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By: - Shubham Pati Tripathi
Electronics and Communication Engineering
NIT Agartala
Contents
Acknowledgement
Preface
Introduction
Shop 1: Electronics Lab
Shop 2: MRS
Shop 3: SCADA
Shop 4: Telephone Exchange
Conclusion
Acknowledgement I would sincerely like to thank the employees and the officers of DLW, VARANASI for their help and support during 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
Preface
The objective of this training is to learn something about industries
practically and to be familiar with the working style of the technical
world to adjust simply according to the industrial environment.
In this practical world practical knowledge is very important, apart
from the theoretical learning in the college, an industrial training
provides a platform to explore real life experiences of hat we learn
and working around industry professionals help to build a better
spectrum of professional life as an engineer.
My training at DLW, Varanasi was focused on the electronics and
communication related fields in the wide range of jobs in Diesel and
Electrical Engine production.
Introduction to DLW
The Diesel Locomotive Works (DLW) in Varanasi, India, is a production unit
owned by Indian Railways that manufactures diesel-electric locomotives and
its spare parts. It is the largest diesel-electric locomotive manufacturer in India.
Founded in 1961, the DLW rolled out its first locomotive three years later, on
January 3, 1964. It manufactures locomotives which are variants based on the
original ALCO designs dating to 1960s and the GM EMD designs of the 1990s.
DLW has an annual production capacity of 250 locomotives and plans to
increase it to 275 based on the current demand.
About the Training
Diesel Locomotive Works (DLW) has many Workshops for learning and visiting.
These workshops are HWS, HMS, EES, ETS, LMS, LAS, EL, SAS,RS, HTS, LFS, PS,
TMS, TAS, SMS,MRS, LAS, TE, LPS, SCADA and LTS etc. These are the workshops
in the Diesel Locomotive Works (DLW) where student get knowledge about
practical experience.
There are some workshops in TTC (Technical Training Centre) like Fitting shop,
Machine Shop and Welding Shop.
In Diesel Locomotive Works (DLW) I have visited 4 Works shop in four weeks.
These works shop are Electronics lab, Main Receiving Substation (MRS), SCADA
and Telephone Exchange.
Shop 1-Electronics Lab
The lab deals in following areas:
PCB repair tool for third-party repair
shops.
Small to medium volume production.
Card edge testing with the QT-200.
IC testing is performed by QT-200.
QT-200
The lab also deals with maintenance jobs. It is of two types:
BREAKDOWN MAINTENANCE
In this case of maintenance, repair can be done after the break down occur.
Breakdown of machine can occur due to unpredicted failure of components
which cannot be prevented or due to gradual wear and tear of the part.
PREVENTIVE MAINTENANCE
In this case maintenance is done on the basis of predication checking.
This is sometimes called “maintenance maintenance “or “systematic point
maintenance”. It is an extremely important function for the reduction of
maintenance cost, less expenditure of repairs etc.
• Reduction in production downtime.
• Lesser over-time pay for maintenance personnel.
• Lesser number of standby equipments in needed.
• Less expenditure of repairs.
• Due to planned spare parts replacement, lesser spare parts are needed
to remain in store all time.
• Greater safety to employees because of reduced breakdown.
Three devices were introduced at this lab:-
1. Relay
2. Contactor
3. IGBT
RELAY:
It is an EAS which controls the electrical power flow. There are of following
types:
Relay
Controlling Relay Protection Relay
EMR SSR OLR Microprocessor Relay
Power consumption in controlling Relay is lesser compared to Protection Relay.
Protection Relay is used to detect isolated faults in transmission or distribution
system.
Classification based on pole and throw
Application: - Railway signalling relays are large considering the mostly small
voltages (less than 120 V) and currents (perhaps 100 mA) that they switch.
Contacts are widely spaced to prevent flashovers and short circuits over a
lifetime that may exceed fifty years. BR930 series plug-in relays are widely
used on railways following British practice. These are 120 mm high, 180 mm
deep and 56 mm wide and weigh about 1400 g, and can have up to 16
separate contacts, for example, 12 make and 4 break contacts.
CONTACTOR:
A contactor is an electrically controlled switch used for switching an electrical
power circuit, similar to a relay except with higher current ratings. A contactor
is controlled by a circuit which has a much lower power level than the switched
circuit.
It is an electro-mechanical device which has a fixed part and a movable part.
