Dgvcl rerport

DGVCL WINTER INTERNSHIP REPORT

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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

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PREFACE

Theory of any subject is important but without its practical knowledge it becomes useless, particularly
for technical students. A technical student cannot become a perfect engineer or technologist without
practical understanding of their branch, hence training provides a golden opportunity for all technical
students to interact with the working environment.

While undergoing training at DGVCL (Pal Subdivision) Surat, we learned a lot of practical aspect. Our
theoretical Knowledge was exposed here practically. In this report we have tried to summarise what
we have learned at DGVCL. For preparing this report we visited the substation and various other sites
and cleared related doubts to the responsible personal.

This training helped us to understand the basic concept of the power distribution. During this period,
we became aware of the problems faced in the company and also of the working environment of the
company.

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ACKNOWLEDGEMENT

Training has an important role in exposing the real-life situation in a company. It was a great
experience for me to work on training at Dakshin Gujarat Vij Corporation Limited through which I could
learn how to work in a professional environment.

Now We would like to thank the people who guided us and have been a constant source of inspiration
throughout the tenure of our winter training.

We are sincerely grateful to Mr. B.D. Patel (Deputy Engineer at Pal Substation) who rendered us his
valuable assistance and constant encouragement which made this training actually possible. Also, for
continuously guiding throughout various aspects, functioning of the company and allocating us the
appropriate schedule to undertake the training.

Our sincere thanks to Mr. Vedant, Mr. Kuldeep and Mr. Jignesh Patel for having support, guidance at
ground level and sharing valuable technical knowledge.

And at last but not least, we are also thankful to all the staff members of the company for their kind
corporation and valuable guidance throughout the process of work.

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DAY 1: 3/12/2018
About DGVCL
(Dakshin Gujarat Viz Nigam Limited)
DGVCL, Surat. The company is involved in electricity sub-transmission, distribution and retail supply in
the south part of Gujarat or outside the State. Their mandate is to establish and use a power system
network and to buy and sell electrical energy, and to collect information with an eye towards further
system improvements.

The Gujarat Electricity Industry (Re-Organization & Regulation) Act 2003 paved the way for
comprehensive reform and restructuring of the State Electricity Board with an aim to restructure the
Electricity Industry in a manner that will ensure the long-term viability and sustainability of the power
sector in the state. As a part of the reform process, Gujarat Electricity Board has been unbundled into
separate seven Companies with functional responsibilities for generation, transmission, distribution
and trading of electricity with complete autonomous operations.
Accordingly, the distribution undertakings and functions of the Southern Distribution Zone of the
erstwhile GEB are transferred to Dakshin Gujrat Vij Company Limited. The company was incorporated
as a Public Limited Company on 15th September, 2003, primarily to carry out distribution of electricity
to retail and bulk consumers and has become operational effective from 1st April 2005.
The Company is engaged in distribution of electricity in 7 districts namely Bharuch, Narmada, Surat
(except some part of Surat City), Tapi, Dangs, Navsari and Valsad in South Gujarat. The Company is
a wholly owned subsidiary Company of Gujarat Urja Vikas Nigam Limited, a government Company.
The Company was incorporated with an authorized Capital of Rs. 10 Lacs divided into 1,00,000 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 Km
2

 Number of consumers - 27.32 Lac consumers

TERRIF- The amount of money frame by the supplier for the supply of electrical energy to various
types of consumers in known as an electricity tariff. The tariff covers the total cost of producing and
supplying electric energy plus a reasonable 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;

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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
installed capacity of plant and KW generated. Increase in max demand requires more power
to be generated that mean it will require higher capacity plant that would results in increase
in the cost of electricity.
3. Power factor – It is an important parameter for electricity billing. If the power factor is less
than 1 or so, then the electrical system would require some additional power (reactive power)
in addition with the actual power consumed. This additional power is also drawn from the
supply though it is not consumed. For household appliances p.f. is close to 1 so reactive power
is not considered for billing but if it falls below a critical value (generally .9) then additional
charges are employed. For industries reactive power is also being considered for billing and
they have to maintain their p.f. around .7 otherwise additional charges are employed.
4. Time at which load is consumed- In “time of billing” system, electricity is supplied at different
rates during different intervals of time (peak, off-peak, night, rest hours) so as 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

