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Uninterruptible Power Supply (UPS) systems are typically designed to provide power to computers for five to thirty minutes after all utility company power has failed. In addition to providing blackout and brownout protection, many UPS systems also protect against spikes, surges, sags, and noise, and some also offer many of the features found in power distribution units (PDUs). The major components or subsystems of a typical UPS system are detailed, and a sample bid specification is appended. Three sidebars discuss UPSs and air conditioning, the maintenance bypass switch (MBS), and literature for further reading.

The purpose of this paper is to minimize and prevent current overloads (including the elimination of abnormal and fire hazardous situations) in photovoltaic solar arrays by using low-cost functional electronic elements, in particular, the new PolySwitch PPTC fuses.

The modeling method has been used to investigate the circuit solution of the use of PolySwitch type fuses to prevent and minimize current overloads in photovoltaic solar arrays.

It is shown that the limitation of the short-circuit current with parallel connection of photovoltaic components (photovoltaic cells or their modules) can be implemented when the following conditions are met: the resistance of the fuse in the conducting state is much lesser than the parallel connection of the series resistances of the photovoltaic components; and the tripping current of the fuse must be greater than the maximum current of the separate photovoltaic components and lesser than the current of a parallel connection of several photovoltaic components.

The influence of the magnitude of the resistance in the conducting state and the response current of the fuses to the current–voltage and volt–watt characteristics of parallel connections of the photovoltaic components (photovoltaic cells or their modules) is analyzed. The modeling results are confirmed by experimental data on the transformation research of light current–voltage and volt–watt characteristics of parallel connections of industrial photovoltaic modules using resettable fuses of the PolySwitch type.

Computers need clean, reliable, electrical power. The various faults of electrical power, such as spikes, sags, outages, noise, frequency variations, and static electricity, are defined and described. Preventive measures that computer users can employ to reduce the potential of electrical problems are discussed, as are the processes for detecting, diagnosing, and curing electrical problems when they do occur. Sidebars consider: transformers; power distribution units (PDUs); surge currents/ linear and non‐linear loads; and sizing the power conditioning system. The next issue will conclude this series with an article on uninterruptible power supplies and a bibliography.

Power and communications wiring can be brought to computers and computer terminals in a variety of ways. Each method has its strengths and weaknesses; some that are ideal for one library may be forbidden another. Options include use of extension cords, perimeter raceway (such as conduit, wiremold, and armored cable), and interior raceway (such as underfloor duct, flat conductor cable, and power poles). Three sidebars discuss 1) the National Electrical Code; 2) volts, amps, watts, etc.; and‐3) transformers, circuit breakers, and circuits.

THE last decade has seen great progress in the development of the electronic flash tube and there are today few scientific or engineering projects which do not employ the tube as a high‐speed photographic light source to secure data which cannot otherwise be obtained. Aeronautical research is no exception; the technique of flash photography was accelerated during the war years, both in this country and America, primarily to meet the many and varied problems which arise in aircraft engineering.

THE Funk Gerat 10 equipment is the latest standardized type, and is installed in all the later bombers and reconnaissance machines of the Luftwaffe.

Considers the use of surge suppressors to protect computers from surges in voltage and ′spikes′ – sudden sharp rises caused by switching on equipment such as air conditioners in the vicinity. Describes the tests that the technology has to go through in order to be awarded one of the two industry standards, as well as explaining the meanings of some of the important terminology.

DURING the past few years, air transport companies have found it necessary to operate on 24‐hour schedules in order to compete successfully and economically with other transportation facilities in carrying passengers, mail and express. Commercial success of these privately owned air transport companies cannot come through Government subsidy, but must come through the rendering of improved service for which the public at large will pay. This improved service is only given by the saving of time and, therefore, both airway navigation facilities and general airport illumination must be such that the pilot may handle his aircraft from starting‐point to ultimate destination with minimum time delay at intermediate stopping points.

THE forbearance of readers is requested at the outset for a personal note, considered to be inseparable from the basic purpose of this paper. The author's professional duties for many years prior to this war were concentrated on the specialist work of the design of distribution and transmission networks of various electricity supply undertakings, covering the main development period of electricity supply in this country, and also including the change‐over of direct current consumers to alternating supply. The author was directed for the period of the war into the aircraft industry and again specialized on the electrical side, and the similarity of the technical problems which have arisen in both his experiences leave no doubt that aircraft electrical systems can benefit from the hard‐won success of the electricity undertakings, whose achievements and mistakes alike are given publicity and opportunity for discussion. The technical success of supply systems is generally admitted to be in a large measure due to the freely‐pooled contributions from the experience of engineers in the profession. The author airs very decided personal views, many of them contrary to present practice and forecasts, and in order that the criticism it is hoped to arouse should not be marred by any misunderstandings, it is made clear that his experience is limited to British aircraft; with no knowledge of American practice. The scope of electrical applications in aircraft is very great and it does seem that as each new application arises, those responsible endeavour to design suitable systems and apparatus de novo instead of ascertaining first whether or no there is a similar application in the electrical industry which has been tried out over the years, and which if applied with suitable modification to aircraft would cut out the inexcusable “teething” troubles. For example, the risk of fire being carried along by cables has been very thoroughly studied in switching stations; the deleterious effects of oil upon rubber insulation were appreciated years ago; and telephonic intercommunication has been utilized always in generating stations where the noise is quite equal to that which obtains in aircraft; also the practice of endeavouring to classify cables by their current carrying capacities was abandoned a very long time ago. These are only a few examples in which the author feels that aircraft electrical systems can be improved as a result of experience in the allied industry.

WE do not need to be reminded of the increasing importance of the electrical system in the modern aeroplane, either from the point of view of efficient operation of the aircraft or from the point of view of reliability and safety.