RAILWAY CONTROLS AUTOMATION USING PLC

A PROJECT REPORT

Submitted by

S.HARIHARA SUDHAN (99409105312)

L.SIVARAMAN (99409105320)

M.UMASANKAR (99409105321)

in partial fulfillment for the award of the degree

of

BACHELOR OF ENGINEERING

IN

ELECTRICAL AND ELECTRONICS ENGINEERING

J.P COLLEGE OF ENGINEERING, AYIKUDY

ANNA UNIVERSITY : CHENNAI 600025

APRIL 2013

ANNAUNIVERSITY : CHENNAI 600 025

BONAFIDE CERTIFICATE

Certified that this project report “RAILWAY CONTROLS AUTOMATION

USING PLC” is the bonafide work of the S.HARIHARA SUDHAN,

L.SIVARAMAN, M.UMASANKAR. who carried out the project work under

my supervision.

SIGNATURE SIGNATURE

Prof.K.PAUL JOSHUA MR.S.KUMARAN,

B.E.,M.E.,Ph.D., B.E.,M.TECH.,M.I.S.T.E.

HEAD OF THE DEPARTMENT SUPERVISOR

Assistant Professor

Department of Electrical and Department of Electrical and

Electronics Engineering Electronics Engineering

J.P.College of Engineering J.P.College of Engineering

Ayikudy – 627852 Ayikudy – 627852

INTERNAL EXAMINER EXTERNAL EXAMINER

ABSTRACT:

Railways, being the cheapest mode of transportation are preferred over all

the other means. Many railway accidents occurring at unmanned railway

crossings, signal faults etc. This is mainly due to the carelessness in manual

operations or lack of workers. The main aim of this project is to find out the

solutions for the above problems using modern technology. Using simple

electronic components we have tried to automate the four controls, such as

Railway gates control, Signal control, Track change control, Train power supply

control. This control system contains IR sensors, relays and a PLC. The

controlling device of the whole unit is PLC (programmable logic controller).

The signals from the sensors are fed to the PLC through the relays. The control

of all the actions based on the signals received from the sensors. The PLC

contains a ladder diagram through the output units are controlled. The IR

sensors from various locations are given to the PLC through relays, depends

upon this signal the ladder diagram will operate the output unit.

When the train is sensed by the railway gate sensor, it will send the information

to the PLC and now the PLC will close the railway gate, and when the train

leaves from the sensor at the other side the gate will be opened by the PLC

control circuit. At the railway station the signal control and track change control

is also an important control operations. This also controlled by the respective

signals received from the sensors. In addition to avoid the electric accidents and

to save the wasted power at the railway lines, the power will be switched off

until the train comes. This is also done by the IR sensors placed at various

locations in the track.

INTRODUCTION:

This project work aims at the design, development, fabrication and testing

of working model entitled Automatic Railway Gate Controller. It is basically

related to Radio communication and signaling system. An Automatic Railway

gate controller is unique in which the railway gate is closed and opened or

operated by the Train itself by eliminating the chances of human errors.

The largest public sector in India is the Railways. The network of

Indian Railways covering the length and breath of Indian Railways covering the

length and breath of our country is divided into nine Railway zones for

operational convenience.

The railway tracks criss-cross the state Highways and of course

village road along their own length. The points or places where the Railway

track crosses the road are called level crossings. Level crossings cannot be used

simultaneously both by road traffic and trains, as this result in accidents leading

to loss of precious lives.

NEED FOR PROJECT:

Many railway accidents occurring at unmanned railway crossings, signal

faults etc. This is mainly due to the carelessness in manual operations or lack of

workers. The main aim of this project is to find out the solutions for the above

problems using modern technology. Using simple electronic components we

have tried to automate the four controls, such as Railway gates control, Signal

control, Track change control, Train power supply control.

This control system contains IR sensors, relays and a PLC. The

controlling device of the whole unit is PLC (programmable logic controller).

The signals from the sensors are fed to the PLC through the relays. The control

of all the actions based on the signals received from the sensors.

The PLC contains a ladder diagram through the output units are

controlled. The IR sensors from various locations are given to the PLC through

relays, depends upon this signal the ladder diagram will operate the output unit.

When the train is sensed by the railway gate sensor, it will send the

information to the PLC and now the PLC will close the railway gate, and when

the train leaves from the sensor at the other side the gate will be opened by the

PLC control circuit.

