rural electrification

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A detailed description on rural electrification


  • Rural Electrification

  • Overview of topics

    Survey of OHL

    Design of Transmission and distribution system

    Cost Estimate


    Some pictures

  • Softwares you need


    MHP(Microhydro) design aids

    MS Excel


    ETAP, Power world simulator, Netbas

  • T/D process

    Survey Design Construction

  • Transmission and Distribution(T& D)


    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

  • 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)

  • Components used




    Lightning arrestors and Earthing plates

  • 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

  • Data sheet

  • 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

  • Comparison between conductors

  • Poles

    Voltage level

    230V 400V 11, 33kV

  • 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


  • S. No



    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


  • 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

  • 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

  • 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

  • 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

  • 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

  • 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

  • c

    5 3





    Talu dada



    Tr3 Tr1 5





  • Design of Transmission system

    Selection of voltage level


    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%

  • Find optimum line voltage

    using = 5.5



    0.5 where

    l=length(kms) and P=Power in MW

    Take the nearest standard voltage

    Find line current using = / 3*V*pf

    Select the ambient temperature(25degrees)

    Select the allowable range of temperature and find the resistance at new temp value

  • Use the relation: R = 20 ((1

    +) /(



    Where R20= resistance of conductor at 20degrees

    Calculate the total resistance multiplying by length of line

    Find efficiency using relation: =



  • Model the transmission line as short and find the receiving end parameters

    =1 0 1




    Is Ir

  • Distribution line voltage drop calculation

    I1,1 I3,3 I2,2

    Z Z Sending 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

  • Final design








    10/1/3/dog Talu dada



    11/0.4 0.4/11 89/1/3/dog

    11kV 0.5kV

    A/B/C/D A-power(kW) B-length(km) C-phase D-conductor type HH-House holds

    lightning arrestor

  • Typical drawings

  • 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

  • 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 its a 3phase

    system multiply by 3 to get no. of lightning arrestors . If its 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

  • 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

  • Sample of cost estimate

  • 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

  • Unrolling

  • Method of joining

  • Earthing

  • Lightning arrestor installation

  • 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

  • Pictures

  • References

    MHP design aids, Pushpa Chitrakar, GIZ Nepal

    Microhydro Design manual, Adam Harvey

    Mini grid manual, Allan Inversin

    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


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