BSNL
(Bharat Sanchar Nigam Limited)
A
Presentation
On
“Role of batteries and power plant in
telecommunication installations”
Presented by:
Animesh Sinha
G. Geeta
Pankaj Nema
Aman Kumar Saha
Jitendra Kumar
Valve-Regulated lead-acid(VLRA) Batteries
Introduction
 Ensures a reliable, effective & user friendly source of
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power.
It is spill proof, leak proof, & explosion resistant.
There is no need to add water or to clean terminals.
It has a low self discharge rate which eliminates the
need for equalizing charges.
The water loss throughout the life due to gassing is
roughly 0.1% of the total electrolyte present in the
cell.
Valve-Regulated lead-acid(VLRA) Batteries
Freshening Charge
 Batteries lose some charge during as well as during the
period prior to installation.
 A battery should be installed and given a freshening
charge after receipt as soon as possible.
 Battery positive (+) terminal should be connected to
charge positive (+) terminal and battery negative (-)
terminal to charger negative (-) terminal.
 Constant voltage is the only charging method
recommended. Most modern chargers are of the constant
voltage type.
Valve-Regulated lead-acid(VLRA) Batteries
Equalizing Charge
 An equalizing charge is a special charge given to a
battery when non-uniformity in voltage has
developed between cells.
 Under normal operating conditions an equalizing
charge is not required.
 It is given to restore all cells to a fully charged
condition.
Valve-Regulated lead-acid(VLRA) Batteries
Pilot Cell
 A pilot cell is selected in the series string to reflect
the general condition of all cells in the battery.
 The cell selected should be the lowest cell voltage in
the series string following the initial charge.
 Reading and recording pilot cell voltage monthly
serves as an indicator of battery condition between
scheduled overall individual cell readings.
Valve-Regulated lead-acid(VLRA) Batteries
Determination of State of Charge
 Sealed Maintenance Free Valve Regulated Lead Acid
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Batteries represent the state of the art in Lead Acid
technology.
The terminal voltage of the battery is directly related to the
concentration of the electrolyte.
Therefore, if the open circuit voltage of the battery is
measured then, the state of charge can be determined.
The Open Circuit Voltage (OCV) readings should be taken
24 hrs. after charging is discontinued.
The OCV value is co-related to the state of charge of VRLA
batteries as per the table.
Valve-Regulated lead-acid(VLRA) Batteries
 Table for determining the state of charge from the
corresponding Open Circuit Voltage
% State of Charge
Open Circuit Voltage
100
2.15
90
2.13
80
2.11
70
2.09
60
2.07
50
2.05
40
2.03
30
2.01
20
1.97
0
1.95
SMPS (Switch Mode Power Supply)
What is SMPS?
 SMPS means Switch Mode Power Supply.
 This is used for D.C-to-D.C conversion.
 This works on the principle of switching regulation.
 The SMPS system is highly reliable, efficient,
noiseless and compact because the switching is done
at very high rate in the order of several KHz to MHz.
SMPS (Switch Mode Power Supply)
Necessity
 The SMPS regulators are used in B.S.N.L at various
locations like CDOT, E 10 B Transmission systems
etc.
50V – 2000A Power Plant
Suitable for VRLA Batteries with 100A SMPS Rectifier
Modules
 The power system is intended primarily to provide
uninterrupted DC power Telecom. equipments and current
for charging the batteries in the presence of AC Mains.
 The system works from commercial AC mains which is
rectified and regulated to –50V DC and is fed to the
equipment (exchange).
 The system has provision to connect three sets of VRLA
batteries and facility to charge them simultaneously to
ensure that uninterrupted DC power supply is always
available to the exchange.
Functional description of power system
This Power System is of multi rack type and consists of the
following:
 Eight racks – One main, one auxiliary and six extension
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racks.
AC Distribution module in each rack.
Rectifier modules (A maximum of three modules in
extension rack and two each in main rack and auxiliary
rack).
DC distribution module in each rack.
Metering in each rack.
Power system controller in main rack.
Functional Description of Rectifier
 The SMPS 50V-5600W rectifier is a state-of-the-art switch
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mode power conversion equipment.
The unit consists of two cascaded power converters
performing power factor correction and DC/DC conversion.
The power stages are synchronized and working with constant
switching frequency of 100 kHz.
The rectified AC mains voltage is processed first in the power
factor corrector circuit, which is based on a boost topology.
The boost converter has the inherent advantage of continuous
input current waveform, which relaxes the input filter
requirements.
The output of the boost converter is a stabilized 400V DC
voltage.
Functional Description of Rectifier
 Conversion of the stabilized high voltage output of the
power factor corrector circuit is necessary to generate the
isolated low voltage output and to provide the required
protection functions for telecommunication application.
 These tasks are achieved in the DC/DC converter circuit,
which is based on a full-bridge topology.
