4 Shops are:- MRS, TAS, LTS & COLONY

1. Acknowledgement
I would sincerely like to thank the employees and the officers of DLW,
VARANASI for their help and supportduring the vocational training. Despite their
busy schedules, they took time out and explained to us the various aspects of the
working of the plant and technological knowhow.
I would sincerely like to thank Shri Amit Kumar (ACWI/Elect.), Miss. Ratna Singh
(SSE/Telephone Exchange) and other JEs who were instrumental in arranging the
vocational training at DLW Varanasi, and without whose help and guidance the
training could not have materialized.
I express my deep sense of gratitude to the Principal, TTC for given me such a great
opportunity

2. Preface
The objectives of the practical training are to learn something about industries practically
and to be familiar with the working style of a technical person to adjust simply according
to the industrial environment.
It is rightly said practical life is far away from theoretical one. We learn in class room can
give the practical exposure or real life experience no doubt they help in improving the
personality of the student in long run of life and will be able to implement the theoretical
knowledge. As a part of academic syllabus of four year degree course in Electrical
Engineering, every student is required to undergo a practical training.
I am student ofthe Final Year ElectricalEngineering & this report is written on the basis
of practical knowledge of acquired by me during the period of practical training taken at
Diesel Locomotive Works, Varanasi.
This report is presented in very simple & understanding language on the basis of Primary
and Secondary data.
Gaurav Singh
EE(4th Year)

3. ABSTRACT
The industrial training report of DLW (DIESEL LOCOMOTIVE WORKS) is
various trade. i.e. Electronics and communication, Electrical, Mechanical,
Electrical & Electronics and many engineering holders are participated. The
content of my industrial topic Main Receiving Substation, TRACATION
ASSEMBLY SHOP, Maintenance area 2 and Loco Testing Shop, we are discus
about how to remove defect from the circuit board and any part of system. The
second is TAS (Traction Assembly Shop), I learn about assemble of loco engine.
After completed the Traction Assembly Shop going to discuss about Electrical
lab. Than the last of my section is Maintenance area 2, in this shop I learn to
explain the manufacturing of component .this report is written on the basis of
practical knowledge of acquired by me during the period of practical training
taken at, Diesel Locomotive Works Varanasi. This report is presented in very
simple & understanding language and it is compriseoffour sections namely Main
Receiving Substation, Traction assembly Shop, Colony and Loco Testing Shop.

4. CONTENTS
1.CHAPTER-1(INTRODUCTION)............................................................1
1.1Brief History...................................................................................................................2
1.1 Salient Features……….................................................................................................3
1.2 Product of DLW…........................................................................................................3
1.3 Design Office…….......................................................................................................4
2. CHAPTER-2(MAIN RECEIVING SUBSTATION).............................5
2.1Description of layout of the plant...................................................................................6
3. CHAPTER-3(TRACTIONASSEMBLYSHOP)……...........................8
3.1 Control Panel………….................................................................................................8
3.2 Dynamic Braking………….........................................................................................10
3.3 Alternator…………….................................................................................................11
3.4 Traction Motor…….....................................................................................................12
3.5 16 Cylinder Desiel Engine...........................................................................................13
3.6 Cab…………………...................................................................................................14
3.7 Governer……………..................................................................................................15
3.8 Mechanical Assembly..................................................................................................16
4. CHAPTER-4(LOCO TESTSHOP)……..............................................17
5. CHAPTER-5(COLONY)………………………....................................19
5.1 Substation Model........................................................................................................20
5.2 Step-Up &Stepdown:..................................................................................................22
5.3 Busbars……................................................................................................................23
5.3 Circuit Breaker............................................................................................................26
5.3.1 Low-voltage Circuit Breaker....................................................................................26
5.3.2 Magnetic Circuit Breaker ........................................................................................26
5.3.3 Thermal magnetic Circuit Breaker ..........................................................................27

