摘要:

The mechanism of arc extinction in circuit-breakers is discussed. Records of voltage, current, and arc resistance near current zero for an air-blast circuit-breaker are given to illustrate the process and to show how the current may be brought to zero prematurely.Sudden changes of arc resistance are shown to occur near current zero, when the r.m. s. current is low, as for unloaded transformers or shunt reactors, and the way in which these can give rise to current oscillations and sudden interruption of current (current chopping) is illustrated. It is shown that this process is affected by the circuit capacitance and by the circuit-breaker characteristics.The process of current chopping may give rise to high voltages across the shunt reactor or transformer, and the way in which such voltages can be limited by restriking of the circuit-breaker gap is illustrated for both air-blast and oil-break circuit-breakers. Ways of estimating the limiting effect of these gaps from the electric strength of circuit-breaker contact-gaps are given.Comparison of three-phase site conditions and test conditions is made, and limitations of the latter are pointed out.The relation between switching voltages and r.m. s. magnetizing current is studied, and it is concluded that the switching of unloaded transformers gives lower voltages than the switching of shunt reactors. Suitable ways in which the voltage across a shunt reactor may be reduced are described.

DOI:10.1049/pi-2.1953.0116

出版商:IEE    

年代:1953

数据来源: IET

摘要:

The magnetic inverter is a low-level magnetic amplifying device suitable for the input of multi-stage magnetic amplifiers requiring a high sensitivity. The principle of its operation differs from the conventional magnetic amplifier in that the load current corresponds to the even-harmonic m.m.f.'s which are present in any asymmetrically-excited iron-core system.It is found that a capacitor in parallel with the load can increase the gain by a factor of about 15, but that this occurs at the expense of linearity for large input signals.The inverter can have power gains ranging up to about 1 000 with corresponding time-constants of about 1 sec when operating at 50 c/s, whilst the zero stability is well within 10−12watt.The inverter is a valuable addition to measuring and control instruments, and its mode of operation forms an interesting comparison with the theory of the 100% self-excited transductor.

DOI:10.1049/pi-2.1953.0119

出版商:IEE    

年代:1953

数据来源: IET

摘要:

An instrument has been developed for use by airfield maintenance personnel in the checking of turbine-blade clearances, both in turbo-jet and turbo-prop engines. The measurements are made by plugging a cable into various capacitance pick-up points around the shroud ring and spinning the rotor, cither by hand cranking or by the starter motor.The instrument works on a capacitance principle, but the measurement does not depend for its accuracy on the similarity between the pick-ups; balancing, calibration and—ultimately—measurement at a pick-up point are possible without moving the attachment cable, except when changing to the next pick-up. Clearances are indicated on a peak voltmeter, scaled to show the clearance being measured as a fraction of the value to which the instrument has been calibrated. The instrument selects the longest blade and measures its clearance.The instrument has several novel features. The use of a transformer, placed part-way along the pick-up lead and designed to make the whole lead parallel-resonant, not only makes possible the measurement of minute capacitance changes at the end of a long cable but enables a simple resistance bridge to be used for this measurement. This bridge is fed by a stable crystal-controlled 50-kc/s oscillator. With the present equipment it is possible to detect capacitance changes of approximately 0.003 µµF at the end of a cable 23 ft long, requiring an overall capacitance sensitivity, δC/C, of 10−5.The method of calibrating the instrument results in the greatest accuracy of measurement for clearances near the calibration value, the estimated error being less than +5%.The underlying technique may have many other applications in measuring minute capacitance changes, especially where the pick-up is unavoidably remote from the main measuring apparatus.

DOI:10.1049/pi-2.1953.0124

出版商:IEE    

年代:1953

数据来源: IET

摘要:

The design of circuits for fluorescent discharge tubes is considered in general from the point of view of economy in equipment. Various types of switch- and instant-start circuits on a.c. and d.c. supplies, and operating problems in connection with them, are considered in detail. A few general operating problems, such as the neutral current on 3-phase supplies and operation at low temperatures, are also dealt with.

