摘要:

The significance of gaseous discharges in the electrical breakdown of solid and composite solid-liquid dielectrics has emerged with increasing clarity over the past three decades. Arising from researches in England and North America, substantial advances in the detection and interpretation of discharge phenomena were made in the second decade, principally by the British Electrical and Allied Industries Research Association. Towards the end of the second decade the usefulness of applying discharge tests continuously to extruded insulating coverings over conductors to be operated at high voltages came to be recognized in several quarters in this country, on the Continent and in the United States.Discharges may be detected by measuring the transient electrical disturbance to the system caused by the discharge, or by measuring the electromagnetic r.f. or light waves or the sound pressure waves emanating from the discharge. Reference is made to continuous discharge detectors based on some of these methods.The various practical forms of the method based on electrical observations are discussed in greater detail, since this method is the one more widely used and more highly developed at the present time. The particular arrangement used by the company with which the author was associated is described, and the results obtained in testing more than 400 miles of polythene-insulated high-voltage core are reviewed. Reference is made to technical difficulties encountered in the design and operation of the equipment.The limitations in the usefulness of the present form of testing are stated in the light of the experience gained and some suggestions are made for the further development of the method.

DOI:10.1049/pi-a.1962.0023

出版商:IEE    

年代:1962

数据来源: IET

摘要:

Although midspan joints and anchor clamps for overhead power lines are designed to satisfy stringent specifications, failures occur due to faulty manufacture or erection. Compression fittings are now the only types being fitted by the Central Electricity Generating Board, and statistics are given of their relatively low rate of failure. The usual mechanism of failure is by overheating of the steel core by the current it is forced to carry when high-resistance contacts exist between the aluminium strands of the conductor and the fitting.The testing of fittings during erection or on unenergized lines can be performed by resistance measurements, with suitable precautions, by radiographic examination, or by magnetic location methods. On energized lines, the fitting can be tested with a hook-on voltmeter or thermistor, or with an infra-red bolometer. The results are given of resistance and bolometer tests on 132kV lines in South-East England. The two methods detected a similar percentage of defective fittings.It is concluded that failure of fittings can be practically eliminated if care is taken during manufacture and erection. The testing during erection and at regular intervals during service should ensure that no further faults occur. It is recommended that all jointers be properly trained.

DOI:10.1049/pi-a.1962.0024

出版商:IEE    

年代:1962

数据来源: IET

摘要:

The paper includes a brief description of a typical modern extrusion line used for the manufacture of cable components, together with the reasons why instrumentation is necessary. Foremost among these is the maintenance of product quality, which is discussed in terms of (a) meeting precise dimensional and electrical requirements, (b) the need for indicating to the operator any trends away from desired values, and (c) the saving of materials. A distinction is made between the processes of core insulation and cable sheathing and the respective instrument accuracy and stability limits required.In addition, the arrangements of a number of systems which are commonly employed to monitor the various parameters are described and their advantages and disadvantages discussed. The reasons for the choice of the types adopted in particular applications are also given.Also considered are the use of instruments described as elements of automatic control systems for extrusion lines and the difficulties encountered.

DOI:10.1049/pi-a.1962.0025

出版商:IEE    

年代:1962

数据来源: IET

摘要:

Two methods of using the radioactive gas krypton 85 for leak detection are described. In the first, components to be tested are immersed in the gas, after which they are removed and individually monitored for radioactive content. Application of the method to detection of leaks in transistor encapsulations is discussed. Correlation has been obtained between leak rate and time for subsequent electrical failure.The second method of using krypton 85 is to insert a small quantity into each component before the final seal is made. Leak rates are then measured by collecting gas which leaks out and assaying it with a scintillation counter. This technique is illustrated by tests carried out on a hermetically-sealed pressure switch. The method is compared with the helium mass spectrometer, and it is concluded that using krypton 85 is just as sensitive, cheaper and more reliable.

