A brief report on internship at PGCIL Hassan. This gives a brief information reguarding equipments which are used in a power grid. Classified information.

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VISVESVARAYA TECHNOLOGICAL UNIVERSITY
BELAGAVI – 590 018
Internship Report
On
“POWER TRANSMISSION AND EQUIPMENTS OF
POWER GRID CORPORATION OF INDIA LIMITED 400KV/220KV Sub Station,
HASSAN.”
Submitted By
Sai Chaithanya (4SU15EE027)
Department Of Electrical and Electronics
SDMIT- UJIRE (D.K)
Academic Year:2016-17

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DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING
Shri Dharmasthala Manjunatheshwara Institute of Technology (SDMIT)
UJIRE- 574 240, Karnataka – State, INDIA
Shri Dharmasthala Manjunatheshwara Institute of Technology (SDMIT)
(Affiliated VTU, Belagavi & Approved by AICTE, New Delhi)
ELECTRICAL & ELECTRONICS ENGINEERING DEPARTMENT
Ujire – 574240, Karnataka – State, INDIA.

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Acknowledgement
To begin with, I wish to convey my heartfelt gratitude to Almighty for his help to complete the
internship successfully. I also thank to the management of POWER GRID CORPORATION OF
INDIA LIMITED for providing me such opportunity to accomplish my industrial training.
I would specially thank to Engr. Sunil . T , DGM of POWER GRID CORPORTION OF INDIA LIMITED,
Hassan (400KV/220KV), who gave me the permission to do internship work at his esteemed
organization.
I would like to thank Suresh Executive engineer in KPTCL, my advisor for his constant support
and many suggestions.
I want to thank all those people who helped to complete my internship successfully. In this
process my special thanks goes to Engr. Prashant who coordinated my internship program and
help me to acquire practical knowledge regarding to the working of the power grid, equipments
of the grid and their specifications and control system of the grid and also for his gentleness,
patience and continual support.
I would also like to mention the name of Justin, Junior engineer(JE) of the power grid, for being
so kind during the period of my internship.
I am also grateful to all my teachers for their cooperation and encouragement throughout my
whole academic life in SDM Institute of technology.

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Executive Summary
I did my internship at Power Grid Corporation of India Limited (400kv/220kv) located on the left
side of the Gadenahalli, shanthigrama which belongs to Hassan district from 23rd January to 31st
January of the year 2018. This internship is the result of 8 days attachment with the PGCIL
Hassan.
Power Grid corporation of India Limited, is a state owned electric utility company
headquartered Gurugram, India. Power Grid transmits about 50%of the total power generated
in India on its transmission network.
My duration of stay was divided to work in five sections as 400kv yard, 220kv yard, control
room, fire fighting system, substation and operation etc. During my internship I gathered
practical knowledge about the incoming and outgoing of the voltage generated from different
parts of our state from Nelamangala, Talaguppa, Udupi 1&2 to Yachenahalli, Shimoga and
Hassan. Operation, major equipments e.g. lightning arrestor (LA), capacitive voltage
transformer (CTV), Wave Trap (WT), Isolator (ISO), Bus Reactor, Current transformer (CT),
Potential Transformer (PT), Bus bars, Circuit Breakers (CB), Transformer etc.
Switch Yard or Bay is the important part of a Power grid for better transmission and distribution
of the power from one place to another. I acquire knowledge about the transformer
(400kv/220kv/33kv), types of circuit breaker (SF6, air blast type and spring type), lightning
arresters, CT,PT and other equipments of the yard which were cleanly taught and shown by
engineer of the Power Grid of PGCIL.

