摘要:

The paper discusses a number of electromagnetic phenomena which may be encountered in the operation of high-voltage testing equipment. Although secondary in magnitude these effects are not secondary in importance, since they may vitiate the accuracy of important tests and lead to the loss of much time and money. Theoretical deductions are throughout supported by actual experimental results.Part 1 deals with wave-form distortion in the usual single-phase normal-frequency transformer equipment. The factors considered include core saturation, capacitance loading, and induction-regulator and alternator characteristics. Information is also given as to the effect of wave-form on breakdown voltage and dielectric losses.Part 2 deals with transient phenomena in testing-transformer circuits. The production of over-voltages by switching and by discharges in the load is discussed in detail. Oscillations in rectifier circuits are also considered.Part 3 deals with wave-form distortion in the impulse generator. Special attention is given to the superimposed oscillations introduced by load capacitance and by measuring circuits. The theory of the oscillation transformer is developed as a special case of the impulse generator, and test results are given for an actual equipment.

DOI:10.1049/jiee-1.1934.0058

出版商:IEE    

年代:1934

数据来源: IET

摘要:

The paper describes an investigation of the effects of leakage flux on the performance of ring-type current transformers with uniformly-distributed secondary windings. If the primary ampere-turns are concentrated on one part of the core, large leakage fluxes are superposed on the working flux, and these cause premature saturation of parts of the core, with a resultant rapid rise in the ratio of primary to secondary current. A copper shield of special design was made for a 10000/5 transformer, and when fitted it was found to reduce the leakage fluxes to one-frith of the value existing without the shield. Saturation of the Gore, which started at about two-fifths of full load without the shield in position, did not begin until twice full load was reached when the shield was fitted. The ratio error of this transformer was 35 per cent at full load without the shield in position, and was 1 part in 10000 at full load with the shield in position. A shield of similar design fitted to a 20000/5 transformer reduced the ratio error at load from 67 per cent to less than 1 part in 10 000.

DOI:10.1049/jiee-1.1934.0063

出版商:IEE    

年代:1934

数据来源: IET

摘要:

A method of testing current transformers by comparison with standard current transformers is described. The apparatus has three ranges. The most sensitive range is capable of measuring ratio differences up to 5 parts in 10000 with an accuracy of approximately 1 part in 1000000, and phase angles up to 2.5 minutes with an accuracy of approximately 0.01 minute. The other two ranges are respectively 10 and 100 times as great, and the sensitivity is correspondingly reduced. The design and construction of suitable standard current-transformers to cover ratios from 5/5 up to 12000/5 are described, and the methods of calibrating these transformers to an accuracy of approximately 2 parts in 100000 for ratio and 0.1 minute for phase angle are outlined.

DOI:10.1049/jiee-1.1934.0064

出版商:IEE    

年代:1934

数据来源: IET

摘要:

A simple method is described for the measurement of impedance and its reactive and resistive components. The method is as easy to use as an ordinary d.c. Wheatstone bridge, no double “balances” being required and the only adjustments necessary being made on a potential divider. The equipment provides a universal testing-set which is extremely easy to operate and which will give results accurate to about 0.5 percent

DOI:10.1049/jiee-1.1934.0066

出版商:IEE    

年代:1934

数据来源: IET

摘要:

A method is described by which the presence of adsorbed moisture on the surface of a solid insulating material in the form of an ellipsoid freely suspended in a closed vessel can be observed and its electrical properties measured.The theory of the instrument is set out, together with a numerical example, and expressions are found for the polarization and conduction currents, and for the resistivity of the film on glazed porcelain. This is of the mean order of 102ohms per cm2. An example is given of the change of the of the film with time.Chemical and physical drying are compared, and a form of electrical hygrometer is described depending on the change of distribution of electric fields on a glazed surface produced by a change in the hygrometric state of the air. By the use of a relay an alarm-bell is rung when a certain hygrometric state is reached.

DOI:10.1049/jiee-1.1934.0067

出版商:IEE    

年代:1934

数据来源: IET

摘要:

The paper deals with the accepted methods of representing ferromagnetic properties and with the vector diagrams and equivalent electric circuits commonly employed to indicate the behaviour of iron-cored coils under a.c. excitation. The. point of view adopted is that such vector and circuit representations must not be interpreted literally when, for example, fundamental measurements of the properties of iron are undertaken by a.c. methods. For instance, the wattless component of no-load current of a transformer—frequently termed the magnetizing current—is shown to be in no sense a measure of the amplitude of the magnetizing force experienced by the core, even though, in the r.m.s. system of measurement, it must be used in assessing the so-called reactance of the winding. An inductance coefficient deduced from this reactance is an artificial quantity because it infers a permeability value which cannot be related with the true reversals curve of the core material at any point. It is demonstrated by experiment that the total no-load current (r.m.s.) is a closer measure of true peak magnetizing force, though this current needs to be corrected for eddy-current effects and, even then, has still a very limited application in fundamental investigations.Attention is directed towards precise methods of measurement of magnetic properties using alternating current, and a means of expressing results is suggested which avoids the worst anomalies of the r.m.s. equivalent circuit and vector diagrams. The mathematical treatment of the excitation ellipse associated with the latter is extended and its full implications are discussed. The relations between the ellipse and the true hysteresis figure are shown by an analysis of the harmonics of excitation. The true cycle of permeability is derived, thus enabling an expression to be formed which is general for all conditions in the core, so covering the cases of remanent magnetism and of excitation by reversed direct current such as is customary in ballistic measurements.The aim throughout the paper is to re-establish a clear outlook upon the elements of cyclic ferromagnetism, in the belief that the half-truths of the common a.c. vector treatments have an undue influence upon the engineer's mode of thought.

DOI:10.1049/jiee-1.1934.0068

出版商:IEE    

年代:1934

数据来源: IET

DOI:10.1049/jiee-1.1934.0069

出版商:IEE    

年代:1934

数据来源: IET