At the railway station the signal control and track change control is also

an important control operations. This also controlled by the respective signals

received from the sensors. In addition to avoid the electric accidents and to save

the wasted power at the railway lines, the power will be switched off until the

train comes. This is also done by the IR sensors placed at various locations in

the track.

LITERATURE REVIEW

EXISTING SYSTEM:

Gate will be controlled by Manual.

Track will be controlled and changed by Mechanical.

PROPOSED SYSTEM

Railway gates control

Signal control

Track change control

Train power supply control

The above process is fully controlled by automatic manner using PLC.

PROGRAMMABLE LOGIC CONTROLLER:

A Programmable Logic Controller, PLC or Programmable Controller is

a digital computer used for automation of electromechanical processes, such as

control of machinery on factory assembly lines, amusement rides, or light

fixtures. The abbreviation "PLC" and the term "Programmable Logic

Controller" are registered trademarks of the Allen-Bradley Company (Rockwell

Automation).

PLCs are used in many industries and machines. Unlike general-purpose

computers, the PLC is designed for multiple inputs and output arrangements,

extended temperature ranges, immunity to electrical noise, and resistance to

vibration and impact.

Programs to control machine operation are typically stored in battery-

backed-up or non-volatile memory. A PLC is an example of a hard real

time system since output results must be produced in response to input

conditions within a limited time, otherwise unintended operation will result.

A Programmable controller is a solid state user programmable control

system with functions to control logic, sequencing, timing, arithmetic data

manipulation and counting capabilities. It can be viewed as an industrial

computer that has a central processor unit, memory, input output interface and a

programming device.

The central processing unit provides the intelligence of the controller. It

accepts data, status information from various sensing device like limit switches,

proximity switches, executes the user control program store in the memory and

gives appropriate output command to device like solenoid valves, switches etc.

Input output interface is the communication link between field device and

the controllers; field device are wired to the I/O interfaces. Through these

interfaces the processor can sense and measure physical quantities regarding a

machine or process, such as proximity, position, motion, level temperature,

pressure, etc. Based on status sensed, the CPU issues command to output

devices such as values, motor, alarm, etc.

HISTORY:

Before the PLC, control, sequencing, and safety interlock logic for

manufacturing automobiles was mainly composed of relays, cam timers, drum

sequencers, and dedicated closed-loop controllers. Since these could number in

the hundreds or even thousands, the process for updating such facilities for the

yearly model change-over was very time consuming and expensive, as

electricians needed to individually rewire relays to change the logic.

Digital computers, being general-purpose programmable devices, were

soon applied to control of industrial processes. Early computers required

specialist programmers, and stringent operating environmental control for

temperature, cleanliness, and power quality. Using a general-purpose computer

for process control required protecting the computer from the plant floor

conditions.

An industrial control computer would have several attributes: it would

tolerate the shop-floor environment, it would support discrete (bit-form) input

and output in an easily extensible manner, it would not require years of training

to use, and it would permit its operation to be monitored. The response time of

any computer system must be fast enough to be useful for control; the required

speed varying according to the nature of the process.

DEVELOPEMENT:

Early PLCs were designed to replace relay logic systems. These PLCs

were programmed in "ladder logic", which strongly resembles a schematic

diagram of relay logic.

This program notation was chosen to reduce training demands for the

existing technicians. Other early PLCs used a form of instruction

list programming, based on a stack-based logic solver.

Modern PLCs can be programmed in a variety of ways, from the relay-

derived ladder logic to programming languages such as specially adapted

dialects of BASIC and C. Another method is State Logic, a very high-level

programming language designed to program PLCs based on state transition

diagrams.

Many early PLCs did not have accompanying programming terminals

that were capable of graphical representation of the logic, and so the logic was

instead represented as a series of logic expressions in some version of Boolean

format, similar to Boolean algebra. As programming terminals evolved, it

became more common for ladder logic to be used, for the aforementioned

reasons and because it was a familiar format used for electromechanical control

panels. Newer formats such as State Logic and Function Block (which is similar

to the way logic is depicted when using digital integrated logic circuits) exist,

but they are still not as popular as ladder logic.

A primary reason for this is that PLCs solve the logic in a predictable and

repeating sequence, and ladder logic allows the programmer (the person writing

the logic) to see any issues with the timing of the logic sequence more easily

than would be possible in other formats.