Application: - A magnetic starter is a device designed to provide power to
electric motors. It includes a contactor as an essential component, while also
providing power-cut-off, under-voltage, and overload protection.
IGBT:
An insulated-gate bipolar transistor (IGBT) is a three-terminal power
semiconductor device primarily used as an electronic switch which, as it was
developed, came to combine high efficiency and fast switching. It switches
electric power in many modern appliances: variable-frequency drives (VFDs),
electric cars, trains, variable speed refrigerators, lamp ballasts, air-conditioners
and even stereo systems with switching amplifiers. Since it is designed to turn
on and off rapidly, amplifiers that use it often synthesize complex waveforms
with pulse-width modulation and low-pass filters. In switching applications
modern devices feature pulse repetition rates well into the ultrasonic range—
frequencies which are at least ten times the highest audio frequency handled
by the device when used as an analog audio amplifier.
The IGBT combines an isolated-gate FET for the control input and a bipolar
power transistor as a switch in a single device.
Cross section of a typical IGBT showing internal connection of MOSFET and Bipolar Device
An IGBT cell is constructed similarly to a n-channel vertical construction power
MOSFET except the n+ drain is replaced with a p+ collector layer, thus forming
a vertical PNP bipolar junction transistor. This additional p+ region creates a
cascade connection of a PNP bipolar junction transistor with the surface n-
channel MOSFET.
Shop 2-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
2. Radial System-A single main line runs down the MRS and various
substations are connected to it forming branches.
Generator SUB 1 SUB 2 SUB 3
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.
ACBs are being replaced by SF6 Circuit Breakers in a phased manner.
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/consumption of 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.
Shop 3- SCADA
Supervisory control and data acquisition (SCADA) is a control system
architecture that uses computers, networked data communications and
graphical user interfaces for high-level process supervisory management, but
uses other peripheral devices such as programmable logic controllers and
discrete PID controllers to interface to the process plant or machinery. The
operator interfaces which enable monitoring and the issuing of process
commands, such as controller set point changes, are handled through the
SCADA supervisory computer system. However, the real-time control logic or
controller calculations are performed by networked modules which connect to
the field sensors and actuators.
A SCADA system is used to control physical output through logical input.
In DLW, SCADA is used to control power flow to all sections in the factory and
colony. It is also being upgraded to control motors and all other equipments in
the facility.
The SCADA systems are installed at MRS and all substations and controls are
provided accordingly. The MRS SCADA system acts as parent to all other
substations, i.e.- It’s commands will override all other substations.
A general SCADA screen showing different equipments and substations.
Shop 4-Telephone Exchange
Provides telephone connections to the administrative blocks and colony
area.
The exchange works on a D.C. supply of 50V obtained from battery set
which is connected in parallel to the charger which is operating on 230V
A.C.
The exchange is designed to perform satisfactorily for line loop
resistance of 1000 ohm for each subscriber.
The voltage required when two subscribers talk is 12V.
Block Diagram of Telephone Exchange
Parts in a Telephone exchange:-
Internal Distribution Frame (IDF) - In if the framing of jumper is done .
The cables which are coming out of the exchange are terminated in IDF
and in MDF
1. Crown type
2. Block type
Main Distribution Frame (MDF) - Exchange is also provided in the rack
type of tag block which is called MDF which is the main distribution
frame. In MDF we mount the fuse hold tag at the Back of the Block and
jumper in front.
Distribution Board (DB) - it is the box board in which cable pads are
distributed according to the number which are to be provided near the
distribution .DB are installed after accretion interval of the distance
making a proper distribution of cable which is easier with the consumer.
Distribution Pole- Distribution poles are much nearer to the consumer
here it is easier to take cables from the consumer.
Faults in a Telephone Exchange:-
There are three types of faults-
1. Line Contacts – It mean that the drop wire is connected either with a
pole or a tree if is broken down and a husky voice is obtain when we
ring.
2. Line Earth – It means that drop wire breaks on its own when it touches a
pole or a tree; a soft humming sound comes when we dial a number.
3. Line Disc - The wire has been broken down.
Conclusion
The Four weeks Training program lasted from 01-June-2016 to
28-June-2016 with one week each spent at Electronics Lab, MRS, Telephone
Exchange and SCADA.
A certificate of completion of training was provided
(No. Voc./TTC/DLW/16/1438).
The training program was very fruitful and I got to 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.