DGVCL WINTER INTERNSHIP REPORT

1. 1
Dakshin Gujarat Vij Company Limited
SURAT(GUJARAT)
INTERNSHIP REPORT
B. TECH II
PERIOD -3 DEC, 2018 – 25 DEC, 2018
SUBMITED BY-
• ABHIJEET BANSAL
• ANSHUMAN SINGH JHALA
• RINKU
• SHANTI SHAVROOP
• SHYAM LAL KUMAWAT
SUBMITED TO-
Mr. B.D. PATEL,
Deputy Engineer,
Pal Subdivision, DGVCL, Surat

2. 2
PREFACE
Theoryof anysubjectisimportantbutwithoutitspractical knowledgeitbecomesuseless, particularly
for technical students.A technical studentcannotbecome a perfectengineerortechnologistwithout
practical understandingof theirbranch,hence trainingprovidesagoldenopportunityforall technical
students to interact with the working environment.
While undergoingtrainingatDGVCL (Pal Subdivision) Surat, we learneda lot of practical aspect.Our
theoretical Knowledge wasexposedhere practically.Inthisreportwe have triedto summarise what
we have learnedatDGVCL.For preparingthisreportwe visitedthe substationandvariousothersites
and cleared related doubts to the responsible personal.
Thistraininghelpedustounderstandthe basicconceptof the powerdistribution.Duringthisperiod,
we became aware of the problemsfacedinthe companyandalso of the workingenvironmentof the
company.

3. 3
ACKNOWLEDGEMENT
Training has an important role in exposing the real-life situation in a company. It was a great
experience forme toworkontrainingatDakshinGujaratVij CorporationLimitedthroughwhichIcould
learn how to work in a professional environment.
NowWe wouldlike tothankthe peoplewhoguidedusandhave beenaconstantsource of inspiration
throughout the tenure of our winter training.
We are sincerelygrateful to Mr. B.D. Patel (Deputy Engineer at Pal Substation) who rendered us his
valuable assistance andconstantencouragementwhichmade thistrainingactuallypossible.Also,for
continuously guiding throughout various aspects, functioning of the company and allocating us the
appropriate schedule to undertake the training.
Our sincere thanksto Mr.Vedant,Mr. Kuldeep andMr. JigneshPatel forhavingsupport,guidance at
ground level and sharing valuable technical knowledge.
And at last but not least,we are also thankful to all the staff membersof the companyfor their kind
corporation and valuable guidance throughout the process of work.

4. 4
DAY 1: 3/12/2018
About DGVCL
(Dakshin Gujarat Viz Nigam Limited)
DGVCL,Surat.The companyisinvolvedinelectricitysub-transmission,distributionandretailsupplyin
the southpart of Gujarat or outside the State.Theirmandate is to establishanduse a powersystem
networkandto buy and sell electrical energy,andtocollectinformationwithaneye towardsfurther
system improvements.
The Gujarat Electricity Industry (Re-Organization & Regulation) Act 2003 paved the way for
comprehensive reformandrestructuringof the State ElectricityBoardwithan aimto restructure the
ElectricityIndustryinamannerthatwill ensurethe long-termviabilityandsustainabilityof the power
sectorinthe state.Asa part of the reformprocess, GujaratElectricityBoardhasbeenunbundledinto
separate seven Companies with functional responsibilities for generation, transmission, distribution
and trading of electricity with complete autonomous operations.
Accordingly,the distributionundertakingsandfunctionsof the SouthernDistributionZone of the
erstwhileGEBare transferredto DakshinGujratVij CompanyLimited. The companywasincorporated
asa PublicLimitedCompanyon 15thSeptember,2003,primarilytocarryoutdistributionof electricity
to retail and bulk consumers and has become operational effective from 1st April 2005.
The Companyis engagedin distributionof electricityin7 districts namely Bharuch, Narmada, Surat
(exceptsome part of Surat City), Tapi, Dangs, Navsari and Valsad in South Gujarat. The Companyis
a wholly owned subsidiary Company of Gujarat Urja Vikas Nigam Limited, a government Company.
The Companywas incorporatedwithanauthorizedCapitalof Rs.10 Lacs dividedinto1,00,000 equity
shares of Rs.10/- each, the same has been increased to Rs. 500 Crores.
 Registered office - Nana Varachha Road, Nr. Kapodra Char Rasta, Surat-395006.
 Covered area - 23,307 Km2
 Number of consumers - 27.32 Lac consumers
TERRIF- The amountof moneyframe bythe supplierforthe supplyof electrical energytovarious
typesof consumersinknownas an electricitytariff.The tariff covers the total costof producingand
supplyingelectricenergyplusareasonable cost.
There are two parts of it-
• Fixed part – for meter’s rental charges and other maintenance
• Variable part – for daily supply of energy
Total bill of consumer has three parts –
• fixed charge
• semi fixed charge
• running charge (variable charge)
C = A.x +B.y +D;

5. 5
Here,
C= total charge for a period
x= maximum demand during the period
A= cost per kW or kVA of max. demand
B= cost per kWh of energy consumer
y= total energy consumed during the period (kW or kVA)
Factor affecting tariffs
1. Type of load
 Domestic
 Commercial
 Industrial
2. Max demand – Cost of electrical energy supplied by generation station (GS) depends on
installedcapacityof plantand KW generated.Increase inmax demandrequiresmore power
to be generatedthatmeanit will require highercapacityplantthatwouldresultsinincrease
in the cost of electricity.
3. Power factor – It is an important parameter for electricity billing. If the power factor is less
than1 or so,thenthe electricalsystemwouldrequiresomeadditionalpower(reactivepower)
in addition with the actual power consumed. This additional power is also drawn from the
supplythoughitisnotconsumed.Forhouseholdappliancesp.f.iscloseto1soreactive power
is not considered for billing but if it falls below a critical value (generally.9) then additional
charges are employed. For industriesreactive power is also being considered for billingand
they have to maintain their p.f. around .7 otherwise additional charges are employed.
4. Time at whichload isconsumed- In“time of billing”system,electricityissuppliedatdifferent
rates duringdifferentintervalsof time (peak,off-peak,night,resthours) soas to control the
electricity consumption during particular period of time (Peak hours).
For improving the power factor, power factor correction equipment is installed and measures are
adopted at generating stations.
Type of electrical tariff: -
 Flat demand tariff
 Straight line meter rate tariff
 Block meter rate tariff
 Two port tariff
 PT tariff
 Seasonable rate tariff
 Peak load tariff
 Three port tariff