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TYPE OF CONSUMERS
1. RGP - For Residential General Purpose having load up to 6kW. The following are the categories
of RGP:
 Rural
 Urban
 BPL (Below Poverty Line)
2. GLP- For GLP used in educational institutes and other institutions registered with the Charity
Commissioner or similar placed authority and research and development laboratories.
3. NON-RGP - For aggregate load up to and including 40 kW.
4. NON RGP NIGHT - For using supply during night hours and having charges less than NON-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 regular supply of electricity and purpose not specified in any other HT categories.
 HTP-II - For Water works and sewage pumping stations run by Local authorities and GW & SB
GIDC Water works.
 HTP-III - For consumer using electricity on regular basics.
 HTP-IV - For consumer using electricity during Night hours (10:00PM TO 06:00AM next 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-
Mainly the following types of conductors in the basis of material used for the over-head transmission
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.

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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. Class C- It includes the survey to verify the increased capacity for providing transformer in the
LT lines.
4. Class D- It is carried out for mega projects.

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Day 2 & 3: 4/12/2018 & 6/12/2018
Electric metres- An electricity meter, electric meter, electrical meter, or energy meter is a device that
measures the amount of electric energy consumed by a residence, a business, or an electrically
powered device.
 For residential and official buildings, the billing is done for the kilowatt hour (kWh) consumed
as for such buildings is power factor of loads is as high as .9 or more. But in case of industries,
extra charges are being employed depending 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
excess power consumption during certain period (mainly peak hours) by increasing the billing
rate.
 Electricity meters operate by continuously measuring the instantaneous voltage (volts)
and current (amperes) to give energy used (in joules, kilowatt-hours etc.).
Mainly the electric meters are of two types- The reading of the meters is to observed regularly by the
supplier company for making the electricity bill. However, smart meters are also available now a days
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
measures the electric power in terms of number of revolutions made by a non-magnetic but
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 and the other produces a magnetic flux in proportion to the 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

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 This produces eddy currents in the disc and the effect is such that a force is exerted on
the disc in proportion to the product of the instantaneous current, 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 disc drives a register mechanism equipped with gears which counts revolutions, much
like the odometer in a car.
 Different phase uses additional voltage and current coils.
 The amount of energy represented by one revolution is denoted by Kh whose value differs
for different meters. Power in one revolution of disc is given by-
P=
3600 .??????ℎ
??????
where t (sec) is time taken by disc to complete one revolution and P (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 easily transformed for the thefts like use of magnet for opposing the
disc motion, reducing number of turns of voltage or current coil, by keeping meter in
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 current coils

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 They display the energy consumed on LED or LCD screen. Apart from the energy
consumed, they also show a number of other parameters like power factor, voltage,
current, frequency, total or the active power (kVAh), reactive power (kVARh), date,
time, temperature, cumulative active power, current and last month active power and
many others.
 They can support “time of billing” format by recording the energy consumed during
different durations – peak, off-peak, night, and rest.
 It contains metering engine, microcontroller (processing and communicating engine),
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 metering engine is given the voltage and current inputs and has voltage reference,
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 (processing and communicating engine) is having the responsibility of
calculating the other derived quantities from 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 largest source of long-term errors in the meter is drift in the preamp, followed
by the precision of the voltage reference. Both of these vary with temperature as
well and vary wildly because most meters are outdoors. These errors can be
minimised by modification in the design.
Thefts are possible even in such meters. Ex- One such thievery is caught in which
the burglary is done by soldering the wires.
Blinking rate of LED for
per unit of consumption
Current rating for
all 3 phases
Time periods for “time
of billing” system