5. 5.3.4 Common trip breakers.............................................................................................27
5.3.5 Air Circuit Breaker..................................................................................................28
5.3.6 Vaccum Circuit Breaker..........................................................................................28
5.3.7 Oil Circuit Breaker..................................................................................................29
5.3.8 Sulphur hexafloride Circuit Breaker........................................................................29
5.4 Isolators…………......................................................................................................30
5.5 Insulators....................................................................................................................31
5.5.1 Pin type Insulators...................................................................................................31
5.5.2 Suspension Insulators..............................................................................................31
5.5.3 Strain Insulators........................................................................................................32
5.5.4 Shackle Insulators.....................................................................................................32
5.5.5 Relays………….......................................................................................................33
5.5.6 Differential Relays...................................................................................................33
5.5.7 Over Current Relays................................................................................................34
5.5.8 Earth Fault Relays...................................................................................................34
5.5.9 Tripping Relays.......................................................................................................35
5.5.10 Auxiliary Relays.................................................................................................35
5.5.11 Capacitor Relays...................................................................................................35
11.CONCLUSION......................................................................................37

6. 1. Main Receiving Substation (MRS)
MRS receives main supply from UPPCL at 33kv.
This is step down with 7.5MVA transformer. The 33kv feeder is transformed
into two 11kv feeder with a bus coupler in between.
There are two types of distribution techniques:
1. Ring System- Under this system, each substation is connected to the
distribution system with two different transmission lines coming from the
MRS. Hence the substations receive power from any one of the lines.
Generator
SUB 1 SUB 5
SUB 2 SUB 4
SUB 3
v Radial System-A single main line runs down the MRS and
various substations are connected to it forming branches.

7. Generator SUB 1 SUB 2 SUB 3

8. The MRS follows the ring type distribution system for supplying power to
DLW. The advantage of ring type system is that each substation is fed from two
sides. If in case one line is faulted then the substation is fed by other line. But
major disadvantage of ring type system is that it is too costly.
Safety Precautions at MRS: The most important responsibility while handling
such high power is safety of the employees and equipments. The following
measures are undertaken at MRS for protection-
1. Protection Relays:
i. Over Current Relay- It is set at the current limit of the device with
lowest current rating.
ii. Differential Relay- It prevents imbalance in current in different
phases.
iii. Negative Phase Sequence Relay- It detects if the R-Y-B
sequence is put wrongly.
iv. Under/Over Voltage Relay
v. Reverse Power Relay- Prevents clashing of power from different
sources.
2. Air Circuit Breaker (ACB) - Air Circuit Breaker is a device used to
provide over current and Short Circuit Protection for circuits ranging
from 800 Amps to 10000 Amps. One should not be confused between
Air Circuit Breaker and Air Blast Circuit Breaker. Air Circuit Breakers
are usually used in low voltage applications below 450 volts.

9. ACBs are being replacedby SF6 Circuit Breakers in a phasedmanner.
Fig 1.2 SF6Circuit Breaker (ACB)
The gaseous medium SF6 possesses excellent dielectric and arc quenching
properties. After arc extinction, the dissociated gas molecules recombine
almost completely to reform SF6. This means that practically no
loss/consumptionof the quenching medium occurs. The gas pressure can be
very simply and permanently supervised. This function is not needed where
the interrupters are sealed for life.

10. 2. TRACTION ASSEMBLY SHOP
Traction assembly shop is the unit in which all the locomotive parts are
assembled that includes:
1. CP (Control Panel)
2. Alternator
3. Traction Motors
4. 16 cylinder Diesel Engine
5. Master Control
6. Cab
7. Auxiliary Generator & Excited
8. Governor
9. Crank Case Exhauster
10. Mechanical Assembly
2.1 Control Panel
The CP or the Control Panel (wrt WG3A loco) consists of:
a) Control Switch
b) Display Unit
c) LED Panel
d) Microprocessor based Control Unit
e) Reverser

11. f) BKT
g) Valves
h) Hooter
i) CK1/CK2/CK3
The top portion of CP has sensors and relays connected to the microprocessorunit.
The display unit of microprocessor shows working condition of items in engine
(electrical equipment’s apart from engine).
The LED Panel displays the overload, auxiliary generator failure, hot engine,
rectilinear fuse blown, etc. The battery ammeter shows the charging state of the
batteries.
REV: Field wiring goes to reverser (REV) and hence it is used to control the
polarity of the field which in turn controls the direction of train.
BKT: It is a switch which in one direction is used to motor the loco while in other
it is used for dynamic braking.
Microprocessor based Control Unit: On-board microprocessors control engine
speed, fuel injection, and excitation of the alternator. These computers also inter-
connect with improved systems to detect slipping or sliding of the driving wheels,
producing faster correction and improved adhesion. An additional function of the
microprocessor is to monitor performance of all locomotive systems, thereby
increasing their reliability and making the correction of problems easier. Hooter:
It is a vigilance control de-vice (VCD) to keep the driver alert. If the driver isn’t
doing anything with the controls for over a minute, the hooter ‘hoots’ and brings
the engine speed to the normal speed (low) without asking the driver. It can only
be reset after 2 minutes and hence the driver will be held responsible for delay in
reaching the next station.

