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IV B. Tech I semester (JNTUH-R15)

Prepared

By

Dr. P Sridhar

ELECTRICAL AND ELECTRONICS ENGINEERING

INSTITUTE OF AERONAUTICAL ENGINEERING(AUTONOMOUS)

DUNDIGAL, HYDERABAD - 500043

UNIT - I

INRODUCTION &GENERAL CONCEPTS

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Hello viewers ,in this lecture we shalllearn about the distribution system. Sothat dc as well as ac distribution systemalso we shall discuss about Thecomponents of a pole mountedsubstation and components fitted onlattice steel tower for transmission of aHT line. some insulators will also bediscussed…..

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The Transmission system can be divided into two parts:----Primary Transmission Secondary Transmission

The Distribution system can be divided into two parts:----Primary DistributionSecondary Distribution

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A distributor is set to the legalrequirement that power must besupplied at a voltage within ± 6% of thedeclared voltage., whereas atransmission system is not subject to anysuch restriction . Its voltage can vary asmuch as 10% to 15% due to variation inloads. any restriction in transmissionsystem is technical and not legal. Thetransmission system of an area is calledGRID.

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The different grids are inter connectedthrough the lines to form a regional gridand the different regional grids are furtherinterconnected to form a national grid.Each grid operates independently.However power can be transmitted fromone grid to another. The maximumgeneration voltage in advanced countries is33 kV while that in India is 11 kV. Theamount of power that has to betransmitted through transmission lines is

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The amount of power that has to betransmitted through transmission lines isvery large and if this power is transmittedat 11kV the line current and power losswill be large. There fore the voltage isstepped to a higher level by using step-uptransformers located in sub-stations.

Also volume of conductorused in transmission lines depends uponthe voltage and current.

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The three phase transmission anddistribution system may consist of

Overhead lines

Underground cables

The main advantage ofunderground system are that it is lessprone to electric hazards like rain , wind& lightning. and that it does not interferewith other amenities.

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F E E D E R S D IS T R IB U T O R S S E R V IC E M A IN S

D is tr ib u t io n

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Fig.Classification Of Distribution Systems

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UNIT - II

DISTRIBUTION FEEDERS &SUBSTATIONS

FEEDERS• These are the cables supplying power

in bulk to a selected number of pointscalled feeding points The feeders runalong streets overhead (orunderground, in some cases) andpower the distribution transformersat or near the customer premises.

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DISTRIBUTORS

• Distributors are used for current Tapping for the various consumers these cables are generally having the main street for there route .

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SERVICE MAIN

• Service mains are the small cables teed of off from the distributors and taken into the premises of the various consumers these are low tension cables.

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EFFECT OF SUPPLY VOLTAGE ON THE SIZE OF DISTRIBUTOR

The allowable current density for giventype of cable laid is not constant butdecreases somewhat as the cable sizeincreases. If voltage of the system isincreased N folds then for a given powerdelivered The current is reduced to1/Nth.Size of cable is reduced to 1/Nth.

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BALANCERS

The generators supplying a three-wire feeder are all connected inparallel across the outers, and it istherefore necessary to fix thepotential of the middle wire midwaybetween that of the outers,otherwise voltages will not be equal,unless the currents taken from theouters are equal.

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POLE-MOUNTEDSUBSTATION

The substation consisting of a transformer and other apparatus installed on the pole structure is known aspole mounted substationAs the name implies such substation are installed on H-pole structure many times

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COMPONENTS OF11kV/ 400V POLE MOUNTED SUB-

STATION

It is an out-door type substationand is erected on a pole structure. thiserected pole is also called H-polestructureThe various components of sucha sub-station numbered as under:-

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1)---R.C.C. Pole Structure2)--Platform for transformer3)--Transformer4)--Pin-Type insulator5)-Jumpers6)--Strain insulator7)--Fuses8)--Gang Operating switch9)--P.G. Clamps

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10)-Earthing11)--Caution Plates12)--Stay wire13)-Anchor road14)-Stay insulators15)-Anti-climbing devices16)-G.I. Pipe and bends17)-V.I.R. Cable18)-T.P.I.C. Switch

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20Fig. Pole Mounting

ESTIMATING OF 11KV/440V POLE MOUNTED

OUTDOOR SUBSTATION

M.S.channel

for cross arm 10cm x 5 cm x 1.5mt long 1no

H.T. 11 kV

disc insulators

with fittings

11kv grade, porcelain body,

glazed

3nos

H.T. 11 kV

pin insulators

with fittings

11kv grade, porcelain body,

glazed 3nos

Stay sets

complete

Stay clamp ,stay insulator,

stay bow, egg insulator

2 sets

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Fig. Outdoor Transformer

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UNIT - III

Distribution System Analysis: Voltage drop and

power-loss calculations

Earth wire

clamp.

