An
INTERNSHIP REPORT
ON
ELECTRICAL MACHINES
FOR
MACHINE OVERHAULING SHED, BHUSAWAL
Submitted to Savitribai Phule Pune University, Pune in partial fulfillment of the
requirement for the award of the Degree of BACHELOR OF ENGINEERING in
ELECTRICAL ENGINEERING
By
“Kunal Singh Thakur”
(Exam Seat No.: T1904702550)
MET’s
INSTITUTE OF ENGINEERING
Department of Electrical Engineering
Adgaon, Nashik - 422 003
Maharashtra, India
https://metbhujbalknowledgecity.ac.in/engineering/
Academic Year: 2021-22
MET’s INSTITUTE OF ENGINEERING,
ADGAON, NASHIK 422003
Department of Electrical Engineering
CERTIFICATE
This is to certify that the Internship entitled “ELECTRICAL MACHINES” is
a bonafide record of the internship done by KUNAL SINGH THAKUR under my supervision
and guidance, submitted to Savitribai Phule Pune University in partial fulfillment of the
requirements for the award of Degree of Bachelor of Engineering in Electrical Engineering
from MET’s Institute of Engineering, Adgaon, Nashik affiliated to Savitribai Phule Pune
University, Pune, for the academic year 2021-22
Prof. Yogesh Patni
Assistant Professor in Electrical Engg
Guide
Prof. Dr. V. P. Wani
Principal
Prof. Dr. D. P. Kadam
HoD Electrical Engineering
College Seal
DECLARATION
I hereby declare that the presented report of internship titled ELECTRICAL MACHINES of
MACHINE OVERHAULING SHED is uniquely prepared by me after the completion of 30
days at MACHINE OVERHAULING SHED,BHUSAWAL.
Place: Nashik
Date: 07/03/2025
KUNAL SINGH THAKUR
ABSTRACT
This report summarizes my one-month internship training at the Machine Overhauling Electric
Locomotive Shed in Bhusawal, where I gained hands-on experience in the maintenance and
overhauling of electric locomotives. The internship focused on four key sections: the static
section, electronics section, traction motor section, and auxiliary section. I worked on critical
components such as step-down Transformers, tap changers, static inverters, traction motors,
and auxiliary systems, learning their functions, maintenance procedures, and common issues.
In the static section, I inspected Transformers, tested Transformer oil using the breakdown
voltage test, and examined tap changers and notches for wear and tear. The electronics section
involved understanding the role of static inverters and power electronics like IGBTs and
MOSFETs in converting DC to AC power for traction motors. In the traction motor section, I
studied both DC and AC traction motors, focusing on their speed control mechanisms,
regenerative braking, and maintenance requirements. The auxiliary section covered systems
like air compressors, cooling fans, and HVAC, which are essential for the locomotive's
operation.
Throughout the internship, I applied methodologies such as visual inspection, diagnostic
testing, performance monitoring, and thermal analysis to identify and address problems. This
experience not only enhanced my technical skills but also provided valuable insights into the
complexities of electric locomotive maintenance. The internship was a transformative learning
opportunity, bridging theoretical knowledge with practical application and preparing me for a
career in electrical engineering.
TABLE OF CONTENTS
Sr. No.
Name of the Topic
Page No.
1
2
Cover Page
Certificate
I
II
3
4
Declaration
Abstract
III
IV
5
6
7
8
9
10
11
12
13
14
15
Table Of Contents
List of Figures
Introduction
Scope Of The Topic
Electrical Machines
Conclusion
Suggestions/Feedback
Logbook
Internship Certificate
Acknowledgement
List Of References
V
VI
7
11
14
33
35
38
39
40
41
LIST OF FIGURES
SR.NO.
NAME OF THE FIGURE
PAGE NO.
1
2
3
CGR Switch And Notch
25KV/960 V Step Down Transformer
1.Transformer Equipment
2. TAP Changer Mechanism
1.Transformer Oil Tank
2. Air Filter In Transformer
1. Transformer Oil Cooling Motor
2. Radiator Figure
Static Inverter
6 Pole DC Series Motor
3-Ph Induction Motor
1.Air Compressor
2. Radiator In Air Compressor
1.Air Compressor Pressure Cylinder
2. Pressurized Air
Air Compressor Present In Electric Locomotive
(Type – WAG-9)
Information Of Transformer Oil Pump Motor
Insulation Table Chart w.r.t. Temperature
Dielectric Breakdown Strength Test Machine For
Transformer Oil
14
17
18
18
18
18
19
19
20
23
25
28
4
5
6
7
8
9
10
11
12
13
14
29
29
30
31
32
CHAPTER 1
INTRODUCTION

Indian Railways
Indian Railways (IR) is one of the world's largest railway networks, operated by the
Government of India under the Ministry of Railways. Established in 1853, it has grown to
become the fourth-largest railway network globally, covering over 68,000 km of track and
connecting almost every part of India.

Key Features of Indian Railways
1. Government-Owned: Fully owned and operated by the Indian government.
2. Vast Network: Covers 7,325 stations across urban and rural India.
3. Diverse Operations: Includes passenger trains, freight trains, and special tourism trains.
4. Employment Provider: One of the largest employers in the world, with over 1.2 million
employees.
5. Electrification & Modernization: More than 80% of routes are electrified, and projects like
Vande Bharat Express and Bullet Train are boosting modernization.
6. Economic Backbone: Handles over 8 billion passengers annually and transports over 1.4
billion tonnes of freight.
7. Zones & Divisions: Divided into 19 zones and 70+ divisions for efficient management.