12. Fig.2.1 Control Panel of WG3A loco
2.2 Dynamic braking
It is the use of the electric traction motors of a railroad vehicle as generators when
slowing the vehicle. It is termed rheostatic if the generated electrical power is
dissipated as heat in brake grid resistors, and regenerative if the power is returned
to the supply line.
Dynamic braking lowers the wear of friction-based braking components, and
additionally regeneration can also lower energy consumption.
During braking, the motor fields are connected across either the main traction
generator (diesel-electric loco) or the supply (electric locomotive) and the motor
armatures are connected across either the brake grids or supply line. The rolling
locomotive wheels turn the motor armatures, and if the motor fields are now
excited, the motors will act as generators.
For a given direction of travel, current flow through the motor armatures during
braking will beoppositeto that during motoring. Therefore, the motorexerts torque
in a direction that is opposite from the rolling direction. Braking effort is
proportional to the product of the magnetic strength of the field windings, times
that of the armature windings. In DLW Locomotives the braking method used is
rheostatic, i.e. the traction motors behave as generators (separately excited) and
their electrical power is dissipated in brake grid resistors. This method is used for
minimizing speed of the loco. The loco actually comes to a halt due to factors like
air resistance, friction with the rail, etc.

13. 2.3 Alternator
An alternator converts kinetic energy (energy of motion) into electrical energy.
All recently manufactured automobiles rely on alternators to charge the battery in
the ignition system and supply powerto other electrical equipment. Alternators are
sometimes called AC generators because they generate alternating current (AC).
Electric current can be generated in two ways: The magnet may rotate inside the
coil, orthe coil may rotate in a magnetic field created bya magnet. The component
that remains stationary is called the stator, and the component that moves is called
the rotor. In alternators, the coil is the stator and the magnet is the rotor. A source
of mechanical power, i.e. the diesel engine turns the rotor.
In WDM-3D and WDM-3A locos, the diesel engine’s mechanical output is used
to run the shaft of the Alternator. The alternating output of the Alternator is then
rectified to DC via solid-state rectifiers and is fed to traction motors (DC) that run
the loco wheels. Thus they operate on AC-DC Traction mechanism. WDG4 and
WDP4 locos have AC-AC traction with microprocessor control, i.e. AC Traction
motors are used thus eliminating the motor commutator and brushes The result is
a more efficient and reliable drive that re-quires relatively little maintenance and
is better able to cope with overload conditions.
Why not feed direct DC to the traction motors via DC generators?
In a DC generator, the rotor is the coil. Alternators normally rotate the
magnet, which is lighter than the coil. Since alternators are built to spin the lighter
componentinstead of the heavier one, they generally weigh only one-third as much
as generators of the same capacity. DC generators, in particular, require more
maintenance because of wear on the parts that brush against one another in the
commutator switch and the stress of rotating the heaviest componentinstead ofthe
lightest. Also, when generators are run at higher speeds, electricity tends to arc, or
jump the gap separating metal parts. The arcing dam-ages parts and could make
generators hazardous to touch. Alternators can run at high speeds without arcing
problems.

14. Fig.2.3 Alternator
2.4 Traction Motor
It’s an electric motor providing the primary rotational torque of the engine, usually
for conversion into linear motion (traction).
Traction motors are used in electrically powered rail vehicles such as electric
multiple units and electric locomotives, other electric vehicles suchas electric milk
floats, elevators and conveyors as well as vehicles with electrical transmission
systems suchas diesel-electric and electric hybrid vehicles. Traditionally, these are
DC series-wound motors, usually running on approximately 600 volts.

