This document provides a summary of Vikas Singla's four-week industrial training at BHEL in Hardiwar. It discusses the organization of BHEL and the telecommunications department. It describes the different types of electronic exchanges used, including tone and pulse types, and details the various tones used in telephony systems. It also covers telephone lines, connection types, faults in exchanges, and special user features of different systems.

1. Report on Four Weeks Industrial Training At
BHEL, Hardiwar.
A Training Report submitted in partial fulfillment of the
Submitted by: Submitted to:
VIKAS SINGLA
Reg. No.: (Dy. Manager, Tel.)
Batch No.:
I
requirement for the award of degree of Bachelor of Technology in
“ELECTRONICS & TELECOMMUNICATION ENGINEERING”
Of
COLLEGE OF ENGINEERING ROORKEE.

2. CERTIFICATE
This is to certify that Mr. xxxxxxxxundergoes four weeks training
here from June 30, 20xx to July 30, 20xx in Telecommunication
Department of Bharat Heavy Electrical Limited, Haridwar (UK). His
discipline and performance during the training period was excellent. We
wish him very prosperous and bright career in future.
VIKAS SINGLA
Dy. MANAGER
(TELECOM)
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3. ACKNOWLEDGEMENTS
First and foremost, I would like to thank my respected parents, who
always encouraged me and taught me to think and workout innovatively
what so ever be the field of life. My sincere thanks goes to Mr. Anand
Thakar (Dy. AGM) Telecom for his prodigious guidance, persuasion, and
painstaking attitude, reformative and prudential suggestion throughout my
summer training schedules.
Special thanks go to Mr. V. K. Joshi (Mentor Technician) Telecom,
who helped me a lot in giving minute details of Telecommunication
Department and enlightened me with the knowledge of Exchange
equipments and their working.
My sincere thanks go to all the staff members and friends for
instilling in me a sense of self-confidence.
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4. CONTENTS
1. Introduction.
2. The Organization.
3. Telecommunications.
4. Electronic Exchange(s).
5. Telephone Lines.
6. Connection Types.
7. General faults occurring in an Exchange.
8. Special User Features of Various Exchanges.
9. Optical Fiber System.
10. Maintenance.
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5. 1. INTRODUCTION.
In past few years the field of communication has been developing
with no leaps or bounds. It has become a necessity of each human being to
be connected with each other. Telephone is rapidly becoming a tool to
quench this thirst.
In Automatic Telephony, operators are not required to establish
connections manually between the different calling and the called
subscribers as are required in the case of manual telephone systems. In
these system subscribers those selves establish required connections by
operating the different switches placed at the central place known as the
EXCHANGE from their telephones at remote place from it. The automatic
telephone systems are rapidly replacing manual ones due to their
outstanding merits over the latter types, some of which are enumerated
below:
Fig. 1 Communication System
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6.  In Automatic Telephony higher level of secrecy is maintained due to
absence of operators who can overhear the conversation if they like
in the manual telephone systems. The working of an Automatic
Telephone system does not depend for its efficiency on the personal
efficiencies of the operators.
 There is no possibility of the calls being missed or wrong metering
being done due to faults of operators or due to phonetic errors
between the subscribers and the operators. As no operator is
required, the running cost of the exchange is reduced.
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7. 2. THE ORGANIZATION.
BHEL was primarily set up to meet the needs of the power sector in
the country. The first plant was established nearly 35 years ago at Bhopal,
which heralded the genesis of the heavy electrical equipment in India.
BHEL is today the largest engineering enterprise in India, with excellent
track record of performance, making profits continuously since 1971-72. It
achieved a sales turnover of Rs. 3154 crores with a pretax Profit of Rs.201
crores, in 1990-91.
The areas of BHEL operations broadly cover conversion,
transmission, utilization and conservation of energy in core sectors of the
economy like Power, Industry and Transportation, etc., and fulfill vital
infrastructure needs of the country.
Today, BHEL has 13 manufacturing divisions, 8 service centers and 4
Power Sector Regional Centers, in addition to over 150 project sites spread
all over India and even abroad to provide prompt and effective service to
customers.