MOH Locomotive Shed Workshop Bhusawal :
•
I had the privilege of completing a one-month internship at the Machine Overhauling
Electric Locomotive Shed in Bhusawal, a facility renowned for its expertise in the
maintenance and overhauling of electric locomotives used by Indian Railways.
•
The Electric Locomotive Workshop (Periodical Overhauling or POH) at Bhusawal was
established in 1974 at a cost of ₹3.52 crore. This facility was set up to perform periodical
overhauls of electric locomotives. Additionally, the Electric Loco Shed at Bhusawal,
responsible for maintenance and repair of electric locomotives, was also established in 1974.
•
During my internship, I was exposed to the intricate processes involved in the maintenance
and overhauling of electric locomotives, with a particular focus on the static, electronic,
traction motor, and auxiliary systems. I had the opportunity to work alongside experienced
technicians and engineers, who guided me through the various stages of locomotive
maintenance, from diagnosing issues to implementing solutions. This hands-on experience
was complemented by theoretical knowledge, as I learned about the working principles of
key components such as transformers, tap changers, static inverters ,traction motors, and
auxiliary systems.
•
The static section of the locomotive includes critical components like the step-down
transformer, which reduces the high voltage from the catenary (typically 25 kV AC) to a
lower voltage suitable for traction motors (around 960 volts). The transformer's tap changer
mechanism, which operates through notches, allows for precise control of the output voltage,
ensuring that the locomotive can adapt to varying load and speed requirements. I also learned
about the importance of transformer oil for insulation and cooling, and the breakdown
voltage test used to assess the oil's insulation strength, which must be at least
2.5 times the working voltage (62.5 kV for a 25 kV system) as per Indian Railways
standards.
•
In the electronics section, I gained insights into the role of static inverters and power
electronics in modern electric locomotives. Static inverters are responsible for converting
high-voltage DC (or rectified AC) into low-voltage AC to power auxiliary systems. The use
of IGBTs (Insulated-Gate Bipolar Transistors) and MOSFETs (Metal-Oxide- Semiconductor
Field-Effect Transistors) in these inverters is crucial for efficient switching and power
conversion. These components enable precise control of AC power for traction motors,
contributing to better performance and energy efficiency. I also learned about the role of
silicon rectifiers in converting AC voltage to DC for traction motors, further illustrating the
complexity and sophistication of the power electronics systems in electric locomotives.
•
The traction motor section provided me with a comprehensive understanding of both DC and
AC traction motors. DC traction motors, which have been widely used in the past, are known
for their simplicity, reliability, and good speed control characteristics. However, modern
locomotives are increasingly using AC traction motors due to their higher efficiency, better
speed and torque control, and reduced maintenance requirements. I learned about the
working principles of these motors, including the role of variable voltage variable frequency
(VVVF) drives in controlling the speed and torque of AC induction motors. The shift from
DC to AC traction motors in modern locomotives is a significant trend, and I observed how
these motors are maintained and tested in the workshop.
•
The auxiliary section covers the various auxiliary motors and their functions in supporting
the locomotive's operation. These motors drive essential systems such as cooling, braking,
and power supply for auxiliary systems like lighting, air conditioning, and control circuits. I
had the opportunity to work on components like the air compressor and radiator, which are
critical for maintaining the locomotive's operational efficiency.
The air compressor, for example, works on the principles of thermodynamics, compressing
atmospheric air and storing it in a reservoir for use in the braking system. The radiator,
powered by a 3-phase induction motor, dissipates heat from the transformer oil, ensuring
that the locomotive's electrical systems remain within safe operating temperatures.
•
This report aims to document my learning experiences and the knowledge I gained during
my internship at the Bhusawal Electric Locomotive Shed. It is divided into sections that
cover the various aspects of locomotive maintenance, including the static section, electronics
section, traction motor section, and auxiliary section. Each section provides a detailed
account of the components and systems I worked on, the challenges I encountered, and the
skills I developed. Through this report, I hope to convey the significance of the work carried
out at the Bhusawal shed and the impact it has on the overall performance and reliability of
Indian Railways' electric locomotives.

Objectives :
The primary objective of my one-month internship at the Machine Overhauling Electric
Locomotive Shed in Bhusawal was to gain practical, hands-on experience in the maintenance and
overhauling of electric locomotives. Specifically, the internship aimed to:
1. Understand the Functioning of Key Components: Gain in-depth knowledge of the various
systems and components of electric locomotives, including the static section (transformers, tap
changers, and notches), the electronics section (static inverters, IGBTs, and MOSFETs), the traction
motor section (DC and AC traction motors), and the auxiliary section (auxiliary motors, air
compressors, and cooling systems).
2. Learn Maintenance and Testing Procedures: Observe and participate in the maintenance and
testing procedures for critical components such as transformer oil, tap changers, traction motors,
and auxiliary systems. This included understanding the importance of regular maintenance and the
use of diagnostic tools like the breakdown voltage test for transformer oil.
3. Develop Technical Skills: Enhance my technical skills by working alongside experienced
technicians and engineers, learning how to diagnose issues, implement solutions, and ensure the
efficient and reliable operation of electric locomotives.
4. Bridge Theoretical Knowledge with Practical Application: Apply the theoretical knowledge
gained during my academic studies to real-world scenarios, understanding how concepts like
electromagnetic induction, power electronics, and thermodynamics are implemented in the
functioning of electric locomotives.
5. Gain Insight into Industry Standards: Learn about the standards and protocols followed by Indian
Railways, particularly in the maintenance and overhauling of electric locomotives, and understand
the importance of adhering to these standards for safety and efficiency.

Motivation :
My motivation for pursuing this internship stemmed from a deep interest in electrical engineering,
particularly in the field of power systems and transportation. Electric locomotives are a fascinating
blend of electrical, mechanical, and electronic systems, and I was eager to explore how these
systems work together to power one of the most critical modes of transportation in India. Below
are the key factors that motivated me to undertake this internship:
6. Passion for Electrical Systems: I have always been fascinated by the complexity and efficiency
of electrical systems, especially those used in large-scale applications like railways. The
opportunity to work on electric locomotives, which are among the most advanced electrical
machines, was a dream come true.
7. Desire for Hands-On Experience: While academic studies provide a strong theoretical
foundation, I wanted to gain practical experience in a real-world industrial setting. The Bhusawal
Electric Locomotive Shed, being one of the oldest and most renowned workshops in India, offered
the perfect environment for this.
8. Interest in Indian Railways: Indian Railways is one of the largest railway networks in the world,
and its electric locomotives are a testament to the country's engineering prowess. I was motivated
to learn about the systems that keep these locomotives running efficiently and safely, contributing
to the nation's transportation infrastructure.
9. Career Aspirations: As someone aspiring to build a career in the field of electrical engineering,
particularly in power systems and transportation, this internship provided me with a unique
opportunity to explore my interests and gain valuable industry experience. It allowed me to
understand the challenges and complexities of maintaining electric locomotives, which will be
invaluable in my future career.
10.
Learning from Experts: The chance to work with experienced technicians and engineers
at the Bhusawal shed was a significant motivator. I was eager to learn from their expertise and
gain insights into the best practices and techniques used in the industry.
11.Contribution to Sustainability: Electric locomotives are a sustainable mode of transportation,
reducing reliance on fossil fuels and minimizing environmental impact. By learning about their
maintenance and operation, I hoped to contribute to the broader goal of promoting sustainable
transportation solutions.
In conclusion, the internship at the Bhusawal Electric Locomotive Shed was driven by my passion
for electrical engineering, my desire to gain practical experience, and my interest in contributing to
the efficient and sustainable operation of Indian Railways. The knowledge and skills I gained during
this internship have not only enhanced my technical expertise but also reinforced my commitment
to pursuing a career in this field.
 Organization of the report
This report has organized in 5 chapters :
Chapter 1 : Introduction
Chapter 2 : Statements/Defining training work/Problem Identifications
Chapter 3 : Methodologies/Explaination in details
Chapter 4 : Conclusion
Chapter 5 : Suggestions/Feedback
Along with these chapters the report has Cover Page, list of tables, contents ,
Acknowledgement, Logbook, Certificate and list of references.
CHAPTER 2
SCOPE OF THE TOPIC
This section provides an overview of the internship, including the reasons for undertaking this
study, the problem statement, scope, objectives, and the purpose of the internship. It sets the
context for the detailed discussions and findings presented in the main body of the report. The
internship aligns with the curriculum and objectives of the Savitribai Phule Pune University
(SPPU) Electrical Engineering program, which emphasizes practical application, industry
exposure, and skill development in the field of electrical engineering.