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Table of Content
Chapter-1 Company Objective……………………………………………………………………………………………....
1.1 Introduction………………………………………………………………………………………………………………………
1.2 Future of Power grid corporation of India (400kv/220kv) substation…………………………………
1.3 Single line Diagram of Hassan Sub Station (400kv Network)………………………………………………
1.4 Single line Diagram of Hassan Sub Station (220kv Network)………………………………………………
Chapter-2 SUBSTATION……………………………………………………………………………………………………………
2.1 Introduction to Substation…………………………………………………………………………………………………….
2.2 Equipments of Substation……………………………………………………………………………………………………..
2.2.1 Lightning Arrestor [L A]……………………………………………………………………………………………………….
2.2.2 Capacitive Voltage Transformer [C V T]……………………………………………………………………………….
2.2.3 Wave Trap [W T]…………………………………………………………………………………………………………………
2.2.4 Isolator [ISO]……………………………………………………………………………………………………………………….
2.2.5 Circuit Breaker [C B]…………………………………………………………………………………………………………….
2.2.6 Current Transformer [C T]……………………………………………………………………………………………………
2.2.7 Potential Transformer [P T]…………………………………………………………………………………………………
2.2.8 Bus Bars………………………………………………………………………………………………………………………………
2.2.9 Transformer………………………………………………………………………………………………………………………..
2.2.10 Bus Reactor……………………………………………………………………………………………………………………….
2.3 Types of Bus bar System…………………………………………………………………………………………………………
2.3.1 Double Main Bus Bar Arrangement…………………………………………………………………………………….
2.3.2 Quad Bus Bar Arrangement…………………………………………………………………………………………………

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2.4 TRANSFORMER
2.4.1 Transformer Construction……………………………………………………………………………………………………
2.4.2 Core…………………………………………………………………………………………………………………………………….
2.4.3 Winding………………………………………………………………………………………………………………………………
2.4.5 Cooling………………………………………………………………………………………………………………………………
2.4.6 Bell Tank and Bottom Tank………………………………………………………………………………………………….
2.4.7 Conservator…………………………………………………………………………………………………………………………
2.4.8 Pressure Relief Device…………………………………………………………………………………………………………
2.4.9 Silica Gel Breather………………………………………………………………………………………………………………
2.4.10 Winding Temperature Indicator………………………………………………………………………………………..
2.4.11 Oil Temperature Indicator…………………………………………………………………………………………………
2.4.12 Bushings……………………………………………………………………………………………………………………………
2.4.13 Tap Changer………………………………………………………………………………………………………………………
2.4.14 Control and Monitoring System…………………………………………………………………………………………
2.4.15 Installation of Breather……………………………………………………………………………………………………..
2.4.16 Recharging………………………………………………………………………………………………………………………..
2.5 CIRCUIT BREAKER…………………………………………………………………………………………………………………
2.5.1 SF6 Circuit Breaker………………………………………………………………………………………………………………
2.5.2 Oil Circuit Breaker……………………………………………………………………………………………………………….

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CHAPTER-1 Company Profile
I did My Internship at POWER GRID CORPORATION OF INDIA LIMITED from 20th of January 2018
to 31st of January 2018 and this internship report is the result of these 11 Days attachment with
PGCIL.
1.1 INTRODUCTION
An electrical grid or An Power grid is an interconnected network for delivering electricity from
producers to consumers. It consists of generating stations that produce electrical power, high
voltage transmission lines that carry power from distant sources to demand centers, and
distribution lines that connect individual customers.
Power stations may be located near a fuel source, at a dam site, or to take advantage
of renewable energy sources, and are often located away from heavily populated areas. They
are usually quite large to take advantage of economies of scale. The electric power which is
generated is stepped up to a higher voltage at which it connects to the electric power
transmission network.
The bulk power transmission network will move the power long distances, sometimes across
international boundaries, until it reaches its wholesale customer (usually the company PGCIL
owns the local electric power distribution network in Hassan).
On arrival at a substation, the power will be stepped down from a transmission level voltage to
a distribution level voltage. As it exits the substation, it enters the distribution wiring. Finally,
upon arrival at the service location, the power is stepped down again from the distribution
voltage to the required service voltage(s).
In Hassan POWER GRID, ONE and a HALF Scheme of connection is used to the 400kv yard
which has both incoming and out going of electricity from four different stations namely
Neelamangala line(213 km), Talaguppa Line(284 km), Udupi-2 Line(180 km), Udupi-1(180 km).
Where as in 220kv network they have used Double Main and Transfer bus scheme for the
receiving and distribution of the voltage received and transmitted to different stations such as
Hassan city line which ranges from a distance of 28km and Shimoga Line(143.4km),
Yachenahally Line(43.2km), Suzlon Line(44.1 Km), To 315 MVA ICT-1 (220kv side) and To 315
MVA ICT-2 (220kv side). Few bays are left for the purpose of further expansion so that they can
fulfill the dream of having a Interconnection system from KASHI (North INDIA) to
KANYAKUMARI (tip of the South INDIA).