BHEL Haridwar is one of the premier organizations which is honored
by I.S.O.-9002 specifications.
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8. 3. TELECOMMUNICATION.
BHEL manufactures EPABX and MAX systems based on C-Dot
technology and has plans to make other ranges of telecommunication
equipment also.
These are basically used for connecting links between various
modules like peripherals, exchange and its equipments. It is necessary to
run a number of internal cables of suitable conductors between the
following stages and frames:-
1. Handset to exchange's cable chamber
2. Cable chamber to M.D.F.
3. M.D.F. to I.D.F.
4. I.D.F. to Number Block
5. Number Block to Exchange Equipment
6. Between two exchanges
7. Between two cities
8. Between two countries
Prior to advent of Electronic Exchanges inter-connection of various
circuits are made by mechanical contacts that are operated by mechanical
movements produced by the attraction of an iron armature of an electro-magnet
or by the operation of an electric motor. There are some
disadvantages of such systems for using mechanical contacts, due to
following reasons:
· Contacts are subjected to wear and tear.
· Require adjustments time to time.
· Maintenance is highly precise.
· Prone to corrosion. etc...
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9. But now-a-days Electronic Exchanges are used. In Electronic
exchange electronic devices effect the inter-connection between different
transmission circuits and Electro-mechanical relays and switches are
dispensed with. Such electronic devices remove difficulties associated with
mechanical contacts. The greatest advantage of using electronic devices in
place of electromechanical devices is that no time is loosed in making a
connection and a very high speed of operation is possible.
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10. 4. ELECTRONIC EXCHANGES.
Electronic Exchanges are of two types:
1. Tone type
2. Pulse type
1. Tone type: In this type of exchange sine waves are used. There
speed of dialing for a given number is more than that of Pulse type.
2. Pulse type: In this type of exchange square wave is used due to
which the dialing speed is lesser. The telephone apparatus used for
both types are different in construction. But now days both types of
apparatus are integrated in a single machine in which switch-over can
be made via a selector switch.
Tones used in modern telephony
1. Dial Tone: When handset is picked up from the cradle, then Dial
tone is heard if a free line is available. This means that the instrument
is ready to send the signals to the exchange. When the subscriber
takes up the receiver then signals are sent M.D.F. then to I.D.F., line
Number block and to Peripherals where in various line-cards are
mounted in a shelf. When corresponding number on the line-card is
free then the Ringer section of that Peripheral generates a signal
called tone. This tone is a continuous burble sound of 400 Hz.
modulated by 25Hz. and is sent to the calling subscriber as soon as
his line seizes the free line. The subscriber must not dial before
receiving this tone; otherwise he is liable to get wrong connection. If
he does not get this tone, he should try after some time.
2. Busy Tone: When the called subscriber is engaged with other call,
this tone is heard. It consists of a sound of 400 Hz. which is regularly
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11. interrupted at equal intervals. It is generally on for 0.75 sec. and off
for also 0.75 sec.
3. Ringing Tone: When a number is dialed by calling subscriber, the
telephone of the called subscriber starts ringing. Calling subscriber
should get this information and this is indicated by sending ringing
tone of interrupted 400 Hz. supplies modulated by 25 Hz. and its
durations are generally equal to the duration of ringing current, which
rings the bell. It may be 0.4 sec. on, 0.2 sec. off , 0.4 sec. on and 2
sec. off and so on or it may be 0.75 sec. on and 0.75 sec. Off and so
on. When this ringing tone is received, the calling subscriber knows
that the connection is completed and that the bell of the called
subscriber is ringing.
4. Number Unobtainable Tone: This tone is sent when the number
dialed cannot be obtained. If any subscriber dials which is not actually
connected to the exchange, this indication is send. This is also a tone
of 400 Hz. with interruption of 200 msec. every 3 sec.