Why to Study This in Internship (Why I’m Doing This)
The study of electric locomotive maintenance and overhauling during my internship was
essential for several reasons, particularly in the context of the SPPU Electrical Engineering
curriculum:
Practical Application of Theoretical Knowledge: The SPPU Electrical Engineering program
emphasizes the application of theoretical concepts in real-world scenarios. This internship
allowed me to apply concepts like electromagnetic induction, power electronics, and
thermodynamics in the maintenance of electric locomotives, bridging the gap between
classroom learning and industrial practices.
Exposure to Industry Practices: The internship provided me with firsthand exposure to the
maintenance and overhauling practices followed in one of the largest railway networks in the
world. This aligns with SPPU's focus on industry-oriented learning and understanding the
challenges and complexities of the electrical engineering industry.
Skill Development: Working on critical components like transformers, traction motors, and
power electronics helped me develop technical skills in diagnosing issues, implementing
solutions, and ensuring the efficient operation of locomotives. This aligns with SPPU's
emphasis on skill-based education and hands-on training.
Career Preparation: As part of the SPPU Electrical Engineering program, this internship was a
crucial step in gaining industry-specific knowledge and experience, preparing me for a career
in power systems, transportation, or related fields.
Contribution to Sustainable Transportation: Electric locomotives are a sustainable mode of
transportation, and understanding their maintenance and operation aligns with SPPU's focus
on sustainable engineering solutions and environmentally friendly technologies.

Problem Statement
The maintenance and overhauling of electric locomotives involve several challenges, which
are relevant to the SPPU Electrical Engineering curriculum:
Efficient Maintenance of Critical Components: Ensuring the reliable operation of transformers,
traction motors, and power electronics requires regular maintenance and timely identification
of faults. This aligns with SPPU's focus on power systems and electrical machines.
Energy Efficiency: Optimizing systems like regenerative braking and cooling systems to
improve energy efficiency and reduce operational costs. This is relevant to SPPU's emphasis
on energy conservation and efficient power utilization.
Safety and Reliability: Ensuring the safety of personnel and the reliability of locomotives
through strict maintenance protocols and advanced diagnostic tools. This aligns with SPPU's
focus on safety standards and reliability engineering.
Modernization of Older Locomotives: Upgrading older locomotives with modern technologies
like AC traction motors and automated auxiliary systems to improve efficiency and reduce
maintenance requirements. This is relevant to SPPU's focus on modernization and
technological advancements in electrical engineering.
This internship aimed to address these challenges by studying the maintenance practices and
identifying areas for improvement, in line with the SPPU Electrical Engineering program's
objectives.

Scope of the Internship
The scope of the internship covered various aspects of electric locomotive maintenance and
overhauling, which are directly related to the SPPU Electrical Engineering curriculum:
Static Section: Maintenance of transformers, tap changers, and notches, including transformer
oil testing and insulation checks. This aligns with SPPU's focus on electrical machines and
power systems.
Electronics Section: Study of static inverters, power electronics (IGBTs and MOSFETs), and
their role in power conversion and control. This is relevant to SPPU's focus on power
electronics and control systems.
Traction Motor Section: Maintenance of DC and AC traction motors, including speed control
mechanisms and regenerative braking systems. This aligns with SPPU's focus on electrical
drives and motor control.
Auxiliary Section: Maintenance of auxiliary systems like air compressors, cooling fans, and
HVAC systems, which are essential for the locomotive's operation. This is relevant to SPPU's
focus on auxiliary power systems and industrial applications.
Diagnostic and Testing Procedures: Participation in diagnostic testing, performance
monitoring, and thermal analysis to identify and address issues in locomotives. This aligns with
SPPU's focus on testing and measurement techniques in electrical engineering.
The internship provided a comprehensive understanding of the various systems and
components that ensure the efficient and reliable operation of electric locomotives, in line with
the SPPU Electrical Engineering program's objectives.

Purpose of Doing Internship at MOH Shed Bhusawal
The purpose of undertaking this internship was multifaceted and aligned with the SPPU
Electrical Engineering program's goals:
Professional Growth: To gain practical experience and technical skills that are essential for a
career in electrical engineering, particularly in the railway industry. This aligns with SPPU's
focus on career readiness and professional development.
Contribution to Industry: To contribute to the efficient and reliable operation of electric
locomotives by identifying areas for improvement and suggesting solutions. This is relevant to
SPPU's emphasis on industry collaboration and problem-solving.
Knowledge Enhancement: To deepen my understanding of electric locomotive systems,
including transformers, traction motors, and power electronics, and their maintenance
requirements. This aligns with SPPU's focus on advanced learning and specialization in
electrical engineering.
Preparation for Future Challenges: To prepare myself for the challenges of modern engineering
by working on advanced technologies like static inverters, IGBTs, and regenerative braking
systems. This is relevant to SPPU's focus on technological advancements and innovation in
engineering.