BLOCK DIAGRAM OF PLC:

BENEFITS OF PROGRAMMABLE CONTROLLERS:

Programmable controllers are made of solid state components and hence

provide high reliability.

They are flexible and changes in sequence of operation can easily be

incorporated due to programmability.

They may be modular in nature and thus expandability and easy

installation is possible.

Use of PLC result in appreciable savings in hardware and wiring cost.

They are compact and occupy less space.

Eliminate hardware items like Timers, Counters and Auxiliary relays.

The presence for timers and counters has easy accessibility.

PLC can control a variety of devices and eliminate the need for

customized controls.

FUNCTIONALITY:

The functionality of the PLC has evolved over the years to include

sequential relay control, motion control, process control, distributed control

systems and networking. The data handling, storage, processing power and

communication capabilities of some modern PLCs are approximately equivalent

to desktop computers.

PLC-like programming combined with remote I/O hardware, allow a

general-purpose desktop computer to overlap some PLCs in certain

applications. Regarding the practicality of these desktop computer based logic

controllers, it is important to note that they have not been generally accepted in

heavy industry because the desktop computers run on less stable operating

systems than do PLCs, and because the desktop computer hardware is typically

not designed to the same levels of tolerance to temperature, humidity, vibration,

and longevity as the processors used in PLCs.

In addition to the hardware limitations of desktop based logic,

operating systems such as Windows do not lend themselves to deterministic

logic execution, with the result that the logic may not always respond to

changes in logic state or input status with the extreme consistency in timing as

is expected from PLCs.

Still, such desktop logic applications find use in less critical

situations, such as laboratory automation and use in small facilities where the

application is less demanding and critical, because they are generally much less

expensive than PLCs.

FEATURE:

The main difference from other computers is that PLCs are armored for

severe conditions (such as dust, moisture, heat, cold) and have the facility for

extensive input/output (I/O) arrangements. These connect the PLC

to sensors and actuators. PLCs read limit switches, analog process variables

(such as temperature and pressure), and the positions of complex positioning

systems. Some use machine vision. On the actuator side, PLCs operate electric

motors, pneumatic or hydraulic cylinders, magnetic relays, solenoids, or analog

outputs. The input/output arrangements may be built into a simple PLC, or the

PLC may have external I/O modules attached to a computer network that plugs

into the PLC.

PROGRAMMING:

PLC programs are typically written in a special application on a personal

computer, then downloaded by a direct-connection cable or over a network to

the PLC. The program is stored in the PLC either in battery-backed-up RAM or

some other non-volatile flash memory. Often, a single PLC can be programmed

to replace thousands of relays.

Under the IEC 61131-3 standard, PLCs can be programmed using

standards-based programming languages. A graphical programming notation

called Sequential Function Charts is available on certain programmable

controllers. Initially most PLCs utilized Ladder Logic Diagram Programming, a

model which emulated electromechanical control panel devices (such as the

contact and coils of relays) which PLCs replaced. This model remains common

today.

IEC 61131-3 currently defines five programming languages for

programmable control systems: function block diagram (FBD), ladder

diagram (LD), structured text (ST; similar to the Pascal programming

language), instruction list (IL; similar to assembly language) and sequential

function chart (SFC). These techniques emphasize logical organization of

operations.

While the fundamental concepts of PLC programming are common to all

manufacturers, differences in I/O addressing, memory organization and

instruction sets mean that PLC programs are never perfectly interchangeable

between different makers. Even within the same product line of a single

manufacturer, different models may not be directly compatible.

RELAY:

A simple electromagnetic relay, such as the one taken from a car in the

first picture, is an adaptation of an electromagnet. It consists of a coil of wire

surrounding a soft iron core, an iron yoke, which provides a low reluctance path

for magnetic flux, a movable iron armature, and a set, or sets, of contacts; two

in the relay pictured. The armature is hinged to the yoke and mechanically

linked to a moving contact or contacts. It is held in place by a spring so that

when the relay is de-energized there is an air gap in the magnetic circuit. In this

condition, one of the two sets of contacts in the relay pictured is closed, and the

other set is open. Other relays may have more or fewer sets of contacts

depending on their function.

The relay in the picture also has a wire connecting the armature to the

yoke. This ensures continuity of the circuit between the moving contacts on the

armature, and the circuit track on the printed circuit board (PCB) via the yoke,

which is soldered to the PCB.

