摘要:

An induction motor can be constructed in such a way as to produce a magnetic field travelling in a straight line. Such a device can be used to propel a shuttle across a loom. A stator arrangement is described by which the shuttle can be caused to oscillate without the use of switches. With suitable design there is an inherently stable condition. Expressions are derived for the amplitude and period of this oscillation, for an unloaded motor, and for a motor operating against a constant load force. These are used to derive theoretical curves and phase-plane diagrams which are compared with those obtained in practice. Proposed practical schemes are discussed.

DOI:10.1049/pi-a.1957.0028

出版商:IEE    

年代:1957

数据来源: IET

摘要:

The first part of the paper describes experiments performed on a spherical machine. These experiments show that speed ranges up to 5.5:1 can be obtained, and that the speed range obtained depends markedly on the ratio of pole width to pole pitch. They also show that the losses in the machine cannot be accounted for by conventional induction-motor theory. It is shown, however, that the extra losses are due to the fact that the stator is ‘short’ in that it is not continuous round the machine; they are not due to the variable-speed feature.The second part is devoted to a theoretical analysis of the properties of short-stator machines, in the first place without reference to variable-speed properties. Equations are developed which permit the formulation of the salient external characteristics of such machines, it being shown in particular that high efficiencies can be obtained provided there are four or more poles on the ‘short’ stator. This general theory is then applied to the variable-speed case. The theoretical findings are supported by numerous experimental results.Broad design criteria are laid down, but since one of these is that the machine should be large it has not yet been possible to make and test a properly designed machine.

DOI:10.1049/pi-a.1957.0029

出版商:IEE    

年代:1957

数据来源: IET

摘要:

The electrical insulating properties under pressure of a number of halogenated methane compounds and sulphur hexafluoride are compared; sphere-sphere and point-sphere electrode configurations, and alternating, direct and impulse voltages are used. The influence of irradiation is also investigated. Of the gases studied, sulphur hexafluoride and difluorodichloromethane (known commercially as Arcton 6) have the most favourable properties for high-voltage insulation, and additional data are provided for the comparison of these two gaseous compounds. This includes (a) power-frequency breakdown-voltage characteristics of admixtures with nitrogen in uniform and divergent fields, (b) the comparison of the radio and power-frequency uniform-field breakdown voltages at atmospheric pressure, (c) the breakdown-voltage characteristics for a number of concentric-cylinder electrodes at various gas pressures with alternating, direct and impulse voltage, (d) the surface flashover-voltage/gas-pressure characteristics of solid insulation subjected to various forms of tangential stress.Data pertaining to electronegative gases are compared with corresponding data for nitrogen under the same conditions and with transformer oil at atmospheric pressure.Chemical and physical properties, such as decomposition in the presence of electrical discharges and vapour pressure characteristics, and economic factors are considered in assessing the suitability of sulphur hexafluoride and difluorodichloromethane as insulants for high-voltage equipments.Factors contributing to the high electric strength of some electronegative gases are briefly discussed.

DOI:10.1049/pi-a.1957.0032

出版商:IEE    

年代:1957

数据来源: IET

摘要:

In the paper it is suggested that for electronegative gases, where both ionizing and attachment processes occur, the condition for breakdown in uniform fields and the onset of discharges, which may lead to complete breakdown in certain circumstances, in non-uniform fields (with the positive electrode in the high-field region) is that the ionizing and attachment coefficients have the same value.In non-uniform fields and above a certain critical pressurepcthe breakdown and discharge inception stresses coincide, but belowpcthey differ; the gaps processes operating in these regions are briefly discussed.

DOI:10.1049/pi-a.1957.0035

出版商:IEE    

年代:1957

数据来源: IET

摘要:

The paper details the problem of transient stability in electrical power systems and divides the methods used to date into four categories. These categories, with the relevant literature, are briefly reviewed.The paper then describes the theory, method of construction and mode of operation of an automatic step-by-step computer for power-system swing curves; the machine has facilities for two generators only but may be extended in scope by the addition of equipment similar to that already employed. The limitations of this machine are discussed and a direct-analogue method for use with the generator units of a network analyser is then described.The procedure for calibration of the direct analogue is given, and difficulties in the setting up of the analogues of damping power and inertia constant are mentioned. Comparison of the results of a simple swing-curve problem by integraph, step-by-step and analogue appears at the end of the paper.Automatic generator-unit operation on a network analyser is possible with this type of direct-analogue equipment.

DOI:10.1049/pi-a.1957.0036

出版商:IEE    

年代:1957

数据来源: IET

摘要:

The paper describes a method of solution of synchronous-machine transient-stability problems by a more exact electronic analogue representation of the system equations than has hitherto been employed. In the machine analysis emphasis is placed on the variation of field flux linkage during transient disturbances, and reasons are given why this is necessary. The equations of performance are derived in the most convenient form for analogue computing.The equivalent analogue interconnections are given both for time-varying and for constant field flux linkage. The components required for these analogues are considered briefly.The section on computer control deals with the control of integrators with reference to the introduction of ‘initial conditions’, ‘hold’ and ‘compute’ states. A delay unit is described which enables the switching out of a faulted transmission line to be simulated.The results of various problems solved by the computer are presented in graphical form as boundaries between stable and unstable states. It is shown how instability subsequent to the first rotor oscillation may occur, and an explanation is proposed to account for this phenomenon.Synchronous-machine and transmission-line analysis are excluded from the main text for clarity and are presented in detail in the Appendices.

DOI:10.1049/pi-a.1957.0037

出版商:IEE    

年代:1957

数据来源: IET

DOI:10.1049/pi-a.1957.0040

出版商:IEE    

年代:1957

数据来源: IET

DOI:10.1049/pi-a.1957.0041

出版商:IEE    

年代:1957

数据来源: IET

摘要:

The paper describes an experimental thermionic rheostat in which the spacing between the two thermionic cathodes is controlled by rotating the valve while one cathode is held stationary by means of an external permanent magnet. The valve has a small receiving-valve envelope and will control a.c. loads of up to 60 watts when operated as a series resistor from 240-volt mains. Three experimental closed-loop automatic-control systems are described whose electrical circuits consist simply of experimental valves actuated by mechanical error signals and controlling the current delivered to a.c. motors: the systems are a position control, a velocity-integral control for moving materials and an air-flow control.

DOI:10.1049/pi-a.1957.0042

出版商:IEE    

年代:1957

数据来源: IET

DOI:10.1049/pi-a.1957.0043

出版商:IEE    

年代:1957

数据来源: IET