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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 (Galvanised Iron)
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 immunity to short circuits caused by external forces (wind, fallen branches), unless
they abrade the insulation.
 Can stand in close proximity to trees/buildings and will not generate sparks if touched.
 Little to no tree trimming necessary
 Simpler installation, as crossbars and insulators are not required.
 Ease of erection and stringing, less labour intensive, less construction resources needed.
 More aesthetically appealing.
 Can be installed in a narrower 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 cost for the cable itself.
 Insulation degrades due to sun exposure, though the critical insulation between the
wires is somewhat shielded from the sun.
 Shorter spans and more poles due to increased weight.
 Can lead to much longer repair times for installations in hilly areas due to much higher
line weights requiring bigger and more specialized equipment to repair.
 Older installations are known to cause fires in areas where falling large trees or branches
regularly cause breaks in lines and or in insulation leading to short circuits which can
then lead to burning insulation dripping to ground and starting ground fires.
 Failure modes through punctures, electrical tracking, and erosion.


Types of insulators-
1. Pin insulator- A pin insulator is a device that isolates a wire from a physical support.

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 As the name suggests, the pin type insulator is mounted on a pin on the cross-arm on
the pole.
 There is a groove on the upper end of the insulator. The conductor passes through this
groove and is tied to the insulator with annealed wire of the same material as the
conductor.
 Pin type insulators are used for transmission and distribution of communications, and
electric power at voltages up to 33 kV. Insulators made for operating voltages between
33kV and 69kV tend to be very bulky and have become uneconomical in recent years.

2. Post Insulator- It is a type of insulator that becomes popular in the 1930s. It is more 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. Suspension insulators- For voltages greater than 33 kV, suspension type insulators, consisting
of a number of glass or porcelain or polymer discs connected in series by metal links in the
form of a string. The conductor is suspended at 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 depends on
the voltage. Greater the voltage, greater will be the disc units.

4. Strain Insulator- A strain insulator is an electrical insulator that is designed to work in
mechanical tension (strain), to withstand the pull of a suspended electrical wire or cable. They
are used in overhead electrical wiring, to support radio antennas and overhead power lines.
A strain insulator may be inserted between two lengths of wire to isolate them electrically

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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 earlier days, they were used as strain insulator. But nowadays, they are
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 groves by means of soft-bending wires. The insulators are bolted to the cross-
arm of the pole.
 Shackle Insulators are used at the end of distribution lines or at sharp turns (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-It is replaceable portion of the assembly and it breaks the circuit
by melting during faulty condition.
Note- The above insulators are made up of porcelain or polymer in a multiple disc type 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 porcelain or glass but nowadays use of polymer as insulator is
more preferred because-
 They are more reliable than porcelain which breaks easily.

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 In porcelain insulator, ones the crack even small develop it grows up with time and may cause
damage in the system by allowing the moisture to flow into the system and polymer insulator
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 galvanized steel wire strands that are used for sustaining mechanical load.
Generally, they are made up of 6 wires stranded around 1 wire, twisting 7 wires together. 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 observed that people prefer Torrent company’s electric power over
DGVCL though Torrent is a private company and charge bill at almost double rate. The reason being
the much better service. They have complete underground distribution system, spare cable for every
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 for congested urban areas where overhead lines may be difficult or impossible to
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-ground cable- It consist of 3 wires for 3 phases, each one of them looks like following and are
well insulated from each other through additional insulators. In each wire a wrapping with colour of
corresponding colour is also provided for identification of the phases.

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1. Cable sheath – Particularly protects the cable against moisture.
2. Wire screen – Controls the electric field and discharges fault currents.
3. Insulating layer – Insulates the electric conductor.
4. Electric conductor – Conducts the current.
Depending on the voltage and current ratings different types of cables are available. The cross-section
area of the conductor depends on the current carried by the wire while insulation required depends
on the voltage. For 11 kV lines 185 mm diameter cable is used.

