters
These things will help to go for the next survey.
NOTE: The maximum angle of deviation is less than 60 degrees. The angle of deviation will beabsolute angle like 38 degrees, 42 minutes, 22 seconds with GPS device.
We next have to make a project report for the records.
NOTE: Dead cover will be zero degree of deviation.
12. Preliminary Survey (Field work which is currently outdated in practice): Instrument used isTOTAL STATION. It is a sophisticated machine just like a mini-computer with error of +/- 0.5meters and range of 4 kilometers in vision, also shows exact angle of deviation.
NOTE: Multi-circuit concept is fast catching up, generally used for forest where this can beutilized for procuring future requirements.
Here identification stones are laid down, that are 2 feet, 9 inches long. One AP to AP is calledsection length. With preliminary survey the route ailment is finalized based on the collectedparameters.
13. Detailed Survey: Here with tower spotting data is developed by the engineering departmentand average span, maximum span etc., parameters are calculated.
14. Next tower scheduling is prepared keeping the above in mind. 360 meters is the maximum spanfor 220 kV line and 400 kV for the 400 meter span. The angle tower (2 degree) and suspension(zero degree) should not be loaded.
Notes prepared by Er. Vibhor Mittal
Figure showing tower arrangements
NOTE: The sum should not exceed 800 meters that is 13+2 towers.
NOTE: Here full and final compensation of tree is been provided, that is to the owner. Thecounting of tree and then payment is made according to the tree enumeration (that is its age,width, etc.) This compensation is one time only but in case of crops we have to bear thepayments thrice. The statement of tree enumeration is prepared and fed to TOTAL STATION forfurther computation of the space and route ailment.
Finally, we have to draw our profiles in accordance with the drawing curves.
15. Profiling: For the each span, drawing curves is being prepared which is called profile. It is drawnin the graph sheet called sag template curve.
Sag showing curves Figure showing sag
The software used for drawing profiles is called PLS Cadd, andthe software used for drawing route ailment is called Image Processing software.
After doing all this we will study what type of tower should be placed. They are only two types:
Suspension towers
Tension towers
Suspension towers are of A/DA/MA and they are of zero degree elevation called as A typetower or tangent tower or sometimes P type tower. An elevation of 2 degrees is kept for human
Notes prepared by Er. Vibhor Mittal
error rectification and weight around 4.5 metric tonne. It is no-load bearing tower and itdamage prone tower.
Tension tower are of three types:
B/DB/MB for zero degree to 15 degrees deviation
C/DC/MC for 15 degree to 30 degrees deviation
D/DD/MD for 30 degree to 60 degrees deviation (strongest and heaviest)