6. 6
TYPE OF CONSUMERS
1. RGP- For ResidentialGeneralPurpose havingloadupto6kW. The followingare the categories
of RGP:
 Rural
 Urban
 BPL (Below Poverty Line)
2. GLP- For GLP usedin educational institutesandotherinstitutionsregisteredwiththe Charity
Commissioner or similar placed authority and research and development laboratories.
3. NON-RGP - For aggregate load up to and including 40 kW.
4. NONRGP NIGHT - For usingsupplyduringnighthoursand havingchargeslessthanNON-RGP
5. LTMD - For aggregate load above 40 kW and up to 100 kW.
6. LTMD NIGHT - For using supply during night hours and having charges less than LTMD
7. LTP - For Purpose of Lift Irrigation
8. WWSP - For water works and sewage pumping purpose
9. AG - Applicable to service used for irrigation purposes only excluding installations covered
under LTP
10. SL - For purpose of Street Light
11. LTEV - For purpose of LT Electric vehicle charging stations.
Supply of Electricity at High Tension (3.3KV, 3φ, 50 Hz):
 HTP-I - For regularsupplyof electricityandpurpose notspecifiedinanyotherHT categories.
 HTP-II - For Waterworksand sewage pumpingstationsrunbyLocal authoritiesandGW & SB
GIDC Water works.
 HTP-III - For consumer using electricity on regular basics.
 HTP-IV - For consumer using electricity during Night hours (10:00PMTO 06:00AMnext day)
 HTP-V - For HT Lift Irrigation only
 RAILWAY TRACTION - For power supply to Railway Traction at 132kV/66kV
 HTEV - For consumers who use electricity exclusively for electric vehicle.
Types of Conductor-
Mainlythe followingtypesof conductors inthe basisof material usedforthe over-headtransmission
and distribution-
 AAAC (All Aluminium Alloy Conductor)
 AAC (All Aluminium Conductor)
 ACSR (Aluminium Conductor Steel Reinforced)
 ACAR (Aluminium Conductor Aluminium-Alloy Reinforced)
Depending on the requirement, wires of different cross-section and different material are
required.

7. 7
Types of Technical Survey- Before starting of any electrical project, technical survey of the area is
being carried out.
1. Class A- It incudes the survey within the span of 30m for small works.
2. Class B- It includes the survey for LT lines.
3. ClassC- Itincludesthe surveytoverifythe increasedcapacityforprovidingtransformerinthe
LT lines.
4. Class D- It iscarriedout for megaprojects.

8. 8
Day 2 & 3: 4/12/2018 & 6/12/2018
Electricmetres- An electricitymeter, electricmeter, electricalmeter,orenergymeterisadevice that
measures the amount of electric energy consumed by a residence, a business, or an electrically
powered device.
 For residentialandofficial buildings,the billingisdoneforthe kilowatthour(kWh)consumed
as forsuch buildingsispowerfactorof loads isashighas.9 or more.Butincase of industries,
extra charges are being employeddepending on the power factor which is not as high as in
the former case.
 In some areas “time of day” metering is used where the bill is charged as per the period of
time (peak hours, off-peak hours, night hours, rest hours etc.). This is done to control the
excesspowerconsumptionduringcertainperiod(mainlypeakhours) byincreasingthe billing
rate.
 Electricity meters operate by continuously measuring the instantaneousvoltage (volts)
and current (amperes) to give energy used (in joules, kilowatt-hours etc.).
Mainly the electricmetersare of twotypes- The readingof the metersistoobservedregularlybythe
suppliercompanyformakingthe electricitybill.However,smartmetersare alsoavailable now adays
which sent the readings directly to the company office via internet and hence there is no need for
taking the reading by moving from home to home. But they are not much in use currently due to
technical and financial issues.
1. Electro-mechanical meter- This meter works through electromagnetic induction and
measuresthe electricpowerintermsof numberof revolutions made bya non-magneticbut
electrically conductive disc which rotates at a speed proportional to the power passing
through the meter and hence the energy usage.
 The disc is acted upon by two sets of induction coils, which form, in effect, a two
phase linear induction motor.
 One coil is connected in such a way that it produces a magnetic flux in proportion to
the voltage andthe otherproducesamagneticflux inproportiontothe current.The field
of the voltage coil is delayed by 90 degrees, due to the coil's inductive nature, and
calibrated using a lag coil.
Permanent
magnet
Counter box

9. 9
 This produces eddy currentsin the disc and the effect is such that a force is exerted on
the discin proportionto the product of the instantaneouscurrent,voltage and cosine of
phase angle (power factor) between them.
 A permanent magnet acts as an eddy current brake, exerting an opposing force
proportional to the speed of rotation of the disc. The equilibrium between these two
opposing forces results in the disc rotating at a speed proportional to the power or rate
of energy usage.
 The discdrivesaregistermechanism equippedwithgears whichcountsrevolutions,much
like the odometer in a car.
 Different phase uses additional voltage and current coils.
 The amountof energyrepresentedbyone revolutionisdenotedbyKhwhosevaluediffers
for different meters. Power in one revolution of disc is given by-
P=
3600 .𝐾ℎ
𝑡
where t (sec) istime takenby disc to complete one revolutionandP (watts)
is power in one revolution of the disc.
Errors and thefts in electro-mechanical meter-
It is subjected to environmental factors like humidity, dirt, dust etc., that results in
corrosion, worn out gears and insects can also result in the malfunctioning of the
meter.
Drying of gear lubricants can also results in inaccuracy in measurement.
The above two errors can be minimised by regular maintenance.
They can more easilytransformedforthe theftslike use of magnet for opposingthe
discmotion,reducingnumberof turnsof voltage or currentcoil,by keepingmeterin
horizontal position, by shorting of coils etc.
2. Electronic Meter- They are quite advanced or more reliable as compared with the
electromechanical meters. They are free from mechanical errors due to absence of any
mechanical part unlike the former case. A picture of 3 phase electronic meter-
Voltage and currentcoils