15. 2.5 16 Cylinder Diesel Engine
It is an internal-combustion engine in which heat caused byair compressionignites
the fuel. At the instant fuel is injected into a diesel engine’s combustionchambers,
the air in-side is hot enough to ignite the fuel on contact. Diesel engines, therefore,
do not need spark plugs, which are required to ignite the air-fuel mixture in
gasoline engines. The Diesel engine has 16 cylinders. Pistons inside the cylinders
are connected by rods to a crankshaft. As the pistons move up and down in their
cylinders, they cause the crankshaft to rotate. The crankshaft’s rotational force is
carried by a transmission to a drive shaft, which turns axles, causing mechanical
output. Eight 8V and four 2V Batteries are used in series to run a more powerful
starter motor, which turns the crankshaft to initiate ignition in a diesel engine for
the first time.
Fig.2.5 diesel engine of ALCO loco

16. 2.6 Master Control
It’s the unit that has the handles to regulate the speed of the loco as well as the
direction of motion. It has numbering from 0-9 and each increment causes rise in
speed in forward direction. It can also be used to reverse the direction of motion
by pushing the handle in the oppositesense. It is present on the control deskof the
cab.
2.7 Cab
It’s the driver’s cabin with 2 control desks, the Control Panel (CP) and chairs for
the driver. The Cab is at one end of the locomotive with limited visibility if the
locomotive is not operated cab forward. Each control desk has the Independent
SA9 brake for braking of the engine alone and Auto Brake A9 for the braking of
the entire loco. It also has the following components:
 LED Panel
 Buttons of various engine LED lights (front and side)
 Automatic sand throw button (to prevent sliding ofwheels
on inclined tracks)
 Master Control
 Gauges to monitor booster air pressure and fuel & lube oil
pressures.
 Speedometer
 Service Brakes (Independent and Auto brakes described above)
 Emergency Brake (Type of Air brake to halt the train in the
distance
 nearly equal to the length of the train, to be used only during an
emergency)

17. 2.8 Auxiliary Generator and Exciter
The Alternator has these two components. The exciter and the auxiliary generator
consist of two armatures on a single shaft. The auxiliary generator supplies a
constant voltage of around 72V for supplying power to charge the battery for the
control equipment and to power the locomotive lights. The Exciter supplies
excitation for the main generator. Starting of Engine the supply from the batteries
is given to the exciter. The exciter has armature and field windings. Hence it starts
rotating as it receives the supply voltage. The Ex-citer is coupled with the rotor of
the alternator which in turn is connected with the propeller shaft. When the
propeller rotates at a particular rpm, the
engine gets started. It’s just like starting a bike. The ‘kick’ must be powerful
enough to start its engine. Later the engine runs on diesel oil (fuel). As soonas the
engine starts, the auxiliary generator also coupled with the alternator starts
charging the batteries. Its potential is maintained at ~72V.
Fig .2.7 Auxiliary generator
2.9 Governor
It is the device that has the following functions:
1.To control engine speed
2.Deliver fuel (Diesel oil) according to load
3.To mediate electrical demand and diesel engine output.
2.10 Crank case exhauster
It is the device used to evacuate the diesel engine chamber.

18. Fig.2.9 Crank case exhauster
2.11 Mechanical Assembly
All mechanical parts on the engine apart from the above mentioned units may be
grouped in this category. It essentially consists of:
v Base frame
v Wheels
v Air Brakes
v Batteries
v Sand Box
v Vacuum brakes
v Fuel tank (Loco fuel oil tank capacity is 3000L) etc
Air Braking System of Locomotives: On a train, the brake shoes are pressed
directly against the wheel rim. A compressor generates air pressure that is stored
in air tanks.
Air hoses connectthe brakes on all the train cars into one system. Applying air
pressure into the system releases the brakes, and releasing air pressure from the
system applies the break.