Now-a-days push button type telephone apparatus are used. This
apparatus can be exploded into following sections:
a. Ringer section
b. Speech section (Transmitter and Receiver section)
c. Voltage limiter section
From telephone exchange two wires or connectors run for each
number, in which one is neutral and the other is main or positive. For the
telephone circuit to work the necessary supply is provided by the
exchange. Like other circuits telephone also operates when a circuit is
established between calling and called subscriber. When one dials a
number then the corresponding relays at the exchange established a circuit
automatically. The telephone exchange supplies 40-60 volt D.C. and
110/20 Hz. to operate this circuit. This is required because of voltage drop
that may creep in long transmission wires. As soon as the handset is
picked-up this 48-volt D.C. supply is available at voltage limiter section,
dialing pulse generator and speech section.
In telephone dialing two types of frequencies are used which are:
a. High band tone (1216 Hz. to 1645 Hz.)
b. Low band tone (701 Hz. to 936 Hz.)
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12. Frequencies used in Telephony
The numbers from 1 to 5 falls in low band and 6 to 9, 0 falls in high
band. Till the handset is on-hook, the ringing section of the apparatus is on
through telephone line but on lifting the handset the ringing section
becomes off, also the dialing and speech section becomes ready. On lifting
the handset first the dial tone is received which is amplified by the amplifier
of speech section.
When a number is pressed on the keyboard, the dialing pulses are
made on and off according to the number dialed. For example if 5 is
pressed then dialing pulses are made on and off 5 times. This process can
be heard on the receiver. There is a gap of 1 sec. between consecutively
pressed numbers.
When the handset is placed on or is lifted from the instrument a
switch is operated called the hook-switch. The main function of this switch
is to toggle between telephone-line and ringer, dialing & speech sections of
the telephone. When the handset is on the telephone then ringer section of
the telephone is on while on lifting it ringer section is disconnected and
dialing section is connected.
Process of making telephone call:
Telephone call is characterized into two sections:
1. Outgoing calls: Generally a voltage of 48V-60V D.C. always
remains on the telephone line but as the handset is picked-up the
voltage limiter drops this voltage to 9-12V. On hearing the dial tone it
is confirmed that the apparatus is ready to work and after dialing the
number a ringing pulse is send to the called party. When the calling
party picks-up the handset the billing meter of the exchange becomes
activated. There is a counter in the exchange, which counts the pulse
and converts them into calls.
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13. Fig. 2 Electronic Exchange
2. Incoming calls: These are just opposite of outgoing calls. In the
incoming calls the telephone detects the ringing signal from the
exchange and provides the ring. At the instance of ringing signal,
there remains a voltage of 75-110V/20 Hz. on the telephone. A high
voltage (A.C.) is sent from the ringer section of the exchange to start
the ringer circuit of the telephone. When the ringing signal is received
it should be properly isolated as it may give a shock. This ringing
circuit is on until the handset is not picked-up at the called party. The
duration of this tone, if unattended, is 1 minute after which an engage
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14. tone is heard. After lifting the handset a circuit is established and a
call is made.
There are various powers providing circuits available in the exchange
to run the circuitry. These are broadly categorized in two categories:
a. Outside the exchange
b. Inside the exchange
Outside the Exchange:
Since the voltage supplied in Indian Subcontinent is 220-volts/50 Hz
A.C. But for the normal working of the exchange 48(46-53) volts of D.C. is
required.
Hence a Rectifier circuit, backed with battery array for power-failures,
is used. This rectifier block not only rectifies the input supply but also works
as a battery charger. It is known as Float rectifier cum charger.
Battery backup is utilized for smooth operation of the exchange
during power failures. For battery back-up lead acid battery array is used in
parallel to the supply from the rectifier block, so that during power failures
the exchange supplies are not terminated.
Inside the Exchange:
Inside the telephone exchange various types of power supplies are
used for powering various modules (for example: - Line-cards, Ringer).
Some of them are: -
o -5 V. 12 A
o +5 V. 12 A
o +12 V. 6 A.