10. 10
 They display the energy consumed on LED or LCD screen. Apart from the energy
consumed,theyalsoshow a numberof otherparameterslike powerfactor, voltage,
current, frequency, total or the active power (kVAh), reactive power (kVARh), date,
time,temperature,cumulativeactivepower,currentandlastmonthactivepowerand
many others.
 They can support “time of billing” format by recording the energy consumedduring
different durations – peak, off-peak, night, and rest.
 It containsmeteringengine,microcontroller(processingandcommunicatingengine),
and other add on modules like LCD/LED, RTC (Real Time Clock), communication
ports/modules, temperature sensor, memory and analogue to digital converters
(ADC).
 The meteringengine isgiventhevoltage andcurrentinputs andhasvoltagereference,
samplers and quantiser followed by an ADC that yields the digitalized form of the
input which is then fed to DSP (Digital Signal Processor) for calculating the various
metering parameters.
 Microcontroller(processingand communicatingengine) ishavingthe responsibilityof
calculating the other derived quantitiesfrom the digital quantities generated by the
metering engine. This also has the responsibility of communication using various
protocols and interface with other addon modules connected as slaves to it.
Errors and thefts in electronic meters-
The largestsource of long-termerrorsinthemeterisdriftinthepreamp,followed
by the precisionof the voltage reference.Bothof these varywithtemperatureas
well and vary wildly because most meters are outdoors. These errors can be
minimised by modification in the design.
Theftsare possible eveninsuchmeters.Ex- One suchthieveryiscaughtinwhich
the burglary is done by soldering the wires.
Blinking rateof LED for
per unit of consumption
Current rating for
all 3 phases
Time periods for “time
ofbilling” system

11. 11
Day 4 :10/12/2018-
This day various components of power system are being discussed-
GI strengthen wire- These are the bundled wires in which the central wire is of GI (GalvanisedIron)
having good mechanical properties (hard, strong etc.)
ABC (Aerial Bundled Cable)- ABC are overhead power lines using several insulated phase
conductors bundled tightly together, usually with a bare neutral conductor in contrasts with the
traditional practice of using uninsulated conductors separated by air gaps.
Advantage –
 Relative immunitytoshortcircuitscausedbyexternal forces(wind,fallenbranches),unless
they abrade the insulation.
 Can standin close proximitytotrees/buildingsandwill notgenerate sparksif touched.
 Little tono tree trimmingnecessary
 Simplerinstallation,ascrossbarsandinsulatorsare notrequired.
 Ease of erectionandstringing,less labourintensive,lessconstructionresourcesneeded.
 More aestheticallyappealing.
 Can be installedinanarrower right-of-way.
 Electricity theft is made harder, and more obvious to detect.
 Less required maintenance and necessary inspections of lines.
 Improved reliability in comparison with both bare conductor overhead systems and
underground systems.
 Significantly improved safety for linespersons, particularly when working on live
conductors.
Disadvantages-
 Additional costforthe cable itself.
 Insulationdegradesdue tosunexposure,thoughthe critical insulationbetweenthe
wiresissomewhatshieldedfromthe sun.
 Shorterspansand more poles due toincreasedweight.
 Can leadto muchlongerrepairtimesforinstallationsinhillyareasdue tomuchhigher
line weightsrequiringbiggerandmore specializedequipmenttorepair.
 Olderinstallationsare knowntocause firesinareaswhere fallinglarge treesorbranches
regularlycause breaksinlinesandorin insulationleadingtoshortcircuitswhichcan
thenleadto burninginsulationdrippingtogroundandstartinggroundfires.
 Failure modesthroughpunctures,electrical tracking,anderosion.
Types of insulators-
1. Pin insulator- A pin insulator is a device that isolates a wire from a physical support.

12. 12
 As the name suggests,the pintype insulatorismountedonapinon the cross-armon
the pole.
 There isa groove onthe upperendof the insulator.The conductorpassesthroughthis
groove and is tied to the insulator with annealed wire of the same material as the
conductor.
 Pintype insulatorsare usedfor transmissionanddistributionof communications,and
electricpoweratvoltagesupto33kV.Insulatorsmade foroperatingvoltagesbetween
33kV and 69kV tendto be verybulkyand have become uneconomical inrecentyears.
2. Post Insulator- It is a type of insulatorthatbecomespopularinthe 1930s. It ismore compact
than traditional pin-type insulators and which has rapidly replaced many pin-type insulators
on lines up to 69kV and in some configurations, can be made for operation at up to 115kV
3. Suspensioninsulators- Forvoltagesgreaterthan33kV,suspensiontype insulators,consisting
of a number of glass or porcelain or polymer discs connectedin series by metal links in the
form of a string. The conductor is suspendedat the bottom end of this string while the top
end is connected to the cross-arm of the tower. The number of disc units used dependson
the voltage. Greater the voltage, greater will be the disc units.
4. Strain Insulator- A strain insulatoris an electrical insulatorthat is designed to work in
mechanical tension (strain),towithstandthe pullof asuspendedelectricalwire orcable. They
are used in overhead electrical wiring, to supportradioantennas andoverheadpower lines.
A strain insulator may be inserted between two lengths of wire to isolate them electrically

13. 13
from each other while maintaining a mechanical connection, or to transmit the pull of the
wire to the pole or the support keeping it electrically isolated from it.
5. Shackle Insulator- In earlierdays,theywere usedas straininsulator. Butnowadays,theyare
frequently used for low voltage distribution lines.
 These insulators can be mounted either in the vertical or horizontal position.
 The loading is on circumferential grooves in the insulator. The conductor is secured
in the grovesby meansof soft-bendingwires. The insulators are boltedtothe cross-
arm of the pole.
 Shackle Insulatorsare usedatthe endofdistributionlinesoratsharpturns (90-degree
turn) where there is excessive tensile load on the lines
6. Bushing- will be discussed in the transformer section.
7. Cut-out- A cut out is a device which can be used as a fuse and switch.
 It protects the electrical appliances against the surge and overload currents by
disconnecting the circuit caused by melting of the fuse. They can be reused by
replacing the fuse.
 They can also be removed manually for breaking the circuit.
 A cut-out consists of three major components:
i. Cut- out body- C-shaped frame that supports the fuse holder, covered from
porcelain or polymer insulator.
ii. Fuse holder- Replacing of fuse or opening of the circuit can be achieved by
pulling the fuse holder outside by hot stick.
iii. Fuse element-Itisreplaceableportionof theassemblyanditbreaksthe circuit
by melting during faulty condition.
Note- The above insulatorsare made upof porcelainorpolymer inamultiple disctype structure.This
is done so as to avoid the deposition of dust or water on them. The number of discs in an insulator
depends on the voltage of the line it is supporting.
Non-conducting materials are mainly porcelainor glass but nowadays use of polymer as insulator is
more preferred because-
 They are more reliable than porcelain which breaks easily.

