摘要:

The paper has four sections which discuss:—(1)The electrical characteristics which outdoor bushings should possess for satisfactory operation; (2) the testing of bushings; (3) the factors which control the design of bushings; and (4) types of bushings.The paper deals particularly with bushings for outdoor transformers, but other bushings are briefly considered, e.g. those for oil circuit-breakers and also wall and roof bushings and cable terminations.(1)Electrical Characteristics.Desirable characteristics are discussed, the bushing being considered firstly as part of a transformer and therefore subject to all the transformer tests, and secondly as part of a transmission line and therefore subject to over-potentials which originate in the line.Bushing as part of transformer.—The transformer with its bushings is assumed to be tested in accordance with B.S.S. No. 171-1927. Values are thus obtained for the 1-minute test voltages, particularly for 3-phase transformers with neutral earthed or insulated. Methods of bushing failure by flash-over and by puncture are considered, and figures are given for the various flash-over voltages, viz. air-end flash-over under dry and wet conditions and also oil-end flash-over.Bushing as part of transmission line.—The transmission-line insulators are assumed to conform to the test requirements of B.S.S. No. 137-1930. The magnitudes of over-potentials which originate in the line and impinge on the transformer are considered. A law is given for the relative strengths of transformer insulation as measured by 1-minute test values and as measured under impulse conditions. The law is used to obtain flash-over characteristics for “weak links” in the line insulation. Recommended bushing flash-over characteristics are given.The two sets of flash-over figures now obtained are considered together and final recommendations are made for bushing characteristics. For comparison the characteristics are given for bushings to Central Electricity Board requirements and also for bushings in accordance with the new British Standard Specification B.S.S. No. 223-1931.Indoor transformer bushings ; bushings for oil circuitbreakers and cable terminations ; wall bushings ; roof bushings.—The differences between these and outdoor transformer bushings are considered. Suggested characteristics are given.Lightning arrestors.—These are briefly considered.(2)Testing of Bushings.Dry flash-over voltage.—Effects of barometric pressure, air temperature and humidity.Wet flash-over voltage.—The effects of intensity of rainfall and resistivity of water are considered.Duration of test.—Figures are given of the times taken to carry out various tests.Temperature-rise of metal parts.—The use of thermocouples to measure temperature-rise is described, and results of typical tests are given.Temperature-cycle test.—This test is described.(3)Design of Bushings.Features of electrical design are first considered.Temperature ; duration of test ; shape of electrodes.—These factors are considered as affecting the electric strength of insulation.Permissible voltage gradients.—These are given for porcelain, varnish-paper insulation, air, oil, solid compound, and semifluid compound.Laws of corona and puncture.—These laws are developed for bushings having two or three different dielectrics.Flash-over voltages.—Curves are given connecting axial lengths over bushing surface with flash-over voltages for dry, wet and under oil conditions.Heating of bushings.—Brief consideration is given to the heating of the centre conductor, allowing for skin effect, and to the heating of the earth flange due to hysteresis and eddy-current losses.Features of mechanical design and construction are also considered.Clamps.—For dealing with large currents.Joints.—The making of oil-tight and weather-tight joints.(4)Types of Bushings.The following types are described and discussed:—All-porcelain air-core; compound-filled; oil-filled; condenser; all-porcelain multi-tubular; all-porcelain multi-tubular embodying condenser feature.The incorporation of a current transformer as part of the bushing is described, and capacitance coupling is briefly considered.In conclusion the following Appendices are given:-I. Development of law connecting dry and wet flash-over voltages.II. Corona formation in air-core porcelain bushings.III. Radial electrostatic stresses in bushings having three different dielectrics.IV. Statistics of heavy rainfall.

DOI:10.1049/jiee-1.1932.0024

出版商:IEE    

年代:1932

数据来源: IET

摘要:

An experimental television system designed expressly to examine the conditions necessary for the transmission and reception of comparatively good pictures is described.Five picture channels are used which accommodate a frequency band sufficient to produce an image composed of 15 000 elements. The received picture is projected on to a screen measuring 24 in. by 16 in., and is scanned at the rate of 12½ times per second.The best operating conditions for the Kerr cells of the receiver are investigated, and the effects of geometric, nonlinear, and frequency distortion are examined.

DOI:10.1049/jiee-1.1932.0026

出版商:IEE    

年代:1932

数据来源: IET

摘要:

After a brief reference to phase advancers, the Heyland motor and its modifications and the Osnos motor (to which the paper is chiefly devoted) are described. The theory of the Osnos motor, which is also known by its trade names of “No-Lag” and “Kosfi-Leading”, is then developed, and the equivalent circuits, test results, circle diagrams, and verification of the theory of the machine are given. A general method of obtaining the copper loss, output, torque, etc., from the circle diagram of any motor is developed; an example is worked out and the results so obtained are compared with test figures. A description follows of the Fynn-Weischel and Torda motors (known also by their respective trade names of “Tru-Watt” and “All-Watt”), and the principle of action and characteristic curves of these machines are given.

DOI:10.1049/jiee-1.1932.0030

出版商:IEE    

年代:1932

数据来源: IET

摘要:

In an earlier paper, the author described a graphical method for determining the magnitude and phase of the electric field in the neighbourhood of an aerial carrying a current of known distribution. The major portion of that paper neglected the effect of the earth, although an indication was given of a method for taking account of the image of the aerial in the earth. The first part of the present paper elaborates this explanation and shows how the results given in the earlier paper may be modified in order to take account of the electrical constants of the earth's surface. A formula is deduced for the field at any point near the earth's surface due to a given doublet, and it is shown how this formula may be extended in order to determine the field at various distances from an aerial carrying a current of known distribution. The second part of the paper shows how the field at any distant point may be found directly for any number of equal aerials and reflectors from a knowledge of the field at the same point due to one aerial and reflector alone. The current in the reflector wire need not be equal in magnitude or in phase to that in the aerial, and the components of the array may be either vertical or horizontal.

DOI:10.1049/jiee-1.1932.0031

出版商:IEE    

年代:1932

数据来源: IET