Bus-Bar- It is a metallic strip or bar which is used for high current distribution. It is a pair of very heavy
conductors, usually copper or aluminium to carry heavy currents from one part of a power system to
another. In power system, cables can’t be joined in the way the small wires are joined in the general
purpose. For the inter connection of cables bus bars are used. Through the bus bar, a number of cables
can be connected using cable lugs. They are uninsulated and supported between two supports. 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 in actual electrical power system we deal with high voltage and high current and it
is not feasible and economical to manufacture devices to measure such high values. So, to measure
high values in power system we use CT and PT. The primary of these transformer is placed in main line
and secondary is placed in any meter or relay depending on the application. CT is step up transformer
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.

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Day 5: 11/12/2018
Visit to Mega-Royals, Honey park area, Adajan, Surat
This day we visited to Mega-Royals for observing the installation of new transformer in parallel with
the previous one for load sharing as the load is been increased. Firstly, the supply to the transformer
is disconnected from the feeder and power is supplied in the building through the 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 installation of transformer, its body is grounded because any ungrounded transformer can
build up an electrical charge that could be very dangerous to personnel or equipment. It could
penetrate insulation and ruin the transformer, and also provide a path for transformer voltages to the
outside world. The ground can pass induced voltage to ground and thus prevents the problems.
In addition, to avoid the damage due to surge current or overload current, fuses are provided on both
HT and LT side. LT side fuses are inform of 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 providing the uninterrupted power supply, a spare cable is also provided which supplies power if
fault is present in the first cable.

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Day 6:12/12/2018
Sighting at Surat transformer, diamond Vidhya Sankul, Surat
-By Vedant sir (Mobile No.- 9998628326)
3 phase core transformers are being studied.
Magnetic core- It consist of laminated sheets of CRGO (Cold Rolled Grain Oriented) Silicon Steel. It is
laminated to minimise the eddy current losses which are directly proportional to the square of
thickness of the material. The material (CRGO in this case) chosen is such that to offers low reluctance
for the flow of flux and high resistance to current flow that in turn minimise the core loses.
Windings – They consist of low resistive materials (copper or aluminium). Copper offers less resistance
than aluminium but its cost is quite high so to reduce the cost of the transformer, use of aluminium is
more preferred. Windings are insulated from each other as well as from the magnetic core.
Insulation on the wires- Kraft paper is one of the prime insulating materials for covering conductors
in transformers. ABB Raman Sigma Kraft paper with high purity and mechanical and dielectric strength
is perfect for double paper covering (DPC) applications and as layer insulation in transformer designs.
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 electric power, a bushing is an insulated device that allows an electrical conductor
to pass safely through a grounded conducting barrier such as the case of a transformer
or circuit breaker.
 Bushings are typically made from porcelain, though other materials are possible.
 They are used to provide the ground clearance i.e., to avoid the grounding of the wires
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.
 Their heights depend on the voltage. Greater the voltage, greater will be the electric
field, greater will be the need of ground clearance and thus for high voltage, the height
of bushings required is more.

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3. Conservator and breather- The oil cooled transformers are provided with conservator and
breather. Conservator is a cylindrical tank provided on the top of the transformer along with
the oil level indicator. In most of the transformers oil is used for cooling as well as insulation.
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
explosion due to increase in pressure of the oil with the temperature. Due to expansion and
contraction exchange of air take place through the conservator that may cause the entry of
moisture into the transformer. To avoid this, breather is provided on the conservator for 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
faults then the oil in it may decompose resulting into liberation of the gases that increases the
pressure inside the tank and may cause explosion. To avoid this, explosion vent is provided.
When pressure exceeds the safe level, diaphragm present in it bursts allowing the gases and
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- They are provided for easy movement of the transformer from one place to another.
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 as well as manufacture as weight of the complete HV is quite high due 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.