19. 3. LOCO TESTING SHOP
When all the perform are done then finally engine come in ETS, for the first
inspection report and after this it will be agreed for the performance
Testing of the final locomotive on the basis of several performance
1. Initial filling of lube oil (approx. 4200 ltr)
2. Filling of all fuel (approx. 3000 ltr)
3. Load testing
4. Testing of MR1 and MR2
5. Air brake testing
6. Water circuit check
7. Testing of dynamic brake
8. Lightning inspection
9. Testing of the speed

21. 4 . COLONY
4.1 Introduction
Electricity transmission is the process of
transfer-ring electrical energy to consumers.
Electrical energy generated at power
facilities is transmitted at high voltages
through overhead power lines and cables.
Those transmission lines connect to
substations which transform the power to
lower voltages for distribution to consumers
through the distribution system.
Fig 4.1 From the Power Station to the Home
Inside a generating station, turbines use the driving force of water to set electrons
in motion and generate alternating current.
Fig 4.1 Electricity transmission from the power station to customer
Electricity from the power stationhas a long way to go before reaching your
home.
1. The voltage of the current produced bya generating station can reach
13,800 volts, like at the Robert-Bourassagenerating facility.

22. 2. Thanks to the voltage step-up transformer located in the generating station’s
switchyard, the electricity is transmitted at much higher voltages, from
44,000 to 765,000 volts.
3. Once in the transmission system, electricity from each generating station is
combined with electricity produced elsewhere.
4. The electricity passes through cables which are suspended from towers.
These towers are arranged in a series from the generating stations to source
substations–which lower the voltage–and then reach the satellite substations,
which further reduce the voltage.
5. Leaving the satellite substations, electricity travels through underground
lines. At some distance from the substations, the distribution system goes
from underground to over-head, and transformers attached to poles lower
the voltage one last time. Inside our homes, we use either 120 volts to power
our televisions, radios and other regular electrical appliances, or 240 volts
for the appliances that require a strong current like the dryer or stove.
6. Electricity is consumed as soonas it is produced. Itis transmitted at a very
high speed, close to the speed of light (300,000 km/s).
4.2 Electricalsubstationmodel (side-view)
Fig: 4.2 1.Primary power lines 2.Ground wire 3.Overhead lines 4.Lightning arrester
5.Disconnect switch 6.Circuit breaker 7.Current transformer 8.Transformer for meas-
urement of electric voltage 9.Main transformer 10.Control building 11.Security fence
12.Secondary power lines

23. 4.3 Elements of a substation
Substations generally have switching, protection and control equipment, and
transformers. In a large substation, circuit breakers are used to interrupt any short
circuits or overload cur-rents that may occur on the network. Smaller distribution
stations may use recloser circuit breakers or fuses for protection of distribution
circuits. Substations themselves do not usually have generators, although a power
plant may have a substation nearby. Other devices such as capacitors and voltage
regulators may also be located at a substation.
Substations may be on the surface in fenced enclosures, underground, or located
in special-purpose buildings. High-rise buildings may have several indoor
substations. Indoorsubstations are usually found in urban areas to reduce the noise
from the transformers, for reasons of appearance, or to protect switchgear from
extreme climate or pollution conditions.
Where a substation has a metallic fence, it must be properly grounded to protect
people from high voltages that may occurduring a fault in the network. Earth faults
at a substation can cause a ground potential rise. Currents flowing in the Earth's
surface during a fault can cause metal objects to have a significantly different
voltage than the ground under a person's feet;this touch potential presents a hazard
of electrocution
4.4 Step-up and Step-down Transformers
This is a very useful device, indeed. With it, we can easily multiply or divide
voltage and cur-rent in AC circuits. Indeed, the transformer has made long-distance
transmission of electric power a practical reality, as AC voltage can be “stepped
up” and current “stepped down” for reduced wire resistance power losses along
power lines connecting generating stations with loads. At either end (both the
generator and at the loads), voltage levels are reduced by trans-formers for safer
operation and less expensive equipment. A transformer that increases voltage from
primary to secondary (more secondary winding turns than primary winding turns)

24. is called a step-up transformer. Conversely, a transformer designed to do just the
opposite is called a step-down transformer.
Step-up and step-down transformers for power distribution purposes can be
gigantic in proportion to the power transformers previously shown, some units
standing as tall as a home. The following photograph shows a substation
transformer standing about twelve feet tall.
Fig 4.3 (a)Substation transformer. Fig 4.3 (b) Block diagram
REVIEW:
 Transformers “step up” or “step down” voltage according to the ratios of
primary to secondarywire turns.

