摘要:

The problems associated with the protection of transmission lines and feeders have in recent years become of great moment, and much development of the art has resulted. Some of the difficulties which have arisen in practice are emphasized and some of the methods of overcoming them are described. The design and lay-out of distribution systems, the earthing of the neutral point and the application of arc-suppression coils are briefly discussed, more particularly in their relation to problems of protection. Factors which influence the choice of protective systems are considered and the requirements of schemes to meet the exacting conditions of modern transmission systems are surveyed.The several methods of obtaining discriminative protection are then reviewed. Commencing with modern design of time-discriminative overcurrent relays, emphasis is laid upon the importance of a definite minimum time characteristic and upon correct methods of obtaining directional features. The special requirements of such relays when applied to give sensitive earth-fault protection are indicated, and means of obtaining a suitable polarizing voltage are explained; a description of sensitive earth-fault relays of the wattmeter type is also given.The theory and application of impedance relays is discussed, with reference to definite-impedance and impedance-time relays. A method of compensation for voltage-drop across the arc resistance of a fault is indicated. The field of application of low-voltage release relays is defined and the method of their use illustrated.Attention is then directed to the advantages of pilot-wire feeder protection, and the limiting features of older forms are mentioned. Typical modern opposed-voltages and circulating-current methods which are giving satisfactory service on modern systems are described in some detail. The new field of direct-current pilot-wire protection is discussed; the main classifications of this type of gear are defined and examples are given. The paper concludes with a description of a novel and flexible method of protection for duplicate and multiple parallel feeders.

DOI:10.1049/jiee-1.1930.0090

出版商:IEE    

年代:1930

数据来源: IET

摘要:

Part (1) deals with some observed errors in quartz piezo-electric resonators employed as frequency standards. It is shown that these are due to (a) frictional loading, and (b) losses arising from atmospheric humidity. The methods adopted to eliminate these are discussed, and the development of calibration apparatus employing the resonators as reference standards is dealt with.Part (2) is in the main concerned with the use of the improved quartz crystal as a control element in a valve-maintainted source of oscillations. The frequency-stability characteristic of such a system is investigated, the errors are found to be largely due to the valve system, and methods designed to eliminate these are discussed.Finally a complete calibration equipment consisting of a multivibrator system with a range of 1–6 000 kilocycles per sec. in steps of 1 kilocycle per sec., centrally controlled by a quartz crystal, is shown.

DOI:10.1049/jiee-1.1930.0097

出版商:IEE    

年代:1930

数据来源: IET

摘要:

The paper describes some of the common methods and the author's new null method of testing instrument transformers.The technical points of the method are discussed and examples are given illustrating the simple derivation of ratio and phase-angle error of current and potential transformers.The accuracy of the method is dealt with, tests on a holetype current transformer are described, and the number of standard transformers required is discussed.In conclusion the author sums up the advantages of the method and describes some interesting applications of it in connection with the testing of power transformers etc.In the Appendix is given the proof of the method.

DOI:10.1049/jiee-1.1930.0099

出版商:IEE    

年代:1930

数据来源: IET

摘要:

The paper describes apparatus for obtaining for purposes of measurement a voltage proportional to, and in phase with, a given alternating current. The Introduction outlines defects in the water-cooled tube resistors which have been in use at the National Physical Laboratory for this purpose; these defects have led to the construction of air-cooled resistors for moderate currents, and current transformers with nickel-iron cores for heavy currents. Section (1) deals with the requirements for the air-cooled resistors, and with theoretical and practical points in their design; tests showing very satisfactory performance are described. Section (2) outlines the construction of the special current transformers, and deals at some length with the method of calibrating them. Finally, the effects of a number of variables on the transformer performance are investigated: the characteristics are shown to be very good, and no sign of instability is found.

DOI:10.1049/jiee-1.1930.0100

出版商:IEE    

年代:1930

数据来源: IET

摘要:

The paper describes in detail how the testing of current transformers may be carried out with speed and accuracy by means of a potential-divider bridge. The corrections to be made to the readings are deduced from the theory of the bridge; and it is shown that, by taking a few simple precautions, an accuracy of 0.01 per cent for ration measurements, and of 0.1 minute for phase-angle measurements, is attainable if the transformer characteristics are stable to this limit.A very sensitive and accurate bridge, which is not so convenient for general purposes as the potential-divider bridge, is than described. Results obtained with this bridge are compared with those obtained with the potential-divider bridge, and found to be in close agreement.

DOI:10.1049/jiee-1.1930.0101

出版商:IEE    

年代:1930

数据来源: IET

摘要:

The factors governing the temperature-rise of electrical machines are so interwoven that the only satisfactory method of separating them is to test actual machines with different distributions of losses, different speeds, etc.; conclusions derived form tests on models must be accepted with caution. In this paper are given the results obtained on two electrical machines, one with a rotating armature and the other with a rotating field, which were tested with different load and field currents, different speeds, etc. The machines were also tested when totally enclosed and when cooled by an induced draught. Temperature-rises were measured by thermometer, by thermo-junction and by the increase of resistance. In the case of the machine with the rotating armature it was found possible to follow the temperature variation of the latter by placing a thermo-junction a short distance away from the armature, and it si suggested that this method might be used for shortening the duration of heat-runs.

DOI:10.1049/jiee-1.1930.0103

出版商:IEE    

年代:1930

数据来源: IET

摘要:

If the heating curve of a coil or a machine were exponential the final temperature-rise could be calculated from the initial portion of the curve and the heating test thereby shortened. A large number of heating curves have been examined, and it is found that the final temperature, as calculated from the rate of increase of resistance, is always less than—often considerably less than—the actual value. The greater part of the paper is devoted to an analysis of the influence upon the shape of the curve, and thereby upon the ratio of the calculated to the actual rise, of such factors as the variation of (a) speed, (b)power generated in winding, (c)the temperature-rise per watt as affected by radiation and natural convection, (d)thermal conductivity, (e)specific heat, (f)point of maximum temperature and (g) heating time-constant.

DOI:10.1049/jiee-1.1930.0104

出版商:IEE    

年代:1930

数据来源: IET