Bharat Heavy Electricals limited
Submitted To : Submitted By:
Mrs.Ashita Vermani Mr. AWIK
ET-J, IV Yr
• Bharat Heavy Electricals Limited
• Established more than 50 years
• Today it ranks among the leading
power Equipment Manufacturers in
• Largest engineering and
Manufacturing enterprise in India
• Various energy-related and infrastructure sector
include Power, Railways, Telecom, Transmission and
Distribution, Oil and Gas sectors and many more with
• More than 65% of the installed capacity for electrical
power in India is contributed by BHEL.
• 14 manufacturing divisions, 8 service centers, 4
power sector regional centers, 18 regional offices
and over 150 sites spread all over India & abroad.
• Telecommunication is the assisted
transmission over a distance for the purpose
• It involves the use of electronic devices such
as telephone, television, radio or computer
• Often called Telephone Switch
• First telephone exchange was installed in 1878
• The first switching technology implemented was
MANUAL SWITCHING which required an OPERATOR
• AUTOMATIC SWITCHING was introduced in 1891 and
is of two types:-
1. Electromechanical switching involved –
STEPPING SWITCH called as the STROWGER SWITHING
• It made use of a four number sequence to connect the
call to a neighborhood
• Later on, area codes were created.
2. Electronic switching system
• Stored Program Control
• Made use of computers as central control
• High speed of operation
Powers providing circuits
• Outside the exchange
• Inside the exchange
• Outside the Exchange:
• 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.
• Hence a Rectifier circuit, backed with battery array for power-failures,
• Inside the Exchange:
• Inside the telephone exchange various types of power supplies are
used for powering various modules (for example: - Line-cards,
.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.
TONES USED IN MODERN TELEPHONY
• Heard when handset is picked
• Indicates that exchange is ready to receive dialled
digits from subscriber
• Tone is a continuous burble sound of 400 Hz
modulated by 25Hz
• Heard when the called subscriber is engaged
• 400 Hz signal which is regularly interrupted at equal
• It is generally on for 0.75 sec and off for also 0.75
• Informs the calling subscriber that the called line is
• Has a double ring pattern
• Each ring is separated by 0.2 sec and each double
ring pattern by 2 sec
• Frequency is 133 or 400 Hz
NUMBER UNOBTAINABLE TONE
• Sent when the number dialed cannot be obtained
• Tone of 400 Hz
Frequencies used in Telephony
• High band tone (1216 Hz. to 1645 Hz.)
• Low band tone (701 Hz. to 936 Hz.)
1 to 5 fall in low band
6 to 9, 0 fall in high band
• Off-hook for a tip condition or to describe a
circuit that is in use (i.e., when a phone call is
• On-hook for an idle circuit (i.e. no phone call is
TYPES OF CONNECTION
1) With wires i.e. cables
2) Wireless Microwave Links through
1. Underground cables:
These types of cables run under the
2. Overhead cables
FAULTS IN AN EXCHANGE
1. Faults that occur from Line
• Break fault
"Telephone is dead".
• Loop fault
connectors are shorted
• Earth fault:
Wetting of connectors
Connectors can either touch from earth, with other connector or
with any conductor (such as metallic table, frame etc.)
2 . Faults that occur due to instrument
Dial tone breaks after two or three rings.
Instrument circuitry faulty.
FACILITY OF TELEPHONE
• CONFERENCE-3 PARTY
• LAST CALLER CALLBACK: 851
• APPOINTMENT REMINDER:852 then dial the time
• LAST NO. REDIAL: 854
• 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
• Telecommunication has a significant social,
cultural and economic impact on modern
• Telecommunication is playing an increasingly
important role in social relationships.
• Now-a-days Electronic Exchanges are used.
• Developments have provided opportunities to
go far beyond the vision of telephony on
which this industry was built.