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Telecommunications Energy Conference, 1994. INTELEC '94., 16th International

Date Oct. 30 1994-Nov. 3 1994

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Displaying Results 1 - 25 of 104
  • Proceedings of Intelec 94

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    Freely Available from IEEE
  • A recommendation for centralized powering of local network elements

    Page(s): 108 - 114
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    The challenge for the telecommunications power engineer is to devise a cost-effective and reliable means of providing power for telephone sets (POTS) over an evolving local network in a manner that allows a smooth transition to the network envisioned. This paper discusses the networks, reviews proposed powering arrangements, and recommends that centralized powering of network elements, with hybrid arrangements for wideband services, be used wherever possible View full abstract»

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  • The impact of AC power line disturbances on telecommunications rectifier technologies and powering architectures

    Page(s): 413 - 419
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    Switch mode rectifier (SMR) design needs to consider AC distribution, voltage sags and surges, power line notches and voltage transients, including their causes and effects. Influence from lightning has to be more carefully considered. Also the utility load and grid switching, as well as load changes in the AC distribution network close to SMR power plants, are now important considerations. The author discusses these factors and their effects on the SMR View full abstract»

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  • Constant-power rectifiers for constant-power telecom loads

    Page(s): 630 - 634
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    Constant-power loads that dominate in telecommunication plants feature a constant-power characteristic. Because of this they draw more current at a lower supply voltage than in normal operating conditions. If not over-sized, a power supply plant with constant-current rectifiers can latch after an interruption of the input line, and then the battery remains discharged. This paper shows that the use of rectifiers with constant-power output characteristic is an economic way for avoiding costly over-sizing or a risk of potential system breakdown View full abstract»

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  • A review of single phase power factor correction circuits for telecommunication applications

    Page(s): 334 - 338
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    This paper presents a comparative performance of resonant, soft-switched and hard-switched single phase power factor corrected rectifier circuits for telecommunication power supply applications. Three practical rectifiers employing a boost pre-regulator and a resonant, soft-switched and hard-switched DC/DC power converter topologies respectively are built in the laboratory for the same set of requirements. It is shown that the resonant rectifier has higher efficiency than other two rectifiers. All the three rectifiers with forced air cooling are found to have the same size View full abstract»

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  • Small size and low weight DC/DC converter with no magnetic elements

    Page(s): 573 - 580
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    A new type of DC power supply containing no inductors or transformers is presented. The DC-to-DC boost power converter contains only switches and capacitors. The switching-capacitor circuit is used for controlling the DC energy transfer from an unregulated input voltage to a regulated output. The output voltage is kept constant despite large variation in the input voltage or load. The power converter operates at a constant switching frequency, the regulation being of PWM type. The operation of the main switches in the energy flow path is dictated by the output of a PWM chip. The absence of magnetic elements in the power converter structure guarantees an overall small size, low weight and high power density. The design of the circuit parameters (capacitor values and switching frequency) assures minimum losses of energy at the switching moments. The transient currents have nondangerous peaks; consequently, no overrating of the transistors is necessary, assuring small conduction losses. As a result, the new power converter presents high efficiency. Experimental results, obtained on a prototype built according to the exposed design procedure, are presented View full abstract»

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  • A high efficiency 150 W DC/DC converter

    Page(s): 148 - 154
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    The authors have devised a series resonant circuit, for telecommunication power supplies, in which the charge stored in the parasitic capacitor of the switching device is discharged by the magnetizing current of the transformer in order to reduce loss. In this paper the authors study the details of this new soft switched multi-resonant zero-current-switching converter and report on the modal analysis and the experimental results. They have succeeded in obtaining a high efficiency of 96% in the conversion circuit in an experimental circuit with an input of 15O Voc and an output of 5O Voc at 3A. The features of this circuit are as follows: (i) this is a multi-resonant converter with three resonant operations; (ii) the voltage of the resonant capacitor is charged by the magnetizing inductor of the transformer and the constant voltage regulation is performed by charging the peak value of the resonant current greatly; the lower the switching frequency, the larger the power obtained; (iii) the switching frequency varies little in the whole range from zero to full load; (iv) the voltage in the primary winding of the transformer shall be a half or more of the input voltage; and (v) at turn-on both zero-voltage-switching (ZVS) and zero-current-switching (ZCS) are achieved, and at turn-off only ZVS is achieved View full abstract»

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  • Alternatives for powering the hybrid fiber/coax networks