DOI:10.1049/pi-a.1962.0027

出版商:IEE    

年代:1962

数据来源: IET

摘要:

The paper discusses the requirements for testing and location of leaks in the course of manufacture of various sealed-off vacuum devices. A number of methods are at present in use and others have been assessed in the course of experimental work. Their advantages, limitations and sensitivities as found in practice are discussed.The methods fall into two classes. The non-specific methods involve measuring differences in total gas pressure with time or at different points in a vacuum system. The specific methods detect a particular gas and are generally found to be better suited for the requirements discussed; they include the halogen detector, the hydrogen diffusion detector and various types of mass spectrometer. While more than one method can be used for large leaks, the mass spectrometer has been found the most useful for smaller leaks, using helium as the test gas. The relative merits of the conventional magnetic type, the omegatron and the linear r.f. spectrometer are discussed. The magnetic type is the most generally suitable, and various design features and precautions in use are outlined.

DOI:10.1049/pi-a.1962.0028

出版商:IEE    

年代:1962

数据来源: IET

摘要:

Xeroradiography is a new method of radiography which utilizes the photoconductivity of amorphous selenium when exposed to X-rays or γ-rays. A visible powder image is produced on a thin selenium layer deposited on a supporting metal plate. The plate can be used repeatedly. Development of a visible image after exposure requires only 6–10 sec.The image has a high contrast for sharp changes in the thickness, or X-ray absorption, of the object being inspected, but for a gradual change in X-ray intensity the contrast is very low. These two features enable a sample with a wide thickness range to be examined with one exposure and simultaneously a high contrast of image details can be obtained. In comparison with conventional film radiography, details are more easily seen and viewing is less fatiguing owing to the smaller brightness range of the image.The paper includes xeroradiographs of a number of electrical components and materials used in the electrical industry.

DOI:10.1049/pi-a.1962.0029

出版商:IEE    

年代:1962

数据来源: IET

摘要:

Failure of electrical and mechanical devices during vibration is well known. The stroboscopic X-ray system offers a means of observation of these effects when the parts are concealed by protective enclosures.

DOI:10.1049/pi-a.1962.0030

出版商:IEE    

年代:1962

数据来源: IET

摘要:

Measuring the diameter of a fine textile filament by its electrical capacitance effect between the fixed plates of a capacitor presents the twin problems of the very small capacitance change to be measured and the high degree of stability to be maintained in the capacitor.The present instrument is insensitive to changes in the standing capacitance and achieves this by vibrating the yarn in and out of the gap. The capacitance between the two electrodes is therefore varying at the frequency of the vibrating yarn, and a variable capacitor is switched into circuit in phase with the yarn and used to balance this change in capacitance in a bridge circuit. The output from the bridge is amplified and used to drive a motor which balances the bridge by adjusting the variable capacitor. The movement of the motor also drives a pen recorder. The bridge circuit conveniently provides several measuring ranges and allows the measuring head to be one of several connected to the main instrument by long cables.Synthetic-fibre manufacture involves numerous identical production units in parallel. Monitoring and control gear is therefore fed from a multiplicity of transducers which must be matched, reliable and capable of simple routine test and replacement without upsetting their related circuits.

DOI:10.1049/pi-a.1962.0031

出版商:IEE    

年代:1962

数据来源: IET

摘要:

Polythene is very transparent to X-rays, and unless it is several inches thick it requires special equipment for X-ray testing. An X-ray tube with a window of very low absorption is needed, so that radiation generated in the range 10–20kV can be used. The performances of various types of tube have been investigated. Fluoroscopic inspection is unsuitable with such low operating voltages and film recording is much preferable. It gives considerably enhanced image contrast, allows critical inspection of the image with a lens, and provides a permanent record of the test.X-ray examination of joints in polythene submarine cable core and of cable-entry glands of submerged repeaters is illustrated. When these parts are being checked, exposures from various angles are required because in any one view some of the polythene is hidden by metal. It is desirable to make systematic tests from known angles and to record them side by side on a single film to help locate features of interest. An example of equipment designed for the field testing of cable joints is described.

DOI:10.1049/pi-a.1962.0032

出版商:IEE    

年代:1962

数据来源: IET

摘要:

X-radiography can reveal internal features of importance in certain components. This has been applied to the inspection of resistors, short-circuiting fuses, terminal seals and radio valves required to be of high quality, and to the detection of faults in these components and in capacitors. The usefulness of the technique is demonstrated.

DOI:10.1049/pi-a.1962.0033

出版商:IEE    

年代:1962

数据来源: IET