# rural electrification

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A detailed description on rural electrificationTRANSCRIPT

Rural Electrification

Overview of topics

Survey of OHL

Design of Transmission and distribution system

Cost Estimate

Construction

Some pictures

Softwares you need

Autocad

MHP(Microhydro) design aids

MS Excel

Optional:

ETAP, Power world simulator, Netbas

T/D process

Survey Design Construction

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

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

Transformers

Poles

Insulators

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

Shackle

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

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

3

c

10

100HH

Talu dada

10HH

20HH

Tr3 Tr1 5

Tr2

Sunera

Dharan

N

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%

Find optimum line voltage

using = 5.5

1.6+

100

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

+) /(

1

+20))

Where R20= resistance of conductor at 20degrees

Calculate the total resistance multiplying by length of line

Find efficiency using relation: =

+32

100

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

=1 0 1

Vs

Z

Vr

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

c

89/5/3/sq

2/0.5/1/sq

1/1/3/sq

c

10/5/3/sq

100HH

10/1/3/dog Talu dada

10HH

20HH

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

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

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