    Page(s): 83 - 89
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    The characteristics of three types of power distribution systems for a drop segment of a hybrid optical fiber/coaxial cable telecommunication architecture are compared: DC; low frequency AC; and high frequency AC. It is shown in the paper that the high frequency distribution system has potential advantages in terms of high efficiency, small size of power converters, and low cost of powering. A prototype system which distributes 30 V (RMS) at 128 kHz over coaxial cable is built and experimental results are given which support the high frequency distribution as an attractive and viable option View full abstract»

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  • Tests on valve regulated lead acid batteries at different environmental temperatures and float voltages

    Page(s): 172 - 175
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    This paper describes the behaviour of two different types of valve regulated lead acid batteries which have been exposed to environmental temperatures between 22 and 37°C and at different float voltages. Temperatures inside the batteries and float currents are monitored. Significant difference in performance have been observed between the two battery types View full abstract»

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  • Impedance testing-is it a substitute for capacity tests?

    Page(s): 245 - 249
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    Capacity tests are used to reliably determine lead acid battery capacity. The results of the capacity tests are then used to evaluate whether the battery can continue in service or needs to be replaced. Unfortunately, many batteries do not receive regular capacity tests. This occurs because of perceptions that: the test is difficult to perform; takes too much time; the battery is too important to be removed from service for a test; is too costly, and so forth. Few consider the consequences of a failure that causes the loss of a facility where down time lost revenue is measured in millions of $US per day or even millions of $US per minute. The measurement of battery impedance (or conductance, or internal resistance) has come into vogue. At this point in time, many in the industry have agreed that these tests are useful in detecting problem cells. However efforts are also underway to convince battery users that these tests can replace capacity tests. This paper reviews the internal battery impedance components and shows that internal resistance rather than impedance is the parameter that is important to measure. It also discusses the change in battery impedance as the cell ages. The paper describes how the measurements are made and provides an analysis of the impedance measurements. This analysis includes a discussion of published results of impedance testing to date. Finally, a comparison is made between capacity and impedance tests View full abstract»

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  • Analysis and interpretation of conductance measurements used to assess the state-of-health of valve regulated lead acid batteries

    Page(s): 282 - 291
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    This paper presents data showing conductance aging of new valve-regulated Pb-acid (VRLA) secondary cells and capacity/conductance aging of older cells. It presents data showing the comparative accuracy of several techniques for selection of a cell conductance value suitable for use in field determination of cell pass/fail conditions based on either capacity failures below 80% or below 50% of rated value. The accuracy of the various selected conductance values are determined by actual comparison to cell by cell capacity/conductance data. This data represents 192 cells of 1000 Ah (ampere hour) size in 48 volt telecom use and 96 cells of 600 Ah size in 24 volt strings in another type of telecom usage. The data presented should allow the user to select a technique which appears most suitable to his needs and capabilities View full abstract»

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  • Environmental issues in remote telecommunications sites: hydrogen evolution of VRLA batteries in cellular installations

    Page(s): 163 - 167
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    Modern telecommunications deployment increasingly involves the use of remote sites. Equipment is housed in enclosures that range in size and scope from large concrete buildings containing entire switches to small cabinets containing a few lines of transmission equipment. In most cases, reserve energy during AC power failures is supplied from lead acid batteries collocated with the electronics within the enclosure. The fact that all lead acid batteries generate hydrogen continuously during their operation is an important design parameter for both the enclosure, and the equipment which the batteries are designed to support. While much published material has dealt with VRLA battery operational issues such as hydrogen evolution and thermal runaway from a design and engineering viewpoint, this investigation has attempted to represent a users perspective. In determining the capabilities and limitations of both the batteries and their end users the paper attempts to present some real world principles to aid successful applications. While predominantly focussing on wireless, such principles could also apply to other outside plant type applications View full abstract»

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  • Powering Telstra's broadband and multimedia services

    Page(s): 3 - 6
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    The authors briefly describe the evolution Telstra's broadband and multimedia networks in Australia. They then discusses the power issues. Telstra has used traditional centralised DC power systems to power exchange equipment and basic telephony services to customers. With the advent of switchmode rectifier and VRLA battery technology, distributed power architectures are preferred as they provide improved power system availability by reducing points of failure both on the DC and the AC circuits. Distributed power also offers an integrated and modular solution to the diversity of growth. These networks have also accelerated the use UPS in exchanges to power computing, media storage and video headend facilities. In particular the authors discusses the powering of a single fibre passive optical network View full abstract»

