DOI:10.1049/ji-2.1946.0072

出版商:IEE    

年代:1946

数据来源: IET

摘要:

In recent years there has been a marked increase in the demand for more accurate, commercial a.c. power-measuring instruments. The demand is due largely to changing industrial conditions brought about by legislation, although it already existed for the manufacturer whose a.c. standardizing apparatus was only comparable in sensitivity and accuracy with that of the commercial apparatus he produced.The paper gives a brief review of the sources of error common to dynamometer wattmeters, and emphasizes some of the inherent errors which have been less publicized.A new instrument for measurement of a.c. power and voltage by direct comparison with a standard d.c. potentiometer is described, the principle of operation being a null method based on the balancing of two torques.A summary is given showing the errors inherent in the new instrument and those which have been eliminated by the method of measurement.The stability of accuracy of the new instrument is maintained by self-standardization, and a means of checking the accuracy of the associated apparatus is made available.

DOI:10.1049/ji-2.1946.0073

出版商:IEE    

年代:1946

数据来源: IET

摘要:

The paper records the progress made in the application of powdered mineral insulation to metal-sheathed conductors. It describes manufacturing methods and the application of those products which have reached a commercial stage of development. Mineral-insulated copper-covered (m.i.c.c.) cable is dealt with at greater length and it is thereby hoped that a solution to some cabling problems may be indicated.

DOI:10.1049/ji-2.1946.0077

出版商:IEE    

年代:1946

数据来源: IET

摘要:

The paper deals with the methods of connecting single-phase equipment to 3-phase mains. The single-phase transformer and the open-delta series-connected transformer are compared, both as regards current distribution and the voltages on the substation busbars. Mention is made of the power-factor correction of single-phase loads, from which there has been developed a method of obtaining balanced 3-phase/single-phase conversion by static means. The remainder of the paper gives full details of this phase-converting system for arc and resistance welding machines. Some actual operational results are tabulated.

DOI:10.1049/ji-2.1946.0080

出版商:IEE    

年代:1946

数据来源: IET

摘要:

A servo system may be termed an error-actuated automatic control system, or a closed-cycle control. The basic principle finds wide application: for the automatic close regulation of speed, voltage, mechanical tension, etc., and for the remote-position control of gun mountings and the like.One of the major problems in this field is that of achieving an adequate degree of stability; it is shown that instability is mainly caused by response time-lags in the system, and by the basic control characteristic of the servo.It is already known that the addition of controlling signals proportional to the derivatives of error can theoretically produce stability. Such derivatives are seldom available; hence attention is chiefly directed to:(a) Passive networks, which when placed at the input end of the servo give approximations to derivatives and/or integrals of error, so that the system performance is suitably modified.(b) Feedback methods, which achieve results similar to (a), but often have practical advantages.To facilitate calculations and permit the ready determination of constants of the added stabilizing networks, “standard forms” are given, corresponding to linear differential equations up to the sixth order. These forms are not claimed to be of universal application, but they have been found to apply to widely different electric servos.

DOI:10.1049/ji-2.1946.0083

出版商:IEE    

年代:1946

数据来源: IET

摘要:

One of the chief disadvantages of the small alternator compared with the d.c. generator of similar output has been the difficulty in obtaining substantially constant output voltage under all conditions of load without the use of some type of external automatic voltageregulator. This paper describes a machine which overcomes this difficulty and which can be built in a frame no larger than that of a standard alternator plus exciter. Over-compounding can be obtained if necessary, the degree being adjustable after construction. The theory of the machine is discussed, and results of calculation and test are given.

DOI:10.1049/ji-2.1946.0086

出版商:IEE    

年代:1946

数据来源: IET

摘要:

The difficulties which arise in the measurement of the power factor of cable samples owing to leakage over the surface of the dielectric at the ends have been previously studied, but the remedial measures suggested are not always adequate, particularly when the cable is immersed in water at elevated temperatures. Price's guard wire, which acts so successfully in the direct-current measurement of insulation resistance, fails to eliminate all the leakage in the alternatingcurrent case. The author has modified the simple guard wire to make it effective for a.c. measurements, and in conjunction with a suitable bridge it completely avoids the error due to end leakage.

DOI:10.1049/ji-2.1946.0088

出版商:IEE    

年代:1946

数据来源: IET

摘要:

When a potential was applied between the ends of poles 10 ft long the potential difference between points on the lower portions of the poles and earth (the bases of the poles were earthed) was substantially reduced by using earthing collars or spikes. The former were most effective under damp conditions, whereas the latter were equally effective under damp and dry conditions. Shocks would in any event be obtained only when the surfaces of the poles are wet, and these should not be dangerous. These results were confirmed on a number of 30-ft poles used on 11-kV lines. The risk of shock is eliminated by the use of earthing collars.There is little or no danger of fire to poles having moisture contents up to 23%, which corresponds to an atmosphere of 95% relative humidity. There are, however, indications that the moisture content of the heart wood of poles in service for a considerable time in very wet positions may be abnormally high, so that fire readily occurs should the pole be subjected to a high electric stress (0.5 kV per foot of pole length). The field tests described in Section 9 show that abnormal moisture contents of the heart wood are extremely rare. It should also be borne in mind that poles are subjected to high electric stress only when the conductor comes into contact with the pole, which could normally happen only when disintegration of an insulator allows the conductor to rest on the cross-arm. The rarity of this, coupled with the normal dryness of most poles, probably accounts for the scarcity of recorded cases of ignition of poles, which were intentionally arranged to operate with the insulator steelwork unearthed.

DOI:10.1049/ji-2.1946.0089

出版商:IEE    

年代:1946

数据来源: IET