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144 Initial expenditure. This consists of the acquisition costs for the units and other equipment included in the power supply system together with the installation costs. Operational costs are influenced by the efficiency of the system and the need for maintenance measures. Reliability. In modern telecommunication systems it is a particularly rigorous requirement that sufficient feeding power is always available. This requirement is satisfied in the power supply system, the risk of system failure being minimized by the introduction of standby units (redundancy) and grouping into cut out units. Safety aspects must be taken into consideration when selecting the system voltage. The cost of protective covers and guards, improved insulation and adaptation of the system to varying national and international safety regulations must all be considered. Future power plants Goal The optimum design for future power plants has long been studied by LM Ericsson. Thegoal has been,among other things, to — find alternative methods for the power supply of future telephone systems — give methods for how alternatives can be compared from the viewpoints of costs and function — determine, with the aid of cost relations and prognoses, the solutions that are favourable (optimization), i.e. find suitable voltages and give relative costs for different degrees of centralisation of the power supply equipment. The studies have been concentrated mainly on the choice of the system voltage and the current type for feeding telephone exchanges of the future. In addition the question has been considered as to how the regulation functions should be allocated; decentralized regulation in the vicinity of the load or centralized regulation in the central power supply plant, see fig. 3. Model exchanges During the course of the studies cost relationships have been established which are universally valid, and these have been applied for different model exchanges, representing the various LM Ericsson SPC systems. Thus both AKE and AXE systems have been dealt with. Alternative solutions For more than a decade the present LM Ericson power supply system has proved to be economical, reliable and adaptable to varying system requirements. The system is characterized by a 48 V system voltage and booster converters 2 . The following alternative solu- Fig. 3 Centrally regulated power supply system. The distribution voltage is maintained constant by means of regulated booster converters Rack converters
145 tions have been studied with this system as a reference. 1. Distribution of a.c. voltage, 1-phase or 3-phase, at the mains frequency. 2. Distribution of a.c. voltage at higher frequency. 3. DC voltage distribution with decentralized regulation. Dispensing with the booster converters and feeding all the load via DC/DC converters with increased regulation range. 4. DC voltage distribution a) System voltage of 140 V b) System voltage higher than 140V Distribution of a.c. voltage means more expensive standby energy The advantage of this alternative is that it is very easy to transform a.c. voltages to other voltage values. At the same time relatively simple rack rectifiers can be used as the local rack power units instead of DC/DC converters. However, as has been pointed out earlier, a modern telecommunication system demands a power supply that is completely free of interruptions. This means that the system requires instantaneous access to standby energy in the case of an interruption of the regular energy sources. The studies have shown that the most economic and reliable form of energy storage, which at the same time satisfies the above requirements, consists of some form of modernized variant of the conventional lead-acid accumulator. Since the storage battery operates at d.c, charging rectifiers are also needed in a system with a.c. voltage distribution, as well as DC/AC inverters for converting the standby energy. The latter means that the size of the battery must be greater than in the d.c. system in order to compensate for the efficiency loss. Moreover an extra cost for the inverter must be taken into account. As a result of these disadvantages and other considerations it has been decided that a.c. voltage distribution is unsuitable for feeding the telephone exchanges of the future. Decentralized regulation is expensive The battery voltage varies over a wide range with different operating conditions (charging, discharging). The use of booster converters constitutes one possible method of providing primary regulation of the distribution voltage. Dispensing with this regulation possibility would mean that the regulation range of the rack converters would have to be increased. Thus they would have to be able to provide the full output voltage for a very much lower input voltage, see fig. 4. Calculations on a number of types of rack converters show that this in- Fig. 4 System with decentralized regulation function. Variations in the distribution voltage are compensated by rack power units with a larger input voltage range and by feeding the remaining load via regulated direct converters
Page 1: ERICSSON REVIEW 3 1976 GEOSTATIONAR
Page 4 and 5: Geostationary Telecommunications Sa
Page 6 and 7: 112 forever silent. The next launch
Page 8 and 9: 114 Figs. 1—4 Figs. 5—8
Page 10 and 11: 116 Figs. 17—20 Figs. 21—24
Page 12 and 13: Electronic Push-button Telephone Se
Page 14 and 15: The bottom part (frame) ot the set
Page 16 and 17: Fig. 10 Buzzer unit Fig. 9 Tone rin
Page 18 and 19: Fig. 12 Impulsing unit and ring uni
Page 20 and 21: 126 Fig. 15 Transmission diagram Fi
Page 22 and 23: 128 ed by about 100 kohms. In order
Page 24 and 25: Fig. 20 DC characteristics (speech
Page 26 and 27: 132 use a microphone in which the o
Page 28 and 29: CCM - A Well- tried and Economic Ma
Page 30 and 31: 136 ] Do not allow more staff in th
Page 32 and 33: Ten Years Experience of CCM in the
Page 34 and 35: 140 Table 2 Existing staff requirem
Page 36 and 37: Optimization of Power Supply Equipm
Page 40 and 41: Table 1 Acquisition costs for diffe
Page 42 and 43: 148 Fig. 8 Instead of feeding the p
Page 44 and 45: 150 Fig. 10 Apart from a highly sta
Page 46 and 47: Development, Production and Mainten
Page 48 and 49: 154 combined to meet the needs of e
Page 50 and 51: 156 duction and putting the package
Page 52 and 53: 158 Fig. 5 Working procedure when p
Page 54 and 55: 160 The error message is sent from
Page 56 and 57: Dr. Christian Jacobceus chaired the
Page 58 and 59: 164 Among the reasons that were giv
Page 60: TELEFONAKTIEBOLAGET LM ERICSSON PRI

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