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3. The manufacturing and assembling of the complete coil are easier for lesser turns and thicker
wire
HV is kept on outer side of core-
1. If it is nearer to the core then thicker insulation is required between core and HV that increases
the cost.
2. Apart from this, the HV windings are exposed to better cooling condition on the outer side.
3. As HV winding is in the form axial bundles of coils so it is better to use it on the outer side- 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 regulation is possible with high voltage winding as it carries large number of turns.
2) The low voltage winding of the transformer carries large current. So, if tapings are provided on low
voltage side then then there are difficulties encountered in the interruption of high currents which
makes its impracticable.
3) For the reasons of requirement of insulation, the low voltage (LV) winding is placed near the core
while the LV winding is placed outside. Hence practically it is easier and simpler to provide tapings on
high voltage winding.
4) In case of step-down transformers, it is an added advantage to provide tapings on h.v. side. At light
loads, the LV side voltage increases. It is required to decrease this voltage by adjusting the tapping on
h.v. side to a position where number of turns are large. With large number of turns, the flux and flux
density decreases.
This results in reduction of core loss which increases transformer efficiency at light loads.
5) If the tapings are provided on the LV side then the exact voltage regulation may not be provided.
This can be explained by considering an example of a transformer with rating 3 phase, 11 KV/415 V,
delta/star connected which 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 minimum possible voltage regulation with tapings on LV side is 15 V or 6.25 %. It can be seen
that if a voltage regulation of 5 % is desired with 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 – This test is carried out to verify that the number of turns in the primary and
secondary are as per the voltage ratio requirement or not. In this test, small voltage is applied
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 (Breakdown Voltage) Test- The oil used in the transformer must have dielectric
strength at least 2.5-3 times the maximum voltage of the HV side. In this test two electrodes
are kept at very small distance (2.5 mm) in the oil and voltage across them is increased until 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, impurities like carbon and the other conducting metals or ions. The oil is filtered in
a filtration machine, provided with the pressure gauge and temperature indicator. 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
transformer is performed to determine 'no load loss (core loss)’. The circuit diagram for open
circuit test is shown in the figure below-
4.

Usually high voltage (HV) winding is kept open and the low voltage (LV) winding is connected
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 rated value of the LV side with the help of a variac. When the applied voltage 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
open circuited, there is no output power. Hence, this input power only consists of core losses
and copper losses. As described above, no-load current 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 transformer is short circuited and wattmeter (W), voltmeter (V) and ammeter
(A) are connected on the HV side of the transformer. Voltage is applied to the HV side and

21. 21

increased from the zero until the ammeter reading equals the rated current. All the readings
are taken at this rated current.
The ammeter reading gives primary equivalent of full load current (Isc).
The voltage applied for full load current is very small as compared to rated voltage. Hence,
core loss due to small applied voltage can be neglected. Thus, the wattmeter reading can be
taken as full load copper loss in the transformer.
6. MAGOR test- In this test the output value must be greater than 300 for transformer to be in
working condition.

7. DVDF (Double voltage Double Frequency) test- In this test, double of rated voltage is applied
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- After carrying out the above tests the transformer is kept in the oven for 2 days
at 80-90C to remove its moisture content. This is done to minimise the chances of corrosion.
 General range of capacity of the transformers-
5,10,16,15,25,66,100,200,315,500,630,800,1000,1500 in kVA.
 Transformers are being tested to fulfil the criteria set up by the BIS (Bureau of Indian
standards) under ERDA (Electrical Research and Development Association). Previously IS
2026 standards needs to obeyed for transformers but now a days IS 1180 standards are
followed.
 Turn ratio (a) for the transformer of capacity Q is given by
a = ??????
2
√?????? where k is a coefficient depends upon the material of the winding
k=0.3-0.37 for aluminium winding
k =.38-.45 for copper winding
 Generally, in distribution transformer, HV windings are connected in delta while the LV
windings are connected in star.
 Bridging is basically providing a bridge or the connection between two systems. In case of
thick wires bridging is done by welding.