14. 14
 Inporcelaininsulator,onesthe crack evensmalldevelopitgrowsupwithtimeandmaycause
damage inthe systembyallowingthe moisturetoflow intothe system andpolymerinsulator
are free from this problem. Once they get damaged, they need to be replaced.
 Porcelain insulators are heavier in weight than the polymer insulators.
Stay wire- Stay Wires are galvanizedsteel wire strandsthatare usedfor sustainingmechanical load.
Generally,theyare made upof 6 wiresstrandedaround1 wire,twisting7wirestogether.A common
use for stay wires is in the electricity industry, using the wire to stay power poles and tower
structures.
In many parts of Surat, we have observedthatpeople prefer Torrent company’selectricpowerover
DGVCL though Torrent is a private company and charge bill at almost double rate. The reason being
the much betterservice.Theyhave completeundergrounddistributionsystem, spare cable forevery
supply, RMU for every feeder and many other advanced systems that enables them to provide
uninterrupted power supply.
DGVCL is also preferring underground distribution system for better supply in urban areas.
Advantages of underground cables-
 Suitable forcongestedurbanareaswhereoverheadlinesmaybe difficultorimpossibleto
install
 Low maintenance
 Small voltage drops
 Fewer faults
 Not susceptible to shaking and shorting due to vibrations, wind, accidents, etc.
 Not easy to steal, make illegal connections or sabotage
 Poses no danger to wildlife or low flying aircraft.
Though it provides power unaffected from the natural processes but still it is not much used due to
following disadvantages: -
1. Cable is quite expensive.
2. High insulation is required.
3. Detection of fault is difficult.
4. Once damaged, repairing is also cumbersome and expensive.
5. Damage to cables or electrocution may occur to people digging the ground and if they are
unaware of the cable’s existence
Under-groundcable- It consistof 3 wiresfor3 phases,each one of themlookslike followingandare
well insulatedfromeach otherthrough additional insulators.Ineach wire a wrappingwithcolour of
corresponding colour is also provided for identification of the phases.

15. 15
1. Cable sheath– Particularlyprotectsthe cable againstmoisture.
2. Wire screen– Controlsthe electricfieldanddischargesfaultcurrents.
3. Insulating layer– Insulatesthe electricconductor.
4. Electric conductor – Conductsthe current.
Dependingonthe voltage andcurrentratingsdifferenttypesof cablesare available.The cross-section
area of the conductor dependsonthe current carried by the wire while insulationrequireddepends
on the voltage. For 11 kV lines 185 mm diameter cable is used.
Bus-Bar- Itis a metallicstriporbarwhichisusedforhighcurrentdistribution. Itisapair of veryheavy
conductors,usuallycopperoraluminiumtocarry heavycurrentsfrom one part of a powersystemto
another. In powersystem,cablescan’tbe joinedin the way the small wiresare joinedinthe general
purpose.Forthe interconnectionof cablesbusbarsare used.Throughthebusbar,anumberof cables
canbe connectedusingcable lugs. Theyare uninsulatedandsupportedbetweentwosupports. Copper
bus bar distribution-panel is as shown below: -
CT and PT- CT and PT form the sub parts of instrument transformer. They are extensively used in
power system for metering and protection purpose. These 2 form the most important part of any
substation.Since inactual electrical powersystemwe deal withhighvoltage and high current and it
is not feasible and economical to manufacture devicesto measure such high values.So, to measure
highvaluesinpowersystem weuse CTandPT.The primaryof these transformerisplacedinmainline
and secondaryisplacedinany meterorrelaydependingonthe application.CTisstepuptransformer
giving low current (1-5 A) in the secondary which is proportional to the current in the primary while
the PT is a step-down transformer giving low voltage in the secondary which is proportional to the
voltage in the primary. In this way, measurement of the smaller quantities can be done easily.

16. 16
Day 5: 11/12/2018
Visit to Mega-Royals, Honey park area, Adajan, Surat
This day we visitedtoMega-Royalsfor observingthe installationof new transformerinparallel with
the previousone forload sharingas the load isbeenincreased. Firstly,the supplytothe transformer
is disconnected fromthe feederandpowerissuppliedinthe buildingthroughthe generator.Before
the start of work, all the safety measures are adopted. To avoid shock due to back power from
generator all the phase terminals of transformer are shorted and connected to the neutral which is
already grounded.
Neutral is connected to the ground for
 passing the unbalanced current to the ground
 avoiding the harmonics thus prevents the waveform distortion
 avoiding voltage stress on the insulation due to unbalancing
 supplying the load through each phase
Apart from this, safety kit is used by the linemen that includes
 Rope
 Helmet,
 Jacket for proper holding with rope,
 Shoes
 Gloves.
After the installationof transformer, its body is grounded because any ungroundedtransformer can
build up an electrical charge that could be very dangerous to personnel or equipment. It could
penetrate insulationandruinthe transformer,and alsoprovideapathfortransformervoltagestothe
outside world. The ground can pass induced voltage to ground and thus prevents the problems.
Inaddition,toavoidthe damage due tosurge currentoroverload current,fusesare providedonboth
HT and LT side. LT side fusesare informof cut-outs while on HT side copper wire fuses are provided
on all the 3 phases. They are provided between two horizontal rods on the pole.
For providingthe uninterruptedpower supply,aspare cable is alsoprovidedwhichsuppliespowerif
fault is present in the first cable.

