BSNL (Bharat Sanchar Nigam Limited)

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 • Ensures a reliable, effective & user friendly source of 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. Introduction

Valve-Regulated lead-acid(VLRA) Batteries • 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. Freshening Charge

Valve-Regulated lead-acid(VLRA) Batteries • 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. Equalizing Charge

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 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

SMPS (Switch Mode Power Supply) • 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. What is SMPS?

SMPS (Switch Mode Power Supply) • The SMPS regulators are used in B.S.N.L at various locations like CDOT, E 10 B Transmission systems etc. Necessity

50V – 2000A Power Plant • 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. Suitable for VRLA Batteries with 100A SMPS Rectifier Modules

Functional description of power system • Eight racks – One main, one auxiliary and six extension 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. This Power System is of multi rack type and consists of the following:

Functional Description of Rectifier • The SMPS 50V-5600W rectifier is a state-of-the-art switch-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 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 • 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. Introduction

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 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 • Service Earthing Systems • Protective Earthing Systems Earthing systems are provided to serve many different purposes. They may be divided into two major categories :

Requirements for Service Earthing Systems • Service-earthing systems should have a low D.C. resistance to the 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”. • 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. • Able to withstand indefinitely the corrosive action of soil.

Design Principles for Earthing Systems • 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. Earthing systems should be designed to achieve the following:

Telephone Exchanges • 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. The main requirements of the earthing system at a telephone exchange are :

Earth Electrodes • Rod electrodes. • Plate electrodes. • Strip electrodes. • Ring electrodes. Three types of earth electrodes are commonly used for earthing system:

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

BSNL (Bharat Sanchar Nigam Limited)