When an electric current is passed through the coil, the resulting magnetic

field attracts the armature and the consequent movement of the movable contact

or contacts either makes or breaks a connection with a fixed contact. If the set of

contacts was closed when the relay was De-energized, then the movement opens

the contacts and breaks the connection, and vice versa if the contacts were open.

When the current to the coil is switched off, the armature is returned bya force,

approximately half as strong as the magnetic force, to its relaxed position.

Usually this force is provided by a spring, but gravity is also used

commonly in industrial motor starters.

Most relays are manufactured to operate quickly. In a low voltage

application, this is to reduce noise. In a high voltage or high current application,

this is to reduce arcing.

If the coil is energized with DC, a diode is frequently installed across the

coil, to dissipate the energy from the collapsing magnetic field at deactivation,

which would otherwise generate a voltage spike dangerous to circuit

components. Some automotive relays already include a diode inside the relay

case. Alternatively a contact protection network, consisting of a capacitor and

resistor in series, may absorb the surge. If the coil is designed to be energized

with AC, a small copper ring can be crimped to the end of the solenoid. This

"shading ring" creates a small out-of-phase current, which increases the

minimum pull on the armature during the AC cycle.

By analogy with the functions of the original electromagnetic device, a

solid-state relay is made with a thyristor or other solid-state switching device.

To achieve electrical isolation an optocoupler can be used which is a light-

emitting diode (LED) coupled with a photo transistor.

ADVANTAGES OF RELAY:

Elegant, Sturdy and Light Weight.

Versatile Relay satisfying Low to Medium Power Sources.

Long Life and High Reliability.

Solder, Plug-in & PCB Version.

JSS 50711 Specs.

Assured Deliveries, Attractive and Economically Priced.

TYPES OF RELAY:

Mechanical relays are designed for high currents (typically 2 to15 A) and

relatively slow switching (typically 10 to 100 ms).Reed relays are designed for

moderate currents (typically 500 mA to 1 A) and moderately fast switching (0.2

to 2 ms).

Solid-state relays, on the other hand, come with a wide range of current

ratings (a few micro amps for low-powered packages up to 100 A for high

power packages) and have extremely fast switching speeds (typically 1 to 100

ns).

Some limitations of both reed relays and solid-state relays include limited

switching arrangements (type of switch section) and a tendency to become

damaged by surges in power.

A mechanical relay’s switch section comes in many of the standard

manual switch arrangements (e.g., SPST, SPDT, DPDT, etc.). Reed relays and

solid-state relays, unlike mechanical relays, typically are limited to SPST

switching.

APPLICATION:

RELAYS ARE USED FOR:

Amplifying a digital signal, switching a large amount of power with a

small operating power. Some special cases are:

A telegraph relay, repeating a weak signal received at the end of a long

wire

Controlling a high-voltage circuit with a low-voltage signal, as in some

types of modems or audio amplifiers,

Controlling a high-current circuit with a low-current signal, as in

the starter solenoid of an automobile,

Detecting and isolating faults on transmission and distribution lines by

opening and closing circuit breakers (protection relays),

The change-over or Form C contacts perform the XOR (exclusive or)

function. Similar functions for NAND and NOR are accomplished using

normally closed contacts. The Ladder programming language is often used for

designing relay logic networks.

INFRARED LED SENSOR:

Common infrared LED that emits infrared rays has the same appearance with

visible light LED. It’s appropriate operating voltage is around 1.4v and the

current is generally smaller than 20mA. Current limiting resistances are usually

connected in series in the infrared LED circuits to adjust the voltages, helping

the LEDs to be adapted to different operating voltages.

When using infrared rays to control correspondent unit, the controlling distance

is in direct ratio with the emitting power. In order to lengthen its controlling

distance, infrared LED should be operated under pulse state as the effective

transmitting distance of the pulsed light (modulated light) is in proportion with

the wind-induced current of the pulses. Thus, by increasing the peak value (Ip)

of the pulses, the emitting distance of the infrared LED can also be lengthened.

One way to increase Ip is to diminish the duty ratio of the pulse; that is to

reduce the width of the pulse (T).

The duty ratios of the working pulses for some color TV’s infrared

remote controllers are around 1/3-1/4; and for some other electronic products,

the duty ratios of the infrared remote controllers can even be as small as 1/10.