17. 17
Day 6:12/12/2018
Sighting at Surat transformer, diamond Vidhya Sankul, Surat
-By Vedant sir (Mobile No.- 9998628326)
3 phase core transformers are beingstudied.
Magnetic core- It consistof laminatedsheetsof CRGO (ColdRolledGrainOriented) SiliconSteel.Itis
laminated to minimise the eddy current losses which are directly proportional to the square of
thicknessof the material.The material(CRGOinthiscase) chosenissuchthattoofferslow reluctance
for the flow of flux and high resistance to current flow that in turn minimise the core loses.
Windings–Theyconsistof lowresistive materials(copperoraluminium).Copperoffersless resistance
than aluminiumbutitscostisquite highsoto reduce the costof the transformer,use of aluminiumis
more preferred. Windings are insulated from each other as well as from the magnetic core.
Insulation on the wires- Kraft paperis one of the prime insulatingmaterialsfor coveringconductors
intransformers.ABBRamanSigma Kraftpaperwithhighpurityandmechanical and dielectricstrength
isperfectfordouble papercovering(DPC) applicationsandaslayer insulation intransformerdesigns.
Wrapping of Kraft paper is being done in DPC wrapping machine.
Accessories-
1. Housing/ Tank- It is the outer metallic body of the transformer inside which the complete
transformer is being housed.
2. Bushings –
 In electricpower,abushingisan insulated device thatallowsanelectrical conductor
topasssafelythroughagroundedconductingbarriersuchasthecase of atransformer
or circuit breaker.
 Bushings are typically made from porcelain, though other materials are possible.
 Theyare usedtoprovidethe groundclearancei.e.,toavoidthe groundingof thewires
through the body of the transformer. In their absence, due to strong electric field
around the wires, sparks may appear between the wire and the body of the
transformer.
 Theirheights depend onthe voltage. Greaterthe voltage,greaterwill be the electric
field,greaterwillbe theneedofgroundclearance andthusforhighvoltage,the height
of bushings required is more.

18. 18
3. Conservator and breather- The oil cooled transformers are provided with conservator and
breather.Conservatorisa cylindrical tankprovidedonthe top of the transformer alongwith
the oil level indicator. Inmostof the transformersoil isusedforcoolingaswell asinsulation.
When the temperature of the transformer increase, heat is transformed to oil, oil is heated
and expands. The conservator allows the heated oil to move into it and thus avoiding the
explosiondue to increase inpressure of the oil with the temperature.Due to expansionand
contraction exchange of air take place through the conservator that may cause the entry of
moisture intothe transformer.To avoidthis,breatherisprovidedonthe conservatorfor the
exchange of air. It is provided with silica gel that absorbs the moisture content.
4. Explosion Vent- When the temperature of transformer exceeds certain level due to some
faultsthenthe oil initmaydecompose resultingintoliberation of the gasesthatincreasesthe
pressure inside the tank and may cause explosion. To avoid this,explosionvent is provided.
Whenpressure exceedsthe safe level,diaphragmpresent initbursts allowingthe gasesand
high-pressure oil to come out, thus avoid the serious damage to the transformer.
5. Radiator- They are provided for the natural cooling of the oil. Oil circulates from the
fins/cooling tubes of the radiator and cools down.
6. Wheels- Theyare providedforeasymovementof the transformerfromone placetoanother.
7. Drain valve- It is provided to remove the oil from the transformer during maintenance or
repairing.
On HV side tapings/bundles/layers are provided because this makes-
1. 1.Easy to detect the faults and replace the faulty windings with the new ones, thus this also
reduce the repairing cost.
2. 2.Easy to assemble aswell as manufacture as weightof the complete HV isquite highdue to
higher number of turns.
The LV is not having any axial subdivision because-
1. Wires on LV side are thick so their bridging is difficult.
2. This also increase the chances of faults.

19. 19
3. The manufacturingand assemblingof the completecoil are easierforlesserturnsandthicker
wire
HV is kept on outer side of core-
1. If itisnearertothe core thenthickerinsulationis requiredbetweencore andHV thatincreases
the cost.
2. Apart fromthis,the HV windingsare exposedto better cooling condition on the outer side.
3. AsHV windingisinthe formaxial bundlesof coilssoitisbettertouse itonthe outerside-this
makes possible the tapings on HV side.
Tapings are provided on HV side-
Normally the tapings are provided on high voltage (h.v.) winding due to following reasons,
1) A fine voltage regulationispossible withhighvoltage winding as it carries large number of turns.
2) The lowvoltage windingof the transformercarrieslarge current. So, if tapingsare providedonlow
voltage side then then there are difficulties encountered in the interruption of high currents which
makes its impracticable.
3) For the reasonsof requirementof insulation,the low voltage (LV) windingisplacednear the core
while the LV windingisplacedoutside.Hencepracticallyitiseasierandsimplertoprovide tapingson
high voltage winding.
4) In case of step-downtransformers,itisan addedadvantage toprovide tapingsonh.v.side.Atlight
loads,the LV side voltage increases.Itisrequiredtodecrease thisvoltage byadjustingthe tappingon
h.v.side to a positionwhere numberof turnsare large.With large numberof turns,the flux andflux
density decreases.
This results in reduction of core loss which increases transformer efficiency at light loads.
5) If the tapings are providedon the LV side thenthe exact voltage regulation may not be provided.
This can be explainedby considering an example of a transformer with rating3 phase, 11 KV/415 V,
delta/star connectedwhich is designed for 15 volts/turn. The LV side voltage is 415/√3 = 240 V. The
number of turns on LV side are 240/15 = 16. Minimum number of turns that can be tapped is one.
Hence minimumpossible voltage regulationwithtapings on LV side is 15 V or 6.25 %. It can be seen
that if a voltage regulationof 5% is desiredwith this then it is not possible with tapings on LV side.
Effective turn ratio (a)- For a 11kV/433V delta-star connected 3 phase transformer,
a =
11000
433
√3
=
11000
250
= 44
TESTS – A no. of tests are being performed over the transformer to check its durability and efficient
working. The tests performed in the workshop are-
1. Turn Ratio Test – Thistestis carriedoutto verifythatthe numberof turnsinthe primaryand
secondaryare asper the voltage ratiorequirementornot.Inthistest,small voltage isapplied
at the primary and voltage at the secondary is measured whose ratio provides us the turn
ratio which is then verified with the required one.
2. Oil Test/ BDV (BreakdownVoltage) Test- The oil usedinthe transformermusthave dielectric
strengthat least2.5-3 timesthe maximumvoltage of the HV side.In thistest twoelectrodes
are keptatverysmall distance (2.5mm) inthe oil andvoltage acrossthemisincreaseduntil a
spark appears between them. The voltage at which the spark appears is considered as the