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1.2 SINGLELINE DIAGRAM OF HASSANSUB STATION (400 KVNETWORK)
In PGCIL they have used 1 and a half scheme in 400kv system which can be cleanly observed in
the single line diagram of the 400kv network. The Isolators, circuit breakers and current
transformers are equally divided to the 400kv bus bar-1 and bus bar-2.
This sequence of connection is said to be 1 ½ scheme which is used in 400kv network in Hassan
Sub station.

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1.3 SINGLELINE DIAGRAM OF HASSANSUB STATION (220kv NETWORK)
In PGCIL for 220kv Network they have used double bar arrangement scheme for their
transmission purpose. They provide their power to Hassan Line, Shimoga line, Yachenahally
Line, Suzlon line and other two extra line for the future expansion.
Here each circuit is connected to both the buses. In some cases half of the circuits can be
connected and operated on each bus when circuit breaker failure would loss to half of the
circuits. In double main bus bar arrangement one or two breakers can be connected for each
circuit. Double main bus bar and double breaker scheme provides high reliability for any type of
fault in transmission line or circuit breaker.

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2.2 EQUIPMENTS OF SUBSTATION
2.2.1 LIGHTNING ARRESTER [L A]:
All equipment those are feeding from stations should be protected against direct lightning
stroke. When stroke lightning stroke happens, a huge amount of surge voltage is created on the
transmission line and this high voltage can damage any equipment within a short time. So this
huge amount of lightning voltage are directly grounded through lightning arrester hence
equipment are remains safe.
400kv lightning arrester
2.2.2 CAPACITIVEVOLTAGETRANSFORMER [CVT]:
Capacitor Voltage Transformers convert transmission class voltages to standardized low and
easily measurable values, which are used for metering, protection and control of the high
voltage system. As such, the need for accurate and reliable voltage transformation is essential.
Additionally, Capacitor Voltage Transformers serve as coupling capacitors for coupling high
frequency power line carrier signals to the transmission line.
The main purpose of the capacitive voltage transformer is for measurement purpose and Power
line carrier communication (even for the purpose of data transmission) for one place to
another.

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These CVT’s are constructed a well recognized company named SIEMENS which gives a
complete range of extra high voltage measurement and protection solution for electrical
equipments.

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2.2.3 WAVETRAP [WT]:
Wave trap is a parallel tuned inductor - capacitor tank circuit made to be resonant at desired
communication frequency . It reduces corona losses in transmission lines in power system.
Wave trap is installed in the substation for trapping the high frequency communication signal
sent on the line from remote substation and diverting them to the telecom panel in substation
control room. These high frequency signal should not be coming on the buses as these may
damage the equipments .
A wave trap is a device that allow only a particular frequency to pass through it that it filters the
signals coming on to it . So a wave trap is connected between buses and the transmission line
which allow only 50 Hz signal to pass through it. This is relevant in power carrier
communication (PLCC) system for communication among various substation without
dependence on telecom company network . The signals are primarily teleportation signal and in
addition , voice and data communication signal.
400kv Wave trap