Through reducing the duty ratio of the pulses, the emitting distance for small

power infrared LED can also be increased in a large extent. Ordinary infrared

LEDs can be divided into the following three types: small power one (1mW-

10mW), medium power LED (10mW-50mW) and large power LED (50mW-

100mW and above). The modulated light can be generated by adding pulse

voltage with specific frequency on the driving diode.

The controller with infrared LED can emit infrared rays to take control of

correspondent unit, and at the controlled unit end, there is also a receiving

device to turn the infrared light into electricity, such as infrared light receiving

diode, photoelectric triode and so on. Emitting and receiving matched infrared

diode has also been applied in practical use.

There are two emitting-receiving modes for infrared LED and the

controlled unit, one is direct light emitting mode, and the other is reflecting light

mode. In the direct light emitting mode, the emitting diode and the receiving

diode are installed in the emitting end and the controlled unit end respectively,

with a certain distance between them. As to the reflecting light mode, the

lighting diode and the receiving diode are in parallel. Only when the infrared

rays emitted by the diode were reflected by something can the receiving diode

get the infrared rays, thereby stimulate the controlled unit to operate. Besides,

infrared emitting circuit with double diodes bears higher power and longer

functional distance.

Infrared LED chips with different wavelengths can be applied in

extensive devices, for example:

1. Infrared LED chip with wavelength of 940nm: suitable to be used in remote

controller, such as remote controllers for household appliances.

2. 808nm: suitable to be used in medical treatment appliances, space optical

communication, infrared illumination and the pumping sources of the solid-state

lasers.

3. 830nm: suitable to be used in the automated card reader system in freeway.

4. 840nm: suitable to be used in colored zoom infrared waterproof video

camera.

5. 850nm: suitable to be used in video cameras that are applied in digital

photography, monitoring system, door phone, theft proof alarm and so on.

6. 870nm: suitable to be used in video cameras in marketplace and crossroad.

RAIL TRANSPORT:

Rail transport is a means of conveyance of passengers and goods, by way

of wheeled vehicles running on rail tracks. It is also commonly referred to as

train transport. In contrast to road transport, where vehicles merely run on a

prepared surface, rail vehicles are also directionally guided by the tracks on

which they run. Track usually consists of steel rails installed

on sleepers/ties and ballast, on which the rolling stock, usually fitted with metal

wheels, moves. However, other variations are also possible, such as slab track

where the rails are fastened to a concrete foundation resting on a prepared

subsurface.

RAILWAY SIGNALING:

Railway signaling is a system used to control railway traffic safely,

essentially to prevent trains from colliding. Being guided by fixed rails, trains

are uniquely susceptible to collision; furthermore, trains cannot stop quickly,

and frequently operate at speeds that do not enable them to stop within sighting

distance of the driver. In the UK, the Regulation of Railways Act

1889 introduced a series of requirements on matters such as the implementation

of interlocked block signaling and other safety measures as a direct result of

the Armagh rail disaster in that year.

LEVEL CROSSING:

A level crossing (a primarily British term; usually known as a railroad

crossing in the United States) is an instance of the at-grade intersection of

a railway line and a road or path; that is to say, where the crossing is made

without recourse to a bridge or tunnel.

The term also applies when a light rail line with separate right-of-

way or reserved track crosses a road in the same fashion. Other names

include railway crossing, grade crossing, road through railroad, and train

crossing.

RAILWAY ELECTRIC TRACTION:

Railway electrification as a means of traction emerged at the end of the

nineteenth century, although experiments in electric rail have been traced back

to the mid-nineteenth century. Thomas Davenport, in Brandon, Vermont,

erected a circular model railroad on which ran battery-powered locomotives (or

locomotives running on battery-powered rails) in 1834. Robert Davidson,

of Aberdeen, Scotland, created an electric locomotive in 1839 and ran it on the

Edinburgh-Glasgow railway at 4 miles per hour.[1]

The earliest electric

locomotives tended to be battery-powered.[1]

In 1880, Thomas Edison built a

small electrical railway, using a dynamo as the motor and the rails as the

current-carrying medium. The electric current flowed through the metal rim of

otherwise wooden wheels, being picked up via contact brushes.

Electrical traction offered several benefits over the then

predominant steam traction, particularly in respect of its quick acceleration

(ideal for urban (metro) and suburban (commuter) services) and power (ideal

for heavy freight trains through mountainous/hilly sections). A plethora of

systems emerged in the first twenty years of the twentieth century.