M.S flat with nut & bolt 1no

Binding

wire

Aluminum wire 500

gm

Total

Conductor

ACSR gopher 6/1/2.36

mm diameter: length 50

x 3=150mts sag

allowed1% = 1.5mt

150+

1.5 =

151.5

mts

Galvanized

steel wires

8 SWG ,galvanized steel 50.5

mt or

6 kg

R.S joist

poles

R.S joist, 175 mm x 100

mm x 10 mts long

2nos

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substation plate

100 mm x 50 mm x 6mm long 1no

dropper angle iron

75mm x 75mm x 8mm x 2mts long long

1no

Stay sets complete

a) Stay clamp

b) Stay insulator

40x6 mm,M.S flat

with nut & bolt.

2nos

2nosH.T grade, ,

porcelain body,

glazed

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Disc insulator

11kv grade, porcelain body,

glazed

3nos

Pin insulators

with pins 11kv grade, porcelain body,

glazed 3nos Danger board

with clamp

Written in local, national,

English language

1no

Jump wire for

jumpering

ACSR gopher 6/1/2.36mm dia 1kg

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T.P.M.O switch Iron clad Switch with handle 1no

Painting for

poles and other

attachments

2 ltr

Fuse set 415v,60amp,copper or tinned alloy 1set(3

Nos)

Transformer

Cross channel

for

transformer

50 KVA 11/0.4 kV

75x40x6cm M.S channel, 0.7mtr

long

1no

1no

Earthing

complete

a) salt

b) charcoal

c) Earthing set

Complete Earthing set

25kg

25kg

1set

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1 ) T r a n s fo r m e r

2 ) C r o ss c h a n n e l

fo r t r a n s fo r m e r

5 0 K V A 1 1 /0 .4 k V

7 5 x 4 0 x 6 c m M .S c h a n n e l , 0 .7 m tr

lo n g

1

1

M a in sw itc h T P IC N ( T r ip le P o le ir o n c la d a n d

N e u tr a l ) m a in sw itc h w ith 3 fu se s

& w ith o n e n e u tr a l l in k , 1 0 0 a m p ,

a n d b u i l t in H R C fu se u n i t .

1 n o

E a r th in g fo r

tr a n sfo r m e r

C o m p le te e a r th in g 1

F e e d e r 3 p h a se , 4 w ir e , 5 0 c y c le s , 4 0 0 /4 4 0

vo l ts

3 N o s

T r a n s p o r ta t io n &

la b o u r c h a r g e

A s

r e q u i

r e d

L ig h tn in g a r r e ste r 1 1 k V g r a d e ,g la ze d 3 N o s

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Dimensions of Danger PlateTwo sizes of Danger Notice Plates as follows are recommended:For display at 415 V installations –200x150mm---For display at 11 KV (or higher voltages) installations – 250x200mmThe corners of the plate shall be rounded off. The location of fixing holes is provisional and can be modified to suit the requirements of the purchaser.

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Lettering of Danger PlateAll letterings shall be centrally spaced.The dimensions of the letters, figures andtheir respective position shall be asshown in figs on next slideThe size of letters in the words in eachlanguage and spacing between themshall be so chosen that these areuniformly written in the space earmarkedfor them.

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Fig. Safety Precautions

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UNIT - IV

Protective devices & co-ordination:

Languages of Danger PlateUnder Rule No. 35 of Indian Electricity Rules,1956, the owner of every medium, high andextra high voltage installation is required toaffix permanently in a conspicuous position adanger notice in Hindi or English and, inaddition, in the local language, with the sign ofskull and bones.The type and size of lettering to be done inHindi is indicated in the specimen dangernotice plates shown in Fig. 2 and those inEnglish are shown in Figs.

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Now let us discuss about the componentsRegarding the lattice steel tower fordistribution the ac voltage. The mainsupporting unit of overhead transmission lineis transmission tower. Transmission towershave to carry the heavy transmissionconductor at a sufficient safe height fromground. In addition to that all towers have tosustain all kinds of natural calamities

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•So transmission tower designing is

an important engineering job where

all three basic engineering

concepts, civil, mechanical and

electrical engineering concepts are

equally applicable.

• Main parts of a transmission

tower A power transmission tower

consists of the following parts,

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•1) Peak of transmission tower

2) Cross Arm of transmission tower

3) Boom of transmission tower

4) Cage of transmission tower

5) Transmission Tower Body

6) Leg of transmission tower

7) Stub/Anchor Bolt and Base plate

assembly of transmission tower

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Fig.Lattice steel tower

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•Peak of transmission tower

•The portion above the top cross arm is

called peak of transmission tower.