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2.2.4 ISOLATOR [ISO]:
Isolators are used for isolating the circuit when the current has already been interrupted. They
allow currents into the circuit until circuit is repair again. Isolators are used for connecting and
disconnecting parts of the electrical installation after de energizing.
Terminal head / stud of isolator arms where conductors will be terminated shall be strong,
robust and shall be adequate to carry rated current and short circuit rating of isolator. It should
have 360 degree freedom of rotation and should have built in cover to eliminate deposition of
dust and foreign particles.
ISOLATOR at closed position
2.2.5 CIRCUIT BREAKER [CB] : Circuit breakers are generally located so that each generator,
transformer, bus, transmission line, etc.., can be completely disconnected from the rest of the
system. These circuit breakers must have sufficient capacity so that they can carry
momentarily the maximum short circuit current that can flow through them, and then interrupt
this current; they must also withstand closing in on such a short circuit and then interrupting it
according to certain prescribed standards. In the PGCIL they have used ACB (Air Circuit Breaker)

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SF6 Circuit breaker
SF6 is inert gas the property of this gas the higher pressure and temperature is dielectric
strength will be SF6 has two gas chamber when contact is close the pressure is two chamber
have the same pressure but when the contact is pen then one of the chamber get totally close
and other remain open, there is a narrow channel between two chamber and when contact
open the SF6 flow a plane of high pressure region to the low pressure region there will be
turbulence of SF6. At zero current the turbulence of SF6 absorb all the ions and since it is
flowing from a narrow region hence it provide high dielectric strength but there is a problem
that the pressure of SF6 is not always remain fixed due to leakage in the cylinder of SF6 so there
is pressure gauge as well as alarm attached with it. When ever pressure decreases the alarm
ringing and the gas is refilled to increase pressure.
SF6 CIRCUIT BREAKER

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2.2.6 CURRENTTRANSFORMER [CT]:
In electrical engineering, a current transformer is used for measurement of electric currents.
When current in a circuit is too high to directly apply to measuring instruments, a current
transformer produces a reduced current accurately proportional to the current in the circuit,
which can be conveniently connected to measuring and recording instruments. A current
transformer also isolates the measuring instruments from what may be very high voltage in the
monitored circuit. Current transformers are commonly used in metering and protective relays
in the electrical power industry.
Current transformer
2.2.7 POTENTIAL TRANSFORMER:
It is used to measure or monitor the voltage on transmission lines and to isolate the metering
equipment from the lines. It is also known as voltage transformer. PT’s are designed to have a
precise voltage ratio to accurately step down high voltages so that metering and protective
relay equipment can be operated at lower potential. Normally the secondary of a voltage
transformer is rated for 69 V or 120v at rated primary voltage.

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2.2.8 BUS BARS
A bus bar is used for a conductor carrying current to which many connections are made. These
are generally used in sub-stations where the need number of incoming and outgoing lines at a
same voltage. Normally bus bars used in the substations are of copper or aluminum are they
are basically round and solid.
BUS BARS
2.2.9 TRANSFORMERS
Transformer is a static device used to transform power from one voltage level without changing
the frequency. There are different parts of a transformer given below:

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1. Bushing: This maintains the incoming and out going connections of a
transformer.
2. Radiator: This is used to radiate the heat of a transformer when transformer is
heated up at a certain level.
3. Oil temperature meter: This meter indicates the temperature of transformer oil.
If temperature crosses a certain level then it makes an alarm.
4. Temperature meter: This meter indicates the temperature of transformer
windings. If temperature crosses a certain level then it starts the winding fans.
5. Oil Level meter: This meter indicates the oil level of transformer. If oil is lower
than a certain amount it makes an alarm that means that transformer have to
feed oil.
6. Silica gel: It Works like breathing. There have a little amount oil under the silica
gel which suck the moisture of air and further sends this air to silica gel which is
further sucks the rest of the moisture of the air.