RAILROAD SWITCH:

A railroad switch, turnout or [set of] points is a mechanical installation

enabling railway trains to be guided from one track to another, such as at

a railway junction or where a spur or siding branches off.

The switch consists of the pair of linked tapering rails, known

as points (switch rails or point blades), lying between the diverging outer rails

(the stock rails). These points can be moved laterally into one of two positions

to direct a train coming from the narrow end toward the straight path or the

diverging path. A train moving from the narrow end toward the point blades

(i.e. it may go either left or right) is said to be executing a facing-point

movement.

Unless the switch is locked, a train coming from either of the converging

directs will pass through the points onto the narrow end, regardless of the

position of the points, as the vehicle's wheels will force the points to move.

Passage through a switch in this direction is known as a trailing-point

movement.

A switch generally has a straight "through" track (such as the main-line)

and a diverging route. The handedness of the installation is described by the

side that the diverging track leaves. Right-hand switches have a diverging path

to the right of the straight track, when coming from the narrow end, and a left-

handed switch has the diverging track leaving to the opposite side.

A straight track is not always present; for example, both tracks may

curve, one to the left and one to the right (such as for a wyes switch), or both

tracks may curve, with differing radii, while still in the same direction.

DC MOTOR:

A DC motor is a mechanically commutated electric motor powered

from direct current (DC). The stator is stationary in space by definition and

therefore it’s current. The current in the rotor is switched by the commutator to

also be stationary in space. This is how the relative angle between the stator and

rotor magnetic flux is maintained near 90 degrees, which generates the

maximum torque.

Motors have a rotating armature winding (winding in which a voltage is

induced) but non-rotating armature magnetic field and a static field winding

(winding that produce the main magnetic flux) or permanent magnet. Different

connections of the field and armature winding provide different inherent

speed/torque regulation characteristics. The speed of a DC motor can be

controlled by changing the voltage applied to the armature or by changing the

field current. The introduction of variable resistance in the armature circuit or

field circuit allowed speed control. Modern DC motors are often controlled

by power electronics systems called DC drives.

The introduction of DC motors to run machinery eliminated the need for

local steam or internal combustion engines, and line shaft drive systems. DC

motors can operate directly from rechargeable batteries, providing the motive

power for the first electric vehicles. Today DC motors are still found in

applications as small as toys and disk drives, or in large sizes to operate steel

rolling mills and paper machines.

LADDER LOGIC DIAGRAM:

FEATURES:

This project is fully controlled by automatic manner.

Efficient and reliable.

PLC allows dynamic and faster control.

Number of operation can be control at a time.

Required low cost for automation.

Required low power supply for operation of the circuit.

Easy to change the control settings.

Rewiring of the circuit is easy.

Simple & flexible program.

Compact size.

COMPONENTS USED:

IR sensor

PLC (programmable logic controller)

Relays

Motors

LED

And some electronic components.

SOFTWARE USED:

Ladder diagram.

ESTIMATION

S.NO NAME OF

COMPONENTS

QUANTITY AMOUNT

1 PLC 2 5000/-

2 RELAY 8 1280/-

3 DC MOTOR 2 300/-

4 INDICATING

LAMP(LED)

2

100/-

5 SENSOR(IR) 7 1750/-

6 TRAIN 2 1000/-

7 WIRES,COMPONENTS 50m 1000/-

8 BOARD 1 1200/-

REFERENCE:

[1] María Domínguez, Antonio Fernández-Cardador, Asunción P. Cucala, and

Ramón R. Pecharromán. “Energy Savings in Metropolitan Railway Substations

Through Regenerative Energy Recovery and Optimal Design of ATO Speed

Profiles” IEEE transactions on automation science and engineering, vol. 9, no.

3, july 2012.

[2] L. Abrahamsson and L. Söder, “Fast estimation of relations between

aggregated train power system data and traffic performance,” IEEE

Trans. Veh. Technol., vol. 60, no. 1, pp. 16–29, Jan. 2011.

[3] A. Adinolfi, R. Lamedica, C. Modesto, A. Prudenzi, and S.

Vimercati,“Experimental assessment of energy saving due to trains regenerative

braking in an electrified subway line,” IEEE Trans. Power Deliv., vol. 13, no. 4,

pp. 1536–1542, Oct. 1998.