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  • On the low-frequency noise of DC-to-DC converters with random-switching control

    Page(s): 451 - 456
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    The low-frequency output noise that is caused by introducing random-switching control into the DC-to-DC power converter is discussed quantitatively. A modified power converter model involving the unintended effect of random switching is derived from the consideration of noise-generation mechanisms. After a theoretical analysis based on the model, it is clarified that the magnitude of output noise is in proportion to the variance of switching interval. Experimental results from a buck-type power converter are compared with those obtained theoretically, so that the validity of the theoretical results is confirmed View full abstract»

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  • Case studies of central office cable tray support failures

    Page(s): 219 - 223
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    Concrete anchor devices are an extremely important consideration when designing for network reliability. Most telephone central office cabling is supported on overhead cable racks or trays. Stored program control switching systems (SPCS) frames and modern transport equipment frames tend to be approximately 7 feet (178 cm) tall. Express cable trays to the power plant and main distributing frame (MDF) areas are usually supported by an auxiliary framing grid suspended from the ceiling slab. From a structural and earthquake protection viewpoint, both the equipment frames and the overhead structures are now separate and independent systems. This is a superior design plan, especially where building vibration or seismic activity is a consideration. Since metallic cabling, especially copper power cables, are quite heavy, all support elements must be capable of handling massive loads safely and reliably. Virtually all of the weight is borne by cast-in-place structures such as ceiling inserts, and embedded channel struts, or by anchors which are drilled and set by a variety of fastening systems. Two cable tray collapse failures in eastern Pennsylvania underscore the fact that some anchor designs are more prone to failure than others. This paper describes case studies of the two failures, and their root-cause investigations. Additionally, the paper discusses the results of dynamic pull-out tests, performed both in the laboratory and the field, on several traditional and newer style anchor designs, exploring their merits and drawbacks View full abstract»

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  • Electrical protection for multimedia workstations

    Page(s): 238 - 244
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    Electrical protection for multimedia workstations is essentially dependent upon the product safety listing process. In other words, workstation assemblies and peripherals utilize power, grounding and protection schema that are necessary to obtain the listing mark (such as UL or CSA) for certified product safety. At the time of writing, there is no standard that specifically addresses workstations. This paper explores the acceptability of depending upon just the product safety listing for suitability of electrical protection. A straightforward methodology is applied to determine to what level additional site conditioning may be necessary. The author deliberately utilizes existing codes, standards, draft standards and leading industry articles to illustrate that a straightforward resolution is feasible View full abstract»

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  • A novel three-phase utility interface minimizing line current harmonics of high-power telecommunications rectifier modules

    Page(s): 367 - 374
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    Based on the combination of a three-phase diode bridge and DC/DC boost converter a new three-phase three-switch three-level PWM rectifier system is developed. It can be characterized by sinusoidal mains current consumption, controlled output voltage and low blocking voltage stress on the power transistors. The application could be, e.g., for feeding the DC link of a telecommunications power supply module. The stationary operational behavior, the control of the mains currents and of the output voltage are analyzed. Finally, the stresses on the system components are determined by digital simulation and compared to the stresses in a conventional PWM rectifier system View full abstract»

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  • Operation of from power soft-switched phase-shifted full-bridge dc-dc converter under extreme conditions

    Page(s): 142 - 147
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    No-load and short-circuit conditions are analyzed for the soft-switched phase-shifted full-bridge DC-DC power convertor topology. Some potential problems are identified and possible solutions are discussed View full abstract»

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  • Imperfectness as a useful approach in battery monitoring

    Page(s): 481 - 485
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    Ability to monitor secondary battery state of health and state of charge has become increasingly important. Earlier methods were entirely based on cell or block voltages. In the case of valve-regulated batteries, information of plain cell or block voltage can no longer be used as a sign of failure due to high normal deviation. Discharging a battery is still the only reliable method by which battery state-of-health and state-of-charge can be verified. This paper describes a practical and simple method, as well as the circuitry used, for a battery monitor. The method is based on measurement and comparison of the voltage differences of series connected battery blocks in a way which reduces the number of measurement channels as well as comparisons. For a typical 24-cell battery string containing four 12 V monoblocks, the measuring channels and comparison needed are three. The monitoring process also contains periodical battery discharges. The discharge interval and time can be chosen to ensure sufficient reliability and availability performance of the battery system View full abstract»

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  • The central office power plant of the future