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2.2.10 BUS REACTORS:
A bus reactor is a type of air core inductor, or in some cases, oil filled, connected between two
buses or two sections of the same bus in order to limit the voltage transients on either bus. It is
installed in a bus to maintain system voltage when the load of the bus changes. It adds
inductance to the system to offset the capacitance of the line which varies due to load,
humidity, weather, generator excitation and temperature.
BUS REACTOR

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2.4 Transformer Construction:
The techniques used in the design and construction of high voltage transformer vary from
manufacturer to manufacturer. Transformer in PGCIL are of core type construction with the
windings placed concentric to the core.
The active parts of the transformers consists of core and windings.
2.4.1 CORE: Its is manufactured from laminations of cold Rolled Grain Oriented Silicon Steel
which gives very low specific loss at operating flux densities. Joints of the laminations are
designed such that the electromagnetic flux is always in the direction of grain orientation. The
core clamping structure is designed such that it takes care of all the force produced in the
windings in the event of any short circuit. The core is of 3 Phase, 5 Limb design.
2.4.2 WINDINGS: Windings are made from paper insulated copper conductors. Parallel
conductors are transposed at regular intervals thought the windings for ensuring equal flux
linkage and current distributions between strands. Disc construction is adopted for the high
voltage windings to ensure uniform distribution of impulse voltages. Insulation spacers in the
windings are arranged such that oil is directed through the entire windings for ensuring proper
cooling. The disposition windings from core are
CORE- TAP-IV-HV
2.4.3 COOLING: For ONAN cooling oil flows through the winding and external radiators units
attached to the tank by thermos phonic effect. Radiator cooler units consists of pressed steel
sheet radiators mounted directly on the tank. OFAF cooling is achieved by providing adequate
number of in line oil pumps.
2.2.4 BELL TANK and BOTTOM TANK:These are manufactured by welding steel plates and
are suitable for withstanding full vacuum and positive pressure of 1 atmosphere. BELL tank is
bolted to the bottom tank at the curb location.
2.4.5 CONSERVATOR: It is provided to take care of the expansion and contraction of
transformer oil which takes place during normal operation of the transformer.
Flexible separators or air cell is provided in the conservator to prevent direct contact of air with
the transformer oil.
A separate conservator is provided for the On Load Tap changer. Magnetic oil level gauge is
fitted on the main conservator which can give alarm in the event of the oil level falling below
the preset levels due to any reason.

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2.4.6 Pressure Relief Indicators: A device for oil pressure relief for the transformer tank
and cooling system is fitted with a trip relay. The pressure relief device allows for the rapid
release OF EXCESSIVE PRESSURE THAT MAY BE GENERATED IN THE EVENT OF A SERIOUS FAULT.
A pressure relief device is a spring loaded device which provides rapid amplification of its
actuating force. A bright color coded mechanical indicator pin in the cover moves with the valve
disc during the operation of the pressure relief device and is held in position by an ‘O’ ring in
the pin bushing. This pin is clearly visible from ground level indicating that the device has
operated.
The indicator pin may be rest manually by pushing it downward until it is reset on the valve
disc. The relief device is provided with a shielded weatherproof trip contact and is operated by
the movement of valve disc.
2.4.7 Silica gel Breather: Expansion and contraction of oil cause breathing action. Any
humidity in the air breathed is absorbed by the silica gel dehydrating breather. An oil seal in the
air intake prevents external moisture being absorbed by the atmosphere when no breathing
occurs.
The breather container is filled with silica gel crystals. It is arranged such that the air breathed
must pass through it. The desiccant is impregnated with cobalt chloride and when the silica gel
crystals are fully active, they are deep blue color. If the color changes to whitish pink, they are
then saturated with moisture and the change container should be replaced by a new reactive
one. The size of the breather is chosen to operate effectively over a period of six months
approximately.
2.4.8 Winding Temperature Indicator: The winding temperature relay indicates the
winding temperature of the transformer and operates the alarm, trip and cooler control
contacts. Winding temperature indicator consists of a sensor bulb placed in an oil filled pocket
in the transformer tank cover. The bulb is connected to the instrument housing by means of
two flexible capillary tubes. One capillary is connected to the measuring bellow of the
instrument and the other to a compensating bellow. The measuring system is filled with a liquid
with changes its volume with rising of temperature. Inside the instrument is fitted resistance
which is fed by a current proportional to the current flowing through the transformer winding.
The instrument is provided with a maximum temperature indicator. The heating resistance is
fed by a current transformer associated to the loaded winding of the transformer. The increase
in the temperature of the resistance is proportional to that of the winding.