20. 20
dielectric strength of the oil and the oil can withstand only that much voltage before
undergoing breakdown.
The dielectric strength of the materials can be improved by removing the
moisture,impuritieslike carbonandthe otherconductingmetalsorions. The oil isfilteredin
a filtrationmachine,providedwiththe pressuregauge andtemperatureindicator. Depending
upon the capacity of the transformer the oil purified.Greater the purity, greater will be the
dielectric strength.
3. Open Circuit or No-Load Test on Transformer-Open circuit test or no-load test on a
transformerisperformedtodetermine 'noloadloss(core loss)’.The circuitdiagramforopen
circuit test is shown in the figure below-
4.
Usuallyhighvoltage (HV) windingiskeptopenandthe low voltage (LV) windingisconnected
to its normal supply. A wattmeter (W), ammeter (A) and voltmeter (V) are connected to the
LV winding as shown in the figure. Now, applied voltage is slowly increased from zero to
normal ratedvalue of the LV side withthe helpof avariac. Whenthe appliedvoltage reaches
to the rated value of the LV winding, readings from all the three instruments are taken.
The ammeter reading gives the no load current I0. As I0 itself is very small, the voltage drops
due to this current can be neglected.
The input power is indicated by the wattmeter (W). And as the other side of transformer is
opencircuited,there isnooutputpower.Hence,thisinputpoweronlyconsistsof core losses
and copper losses. As described above,no-loadcurrent is so small that these copper losses
can be neglected. Hence, now the input power is almost equal to the core losses. Thus, the
wattmeter reading gives the core losses of the transformer.
5. Short Circuit or Impedance Test on Transformer- The connection diagram for short circuit
test or impedance test on transformer is as shown in the figure below-
The LV side of transformerisshort circuitedand wattmeter(W), voltmeter(V) andammeter
(A) are connected on the HV side of the transformer. Voltage is applied to the HV side and

21. 21
increasedfromthe zero until the ammeterreadingequalsthe ratedcurrent.All the readings
are taken at this rated current.
The ammeterreadinggivesprimaryequivalentof full loadcurrent(Isc).
The voltage appliedforfull loadcurrentisverysmall ascomparedto ratedvoltage.Hence,
core lossdue to small appliedvoltage canbe neglected.Thus,the wattmeterreadingcanbe
takenas full loadcopperlossinthe transformer.
6. MAGOR test- In thistestthe outputvalue must be greaterthan 300 for transformertobe in
workingcondition.
7. DVDF (Double voltage Double Frequency) test- Inthistest,double of ratedvoltage isapplied
at the double frequency (to avoid saturation by keeping V/f constant as in the rated value).
This test is done to verify the ability of the transformer to withstand the overloading
conditions. If the transformer can withstand this without giving the tripping then only the
transformer is passed for the application otherwise not. The frequency of the voltage is
changed by using a different generator and the voltage level is increased by using a 3 phase
step up transformer.
Heating in the oven- Aftercarryingout the above teststhe transformeriskeptinthe ovenfor 2 days
at 80-90C to remove itsmoisture content.Thisisdone tominimise the chancesof corrosion.
 General range of capacity of the transformers-
5,10,16,15,25,66,100,200,315,500,630,800,1000,1500 inkVA.
 Transformersare beingtestedtofulfil the criteriasetupbythe BIS (Bureauof Indian
standards) underERDA (Electrical ResearchandDevelopmentAssociation).PreviouslyIS
2026 standardsneedstoobeyedfortransformersbutnow a daysIS 1180 standardsare
followed.
 Turn ratio(a) forthe transformerof capacityQ isgivenby
a = 𝑘2
√ 𝑄 where kisa coefficientdependsuponthe material of the winding
k=0.3-0.37 for aluminiumwinding
k =.38-.45 for copperwinding
 Generally, indistributiontransformer,HV windingsare connectedindeltawhile the LV
windingsare connectedinstar.
 Bridgingisbasicallyprovidingabridge orthe connectionbetweentwosystems.Incase of
thickwiresbridgingisdone bywelding.
Rating of mediator in Surat Transformers-
Product- 3 phase variac
Capacity- 200A
Input- 3 phase 415V, AC
Output- 3 phase,0-415V, AC
Cooling-Oil cooled
Rating of inter-mediatorinSurat Transformers-
Product- 3 phase step-uptransformer
Capacity- 200kVA
Input- 3 phase 415V, AC
Output- 3 phase,800-1600V, AC
Cooling-Oil cooled

22. 22
Day 7: 13/12/2018
Visit to Pal SS(Sub-Station)
Sub-station- A substation is a part of an electrical generation,transmission, anddistributionsystem.
Substations transform voltage from high to low, or the reverse, or perform any of several other
importantfunctions.Betweenthe generatingstationandconsumer,electricpowermayflow through
several substations at different voltage levels. A substation may include transformers to change
voltage levels between high transmission voltages and lower distribution voltages, or at the
interconnection of two different transmission voltages.
Lighting Arrester- It is providedtoground the surge producedin the line.Surge may be producedin
the line due toa numberof reasonsbutmainlytheyare due tolightening (natural,fromatmosphere)
or switching impulses. Due to these surges, very high transient voltage may appear that lasts for a
little time but develop voltage stress on the insulators can cause huge damage to the electrical
equipment.
To avoidthis,lightingarresterisprovidedwhichpassesthe surge currentstothe ground. Itgenerally
consistsof a numberof discs of metal oxides(ZnO) whichare stackedtoform a cylindrical body.This
cylindrical body is covered by porcelain or polymer insulator act as a fast-acting electronic switch
whichbehave asinsulatorfornormal workingacvoltagesbutforthe surge voltagesitstartsbehaving
like a good conductor allowing the surge current to pass through it. In this way it protects the
equipment to which it is connected in parallel, against the surge.
Breaker- It is a switching device which can be operated automatically or manually for protection,
control maintenance andrepairingwork.Asthe modernpowersystemdealswithhuge currents,the
special attention should be given during designing of circuit breaker for safe interruption of arc
produced during the operation of circuit breaker. It is more reliable than fuses which can’t be used
again, they can come into action as soon as the fault is removed. It is employed for –