25.  A transformer designed to increase voltage from primary to secondaryis called
a step-up transformer. A transformer designed to reduce voltage from primary
to secondary is called a step-down transformer.
 The transformation ratio of a transformer will be equal to the square root of its
primary to secondaryinductance (L) ratio.
By being able to transfer power from one circuit to another without the use of
interconnecting conductors between the two circuits, transformers provide the
useful feature of electrical isolation.
Transformers designed to provide electrical isolation without stepping voltage and
current either up or down are called isolation transformer.
4.5 BUSBARS
It an electrical conductor, maintained at a specific voltage and capable of carrying
a high current, usually used to make a common connection between several
circuits in a system
When numbers of generators or feeders operating at the same voltage have to be
directly connected electrically, bus bar is used as the commonelectrical component.
Bus bars are made up of copperrods operate at constant voltage. The following are
the important bus bars arrangements used at substations:
 Single bus bar system
 Single bus bar system with section alisation.
 Duplicate bus bar system
In large stations it is important that break downs and maintenance should
interfere as little as possible with continuity of supply to achieve this, duplicate
bus bar system is used. Such a system consists of two bus bars, a main bus bar
and a spare bus bar with the help of bus coupler, which consist of the circuit
breaker and isolator.

26. In substations, it is often desired to disconnect a part of the system for general
maintenance and repairs. An isolating switch or isolator accomplishes this. Isolator
operates under no load condition. It does not have any specified current breaking
capacity or current making capacity. In some cases isolators are used to breaking
charging currents or transmission lines.
While opening a circuit, the circuit breaker is opened first then isolator while
closing a circuit the isolator is closed first, then circuit breakers. Isolators are
necessaryon supplyside ofcircuit breakers, in order to ensure isolation ofthe circuit
breaker from live parts for the purpose of maintenance.
A transfer isolator is used to transfer main supply from main bus to transfer bus by
using bus coupler (combination of a circuit breaker with two isolators), if repairing
or maintenance of any section is required.

27. 4.6 CIRCUIT BREAKERS
A circuit breaker is an automatically operated electrical switch designed to protect
an electrical circuit from damage caused by overload or short circuit. Its basic
function is to detect a fault condition and interrupt current flow. Unlike a fuse,
which operates once and then must be re-placed, a circuit breaker can be reset
(either manually or automatically) to resume normal operation. Circuit breakers
are made in varying sizes, from small devices that protectan individual household
appliance up to large switchgear designed to protect high voltage circuits feeding
an entire city. There are different types of circuit breakers which are:-
4.6.1 Low-voltage circuit breakers
Low-voltage (less than 1,000 VAC) types are commonin domestic, commercial and
industrial application, and include Miniature Circuit Breaker (MCB) and Molded
Case Circuit Breaker (MCCB).
Fig 4.4 Circuit breaker
4.6.2 Magnetic circuit breakers
Magnetic circuit breakers use a solenoid (electromagnet) whose pulling force
increases with the current. Certain designs utilize electromagnetic forces in
addition to those of the solenoid

28. Fig 4.5 Magnetic circuit breaker
4.6.3 Thermalmagnetic circuit breakers
Thermal magnetic circuit breakers, which are the type found in most distribution
boards, incorporate both techniques with the electromagnet responding
instantaneously to large surges in current (short circuits) and the bimetallic strip
responding to less extreme but longer-term over-current conditions. The thermal
portion of the circuit breaker provides an "inverse time" responsefeature, which trips
the circuit breaker sooner for larger over currents.
Fig 4.6 Thermal magnetic circuit breakers
4.6.4 Common trip breakers
Three-pole common trip breaker for supplying a three-phase device. This breaker has
a 2A rating. When supplying a branch circuit with more than one live conductor, each
live conductormust be protected by a breaker pole. To ensure that all live conductors
are interrupted when any poletrips, a "commontrip" breaker must beused. Thesemay
either contain two orthree tripping mechanisms within one case, or forsmall breakers,
may externally tie the poles together via their operating handles.