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-mediator in Surat Transformers-
Product- 3 phase step-up transformer
Capacity- 200kVA
Input- 3 phase 415V, AC
Output- 3 phase, 800-1600V, AC
Cooling-Oil cooled

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Day 7: 13/12/2018
Visit to Pal SS(Sub-Station)
Sub-station- A substation is a part of an electrical generation, transmission, and distribution system.
Substations transform voltage from high to low, or the reverse, or perform any of several other
important functions. Between the generating station and consumer, electric power may flow 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 provided to ground the surge produced in the line. Surge may be produced in
the line due to a number of reasons but mainly they are due to lightening (natural, from atmosphere)
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 avoid this, lighting arrester is provided which passes the surge currents to the ground. It generally
consists of a number of discs of metal oxides (ZnO) which are stacked to form a cylindrical body. This
cylindrical body is covered by porcelain or polymer insulator act as a fast-acting electronic switch
which behave as insulator for normal working ac voltages but for the surge voltages it starts behaving
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 and repairing work. As the modern power system deals with huge 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.
For uninterrupted operation of circuit breaker, its two metallic contacts must be removed very quickly,
which is achieved by a suitable mechanism (metal spring, air compression, hydraulic method etc.) 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 is provided to disconnect the line during maintenance or repairing work. We can’t operate
isolator without breaker because without breaker isolation of line may lead to the spark which is quite
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 by the breaker is not physically visible to us so we can’t identify whether the line is on 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
connected with male contact that can fixed perfectly on the female contacts provided on the
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 directions with
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 called a doghouse. These are used to control the
substation equipment, to send power from one circuit to another or to open or to shut down circuits
when needed.
Battery house is a dark room in which number of batteries are present. It is known as the heart of 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.

Important Electrical distribution system according to the feedback connection schemes or topologies-
1. Ring main distribution system-
 It is the most preferred distribution system due to its high reliability.
 Each distribution transformer is fed with two feeders but in different paths. The
feeders in this system form a loop which starts from the substation bus-bars, runs
through the load area feeding distribution transformers and returns to the substation
bus-bars.
 The following is the line diagram for this distribution system-

25. 25

 Advantages over other distribution system-
 There are lesser fluctuations on the consumers terminal.
 The system is very reliable as each transformer is fed with two distribution
system so that in case of the fault in any of the section continuity of the
supply is ensured.

2. Radial distribution system-
 This system is used when the substation is located at the centre of the consumers.
 In this system, different feeders radiate from a substation or a generating station and
feed the distributors at one end. Thus, the main characteristic of a radial distribution
system is that the power flow is in only one direction.
 Single line diagram-

 Although this system is simplest and least expensive this system is not highly reliable
as the failure in any feeder results in cut off of the supply to the associated consumers
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 system provides high reliability, but it is not very popular as the initial
cost is very high as the number of the feeders gets doubled.

4. Interconnected distribution system- When ring main distribution system is energized by two
or more substations or generating station, it is called as interconnected distribution system.
Advantages
 It ensures reliability in case of transmission failure.
 During peak hours, any area can be fed with other substation or generating station to
meet the increased demand.

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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 consumer to which we are visiting was also installing solar panels on his terrace. The
specification of panels is shown in the figure below-