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15. From M.D.F. a number of cables, based upon the requirement of a
place, are connected to cabinets. On the cabinets these cables are divided
into cables of 20 pairs. Now every 20 pair cable goes to the distribution box
(D.B.). At the D.B. this 20 pair cable is further divided into two parts of 10
pairs each. These pairs are then connected to the subscriber ports via
jumpers. The line from these ports then goes to the subscribers through
single pair cables which are usually of P.V.C. type. These wires are
connected to the instrument via Rosette-Box.
M.D.F. :
This frame serves the following purposes: -
1. It is place where both external and internal cables are terminated.
The external individuals cable carry conductors from subscribers who
are necessarily from the same locality and as such their numbers
cannot be in numerical order. On the other hand, the internal cable
conductors come from apparatus side in numerical order. This cross-section
between the two cables is done on the M.D.F. through jumper
wires.
Fig. 3 Old M. D. F.
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16. Fig. 4 New M. D. F.
2. It carries all the protectors used in the exchange. The different
protectors that are used are (a) Fuses, (b) Heat coils and (c)
Lightning protectors.
3. This M.D.F. is an ideal place for testing purpose. Both the internal
and the external cables are available at this frame and, therefore,
both external and internal wiring and lines can be tested for this
purpose.
I.D.F.:
These frames like M.D.F. consists of a large number of verticals with
horizontal cross-arms fitted with tag blocks at both the ends. The cable
from M.D.F. is terminated on the multiple sides from where connections are
extended to metering and from the exchange side cables are run to the
respected line-cards. The two tag blocks are joined by means of jumper
wires as in the M.D.F., so that any subscriber can be given connection to
any uniselector on the line-card. The subscriber and, therefore, their
uniselectors are divided into different groups and it is necessary for these
groups to originate more or less the same amount of traffic for smooth
distribution among different trunks.
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17. 5. TELEPHONE LINES.
In BHEL-Haridwar three types of telephone lines are used. They are:
a. MAX Lines
b. EPABX Lines
c. C-DOT Lines
1. MAX Lines: Before MAX Ex. Lines are used only Internal Exchange.
But New (CORAL) MAX lines are used for both internal (Intercom)
and external communication links BHEL.
2. EPABX Lines: EPABX lines are used for both internal and external
communication links in BHEL. If the user wants to dial outside the
periphery of BHEL, he can use these lines. There are about 500 lines
available here. These lines are distributed in 17 line-cards with 24 line
numbers in each. Its I.D.F. section has 40 tag blocks. 96 numbers
available here are connected via digital lines in which a host of
facilities are provided that can be accessed using code 69.
3. C-DOT Lines: These lines are the direct telephone lines from C-DOT
The facility they provide is called DID (Direct Inward Dialing). It
has 24 lines and any BHEL number starting with digit 5 can be
accessed using code 48.
Fig. 5 BHEL Network
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18. 6. CONNECTION TYPES.
Types of Connections:
a. With wires i.e. Cables
b. Wireless Microwave Links through Satellite
Cables: Basically two types of cables are used. These are:
1. Underground cables: These types of cables run under the earth and
are basically used to connect the exchange to the subscriber's
Distribution Box (D.B.). They are further of two types based upon
their construction and the insulating material used.
a. Paper core A.T.C. (Armored Tin Cable)
b. Jelly filled A.T.C. (Armored Tin Cable)
2. Overhead cables: These types of cables are used to connect the
equipments inside the exchange and to connect the peripheral
devices to the subscriber's Distribution Box (DB).They are generally
of P.V.C. type.
In an exchange, based upon the number of conductor pairs, following
types of cables are used:
a. Single Pair cable
b. Two Pairs cable
c. Five Pairs cable
d. Ten Pairs cable
e. Twenty Pairs cable
f. Fifty Pairs cable
g. Hundred Pairs cable
COLOR-CODING:
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19. Type of Cable Color of Wires
Single pair Blue-White
Two pair cable Blue-White/Orange-White
Five pair cable Blue-White/Orange-White/Green-White/Brown-
White/Grey-White
Ten pair cable Blue-White/Orange-White/Green-White/Brown-White/
Grey-White/Blue-Red/Orange-Red/Green-
Red/Brown- Red/Grey-Red
Twenty pair cable Blue-White/Orange-White/Green-White/Brown-
White/Gray-White/Blue-White-Blue/Orange-
White Blue/Green-White-Blue/Brown-White-
Blue/Gray- White-Blue/Blue-White-Orange/Orange-
White Orange/Green-White-Orange/Brown-
White- Orange/Gray-White-Orange/Blue-
White-Green/ Orange-White-Green/ Green-
White-Green/Brown White-Green/Gray-White-
Green.