DOI:10.1049/pi-2.1953.0129

出版商:IEE    

年代:1953

数据来源: IET

摘要:

Some existing methods of determining power-system performance are mentioned, and the need of a quick-acting power-system simulator is indicated.Factors involved in power-system simulation are discussed, methods for simulating a synchronous machine using electronic techniques and their application in a power-system simulator are described, and the resulting simulator is shown to behave similarly to the power system represented.By employing comparatively high frequencies and recurrent techniques in conjunction with cathode-ray-oscillographic display equipment, dynamic performance data such as angle/time or swing curves, electrical transients, etc., can be obtained as stationary patterns on the screen of the cathode-ray tube, and effects of change in network parameters can be noted immediately. The method can readily take into account factors normally included in a.c. network-analyser studies: multi-machine problems are handled as readily as simpler ones.Use of the simulator is illustrated. Although the solution of transient stability problems is emphasized, it is pointed out that the instrument is just as useful for other problems, both steady-state and transient. It is concluded that the electronic simulator can provide a quick, convenient, sufficiently accurate and comparatively cheap method of determining power-system performance.

DOI:10.1049/pi-2.1953.0132

出版商:IEE    

年代:1953

数据来源: IET

摘要:

The preparation of large single crystals of silicon-iron in sheet form by the strain-anneal method is described in detail. Whole-sheet single crystals up to 2¾ in wide and 21 in long, and having a crystallographic plane either of the form {100} or {110} in the plane of the sheet, have been made successfully from 2% silicon commercial electrical sheet using Dunn's method. Certain limitations in the orientations it was possible to produce by this means were observed with the materials used, attempts to grow crystals having a {1ll} in their plane, for example, being unsuccessful. The many factors affecting recrystallization are discussed. Carbon contents of the order of 0.015% were observed in several of the crystals prepared.One of the crystals with a silicon content of 2.11% exhibited no phase change up to a temperature of 1 140°C, i.e. 40–50°C above the temperature at which it was grown, and examination by X-rays showed it to be of exceedingly high quality with an estimated range of misorientation of not more than ten minutes of arc.A magnetic torque curve for a 1¼-in diameter single-crystal disc having a {100} cube face in its plane is given, and the magnetization curve in the {100} direction for a “picture-frame” sample of external dimensions 1⅞-in square is also included. The former shows that it is more accurate to take a figure of 89% of the unique infinite field value of the anisotropic constant K1when analysing torque curves obtained on 0.014-in thick discs of 1¼-in diameter in applied fields of the order of 2 000 oersteds, and this figure is in good agreement with the correction suggested by Tarasov.

DOI:10.1049/pi-2.1953.0133

出版商:IEE    

年代:1953

数据来源: IET

摘要:

The paper deals primarily with bushings of the synthetic-resin-bonded paper (s.r.b.p.) type, but many of the factors considered are common to other types.The characteristics required of bushings, and consequently the tests to which they are subjected, are dependent on the conditions of voltage, current, temperature and humidity under which they must operate. Various tests, their objects and limitations and their relation to service conditions are discussed, and a series of over-voltage and quality-control tests suitable for specification purposes are suggested.Finally some methods of site testing and the interpretation of results are discussed, illustrated by a number of service experiences. A method of power-factor testing on load is described.

DOI:10.1049/pi-2.1953.0134

出版商:IEE    

年代:1953

数据来源: IET

摘要:

High-speed automatic computing machines are now established as necessary tools for research and development. Such machines usually work with a binary number system, the numbers being represented by trains of electric pulses. An automatic machine must have a “memory” or storage system capable of storing a very large number of pulse patterns. The two main types of storage now in use are cathode-ray-tube systems and delay-line systems. A delay-line system utilizing quartz-crystal-generated ultrasonic waves propagated in a mercury column, was used in the Ace Pilot model because of its intrinsically higher speed and its reliability. It has an apparent disadvantage with respect to cathode-ray-tube systems in that any given item of stored information is available only once per circulation period, but it is shown that this can be obviated by a suitable logical design and the so-called “optimum” system of programming. The Ace Pilot Model will have a 3-tier storage system, i.e. long delay-lines (32 numbers), short delay-lines (up to 2 numbers) and a magnetic drum. It is shown that with this system and optimum programming the overall speed of computation can be practically as high as if all items of stored information were immediately available.The delay lines and the associated circuit technique are described in the paper.

DOI:10.1049/pi-2.1953.0137

出版商:IEE    

年代:1953

数据来源: IET