Rural electrification starting from survey, transmission, cost estimation to distribution

1. Rural Electrification

2. Overview of topics
• Survey of OHL
• Design of Transmission and distribution
system
• Cost Estimate
• Construction
• Some pictures

3. Softwares you need
• Autocad
• MHP(Microhydro) design aids
• MS Excel
• Optional:
• ETAP, Power world simulator, Netbas

4. T/D process
Survey Design Construction

5. Transmission and Distribution(T& D)
• Types
• Suspended Overhead on Poles (Overhead Line)
• Buried Cables (Underground Cable)
OH Line(Features)
• Less Expensive
• Frequent Maintenance Required
• Less cost per maintenance
• Does not look aesthetically good in dense locality
• Not preferred in areas which experience heavy snowfall

6. • UG Cable
• Costly Installation(if done per standard 6 times costly compared to OH)
• Less Maintenance
• Higher cost per maintenance
• Highly desirable in densely located areas
• Obvious choice for areas which experience heavy snowfall
• ACSR (Aluminium Conductor Steel Reinforced) conductors are the norms
of the day(as against hard drawn copper which were used in earlier days)

7. Components used
• Transformers
• Poles
• Insulators
• Lightning arrestors and Earthing plates

8. Transformer
• ONAN type
• Step up transformer near to generating station
of high KVA rating and stepdown of smaller
KVA ratings near to load centers
• Sizing is done taking load demand and dividing
by suitable power factor

11. Data sheet

12. Conductor
• ASCR type
• Mainly Dog, Rabbit, Weasel, and
Squirrel
• If dog is on phase, rabbit is taken
in neutral ;similarly if rabbit is in
phase weasel in neutral and so on

13. Comparison between conductors

14. Poles
Voltage
level
230V 400V 11, 33kV

15. Insulator types
Shackle Insulators of suitable
voltage ratings upto 1000V
OH Line
Shackle Insulators ---
Supported(Clamped)by D-Iron
set which is a clamp made out
of galvanized steel
Shackle

16. S. No Size Dimensions Weight Corresponding
conductor
1 Small 55 mm x 55
mm
200 gm Squirrel,
service wire
2 Medium 75 mm x 90
mm
600 gm Gopher, weasel
and rabbit
3 Large 100 mm x 110
mm
1300 gm Dog

17. Disc insulator
• Disc Insulators along
with suitable tension
Set are used for
deadening a line at
11kV or higher.
Pin Insulator
• Pin Insulators are used for
straight runs of 11kV Line

18. Stay sets
• Stay sets to support poles
• Suitable Stay sets are
provided at first pole, at
line end, at all poles set at
an angle and at every fifth
pole even if the poles are
in a straight line
• Two types 16mm dia for LT
and 20mm dia for HT

19. Lightning arrestor and
Earthing
• Lightning Arrestors to
protect lines from
Lightning
• 0.5kV ,ZnO
(Gapless)Arrestors for
400Volt Line
• 12kV, 5kA ZnO(Gapless)
Arrestors for 11kV Line
• Placed every 500m and on
junctions and last(end)
points
• Drop Out(DO) Fuse to
Protect Transformers from
Over Current

20. Earthing system
• 600mm*600mm*3.15 mm
copper plate is used for
earthing purposes(weighs
around 10kg)
• Plate is connected with
8SWG copper
wire(4.06dia)
• Earth Resistance value <5
Ohm is desirable but in no
case should exceed 10
Ohm

21. Service wire
• Aluminum cable
connecting from pole to
home
• Generally flat twin
sheathed cable is used
• Wrapped once or twice
around the pole to reduce
stress
• Distance is taken average
of 30m

22. Survey
• Equipment required:
• Total power station(TPS), GPS receiver or measuring tapes and
compass
• Steps:
• Start from generating station
• Take the shortest and straight route for transmission line
• Fix the position of transformer
• Transformer should be positioned at the center of load as far as
possible so as to reduce the voltage drop
• Measure distribution lines length in similar way
• For distribution, within a radius of 30m service wire, otherwise
extend the conductor
• Note all the lengths, nodes and drawings on your notebook

26. c
5 3
3
c
10
100HH
Talu dada
10HH
20HH
Tr3Tr1 5
Tr2
Sunera
Dharan
N

27. Design of Transmission system
• Selection of voltage level
• 230/400/11,000/33,000Volts
• Balanced loading is considered
• Whole power system is radial
• Design Criteria of OH distribution line:
• Maximum allowable voltage drop at the
farthest end shall not exceed 10%

28. • Find optimum line voltage
using 𝑉 = 5.5
𝑙
1.6
+
𝑃
100
0.5
where
l=length(kms) and P=Power in MW
• Take the nearest standard voltage
• Find line current using 𝐼 = 𝑃/ 3*V*pf
• Select the ambient temperature(25degrees)
• Select the allowable range of temperature and
find the resistance at new temp value