Generally earth shield wire connected to

the tip of this peak.

•Cross Arm of transmission tower

•Cross arms of transmission tower hold

the transmission conductor. The

dimension of cross arm depends on the

level of transmission voltage,

configuration and minimum forming

angle for stress distribution. 38

•Cage of transmission tower

•The portion between tower body and peak

is known as cage of transmission tower. This

portion of the tower holds the cross arms.

•Transmission tower body

•The portion from bottom cross arms up to

the ground level is called transmission tower

body. This portion of the tower plays a vital

role for maintaining required ground

clearance of the bottom conductor of the

transmission line.

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The “Stockbridge” type vibration damperis commonly used to control vibration ofoverhead conductors and OPGW. Thevibration damper has a length of steelmessenger cable. Two metallic weightsare attached to the ends of themessenger cable. The centre clamp,which is attached to the messengercable, is used to install the vibrationdamper onto the overhead conductor.

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Fig.Stockbridge

Ring Distributor

A ring distributor is a distributor which isarranged to form a closed circuit and whichis fed atone or more than one points. Forthe purpose of calculating voltagedistribution, it can be looked uponasconsisting of a series of open distributorsfed at both ends. By using a ring distributorfed properly, great economy in copper canbe

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affected. If the ring distributor is fed at onepoint then, for the purposes of calculation,it is equivalent to a straight distributor fedat both ends with equal voltages There are3 type of power distribution namelyloop,network and radial.Radial distributionis the type of power distribution where thepower is delivered from the main branch tosub-branches then it split out from thesub-branches again. it is the cheapest butleast reliable network configuration.

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Ring main system –- In this system, variouspower stations or sub-stations areinterconnected alternate routes, thus forminga closed ring. In case of damage to any sectionof the ring, that section may be disconnectedfor repairs and power will be supplied fromboth ends of the ring. A radial system has asingle simultaneous path of power .

The distribution systems are typically radialbecause networked systems are moreexpensive.

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UNIT - V

Voltage Control & Power Factor Improvement

ADVANTAGES OF OUT-DOOR SUBSTATIONS

• Fault location is easier.

• Extension of the installation is easier.

• Less time is required foe their erection.

• The cost of civil engine4ering work is less.

• Practically no danger of a fault which appears at one point being carried over to another point.

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Now let us discuss some insulators used

In distribution systemsPin type insulatorsPost type insulatorsDisc type insulatorsD-Shakle type insulatorsEgg type insulatorsReel insulators ………etc

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Fig. Pin Insulator

Pin Insulator is earliest developedoverhead insulator, but still popularlyused in power network up to 33KVsystem. Pin type insulator can be one part,two parts or three parts type, dependingupon application voltage. In 11KV systemwe generally use one part type insulatorwhere whole pin insulator is one piece ofproperly shaped porcelain or glass. As theleakage path of insulator is through itssurface

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In higher voltage like 33KV and 66KVmanufacturing of one part porcelain pininsulator becomes difficult. Because in highervoltage, the thickness of the insulator becomemore and a quite thick single piece porcelaininsulator can not manufactured practically. Inthis case we use multiple part pin insulator,where a number of properly designedporcelain shells are fixed together by Portlandcement to form one complete insulator unit.For 33KV tow parts and for 66KV three partspin insulator are generally used.

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Post Insulator--Post insulator is more or less similar to Pininsulator but former is suitable for highervoltage application. Post insulator has highernumbers of petticoats and has greater height.This type of insulator can be mounted onsupporting structure horizontally as well asvertically. The insulator is made of one pieceof porcelain but has fixing clamp arrangementare in both top and bottom end.

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Fig.Pin Insulator

Fig. Suspension Insulator

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In higher voltage, beyond 33KV, itbecomes uneconomical to use pininsulator because size, weight of theinsulator become more. Handling andreplacing bigger size single unit insulatorare quite difficult task. For overcomingthese difficulties, suspension insulatorwas developed.

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In suspension insulatornumbers of insulators areconnected in series to form astring and the line conductoris carried by the bottommost insulator. Each insulatorof a suspension string iscalled disc insulator becauseof their disc like shape.

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Fig. Suspension Insulator

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Fig. Strain Insulator

When suspension string is used to sustainextraordinary tensile load of conductor itis referred as string insulator. Whenthere is a dead end or there is a sharpcorner in transmission line, the line hasto sustain a great tensile load ofconductor or strain. A strain insulatormust have considerable mechanicalstrength as well as the necessaryelectrical insulating properties.

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Fig. Shackle Insulator

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Fig. Stay Insulator

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Fig. GlassInsulatorFig. Suspension(Polymer) Insulator

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