 The full-bridge circuit is operated by phase-shift pulse
with modulation with current mode control.
 Proper operation of the power converters is managed by
individual controller circuits and supervised by the
housekeeping electronics.
Functional Description of Power System Controller
 Power system controller is designed to control the modes of
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operation of rectifiers, acknowledge and displays the status of
rectifiers and system and controls parameters of rectifiers.
The controller accepts signal from individual rectifiers
through 8-pin telephone jack and controls the operation of
each individual rectifiers.
The mode of operation of rectifier modules depends on the
coded signal M1 and M2 from the controller.
These signals are decoded to display whether the modules are
in auto float/charge or fail condition.
The total battery current can be suitably programmed to limit
the current supplied from the modules through current
programming pin in modules.
Earthing Systems
Introduction
 Earthing is a effective measure of protection from
hazardous electric currents which may result either
due to power induction, lightning or short circuits.
 The charges of electricity could be dissipated by
connecting the charged body to the general mass of
earth through an electrode.
 Earthing for sake of protection is used at practically
every point of the supply network from generators to
the electrical apparatus used by the consumer.
Earthing Systems
Purpose of Earthing :
 Reduction of Crosstalk and Noise:
One pole of the battery (positive pole) is earthed in
the telephone exchange so that cross talk between
the various circuits due to the speech currents of one
circuit finding path through the other via common
battery feed points of the transmission bridge and
reduced NSN via earthed terminal of the battery.
Earthing Systems
Purpose of Earthing :
 Earth is used to afford convenience & reliability, in the operate path
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of the circuits involved in the switching apparatus of telecom
circuits.
Used as return path for the conductors in some telegraph and voice
circuits.
Protection of costly apparatus and persons against foreign voltages
and leakage currents from power wirings to the metallic frame of
the equipment.
Protection of buildings and equipments from lightning strikes.
Earthing in power supply systems is used to effect reliability of
power as it helps to provide stability of voltage conditions
preventing excess fluctuations and providing a measure of
protection against lightning.
Classes of Earthing Systems
Earthing systems are provided to serve many
different purposes. They may be divided into two
major categories :
 Service Earthing Systems
 Protective Earthing Systems
Requirements for Service Earthing Systems
 Service-earthing systems should have a low D.C. resistance to the
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general body of the earth, in order to ensure that the potential drop
across the earth connection is low.
If any current flows through the service earthing system, a potential
difference will be developed across the earth connection.
This can introduce interference in the form of electrical noise into
any telecommunication circuit connected to that earthing system.
The value of resistance which must be met by a service earthing will
depend on the purpose for which the earth likely to be carried by the
earthing system, and the tolerable voltage drop across the earth
connection.
The value chosen by most administrations is usually not more than
ten ohms, although in some isolated cases higher values are
acceptable.
Requirements for Protective Earthing Systems
 The requirements to be satisfied by a protective earthing
system are governed by the purpose for which the earth
is being provided.
 Earths, which protect against excessive current (e.g.
power supply protective earth) must have a low
resistance in order to:
Carry the anticipated value of over current without overheating
and “burning out”.
2. Enable sufficient current to flow to ground to ensure that any
over current protective devices will operate to disconnect the
current after a very short time.
3. Able to withstand indefinitely the corrosive action of soil.
1.
Design Principles for Earthing Systems
Earthing systems should be designed to achieve
the following:
 Adequate current carrying capability (DC or AC as
appropriate).
 Adequate mechanical strength to withstand the
rigorous of service without fracturing.
 In the case of lightning protective earths adequate –
surge-current carrying ability.
Telephone Exchanges
The main requirements of the earthing system at
a telephone exchange are :
 To provide a low resistance path to ground.
 To be able to discharge the maximum anticipated
current, which the earth system is expected to carry,
both under working conditions and under fault
conditions.
Earth Electrodes
Three types of earth electrodes are commonly used for
earthing system:
(1) Rod
electrodes.
(2) Plate
electrodes.
(3) Strip
electrodes.
(4) Ring
electrodes.
Conditions determining the type of earth electrodes system to
be used
 Spike earth electrode system is generally used for all
new auto exchange installations where adequate
space is available and on sub soil suitable for driving
the pipes to the prescribe depth.
 The lead strip electrode system is used when
adequate is available but rock is encountered at a
depth less than 375 cm below ground level.
 Earth plate electrode system is used when layout of
exchange site is such that adequate space is not
available.
IMPORTANT POINTS FOR CONSIDERATION IN
EARTHING
 Chemical treatment of earth using salts etc. are not
recommended as the chemical treatment does not
last long and needs to be checked periodically.
 Earthing conductors should not pass through any
metallic conduit or pipe, as this will increase surge
impedance.
 There should be no sharp bends along the entire
length of earth conductors. Bending should be done
with a radius of one meter.
 All the joint of the similar metals should be
waterproof