29. Fig 4.7Three-pole common trip breaker
4.6.5 Air circuit breakers
Rated current up to 6,300 A and higher for generator circuit breakers. Trip
characteristics are often fully adjustable including configurable trip thresholds and
delays. Usually electronically controlled, though some models are microprocessor
controlled via an integral electronic trip unit, often used for main power distribution
in large industrial plant, where the breakers are arranged in draw-out enclosures for
ease of maintenance.
Fig 4.8 Air circuit breakers
6. Vacuum circuit breakers
With rated current up to 6,300 A, and higher for generator circuit breakers. These
breakers interrupt the current by creating and extinguishing the arc in a vacuum
container.
Fig 4.9 Vacuum circuit breakers

30. 7. Oil circuit breakers
A high-voltage circuit breaker in which the arc is drawn in oil to dissipate the heat
and extinguish the arc; the intense heat of the arc decomposes the oil, generating a
gas whose high pressure produces a flow of fresh fluid through the arc that furnishes
the necessary insulation to prevent a restrike of the arc.
The arc is then extinguished, both because of its elongation upon parting of contacts
and be-cause of intensive cooling by the gases and oil vapor. They are further of
two types: Bulk Oil Circuit Breaker (BOCB) and Minimum Oil Circuit Breaker
(MOCB).
Fig 4.10 Oil circuit breakers
8. Sulfur hexafluoride (Sf6) high-voltage circuit breakers
A sulfur hexafluoride circuit breaker uses contacts surrounded by sulfur hexafluoride
gas to quench the arc. They are most often used for transmission-level voltages and
may be incorporated into compact gas-insulated switchgear.
Fig 4.11 Sulfur hexafluoride (Sf6) high-voltage circuit breakers

31. 4.7 ISOLATERS
In electrical engineering, a disconnector, disconnect switch or isolator switch is used
to ensure that an electrical circuit is completely de-energized for service or
maintenance. Such switches are often found in electrical distribution and industrial
applications, where machinery must have its source of driving power removed for
adjustment or repair. High-voltage isolation switches are used in electrical substations
to allow isolation of apparatus suchas circuit breakers, transformers, and transmission
lines, for maintenance. The disconnector is usually not in-tended for normal control
of the circuit, but only for safety isolation. Disconnector can be operated either
manually or automatically (motorized disconnector).
Unlike load break switches and circuit breakers, disconnectors lack a mechanism for
suppressionof electric arc, which occurs when conductors carrying high currents are
electrically interrupted. Thus, they are off-load devices, intended to be opened only
after current has been interrupted by some other control device. Safety regulations of
the utility must prevent any attempt to openthe disconnectorwhile it supplies a circuit.
Standards in some countries for safety may require either local motor isolators or
lockable overloads (which can be padlocked).
Disconnectors have provisions for a padlock so that inadvertent operation is not
possible (lock-out-tag out). In high-voltage or complex systems, these padlocks may
be part of a trapped-key interlock system to ensure proper sequence of operation. In
some designs, the isolator switch has the additional ability to earth the isolated circuit
thereby providing additional safety. Such an arrangement would apply to circuits
which inter-connect power distribution systems where both ends of the circuit need to
be isolated.
Fig 4.12 Isolater circuit

32. 4.8 INSULATORS
An electrical insulator is a material whose internal electric charges do not flow
freely, and therefore make it very hard to conductan electric current under the
influence of an electric field. The insulator serves two purposes. Theysupportthe
conductors (bus bar) and confine the current to the conductors. Themost
common used material for the manufacture of insulator is porcelain. There are
several types of insulators (e.g. pin type, suspension type, postinsulator etc.) and
their use in substation will depend upon the service requirement. Different types
of insulator are:-
4.8.1 Pin type insulator
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 electric power at voltages up to 33 kV. Beyond operating voltage of
33 kV, the pin type insulators become too bulky and hence uneconomical.
Fig 4.13Pin type insulator
4.8.2 Suspensioninsulator
For voltages greater than 33 kV, it is a usual practice to use suspension type
insulators shown in Figure. Consist of a number of porcelain 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 other end of the string is secured to the cross-
arm of the tower. The number of disc units used depends on the voltage.