Conclusion of Chapter 2
This internship was a transformative learning experience that not only enhanced my technical
knowledge but also prepared me for a career in electrical engineering, in line with the SPPU
Electrical Engineering program's objectives.
The skills and insights I gained during this internship will be instrumental in my future
endeavors, and I am grateful for the opportunity to learn from some of the best professionals
in the industry.
The following sections of this report provide a detailed account of my experiences, learnings,
and findings during the internship.
CHAPTER 3
ELECTRICAL MACHINES

THE STATIC SECTION
The static department of Machine Overhauling of Electric Locomotive Workshop includes
the Planned/Preventive/Scheduled overhauling and maintenance of static device such as
Step Down Transformer and the micro to macro components inside and outside the
transformer and related to it such as tap changer mechanism , transformer oil chamber ,
filters , notch , primary and secondary windings , radiator etc.
A tap changer is a crucial device in electric locomotives that regulates the output voltage of
the step-down transformer to control power supply to traction motors. It allows for smooth
variation of voltage and power levels without requiring a separate variable voltage
transformer.
A notch is used in tap changer to control the output voltage of secondary winding of the
transformer and to maintain the sufficient current required for traction motors for the
amenities as per intervals and requirements.
When a notch is provided by pilot the tap changer works accordingly. 1
notch = 30 output voltage and total 32 notch can be provided as 960 volts is the maximum
stepped down output voltage given by the transformer.
Fig : CGR Switch
Fig : Notch
Notch standard size is 46 mm , after timely used once it reaches up to or beyond 36 mm
it is replaced with new notch.

TRANSFORMER
INTRODUCTION
Transformer is a static electrical device that transfers electrical energy between two or more
circuits through electromagnetic induction. It is mainly used to step up (increase) or step down
(decrease) voltage levels in power transmission and distribution systems.
Main Components of a Transformer
1. Core – Provides a path for the magnetic flux.
2. Primary Winding – Receives the input voltage.
3. Secondary Winding – Delivers the transformed voltage output.
4. Insulation – Prevents electrical faults between windings and the core.
5. Cooling System – Uses oil, air, or water to prevent overheating.
6. Tap Changer – Adjusts the voltage output by changing winding connections (in some
transformers).
Types of Transformers
1. Power Transformer – Used in substations and transmission networks.
2. Distribution Transformer – Supplies power to residential and commercial areas.
3. Instrument Transformer – Includes CT (Current Transformer) and PT (Potential
Transformer) for measurement and protection.
4. Autotransformer – Has a single winding for both primary and secondary functions
5. Isolation Transformer – Provides electrical isolation between circuits.
In an Electric Locomotives 25 KV supply is given to step down Traction Transformer
which then stepped down to 960 volts. We will discuss about this transformer in detail.
.
25 KV / 960 V Step Down Transformer
The mentioned transformer works according to the notch and CGR switch mechanism applied
to supply power to the traction motors accordingly with load and speed requirements.
Companies such as ABB India Ltd, Bharat Heavy Electricals Limited (BHEL) and Seimens
India Ltd manufactures Traction and Auxilliary Transformers for electric locomotives for the
Indian Railways.
Function of a Step-Down Transformer in Electric Locomotives
1. Voltage Reduction: Electric locomotives, especially those running on AC power, receive
high voltage from the catenary (typically 25 kV AC in many railway networks). A stepdown transformer lowers this voltage to a level suitable for traction motors (typically in the
range of a few hundred to a few thousand volts).
2. Power Distribution: The primary winding of the transformer is connected to the highvoltage supply. The secondary winding supplies the appropriate voltage to traction
converters, rectifiers, and auxiliary systems.
3. Conversion to DC or Variable AC: Many modern locomotives use rectifiers and inverters
to convert the transformed AC voltage into DC or variable AC for use in traction motors.
Older locomotives used tap changers to regulate the output voltage directly
4. Power Supply to Auxiliary Systems: In addition to traction motors, the transformer supplies
power for: Air conditioning, Lighting control , Battery charging and Control systems.
Types of Transformers Used in Electric Locomotives



Single-phase transformers: Common in locomotives running on AC supply.
Multi-winding transformers: Have multiple secondary windings for different voltage
levels.
On-load tap-changing transformers: Allow voltage adjustment during operation to
optimize performance.
Advantages of Step-Down Transformers in Electric Locomotives
Efficient voltage regulation.
Enables high-voltage transmission with reduced losses.
Provides stable power for traction and auxiliary systems.
Allows use of modern AC-DC or AC-AC traction systems
FIG :- 25Kv Step Down Transformer displaying its components like Transformer oil
tank , switch gear mechanism on the right side , filters on the left side , CGR switch on
the top , pressure calibrator.
.

Transformers Equipment and their functions
1. CGR Switch : Circuit Grounding and Closing Switch in electric locomotives performs the
specific functions such as grounding the high voltage circuit, fault isolation, reclosing operation
and protects the transformer and traction equipment. In electric locomotives CGR switch are
commonly found in HV Switch Gear panels that control the power from the pantograph to the
main transformer.
2. Notch : In older locomotives such as WAG-5 , WAP-4 and WAM-4 the speed is controlled
using a tap changer which operates in Notches which is a level of steps in voltage increase.
By increasing the notch increases the motor voltage and simultaneously the locomotives speed.
The locomotives have 32 notches and notch 1 is the lowest power setting and notch 32 is full
power setting.
3. Transformer Oil : The transformer oil is present in two sides one is for tap changer and notch
and other tank is for primary and secondary windings which are dipped in the transformer oil
for insulation and cooling purposes.
For the front facing side of transformer as we see in the figure of the round chamber, there is
oil present in which 16 notches outer (odd) and 16 notches inner (even) rings are dipped.
Notches changes on the rings as it is applied by Loco Pilots cabin and consequently the voltage
increases or decreases.
The transformer oil has standard breakdown voltage of 62.5 KV but it can be used at 54 KV
breakdown voltage too.
2nd chamber of transformer oil which is situated at bottom of transformer where primary ad
secondary windings are present has the same Bd.V.
4. Filter : To protect the oil from moisture and air particles filters are equipped on the left side
of transformer which has silica which absorbs moisture and a air particles filter which filter out
any type of dust present in transformer oil to increase its strength.
5. Radiator : The current flows through the windings is huge so it gets heated and it needs to
be cool down to prevent any short circuit or insulation failure or burning of equipment. So the
transformer oil absorbs the heat and dissipates it by forced air cooling method in to the air.
The auxiliary motor pumps transformer oil in to the radiator forcefully and with air heat
exchange the heat gets dissipated in to the atmosphere and again oil flows back to their
respective chambers.
.