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2.4.9 Oil Temperature Indicator: The oil temperature indicator consists of a sensor bulb,
capillary tube and a dial thermometer. The sensor bulb is fitted at the location of hottest oil.
The sensor bulb and capillary tube are fitted with an evaporating liquid. The vapour pressure
varies with temperature and is transmitted to a bourden tube inside the dial thermometer
which moves in accordance with the changes in pressure which is proportional to the
temperature.
2.4.10 Bushings: The winding connection pass from the windings to terminal bushings.
Terminal bushings up to 36kv class, 3150Amps, are normally of plain porcelain and oil in contact
type. Bushings of 52kv class and above are of oil impregnated paper condenser type. The oil
inside the condenser bushings will not be communicating with the oil inside the transformer.
Oil level gauge is provided on the expansion chambers of the condenser bushings.
2.4.11 Tap Changer: Transformers are provided with On load tap changers. Tap changing can
be designed for changing the taps in following modes:
a) Manually from Local Motor Drive unit
b) Manually from Remote
c) Automatically from the supervisory System
2.4.12 Control and Monitoring System: Local control and monitoring of the cooler, Alarm
and trip circuit are provided out at Marshalling box. Local Tap changer control is provided at the
Drive Mechanism. Automatic control; can be carried out at the supervisory System.
2.4.13 Installation of Breather: To Fix Breather to Transformer 25mm BSP flange on top of
the lid. Before fixing the breather to the transformer please see that Silica gel is blue. Do not
expose the silica gel for undue length of time to the atmosphere. Remove the oil cup and fill the
same with fresh transformer oil to the level indicated on sight window. Replace the cup and
tighten THE nuts properly.
2.4.13 Recharging: When the breather is in service for a long time, the color of silica gel
changes to pinkish which needs recharging. In order to remove silica gel. Remove the oil cup
first then detach tough acrylic plastic body from the top lid and then take out the gel in a pan,
through the hole at the top which is normally closed by the grill reactive the silica gel by
keeping it in a ventilated oven at a temperature of 150 degree till the color of gel changes to
blue. When the gel is cooled down, fill it in the breather and Replace the grill as before.

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2.5 CIRCUIT BREAKER
2.5.1 SF6 Circuit Breaker: SF6 is inert gas the property of this gas the higher pressure and
temperature is dielectric strength will be SF6 has two gas chamber when contact is close the
pressure is two chamber have the same pressure but when the contact is pen then one of the
chamber get totally close and other remain open, there is a narrow channel between two
chamber and when contact open the SF6 flow a plane of high pressure region to the low
pressure region there will be turbulence of SF6. At zero current the turbulence of SF6 absorb all
the ions and since it is flowing from a narrow region hence it provide high dielectric strength
but there is a problem that the pressure of SF6 is not always remain fixed due to leakage in the
cylinder of SF6 so there is pressure gauge as well as alarm attached with it. When ever pressure
decreases the alarm ringing and the gas is refilled to increase pressure.
2.5.2 Oil Circuit Breaker: Oil circuit breaker is a such type of the circuit breaker where oil is
used as arc quenching media as well as insulating media between current carrying contacts and
earthed parts of the breaker. The oil used here is same as transformer insulating oil as
mentioned before.

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Power Grid Corporation of India Limited

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