29. • Use the relation: R𝑡 = 𝑅20 ∗ ((
1
α
+𝑡) /(
1
α
+𝑡20))
Where R20= resistance of conductor at
20degrees
• Calculate the total resistance multiplying by
length of line
• Find efficiency using relation:ῃ =
𝑃
𝑃+3∗𝐼2∗𝑅
∗
100

30. • Model the transmission line as short and find
the receiving end parameters
•
𝑉𝑠
𝐼𝑠
=
1 𝑍
0 1
∗
𝑉𝑟
𝐼𝑟
Vs
Z
Vr
Is Ir

31. Distribution line voltage drop
calculation
I1,ф1 I3,ф3I2,ф2
ZZSending end
voltage (V)
V1 V2 V3
Phase Current(A) Voltage drop (cV)
3phase P/(sqrt3*V*pf) Sqrt3*I*Z*L
1 phase P/(V*pf) 2*I*Z*L

32. Final design
c
89/5/3/sq
2/0.5/1/sq
1/1/3/sq
c
10/5/3/sq
100HH
10/1/3/dogTalu dada
10HH
20HH
11/0.4
0.4/11 89/1/3/dog
11kV 0.5kV
A/B/C/DA-power(kW)
B-length(km)
C-phase
D-conductor type
HH-House holds
lightning
arrestor

33. Typical drawings

37. Cost Estimation
• Conductor estimate
• Add 10% for sag obtained from design length
• Calculate the length of phase conductors and neutral
• Pole estimate
• For HT lines, divide length by 50m to get no. of 8m steel tubular poles
• For three phase section, divide length by 35m to get no. of 7m wooden poles
• For single phase section, divide length by 35m to get no. of 6m wooden poles
• Transformer estimate
• Calculate the cost of no. of transformers in the project
• Insulator estimate
• HT
• Multiply no. of steel tubular poles by 3 to get number of pin insulators
• LT
• For 7m poles multiply by 4 to get number of shackle insulators
• Care must be taken to get medium and large size shackle insulator
• Multiply no. of 6m poles by 2 to again obtain shackle insulator

38. • Pole mounted substation
• Each pole requires 6 disc and 6 pin insulators, 3 DO fuse, 3 lightning arrestors, 1 earthing set
and 1MCCB
• Double station
• Each station requires 4 steel tubular poles, 6 disc insulators and 3 pin insulators
• Lightning arrestors
• HT arrestors:
• Divide the HT straight length by 500 and multiply by 3 o obtain no. Of lightning arrestors
• LT arrestors:
• Divide the LT straight length by 500 to obtain no. Of lightning arrestors. If it’s a 3phase
system multiply by 3 to get no. of lightning arrestors .
• If it’s a single phase system only 1 LA is connected and thus no. is obtained
• Stay set
• On every first, fifth and last pole, it should be provided. Simply, divide total no. of tubular
poles by 5 which gives the no. of HT stay set
• Similarly, divide total no. of 6m and 7m poles by 5 to get no. of LT stay set

39. • Earthing set
• Divide the HT straight length by 500 to obtain no. of earthing
sets
• Divide the LT straight length by 500 to obtain no. Of earthing
sets
• Service wire
• Multiply house hold number by 30m and per metre cost to
get service wire cost
• Multiply all numbers by respective cost to get total
transmission cost estimate

40. Sample of cost estimate

41. Construction
• Choose a straight short line
• Calculate the number of poles required for the
given length and mark it through pegs
• The poles should be buried 1m with bitumen
paint
• Fix D-iron and insulators
• Insert the pole and check the verticality with a
plumb bob
• Commence unrolling of conductor and install
using manual wire puller

42. Unrolling

44. Method of joining

50. Earthing

53. Lightning arrestor installation

55. Salient features
• Low voltage transmission system is still
popular in under-developed and developed
countries where reach of national grid is
difficult
• Off grid settlement or decentralized
generation
• Help in fights on poverty elimination and
sustainable development which is the mean
motto of UNDP, Practical Action, GIZ etc

56. Pictures

69. References
• MHP design aids, Pushpa Chitrakar, GIZ Nepal
• Microhydro Design manual, Adam Harvey
• Mini grid manual, Allan Inversin
• www.etap.com
• www.aepc.gov.np
• Jayaram Karkee, Minigrid Engineer, Resource management
and rural Empowerment Center
• Transmission and Distribution Electrical Engineering Third
edition, Dr C. R. Bayliss CEng FIET and B. J. Hardy ACGI CEng
FIET
• A text book on power systems, BR Gupta