DOI:10.1049/ji-2.1942.0001

出版商:IEE    

年代:1942

数据来源: IET

摘要:

The paper is a transcript of the author's notes of an objective investigation of the thermal, electricity supply and economic problems associated with the warming of surface-type air-raid shelters. It examines—inter alia—the factors of thermal contrast existing between normal buildings and structures of the type under discussion; why, where, when and how heat energy should be transmitted to the occupants; the pros and cons of radiant and convective forms of space-heaters; the thermal capacity of the structure; conditions conducive to surface condensation or sweating, and the like.The design and construction of a floor-warming installation are examined in detail, the performance data obtained during an 8-week test run are analysed, and the paper concludes with a series of estimates of the seasonal consumption of energy, and of the total costs involved in maintaining various standards of thermal comfort in shelters of the type discussed, based on data obtained during the test period.The following conclusions are formulated:—(1) No other form of space-heating provides an equal (or even approachable) standard of thermal comfort for 100% of the occupants of the shelter, in return for the cost of the energy used and the space occupied. Representatives of local authorities, architects and others who have inspected the installation during periods of severe weather have unanimously endorsed this-view.(2) The method provides a satisfactory degree of thermal storage which substantially maintains the specified standard of thermal comfort when the supply of electrical energy is interrupted during periods of peak load (by time switch or otherwise), or by reason of bomb damage to cables, substations, etc.(3) It provides a maximum of safety against burns, shock, etc., due to inadvertent contact with the source of heat energy.(4) The space occupied by the installation is practically nil, as is also the risk of damage by mischievous children and/or ill-disposed persons.(5) The maintenance (excluding the risk of cable failure) is also nil, and an instance of cable failure has still to be experienced.(6) The initial cost of the installation bears a reasonable ratio to the cost of the furnished structure and to the value of the health and morale of its human contents.(7) The total cost of operation compares most favourably with that of the more orthodox forms of space-heating installations, and appears to be substantially lower for an equal standard of thermal comfort.(8) The thermal capacity of substantially constructed buildings of the type discussed (14-in. brick walls and 6-in. concrete floor and roof) is such that it is technically impossible instantaneously—or even rapidly—to induce in them any acceptable standard of thermal comfort for 100% of the occupants, in response to the turn of a switch.(9) This form of space-heater makes no demands on the national stocks of iron and/or steel, and the man-hours of labour per kilowatt capacity involved in its manufacture and installation are probably the lowest for any form of heater.(10) In view of its inherent characteristic of thermal storage at or about room temperature, and its capacity to “carry-on” under conditions of limited-hour supply (during periods of peak-load restriction), it would appear that there is considerable scope for post-war development for certain classes of building.

DOI:10.1049/ji-2.1942.0002

出版商:IEE    

年代:1942

数据来源: IET

摘要:

The impulse puncture characteristics of high-voltage cables have been investigated. Most of the tests have been made on virgin paper-insulated single-conductor cables of the solid or mass-impregnated type, but some tests have been made on varnished cambric, non-bleeding paper, H-type multicore, and belted-type cables. Cables made by two manufacturers were tested. The experimental results are discussed and conclusions drawn.

DOI:10.1049/ji-2.1942.0007

出版商:IEE    

年代:1942

数据来源: IET

摘要:

The paper discusses the electrical characteristics and performance in service of porcelain insulators for outdoor high-voltage apparatus. It is emphasized that if large power systems are to be operated with a minimum of breakdowns a carefully planned scheme of field testing, supplemented by laboratory investigation, is essential.Part 1 describes the laboratory apparatus and the field testing equipment used by the Central Electricity Board. For laboratory investigations, two outdoor high-voltage testing sets are installed, having maximum voltages of 85 kV and 250 kV. A test tower and rack are associated with each equipment, and continuous pollution tests can be made simultaneously on 60 insulators. Counters are installed on all the insulators to record the leakage-current “surges.”Field tests are made with the lines in service, with an apparatus consisting of a capacitance potential-divider and electrostatic voltmeter. The potential distribution on the insulator is measured, and faulty units are detected by the abnormally low potential-drop across them. The surge counter is also applied to equipment in service in order to indicate when insulator cleaning is necessary.Part 2 gives some of the results of investigations made with the apparatus and technique described in Part 1. Information is given regarding the performance of line insulators, post insulators and bushing porcelains. The behaviour of insulators in fog, and similar weather conditions, is discussed, and examples are given of the highly irregular potential distributions and leakage-current surge records obtained under such conditions. Comparative results are given for “normal” and “anti-fog” insulators. The mechanism of insulator flashover in fog is described in detail. The requirements of a good anti-fog insulator are discussed, and for an insulator for use in highly polluted and humid atmospheres a leakage path of 2 in. per kV of applied voltage is recommended. A new design of insulator unit is described in which the potential distribution is stabilized by resistors.Information, based on service experience, is given on the deterioration of insulators. With high-quality modern insulators, the rate of deterioration should not exceed 0.1% per year, but it is nevertheless essential to make field tests, as a single faulty unit may lead to the complete failure of the insulator string. Confirmatory tests made in the laboratory show that in most cases (approximately 90%) the field diagnosis of faulty insulators is correct. Deterioration takes the form of cracks in the porcelain head, and the mechanism of insulator failure due to cracking is described.The cause and characteristics of radio interference due to power lines are discussed, and data are given of the interfering field strength due to high-voltage lines operating in various weather conditions. Under the worst condition—fog—the interference increases by 40 db. above the fine-weather value. The attenuation of the interfering field is very rapid at right angles to the line, and a decrease of 25 db. occurs in 50 yd.; at this distance from the line, local broadcasting stations may be received virtually free from interference even under the worst weather conditions.

DOI:10.1049/ji-2.1942.0008

出版商:IEE    

年代:1942

数据来源: IET