For hundred pair cable the color-coding is same as that of the above 20
pair cable except that the mate color is changed after each bunch of 20
pairs.
Pairmate Color 1st 20 pair white, 2nd 20 pair yellow, 3rd 20 pair
black, 4th 20 pair violet and 5th 20 pairs red
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20. 7. General Faults Occurring In An
Exchange.
There are mainly two types of faults that often occur in the Exchange.
These are basically
a. Faults that occur from Line
b. Faults that occur due to Instrument
1. Faults that occur from Line: Due to line three types of faults may
occur. They are categorized as under:
a. Break fault: They are also called as Disconnection faults. They
can occur in the connectors at home, in line or in exchange. In
common they are broadly called as "Telephone is dead".
b. Loop fault: They are also called as Line-Shorting faults. In this
fault connectors are shorted prior the instrument forming a local
loop. If unattended for a long time they may cause severe
damage to the Exchange.
c. Earth fault: This fault may occur due to:
i. Wetting of connectors
ii. Water in Rosette-Box
iii. Weak insulation or
iv. Oxidation of copper wire
v. Connectors can either touch from earth, with other
connector or with any conductor (such as metallic table,
frame etc.)
 Problems that can occur due to line faults:
a. Subscriber may not dial a number.
b. Ring Trip i.e. connection from the exchange breaks after one ring.
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21. c. False Ring
d. Low speech
e. One sided speech
2. Faults that occur due to instrument: These may be:
a. The number is not being dialed
b. One way speech
c. Receiver coil is faulty
d. Plunger or Push switch faulty: Dial tone breaks after two or
three rings.
e. From second subscriber bell is heard to be going but at first
subscriber only dial tone is heard.
f. Instrument circuitry faulty: When loop or earth fault is
received than exchange can be affected so it is wedged as
soon as possible because if not wedge for longer it can damage
line-card too.
To sense these faults first line-side is checked and then exchange
side is checked at exchange. If however exchange side is correct then line
faults after detection are handed over to the concerned lineman for further
checking.
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22. Fig. 6 Testing Procedure 1
Fig. 7 Testing Procedure 2
Fig. 8 Testing Procedure 3
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23. Fig. 9 Testing Procedure 4
Fig. 10 Testing Procedure 5
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24. Fig. 11 Testing Procedure 6
Fig. 12 Testing Procedure 7
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25. Fig. 13 Testing Procedure 8
8. LIST OF SPECIAL USER FEATURES ON
VARIOUS EXCHANGES.
1. MAX (CORAL INDIA PVT.LTD.NOIDA)
Manufacturer: - JEUMONT SCHINEDIER, FRANCE
Capacity: - 2700 lines
CALL PICK UP: 89-xxxx to pick up a call ringing at another location
xxxx.
CALL TRANSFER: 2 Parties conversing, any party can dial 3rd
party, then conversation among them Hang-up. The party on line
now talks to 3rd party.
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26. PARTY CONFERENCE: While speaking with a party:
From Pulse Instrument: -- If CALLER requires dialing 3rd party
During conversation and maintaining talks, then dial 4.
From Tone Instrument: -- If CALLER requires dialing 3rd party
During conversation and maintaining talks, then flash, and dial
4th one.
MALICIOUS CALL TRACE: Dial 29 during conversation, to trace a
malicious call From a MAX Extension. Then enquire from 4999 or 4424.
APPOINTMENT REMINDER: Dial 80-xx-yy {xx=hr, yy=min}.
To Cancel: Dial 27.