    Page(s): 517 - 522
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    The author describes an integrated system approach which would create a comprehensive power system that would have the flexibility to serve the power needs of the future central office, with systems to support multimedia and various operational support systems. All requirements for surge immunity, even higher than normal, could be met in a manner where a complete pre-engineered, pre-packaged, pre-constructed system would exist. This would remove the traditional E, F and I tasks from the process thus contributing to predictability, easy of installation, ease of expansion, higher reliability and lower service costs, less debate about how to construct each local site, better customer relations, and a higher quality system that would be verified before leaving the factory View full abstract»

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  • Rectifier input current distortion-how much can be permitted? Implications of existing standards and other considerations

    Page(s): 407 - 412
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    Harmonic pollution of electrical power systems is a subject of increasing importance. Power converters are a type of load that generates current harmonics, and the designers of converter equipment are highly concerned with this problem. Two existing standards, the European EN 60 555-2 and the American IEEE Std 519 formulate the requirements on harmonic contents. This paper analyses these standards and their practical implications. It is shown that (a) there is a certain ambiguity in applying EN 60 555-2, (b) although IEEE 519 refers to the power system, not to the equipment, it is possible-by some additional analysis-to formulate the requirements on the AC/DC converter equipment, and (c) despite the differences in the approach, both standards result in similar requirements. Additional considerations are necessary to determine the allowable distortion values. One such consideration is the case of supply from an emergency set diesel engine alternator. Any rectifier design should consider the eventuality of supply from an emergency set of limited power rating. The emergency set is a soft source with high internal impedance. In this case rectifier current harmonics can cause excessive voltage harmonics in the AC distribution, resulting in a severe degradation of service. This paper describes a procedure to determine the permissible requirements on voltage quality-including the case of emergency set supply. On the basis of this analysis, a value of allowable input current distortion is proposed View full abstract»

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  • Standardizing energy management by using simple network management protocol

    Page(s): 537 - 542
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    The evolution within the area of management of telecommunications networks has developed rapidly. Management functions and interfaces have been standardized by standardization bodies. However, most of that work has been towards management of the transmission and switching network element. The development of energy network elements does still lack when it concerns functions and interfaces. It is costly to implement Q3 interfaces and adapters for the energy equipment mostly due to the complex hierarchy of the CMIP protocol stack. As the telecommunication network and computer networks tend to grow together a “new” interface has been discovered, the SNMP interface. This paper deals with the functional and implementation aspects of using the SNMP interface for management of energy networks. The details in this paper cover: the system architecture of an SNMP based energy management system; management functions by using SNMP interfaces; the modelling of a management information base for an energy network; and SNMP versus CMIP View full abstract»

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  • Some field experience with battery impedance measurement as a useful maintenance tool

    Page(s): 263 - 269
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    This paper reports on the initial findings of a coordinated program to assess the usefulness of battery impedance measurements as a maintenance tool. A newly developed impedance meter is being widely used to characterise the online cell and battery impedances of the range of lead-acid batteries used in the network. Early trends and some aspects associated with the use and interpretation of on-line impedance measurements are discussed. Encouraging results of the use of dynamic impedance measurement during discharge testing are also presented View full abstract»

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  • A new current programming technique using predictive control

    Page(s): 428 - 434
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    This paper investigates a new current programming technique for constant frequency switch-mode power converters. In the proposed technique, the duty cycle of the power converter switch is controlled by the input and output voltage as well as inductor current information. The basic idea in predictive control is to force the inductor current to follow the command current within one switch cycle. This new technique removes several drawbacks of conventional current mode control, such as current loop instability and error between inductor peak current and command current. The boost power converter is used as an example of the implementation of this new technique View full abstract»

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  • Three-wire DC distribution to telecommunication equipment

    Page(s): 297 - 300
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    This paper takes a new look at the -48 V power distribution widely used for providing power to telecommunication equipment, and at the methodology used for grounding and bonding of both the power system and the powered telecommunication system. In contrast to AC distribution, the DC distribution used in telecommunications and its associated grounding are not extensively covered in electrical codes such as the National Electrical Code and the Canadian Electrical Code, or in international standards such as IEC 364. The paper identifies analogies and differences between the experience-based, codified requirements for single-phase DC systems and the evolving requirements for DC powering and system grounding used in telecommunications. It suggests that the harmonization efforts of evolving national, regional and global standards for these DC systems could benefit from a critical examination of the proven principles developed for AC distribution View full abstract»

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