23. 23
1. Protection of electrical equipment against the fault currents.
2. For tripping of the line during maintenance or repairing work.
Foruninterruptedoperationofcircuitbreaker,itstwometalliccontactsmustbe removedveryquickly,
whichisachievedbyasuitablemechanism(metal spring,aircompression,hydraulicmethodetc.) and
some arc quenching or deionising mechanism (compressing the ionized arcing, cooling the arcing
media, replacing the ionized arcing media with fresh gases etc.) must be there.
Isolator- It isprovidedtodisconnectthe lineduringmaintenance orrepairingwork. We can’toperate
isolatorwithoutbreakerbecause withoutbreakerisolationof linemayleadtothe sparkwhichisquite
dangerous in case of high voltages. We can operate breaker without isolator but for better safety
isolator is used that provides the physical isolation which is easily detectable. The switching off the
line bythe breakerisnot physicallyvisibletous so we can’t identifywhetherthe line ison or off just
by looking at it.
There are different types of isolators available depending upon system requirement such as
1. Double Break Isolator- It contains of 3 stacks of post insulators. The central post insulator is
connectedwithmale contactthat can fixedperfectlyonthe female contactsprovidedonthe
other two post insulators. The central insulator and its male contact can be rotated for
isolation or reconnection either by the lever and handle mechanism or by the electronic
system in more advanced sub-stations.
2. Single Break Isolator- In this isolator the contact arm is divided into two parts, one carrying
male and the other female contact.The two parts can be rotated is opposite directionswith
lever and handle or electronic system for isolation or reconnection.
3. Pantograph type Isolator.
Depending upon the position in the power system, the isolators can be categorized as
1. Bus side isolator – the isolator is directly connected with main bus
2. Line side isolator – the isolator is situated at line side of any feeder
3. Transfer bus side isolator – the isolator is directly connected with transfer bus.
Current Transformer (CT)- It is provided as measuring instrument in the line for measuring the high
voltage.

24. 24
Control Panel- It contains LT panel board, HT panel board, meters, control switches, recorders and
battery house located in the control building, also calleda doghouse. These are used to control the
substationequipment,tosendpowerfromone circuitto anotheror to openor to shutdowncircuits
when needed.
Batteryhouse isa dark roominwhichnumberof batteriesare present. Itisknownasthe heartof the
substation. These batteries provide power to the panel boards,various meters and other gadgets in
the control panel.
For general appliances (like fan, bulb, tube light etc.) and charging of battery, substation is also
supplied by 230V, 50Hz AC supply by a separate distribution transformer.
ImportantElectrical distributionsystemaccordingtothe feedbackconnectionschemesortopologies-
1. Ring main distribution system-
 It is the most preferred distribution system due to its high reliability.
 Each distribution transformeris fed with two feeders but in different paths. The
feeders in this system form a loop which starts from the substation bus-bars, runs
throughthe loadareafeedingdistributiontransformersandreturnstothe substation
bus-bars.
 The following is the line diagram for this distribution system-

25. 25
 Advantagesoverotherdistribution system-
 There are lesserfluctuationsonthe consumersterminal.
 The systemisveryreliable aseachtransformerisfedwithtwodistribution
systemsothat incase of the faultinany of the sectioncontinuityof the
supplyisensured.
2. Radial distribution system-
 This system is used when the substation is located at the centre of the consumers.
 In thissystem,differentfeedersradiatefromasubstationora generatingstationand
feedthe distributorsatone end.Thus,the main characteristicof a radial distribution
system is that the power flow is in only one direction.
 Single line diagram-
 Althoughthissystemissimplestandleastexpensive this systemisnothighlyreliable
as the failure inanyfeederresultsincutoff of the supplytothe associatedconsumers
due to absence of any alternate feeder as in case of ring main distribution system.
3. Parallel distribution system-
 This type of system is used when the load is higher (i.e., for load sharing) or for
providing high reliability.
 In this system, an alternative feeder is also provided for the same consumer.
 Single line diagram of parallel distribution system-
 Although this systemprovides high reliability,but it is not very popular as the initial
cost is very high as the number of the feeders gets doubled.
4. Interconnecteddistributionsystem- Whenringmaindistributionsystemisenergizedbytwo
or more substations or generating station, it is called as interconnected distributionsystem.
Advantages
 It ensures reliability in case of transmission failure.
 Duringpeakhours,anyarea can be fedwithothersubstationorgeneratingstationto
meet the increased demand.

26. 26
Day-8; 15/12/2018
Visit to Lalji Nagar for sighting solar connection
On this day, we visited first time to a consumer’s location. In that location most of the people are
having efficient and renewable solar energy sources like solar geyser, solar panels for power
generation.The consumertowhichwe are visiting wasalsoinstallingsolarpanelsonhisterrace.The
specification of panels is shown in the figure below-
He hasinstalled12suchsolarpanelssuchthat2 groupsof 6 seriesconnectedpanelsare connectedin
parallel.
 The dc voltage generatedtothe invertorwhichconvertsthe itinto230V,50Hz ac voltage and
is connectedwiththe inputof the house througha meter(M1), installedtoshow the power
generated.
 Apart fromthis,a switchingsystemisalsoprovidedwhichcutoff the powergeneratedwhen
there isnopowerfromthe gridor supply.Thisisdone toavoidthe dangerof electricshockto
the lineman due to the additional power generated.
 The meterwhichshowsthe bill of house wasalso replacedtobidirectional meter(M2).This
is done soas to measure the powersuppliedtothe gridwhenthe powerconsumptionisless
than the power generated. This power is treated as negative power by the meter and is
subtracted from the consumption of the consumer. In this way the bill of the consumer is
greatly reduced.
The connection of the system can be shown as below-

27. 27

28. 28
Day- 9; 17/12/2018
Visit to “Bhagyaratna Heights” (consumer) for meter testing
Before the installation of meter, a number of tests are being performed over the meter and their
accuracy is checked.Theyare consideredsuitable forinstallationonlyif the errorisinthe range from
-3% to +3%. For checking the accuracy of meters, advanced instruments are present in the DGVCL.
Afterinstallation,electricmetersmaymisbehavedue toanumberof reasons whichisreflectedinthe
bill of the consumer. Consequently, the consumer files complain application for the faulty meter for
some of the companiescostsome fee (Rs300 in DGVCL). The metermay belongto the consumeror
the distribution company but the responsibility of the maintenance of the meter is solely with the
distribution company. According to CERC (Central Electricity Regulation Commission), the company
must check the meters once in every 5 years and its cost is also borne by the company.
Fast and slow meters– When meter give reading higher than the actual reading then it is known as
fast meterand if lessthan the actual one than it is knownas slow meter. These errorsmay arise due
to number of technical faults in the meters.
Sometime people complain that their electric bill is increased as their metersare replaced with the
electronic. This happens so because with time the electromechanical meters become slow due to
environmental factorsshowingreadinglessthanthe actual one.Whentheyare replacedbyelectronic
meters,the electronicmetersgive the actual readingwhichishigherthanthe previousfalsereadings
so they believe that their meter is fast but it is not the case.
If any complaintissubmittedbythe consumerthenthe companysendelectriciantocheckthe meter.
The checking of meter is also done by an electronic machine.
Checking the meter-
 The terminals(phase andneutral)of the machine are connectedwiththe outputterminalsof
the meter.
 Current transformer is magnetically connected using clamper.
 On switchingonthe device,itdirectly provides usthe errorinthe measurementof the meter
in percentage and if not found between -3% to +3% then meter needs to be replaced
otherwise not.
Reading of meter-
Reading of electronic meters is taken with the help of MRI (Magnetic Reading Instrument).