2. EPABX=ALCATEL 4400
Manufacturer: - ALCATEL, FRANCE
Capacity: - 500 lines (96 DIGITAL, 404 ANALOG)
Technology used: - P.C.M. - T.D.M.
TONE MODE DIAL: Dial # before no.{If instrument is not tone enabled )
CALL TRANSFER: Hook FLASH: Do Hook Flash - On hearing prompt
"Please dial." Dial the no., wait for party to respond, then Disconnect.
ENQUIRY CALL: FLASH (from Tone mode instrument.) or 2 (from
Pulse mode). During conversation to put the party on HOLD. Then, dial
a 3rd party and speak.
BROKER CALL: (After ENQUIRY CALL): Dial 1 to go BACK & FORTH,
between two parties (one party in conversation & other on HOLD)
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27. CONFERENCE-3 PARTY: While talking to 1st party, first make
ENQUIRY CALL (Put on hold) {FLASH from Tone; or 2 from Pulse}.
Then - Dial 3rd party - Flash-- Dial 3.AUTO CALLBACK: Dial 5 to book
auto-callback when a busy PABX hangs up. To cancel auto-callback
request: Dial 67 or/and 848) PASSWORD MODIFICATION: 847-0000-
xxxx (0000=old password; xxxx = new Password). This facility is
available on STD enabled extensions only.
LAST CALLER CALLBACK: 851 {to ring the last unattended PABX
Caller}
APPOINTMENT REMINDER: 852 then dial the time as {xx (hr) xx
(min)}. To cancel: 853
LAST NO REDIAL: 854 User can use this if instrument. Doesn’t have a
Redial Button.
CALL PICKUP: 72 - XXXX to pickup a call ringing at another extension.
CALL-PARK / RETRIEVE: It is used during an incoming or outgoing
call, to speak from a different set. (To park from own (speaking) set:
FLASH-855- dial own extension number. Then "Hang-up". The call is
now parked, and the other party is kept on hold. (To pick up from a
different set: 855- dial own extension number) (To pick up from own set
(later, if not taken elsewhere) 855)
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28. 9. OPTICAL FIBER SYSTEM.
Fiber optical transmission medium is fast emerging as an alternative
and strong competitor to coaxial cables in telecommunication networks.
Long distance data transmission in electrical cables suffers from
ground loop problems. The merits of the optical fiber stem from the fact tat
the basic material used in their construction is nonmetallic and electrically
non conductive.
In contrast, the nonmetallic and totally dielectric fiber optical cable are
immune to radio frequency another electromagnetic interferences. Ground
loop and common mode voltage problem do not exist and data can be
transmitted between points of vastly different potential. In optical cables the
information is transmitted by packets of photons which have no charge.
There is no possibility of sparks or short circuit when a fiber is cut. The
bandwidth high compared to that of the electrical cables. The standard RG-
58 coaxial cable has bandwidth distance product of a typical optical fiber is
about 100 MHz-Km.
Fiber cables are about the thickness of a human hair any dirt
obstructing the optical port causes poor transmission. The thin dimension
results in a low weight for given length when compared to electrical cables.
However, being thin and somewhat brittle in nature, fiber tend to break
easily if bent beyond a certain limit a direct viewing into the optical point
can be harmful to the eyes.
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29. 10. MAINTENANCE.
The subject of maintenance of Automatic Telephone Exchange can
be broadly divided under two categories: -
a. Prevention of Service Failures
b. Location of Faults and their removal
Prevention of Service Failures: It can be done in following ways: -
1. Suitable design and adoption of suitable adjustment standards of the
equipment parts of the exchange can minimize failures in service.
2. Some preventive measures may also reduce service failures viz.
keeping the rooms dust free, maintaining temperature and humidity
under tolerable limits using air-conditioners etc...
3. Routine inspection, routine tests and routine adjustments also help in
preventing service failures.
4. When faults occur in some parts of the exchange, they should be
detected and removed as quickly as possible.
5. Various tools are also used to check the faults in the telephone lines.
6. For checking fault inside the exchange
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