He has installed 12 such solar panels such that 2 groups of 6 series connected panels are connected in
parallel.
 The dc voltage generated to the invertor which converts the it into 230V, 50Hz ac voltage and
is connected with the input of the house through a meter (M1), installed to show the power
generated.
 Apart from this, a switching system is also provided which cut off the power generated when
there is no power from the grid or supply. This is done to avoid the danger of electric shock to
the lineman due to the additional power generated.
 The meter which shows the bill of house was also replaced to bidirectional meter (M2). This
is done so as to measure the power supplied to the grid when the power consumption is less
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. They are considered suitable for installation only if the error is in the range from
-3% to +3%. For checking the accuracy of meters, advanced instruments are present in the DGVCL.
After installation, electric meters may misbehave due to a number of reasons which is reflected in the
bill of the consumer. Consequently, the consumer files complain application for the faulty meter for
some of the companies cost some fee (Rs 300 in DGVCL). The meter may belong to the consumer or
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 meter and if less than the actual one than it is known as slow meter. These errors may arise due
to number of technical faults in the meters.
Sometime people complain that their electric bill is increased as their meters are replaced with the
electronic. This happens so because with time the electromechanical meters become slow due to
environmental factors showing reading less than the actual one. When they are replaced by electronic
meters, the electronic meters give the actual reading which is higher than the previous false readings
so they believe that their meter is fast but it is not the case.
If any complaint is submitted by the consumer then the company send electrician to check the meter.
The checking of meter is also done by an electronic machine.
Checking the meter-
 The terminals (phase and neutral) of the machine are connected with the output terminals of
the meter.
 Current transformer is magnetically connected using clamper.
 On switching on the device, it directly provides us the error in the measurement of 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).

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Day 10: 18/12/2018
Visit to Pal SS(Sub-Station)
SCADA (Supervisory Control and Data Acquisition) -
Supervisory control and data acquisition (SCADA) is a system of software and hardware elements that
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 systems are crucial for industrial organizations since they help to maintain efficiency, process
data for smarter decisions, and communicate system issues to help mitigate downtime. They are used
in all industrial processes including-
 Energy
 Food and beverage
 Manufacturing
 Oil and gas
 Power
 Recycling
 Transportation
 Water and waste water
 And many more
Working- The basic SCADA architecture begins with programmable logic controllers (PLCs) or remote
terminal units (RTUs). PLCs and RTUs are microcomputers that communicate with an array of objects
such as factory machines, HMIs, sensors, and end devices, and then route the information from those
objects to computers with SCADA software. The SCADA software processes, distributes, and displays
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 commonly used. 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
remains the same for the whole of the voltage range. The increase in rated voltage is handled
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 breaker works 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- Closing the moving contact assembly is manipulated by means of a fast-acting
operating mechanism. Outside these manipulations, no energy is stored. For the

31. 31

circuit breaker and the fuse-switch combination, the opening mechanism is charged
in the same movement as the closing of the contacts.
b) Opening- Opening of the switch is carried out using the same fast-acting mechanism,
manipulated in the opposite direction. For the circuit breaker and fuse-switch
combination, opening is actuated by- Pushbutton or fault.
c) Earthing- A specific operating shaft closes and opens the earthing contacts. The hole
providing access to the shaft is blocked by a cover which can be opened if the switch
or circuit breaker is open and remains locked when it is closed.
 The figure below shows typical outlook of a three-feeder RMU. In the figure, the combination
consists of load disconnectors for the incoming two feeders and a fused load disconnector for
the distribution transformer feeder. The incoming and outgoing medium-voltage cables are
attached using elbow-type plug-in cable ends.

 Quick supply using RMU in case of fault- If the fault is found between the points 1 and 2 then
that particular portion is disconnected from the ring and the transformer T7 is fed by switching
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 design for 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 mechanism at the substation is designed in such 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 cleaning tissue is also provided to clean the hands before joining the ends. This is done
to avoid the soil and dirt to move in the system.
 Joints of the cable are connected with a hollow tube of aluminium 130 mm long which is fixed
at the joints using clamping tool.

 These joints are then covered with number of insulator layers firstly with rubber insulation
tube, then 2 insulation tubes (black and red which are fitted tightly over the system by
burning) for keeping the phases insulated from each other as well as for protection from
moisture.
Ferule aluminium tube for
joining ends of cable
Clamping tool

33. 33


 The wire screen (grounded metallic net that controls the electric field and discharges the
faulty currents) of the two cut cables is firstly joined using a copper strip and is then covered
with the metallic net.

 The complete set-up is then again covered by thick insulation tube that act as metallic sheath
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