THE ELECTRONICS SECTION
Static Inverter and its working
In the conventional locomotives such as WAP-4,WAG-5/7, WACM-3 DC traction motors are
used for which first the voltage is step down and converted in to DC supply and to obtain pure
dc supply SL reactor were used which is type of induction choke coils.
It blocks the alternate or disrupted pulse fed to the dc traction motor and allows only pure dc
to feed.
In case of 3 phase induction motors to avoid frequency mismatch , speed and torque power
flows from the following devices before feed in to the IM.
A Static Inverter (SI) in an electric locomotive is responsible for converting high-voltage DC
(or AC rectified to DC) into low-voltage AC to power auxiliary systems. Unlike traditional
rotary converters, static inverters use solid-state electronics (IGBTs, MOSFETs) for efficient,
maintenance-free operation.
It has 7 diode bridge and total 1 diodes on one side which converts ac to dc and then it stores
in DC Buffer (capacitor) and it supplied to static inverter where it get converted to Ac supply
with 50 Hz frequency which is usable.
It ensures proper speed and torque should be provided to the motors with out frequency
fluctuation.
FIG : CAPACITOR DC SUPPLY BUFFER AND DIODE BRIDGE IN STATIC
INVERTOR
Silicon Rectifier (RSI):- It converts the AC voltage into the DC voltage by means of Diodes.
This DC voltage is used for Traction motors. Traction motor1, 2 & 3 gets supply from RSI-1
and Traction motor 4, 5 & 6 from RSI-2.
In electro locomotives, static inverters convert DC voltage from the locomotive’s power
source (typically from overhead lines or a diesel generator) into AC power to drive the
traction motors. The use of IGBTs (Insulated-Gate Bipolar Transistors) and MOSFETs
(Metal-Oxide-Semiconductor Field-Effect Transistors) in these inverters is essential for
efficient switching and power conversion.

Role of IGBT and MOSFET in Static Inverter:
1. Switching power conversion :
IGBTs and MOSFETs act as switches in the static inverter to regulate the flow of current and
voltage. They rapidly switch the DC voltage on and off, creating a high-frequency AC signal.
These semiconductor devices ensure the inverter can produce a stable, controllable AC output
with variable frequency and voltage suitable for the traction motors.
2. IGBTs
IGBTs are commonly used in high-voltage, high-current applications, like in electro
locomotives. They have the advantage of high efficiency and can handle large power levels.
IGBTs combine the best features of both MOSFETs (voltage-controlled) and bipolar junction
transistors (current-controlled), making them ideal for high-power switching in traction
inverters. They are typically used for switching the DC voltage and modulating it to generate
the required AC waveform for the motor.
3. MOSFETs
MOSFETs are generally used in lower voltage or high-speed applications because of their fast
switching characteristics. They are more suitable for handling smaller current levels in the
static inverter. In some locomotives, MOSFETs may be used in combination with IGBTs to
optimize switching performance, particularly at lower power ranges.
In summary, IGBTs and MOSFETs in static inverters enable the precise control of AC power
for electro locomotives' traction motors, contributing to performance, efficiency, and overall
reliability.
For making these relay there are many pioneer companies such as Omron, Scheindier electric,
panasonnic, Motorola, TE connectivity, siemens.
The voltage drop across these relay should be less for example, a Panasonic relay has masimum
30 mili ohm electrical contact resistance and its voltage drop is 0.01 to 0.1 volts.
.
.

TRACTION MOTOR SECTION
INTRODUCTION
A Traction Motor is an electric motor used to drive a vehicle, typically in railway locomotives,
electric buses, trams, and electric vehicles. These motors convert electrical energy into
mechanical energy to move the vehicle.
Types of Traction Motors :
1. AC Traction Motor
2. DC Traction Motor
Working Principle :
DC Motors: Current flows through the armature winding, creating a magnetic field. This
interacts with the stator field, generating rotation.
AC Motors: AC power creates a rotating magnetic field in the stator, inducing current in the
rotor, which then spins due to electromagnetic force.

DC TRACTION MOTORS
DC traction motors are electric motors that use direct current (DC) to provide the mechanical
energy needed to drive the wheels of a vehicle, such as trains, trams, or electric buses. They
have been widely used in the past for traction applications due to their simplicity, reliability,
and good speed control characteristics.

Key features of DC traction motors:
1. Speed Control: The speed of a DC motor can be easily controlled by varying the voltage or
adjusting the field current. This makes it highly suitable for applications that require precise
speed control, like trains.
2. High Starting Torque: DC motors offer high torque at low speeds, which is essential for
starting a vehicle from rest, especially under heavy load.
3. Simple Design: They have a relatively simple design with fewer components compared to
AC motors, which makes them easier to maintain.
4. Efficiency: DC traction motors generally offer high efficiency, particularly at lower speeds,
but their efficiency can decrease as the motor's load and speed increase.
5. Regenerative Braking: DC traction motors are well-suited for regenerative braking, where
the motor operates as a generator to convert kinetic energy back into electrical energy during
braking, which is then fed back into the power supply or stored.
6. Maintenance: One downside of DC motors is the maintenance required, especially for the
brushes and commutator, which wear out over time.
Conventionally, In electric locomotives such as wap 4 , wag 5 etc DC traction motors are used
as it provides high speed and torque which is required to overcome the inertia of train and to
gain a good momentum.
Working
A DC traction motor operates by converting electrical energy into mechanical motion using
the principles of electromagnetism. When DC power is supplied, current flows through the
field winding, creating a magnetic field, while the armature winding carries current and
generates a second magnetic field. The interaction of these fields produces a force that causes
the armature to rotate, generating torque.
A commutator and brushes ensure continuous rotation by switching the current direction in
the armature windings. DC traction motors provide high starting torque, making them ideal for
locomotives, trams, and electric vehicles.
Their speed is controlled by varying the applied voltage or field current, and they can also
support regenerative braking, converting kinetic energy back into electrical energy.
Fig.: shows 6 pole dc series motor stator which has copper field winding on it painted to
avoid dust on it. The second figure is showing commutator with carbon brushes which supply
power to armature for producing necessary flux in the rotor.
Also there are outer terminals which are connected to stator field windings to produce flux in
stator winding. When both the part produces flux magnetic interlocking takes place and motor
starts accelerating with high torque low speed.
.