33. Fig 4.14Suspension insulator
4.8.3 Strain insulator
A dead end or anchor pole or tower is used where a straight section of line ends, or
angles off in another direction. These poles must withstand the lateral (horizontal)
tension of the long straight section of wire. In order to support this lateral load,
strain insulators are used. For low voltage lines (less than 11 kV), shackle
insulators are used as strain insulators. However, for high voltage transmission
lines, strings of cap-and-pin (disc) insulators are used, attached to the cross-armin
a horizontal direction. When the tension load in lines is exceedingly high, such as
at long river spans, two or more strings are used in parallel.
Fig 4.15Strain insulator
4.8.4 Shackle insulator
In early days, the shackle insulators were used as strain insulators. But now a day,
they are frequently used for low voltage distribution lines. Such insulators can be
used either in a horizontal position or in a vertical position. They can be directly
fixed to the pole with a bolt or to the cross arm.
Fig 4.16Shackle insulator

34. 4.9 RELAYS
In a power system it is inevitable that immediately or later somefailure does occur
somewhere in the system. When a failure occurs onany part of the system, it must
be quickly detected and disconnected from the system. Rapid disconnection of
faulted apparatus limits the amount of damage to it and prevents the effects of fault
from spreading into the system. For high voltage circuits relays are employed to
serve the desired function of automatic protective gear. The re-lays detect the fault
and supply the information to the circuit breaker. The electrical quantities which
may change under fault condition are voltage, frequency, current, phase angle.
When a shortcircuit occurs atany point onthe transmission line the current flowing
in the line increases to the enormous value. This result in a heavy current flow
through the relay coil, causing the relay to operate by closing its contacts. This in
turn closes the trip circuit of the breaker making the circuit breaker open and
isolating the faulty section from the rest ofthe system. In this way, the relay ensures
the safety of the circuit equipment from the damage and normal working of the
healthy portion of the system.
Relay works on two main operating principles:-
 Electromagnetic Attraction
 Electromagnetic Induction
4.10 RELAY USED IN CONTROLLING PANELOF SUBSTATION
4.10.1 DifferentialRelay
A differential relay is one that operates when vector difference of the two or more
electrical quantities exceeds a predetermined value. If this differential quantity is
equal or greater than the pickup value, the relay will operate and open the circuit
breaker to isolate the faulty section.

35. Fig 4.17Differential Relay
4.10.2Over Current Relay
This type of relay works when current in the circuit exceeds the predetermined
value. The actuating sourceis the current in the circuit supplied to the relay from
a current transformer.
These relay are used on A.C. circuit only and can operate for fault flow in the
either direction.
This relay operates when phase to phase fault occurs.
Fig 4.17Over Current Relay
4.10.3 EarthFault Relay
This type of relay sense the fault between the lines and the earth. It checks the
vector sum of all the line currents. If it is not equal to zero, it trips.
Fig 4.18Earth fault relay

36. 4.10.4Tripping Relay
This type of relay is in the conjunction with main relay. When main relay sense
any fault in the system, it immediately operates the trip relay to disconnectthe
faulty section from the section.
Fig 4.19Tripping Relay
4.10.5Auxiliary Relay
An auxiliary relay is used to indicate the fault by glowing bulb or showing various
flags.
Fig 4.20Auxiliary relay
4.11 Capacitorbank
The load on the power system is varying being high during morning and evening
which in-creases the magnetization current. This result in the decreased power
factor. The low power factor is mainly due to the fact most of the power loads are
inductive and therefore take lagging currents. The low power factor is highly
undesirable as it causes increases in current, resulting in additional losses. So in
order to ensure most favorable conditions for a supply system from engineering

37. and economic stand point it is important to have power factor as close to unity as
possible. In order to improve the power factor come device taking leading power
should be connected in parallel with the load. One of such device can be capacitor
bank. The capacitors draw a leading current and partly or completely neutralize the
lagging reactive component of load current.
Main functions of Capacitor Bank are:-
 Supply Reactive Power
 Improve Terminal Voltage
 Improve Power Factor
Fig 4.21 Capacitor bank

38. Conclusion
The Fourweeks Training program lasted from 01-June-2017 to 28-June-2017 with
one week each spent at Main Receiving Substation, Traction assembly Shop,
Colony and Loco Testing Shop
A certificate of completion of training was provided (No.
Voc./TTC/DLW/17/3285).
The training program was very fruitful and I gotto learn about various new devices
and process undertaken at an industry. My interactions with the industry
professionals gave me an idea of practical life of an engineer