29. 29
Day 10: 18/12/2018
Visit to Pal SS(Sub-Station)
SCADA (Supervisory Control and Data Acquisition) -
Supervisorycontrol anddataacquisition(SCADA)isasystemof software andhardware elementsthat
allows industrial organizations to:
 Control industrial processes locally or at remote locations
 Monitor, gather, and process real-time data
 Directly interact with devices such as sensors, valves, pumps, motors, and more through
human-machine interface (HMI) software
 Record events into a log file
SCADA systemsare crucial for industrial organizationssince theyhelptomaintainefficiency,process
data forsmarterdecisions,andcommunicatesystemissuestohelpmitigatedowntime. Theyare used
in all industrial processes including-
 Energy
 Food and beverage
 Manufacturing
 Oil and gas
 Power
 Recycling
 Transportation
 Water andwaste water
 And many more
Working- The basic SCADA architecture beginswithprogrammable logiccontrollers (PLCs) orremote
terminal units (RTUs).PLCsandRTUs are microcomputersthatcommunicate withanarrayof objects
suchas factory machines,HMIs,sensors,andenddevices,andthenroute the informationfromthose
objectsto computerswithSCADA software.The SCADA software processes,distributes,anddisplays
the data, helping operators and other employees analyse the data and make important decisions.
RMU (Ring Main Unit) - A Ring Main Unit (RMU) is a totally sealed, gas-insulated (SF6) compact
switchgear unit. The primary switching devices can be either switch disconnectors or fused switch
disconnectors or circuit breakers.
Different combinations of these primary switching devices within the unit are commonlyused. One
such combination is –

30. 30
 In case a circuit breaker is the switching device, it is also equipped with protective relaying,
either with a very basic self-powered type or a more advanced one with communication
capabilities.
 The rated voltage and current ranges for RMUs typically reach up to 24 kV and 630
A respectively. With many of the manufacturers of RMUs, the basic construction of the unit
remainsthe same forthe whole of the voltage range. The increase inratedvoltageishandled
by an increase in the insulating gas pressure.
 The figure below shows a typical RMU configuration where load disconnectors are the
switching devices for the incoming cable feeders and circuit breakerworks as the switching
device for distribution transformer feeder.
 Three-position design (Closing, Opening and Earthing)- All of the switching devices in RMU
are of three-position design, having the possibility to close or open or earth the feeder in
question.
a) Closing- Closingthe movingcontactassemblyismanipulatedbymeansof afast-acting
operating mechanism. Outside these manipulations, no energy is stored. For the

31. 31
circuit breaker and the fuse-switchcombination,the opening mechanism is charged
in the same movement as the closing of the contacts.
b) Opening- Openingof the switch iscarriedoutusingthe same fast-actingmechanism,
manipulated in the opposite direction. For the circuit breaker and fuse-switch
combination, opening is actuated by- Pushbutton or fault.
c) Earthing- A specificoperatingshaftclosesandopensthe earthingcontacts.The hole
providingaccessto the shaftis blockedbya cover whichcan be openedif the switch
or circuit breaker is open and remains locked when it is closed.
 The figure belowshowstypical outlookof athree-feederRMU.In the figure,the combination
consistsof loaddisconnectorsfor the incomingtwofeedersandafusedloaddisconnectorfor
the distribution transformer feeder. The incoming and outgoing medium-voltage cablesare
attached using elbow-type plug-in cable ends.
 QuicksupplyusingRMU in case of fault- If the faultisfoundbetweenthe points1and 2 then
thatparticularportionisdisconnectedfromthe ringandthe transformerT7 isfedbyswitching
on the RMU3. In this way, the supply to associated consumers is restored very quickly.
Note- Whereas the RMU type of units represents the very compact gas-insulated designfor a
dedicated purpose, the secondary medium-voltage switchgears represent an air-insulated, quite
freely extendable and configurable solution.

32. 32
Day-11; 19/12/2018
Visit to Canal Road, Darshan Society, Palanpur, Jakatnaka, Surat
This day we learnt about the damaged underground cables are repaired. Firstly, the fault is
detected using suitable instruments. There are many electronic gadgets available in the market
for this purpose.
The mechanismat the substationisdesignedinsuch a way that as soon as the conductor of the
cable is being cut, the breaker trips the supply through that line.
 Once the location is identified, digging is done with care as it may cause greater damage to
the line.
 After digging, the damaged part of cable is cut using saw.
 Now a small portion of cable is brought for joining the two cut cables.
 The conductors are made naked at the ends for the connection.
 The conductors are joined using some specialised materials available in a kit.
 In kit cleaningtissue isalsoprovidedtocleanthe hands before joiningthe ends.Thisis done
to avoid the soil and dirt to move in the system.
 Jointsof the cable are connectedwithahollowtube of aluminium 130mmlongwhichisfixed
at the joints using clamping tool.
 These jointsare thencoveredwithnumberof insulatorlayersfirstlywithrubberinsulation
tube,then 2 insulationtubes(blackandredwhichare fittedtightlyoverthe systemby
burning) forkeepingthe phasesinsulatedfromeachotheraswell asfor protectionfrom
moisture.
Ferule aluminiumtube for
joining ends ofcable
Clamping tool

33. 33
 The wire screen (grounded metallic net that controls the electric field and discharges the
faultycurrents) of the twocut cablesisfirstlyjoinedusingacopperstripand is thencovered
with the metallic net.
 The complete set-upisthenagaincoveredbythickinsulationtube thatactas metallicsheath
is made to stick to the system by burning it with gas burner.
 After joining the cable is then charged (with 1kV for 11kV cable) using MAGOR machine.
Copper strip
Metallic net

34. 34