AC TRACTION MOTORS
AC traction motors are electric motors that use alternating current (AC) to generate the
mechanical energy required for propulsion in vehicles like trains, trams, and electric buses.
They are commonly used in modern railways due to their high efficiency, durability, and
ability to handle higher power outputs compared to DC motors.
Key features of AC traction motors:
1. Higher Efficiency: AC motors generally have higher efficiency, especially at higher speeds
and loads, making them ideal for modern high-speed trains and long-distance travel.
2. No Commutator: Unlike DC motors, AC traction motors don’t use a commutator, which
reduces the need for regular maintenance and eliminates the problem of brush wear.
3. Better Speed and Torque Control: Advanced control systems, such as variable frequency
drives (VFDs), allow for precise control of speed and torque, which is essential for dynamic
rail operations, including acceleration, deceleration, and braking.
4. Regenerative Braking: Like DC motors, AC motors can also be used in regenerative
braking systems. During braking, the motor works as a generator to convert kinetic energy
into electrical energy, which can either be returned to the grid or stored.
5. Reliability: AC traction motors are known for their robustness and longer operational life.
They are particularly suitable for heavy-duty applications due to their ability to operate over a
wide range of speeds and torque demands.
6. Types of AC Traction Motors:
Synchronous Motors: These motors operate at a constant speed and are used in systems
where high precision and efficiency are required. However, they need additional equipment
like a synchronizing device or an external power source.
Induction Motors (Asynchronous Motors): These are the most commonly used AC motors for
traction. They are simpler in design and have a self-starting capability. Induction motors are
often used in both high-speed trains and low-speed urban transport systems due to their
durability and cost-effectiveness.
7. Cost and Maintenance: AC motors, especially induction motors, are typically more costeffective to maintain than DC motors since they have fewer parts that require maintenance
(e.g., no brushes or commutators.
.
WORKING
A three-phase AC induction motor (IM) in a locomotive operates on the principle of
electromagnetic induction. When a three-phase AC supply is fed to the stator windings, it
generates a rotating magnetic field (RMF). This RMF induces a current in the rotor windings
(typically a squirrel cage or wound rotor). Due to Lenz’s Law, the induced current in the rotor
generates its own magnetic field, which interacts with the stator’s RMF, producing torque that
rotates the rotor. Since the rotor always lags behind the RMF, it operates as an asynchronous
motor.
In Electric locomotives, Variable Voltage Variable Frequency (VVVF) drives control the
motor’s speed and torque by adjusting the supply frequency and voltage. AC traction motors
are preferred due to their higher efficiency, lower maintenance (no commutator or brushes),
and better performance at varying speeds. They also support regenerative braking, feeding
excess energy back into the power supply. These advantages make three-phase induction
motors the standard choice for modern electric and diesel-electric locomotives.
Fig.: Shows the stator and rotor portion of 3 phase induction motor which is used in
WAG-9, WAP-5/7, WAG-12 . Due to its compact size and good capacity and less
maintenance it is in use for modern locomotives instead of DC series motor.

Speed Control Of DC Series Motor
1. Field Control (Weakening the Field)
The speed of a DC series motor is inversely proportional to the field flux (N ∝ 1/Φ).
By reducing the field current (using series field diverters or tapping resistances), the flux
decreases, increasing the speed. This method is used when the locomotive reaches cruising
speed.
2. Armature Voltage Control
Speed is directly proportional to the applied voltage (N ∝ V).In electric locomotives, a tapchanging transformer or chopper control is used to vary the armature voltage. Chopper control
(modern method) provides smooth and efficient speed regulation by adjusting the voltage
electronically.
3. Series-Parallel Control (for Multiple Motors)
In locomotives with multiple motors, they can be connected in series (low speed, high torque)
or parallel (higher speed, moderate torque). Initially, motors are in series for better starting
torque, then switched to parallel for higher speed.

Speed Control Of 3 Phase Induction Motor
VVVF (Variable Voltage Variable Frequency) Control
The locomotive receives 25 kV AC from the overhead catenary.
This AC is converted into DC using a silicon-controlled rectifier (SCR) based rectifier.
The DC link smoothens the power before feeding it to the IGBT-based inverter.
The inverter converts DC into variable-frequency, variable-voltage AC, which controls the
three-phase induction motors.
By adjusting frequency (f) and voltage (V), the motor speed (N) is controlled while maintaining
a constant V/f ratio.
These are the modern techniques to use and control the speed of motors with regenerative
braking technology for maximum optimisation.
.

AUXILLIARY MOTOR SECTION
INTRODUCTION
Auxiliary motors in electric locomotives are smaller electric motors used to drive auxiliary
systems essential for the locomotive's operation but not directly involved in traction. These
motors support various subsystems that ensure smooth and efficient functioning.
Functions of Auxiliary Motors in Electric Locomotives:
1. Blower Motors – Provide cooling for traction motors and other electrical equipment.
2. Compressor Motors – Operate air compressors that generate compressed air for braking
and pneumatic controls.
3. Pump Motors – Drive pumps for cooling water circulation (in liquid-cooled systems) or
lubrication.
4. Alternator/Generator Motors – Provide auxiliary power for lighting, control circuits, and
battery charging.
5. HVAC Motors – Power heating, ventilation, and air conditioning systems in driver
cabins.
6. Fan Motors – Used for ventilation and maintaining optimal operating temperatures in
various components.
Power Supply for Auxiliary Motors:



Typically powered from the locomotive's auxiliary power supply, which converts highvoltage traction power (e.g., 25 kV AC or 1.5 kV DC) to a lower voltage suitable for
these motors.
In AC locomotives, an auxiliary converter provides the required power.
In DC locomotives, a separate motor-generator set or static converter is used.
Types of Auxiliary Motors:


AC 3 Phase Induction Motors – Common in modern locomotives due to efficiency and
low maintenance.
DC Motors – Used in older locomotives but gradually being replaced.
Auxiliary motors are critical to ensuring the locomotive's operational reliability, as failure in
any subsystem (e.g., cooling or braking) can lead to performance issues or even breakdowns.
In the MOH Locomotive workshop we have got learn and understand how blowers and
compressor works with the help of auxiliary induction motors.
.

Air Compressor
The air compressor works on the principle of thermodynamics which is entropy and enthalpy.
As the machine is compressing atmospheric gas which contains nitrogen, oxygen, carbon and
sulphuric gases as a major content it can change its gaseous state in to liquid state due to high
thermal energy by the extremely high air pressure compact in a cylinder.
To avoid this conversion the compressed air is then passed through the radiator where fan is
blown by 3 phase induction motor which is a type of auxiliary motor. The air then stored in the
reservoir and used for pressurized air braking when train needs to halt.
The auxiliary motor is connected to a piston and fan ; the piston works as first two big air inlets
compress air then it get compressed by small piston and after cooling down by radiator and
heat exchange with air I gets stored in the reservoir.
The compressed air is supplied to the brake pipe, which runs along the train, and is regulated
by the driver’s brake valve. When the driver applies the brakes, the pressure in the brake pipe
drops, causing the control valve to direct air from the auxiliary reservoir into the brake cylinder.
This air pressure pushes a piston, which moves the brake rigging and applies the brake shoes
to the wheels, slowing down the train.
To release the brakes, the brake pipe pressure is increased, causing the control valve to vent air
pipe pressure triggers automatic braking by sending full auxiliary reservoir pressure to the
brake cylinders. The system ensures safe, efficient, and controlled braking for locomotives.
FIG.: AIR COMPRESSOR AND RADIATOR
FIG.: AIR COMPRESSOR PRESSURE CYLINDER AND AIR RESERVOIR
FIG.: AIR COMPRESSOR IN WAG-9 LOCOMOTIVE

Auxiliary motors as blowers, cooling fans, pump in locomotives
As there is heat generation takes place in each equipment due to high current flowing through
it the heat needs to be dissipated in air to prevent insulation breakdown by heat and more
thermal hazards which can disrupt the ongoing process.
Generally if we talk about transformer the transformer oil needs to be cooled down to avoid
overheating of the machine equipment so as a induction motor is used to pump the oil from
the tank and then it forced to the radiator though oil pump and due to entropy its heat get
exchange with atmosphere gas and oil gets cooled down with this the primary and secondary
windings are also cooled and perform efficiently.
This process is continuous when locomotive is working.
FIG.: LABEL OF OIL PUMP TRANSFORMER MOTOR AND MACHINE PICTURE
Figure : Insulation Table Chart wrt Temperature
The Insulation class chart by which we can understand the type of insulation is been on the
motor so as to prevent the temperature cross above it. Mostly ‘H’ class of insulation is provided
to auxiliary motors.

Breakdown Voltage Test For Transformer Oil
FIG. : BREAKDOWN TEST MACHINE FOR TRANSFORMER OIL
It is a simple test used to check the strength of transformer oil , an specified amount of oil is
being placed in a closed vacuum chamber in which two electrodes are present which were
supplied high voltage and then at a point of testing the transformer oil breaks down and the
reading is displayed on the machine which is in Kilo Volt KV. In this test the breakdown
voltage of transformer oil is 54 KV which can be used for transformer as the working voltage
is 25 Kv.
As per standard laws the insulation oil strength should 2.5 times the working voltage
25 KV * 2.5 = 62.5 KV which is the guidelines of Indian Railways.
CHAPTER 4
CONCLUSION
My one-month internship at the Machine Overhauling Electric Locomotive Shed in Bhusawal
was an immensely enriching experience that provided me with a deep understanding of the
maintenance, overhauling, and operation of electric locomotives. This internship was a perfect
blend of theoretical knowledge and practical application, allowing me to explore the intricate
systems that power one of the most critical modes of transportation in India. The experience
not only enhanced my technical skills but also gave me a broader perspective on the challenges
and complexities involved in maintaining electric locomotives.
Key Areas of Learning
The internship was structured around four key sections: the static section, electronics section,
traction motor section, and auxiliary section. Each section played a vital role in ensuring the
efficient and reliable operation of locomotives, and I gained hands-on experience in
maintaining and troubleshooting these systems.
1. Static Section: I learned about the critical role of step-down transformers in reducing the
25 kV supply from the catenary to the required 960 volts for traction motors and auxiliary
systems. I worked on tap changers and notches, understanding how they regulate voltage and
ensure smooth operation under varying load conditions.I participated in the breakdown
voltage test for transformer oil, which is essential for maintaining proper insulation and
cooling. This test highlighted the importance of regular maintenance to prevent equipment
failure.
2. Electronics Section: I studied the functioning of static inverters and power electronics
(IGBTs and MOSFETs), which are responsible for converting DC to AC power for traction
motors and auxiliary systems.I learned about the role of silicon rectifiers in converting AC
voltage to DC for traction motors, and how modern locomotives use advanced electronics for
efficient power conversion and control. This section emphasized the importance of precision
and reliability in electronic systems, which are critical for the locomotive's performance.
3. Traction Motor Section: I gained hands-on experience with both DC and AC traction motors,
understanding their working principles, speed control mechanisms, and regenerative braking
systems. I observed the transition from DC to AC motors in modern locomotives, which
offer higher efficiency, better speed and torque control, and reduced maintenance
requirements. This section highlighted the importance of traction motors in providing the
necessary power and torque to move heavy loads efficiently.
4. Auxiliary Section: I learned about the critical role of auxiliary systems such as air
compressors, cooling fans, and HVAC systems in supporting the locomotive's operation.I
participated in the maintenance of these systems, ensuring they functioned efficiently to
prevent overheating and other operational issues.This section underscored the importance of
auxiliary systems in maintaining the locomotive's overall reliability and performance.
Technical Skills and Practical Experience
The internship provided me with valuable technical skills, including:
1. Diagnostic Testing: I learned how to perform tests like the breakdown voltage test for
transformer oil and how to diagnose issues in traction motors and power electronics.
2. Maintenance Procedures: I gained hands-on experience in maintaining critical components
like transformers, tap changers, and auxiliary systems, ensuring their efficient operation.
3. Problem-Solving: I developed problem-solving skills by identifying and addressing issues
in locomotives using various diagnostic and testing methods.
4. Teamwork and Collaboration: I worked alongside experienced technicians and engineers,
learning the importance of teamwork and collaboration in achieving common goals.
Broader Insights
Beyond the technical aspects, the internship gave me a broader understanding of the railway
industry and its challenges. I learned about the importance of regular maintenance and
proactive fault detection in ensuring the reliability and safety of locomotives. I also gained
insights into the energy efficiency and sustainability of electric locomotives, particularly
through systems like regenerative braking and efficient cooling.
Personal Growth and Future Applications
This internship was a transformative learning experience that not only enhanced my technical
knowledge but also prepared me for a career in electrical engineering. The skills and insights I
gained during this internship will be instrumental in my future endeavors, whether in the
railway industry or other fields of electrical engineering. The experience reinforced my passion
for engineering and my desire to contribute to the advancement of sustainable and efficient
transportation solutions.
Final Thoughts
The internship at the Bhusawal Electric Locomotive Shed was a perfect blend of learning,
practical application, and personal growth. It provided me with a holistic understanding of
electric locomotive systems and the challenges involved in maintaining them. The experience
has prepared me to tackle real-world challenges in the field and has inspired me to continue
learning and growing as a professional. I am grateful to the team at the Bhusawal Electric
Locomotive Shed for their guidance and support, and I look forward to applying the skills and
knowledge I gained in my future endeavors. This internship has been a significant milestone in
my journey as an electrical engineer, and I am excited to build upon this foundation in my
career.
CHAPTER 5
SUGGESTIONS & FEEDBACK

Suggestions/Improvements and Feedback for the MOH Shed Bhusawal
Based on my one-month internship at the Machine Overhauling Electric Locomotive Shed in
Bhusawal, and after studying the documents and discussions, I have identified several areas
where improvements can be made to enhance the efficiency, reliability, and safety of electric
locomotive maintenance. Below are my suggestions and feedback for the industry, presented
in a mixed format to highlight both positive aspects and areas for improvement:
1. Adoption of Advanced Diagnostic Tools
Suggestion: The industry should invest in advanced diagnostic tools such as predictive
maintenance systems, thermal imaging cameras, and real-time monitoring devices. These tools
can help in early detection of faults in transformers, traction motors, and power electronics,
reducing downtime and preventing major failures.
Feedback: While traditional methods like visual inspection and breakdown voltage testing are
effective, incorporating modern technologies can significantly improve the accuracy and speed
of problem identification. The Bhusawal shed already has a strong foundation in maintenance
practices, but integrating advanced diagnostic tools would further enhance its capabilities.
2. Enhanced Training Programs for Technicians
Suggestion: Regular training programs should be conducted for technicians to keep them
updated on the latest technologies and maintenance practices, especially in areas like static
inverters, IGBTs, and MOSFETs.
Feedback: During my internship, I observed that while technicians are highly skilled, there is
a need for more specialized training in modern power electronics and digital control systems
to handle advanced locomotives. The shed’s current training programs are robust, but they
could benefit from more frequent updates to keep pace with technological advancements.
3. Improved Cooling Systems for Transformers and Traction Motors
Suggestion: The cooling systems for transformers and traction motors can be upgraded to more
efficient liquid cooling systems or advanced forced-air cooling systems to prevent overheating
and extend the lifespan of these components.
Feedback: The current cooling systems, though effective, sometimes struggle to manage the
heat generated during peak operations, leading to insulation breakdown and reduced efficiency.
Upgrading these systems would improve the overall performance and reliability of
locomotives.
4. Standardization of Maintenance Procedures
Suggestion: Develop and implement standardized maintenance procedures for all critical
components, including tap changers, notches, and auxiliary systems, to ensure consistency and
quality across different workshops.
Feedback: I noticed slight variations in maintenance practices across different teams, which
could lead to inconsistencies in the quality of work. Standardization would help in maintaining
uniformity and improving overall reliability. The shed already follows a structured approach,
but a more unified protocol could further streamline operations.
5. Increased Focus on Regenerative Braking Systems
Suggestion: More emphasis should be placed on optimizing regenerative braking systems in
both DC and AC traction motors to improve energy efficiency and reduce wear on mechanical
brakes.
Feedback: While regenerative braking is already in use, there is potential to further enhance its
efficiency, especially in older locomotive models, to save energy and reduce operational costs.
The shed’s focus on energy efficiency is commendable, but further optimization could yield
significant benefits.
6. Regular Upgradation of Transformer Oil
Suggestion: Implement a more frequent schedule for testing and replacing transformer oil to
ensure its insulation properties remain effective. The use of synthetic oils with higher
breakdown voltages could also be explored
Feedback: Transformer oil is critical for insulation and cooling, and its degradation can lead to
serious issues. Regular testing and timely replacement can prevent unexpected failures. The
shed already conducts breakdown voltage tests, but increasing the frequency and exploring
advanced oils could further enhance reliability.
7. Automation of Auxiliary Systems
Suggestion: Introduce automation in auxiliary systems such as air compressors, cooling fans,
and HVAC systems to improve efficiency and reduce manual intervention.
Feedback: Automating these systems can lead to better control, reduced energy consumption,
and fewer human errors, especially in large-scale operations. The shed’s current manual
systems are effective, but automation could significantly improve efficiency and reduce labor
costs.
8. Data-Driven Maintenance
Suggestion: Implement a data-driven maintenance approach by collecting and analyzing data
from locomotives in real-time. This can help in predicting failures and scheduling maintenance
proactively.
Feedback: Currently, maintenance is largely reactive or based on fixed schedules. A shift
towards predictive maintenance using data analytics can significantly improve efficiency and
reduce costs. The shed’s current practices are effective, but adopting a data-driven approach
could further optimize maintenance schedules.

My Feedback for the MOH Shed
1. Positive Aspects:
The Bhusawal Electric Locomotive Shed is well-equipped with skilled technicians and stateof-the-art facilities, making it a leader in locomotive maintenance.
The emphasis on regular maintenance and testing, such as the breakdown voltage test for
transformer oil, ensures the reliability and safety of locomotives.
The integration of modern technologies like static inverters and IGBTs in newer locomotives
is commendable and reflects the industry's commitment to innovation.
2. Areas for Improvement:
There is a need for more advanced diagnostic tools and automation to keep up with the
increasing complexity of modern locomotives.
Training programs should be updated to include the latest technologies and maintenance
practices.
Standardization of procedures and increased focus on energy efficiency (e.g., regenerative
braking) can further enhance operational efficiency.

Conclusion of suggestions and feedback
The electric locomotive industry is already highly advanced, but there is always room for
improvement. By adopting modern technologies, enhancing training programs, and focusing
on energy efficiency and safety, the industry can further improve the reliability, efficiency, and
sustainability of electric locomotives.
My internship experience has given me valuable insights into these areas, and I believe that
implementing these suggestions can lead to significant improvements in the industry.