摘要:

The outputs of electrical machines are generally assumed to vary as the product of the square of the diameter and the length of the machine, although an examination of the outputs of ranges of machines for industrial use reveals that it is common to obtain significantly greater increases of output with diameter than would be expected from the square-law relationship. The basis upon which the classical output equation is founded is examined and an alternative equation based on conductor current density rather than ampere-conductors/unit-periphery is developed which indicates that an output varying with the cube of the diameter might be achieved. Effects on the electrical and thermal performance of ranges of machines based on a cube-law relationship are compared with that obtained assuming a square law, and conclusions are drawn which would support the adoption of the intermediate relationship approximating to the 2.5th power commonly found to occur in ranges of commercially produced machines.The paper also considers factors which influence the choice of machine ‘shape’, i.e. the diameter to length ratio, and shows that though simple consideration of costs will yield a long thin machine, there are other factors, notably the number of poles, which serve to limit the length to the so-called ‘square’ configuration where the length is approximately equal to the outer diameter of the stator core, and indicates how the diameter/length ratio affects the electrical performance.

DOI:10.1049/ij-epa.1978.0002

出版商:IEE    

年代:1978

数据来源: IET

摘要:

The steady-state synchronous behaviour of a large-airgap, single-sided segmented-rotor disc machine is investigated theoretically and experimentally. Two methods of calculating normal forces using Maxwell's stresses are described. Their predictions are compared with measured results. A two-axis model is shown to give acceptable results for large-airgap machines but the use of the harmonic airgap flux density is preferred for small airgaps. Equivalence is drawn between Maxwell stress and energy methods in an Appendix. Prediction of the synchronous performance of a prototype motor by existing methods of analysis is shown to be possible provided that an airgap fringe factor is included in calculation of the direct and quadrature axis reactances. Experimental and theoretical results for torque, current, power factor and efficiency are presented and compared. The pull-in capability of a reluctance motor was found to deteriorate when operated with a large airgap, and ways of overcoming this problem are suggested.

DOI:10.1049/ij-epa.1978.0003

出版商:IEE    

年代:1978

数据来源: IET

摘要:

The maximum transfer of electric energy to the metal in an arc furnace depends on the length of arc and the impedance of the electrical supply system from the generators to the arc itself. The use of directly-reduced sponge iron by continuous feeding results in long periods of flat-bath operation, when it is particularly important to keep a short high-current arc to get the heat into the metal rather than to the refractories, which would suffer excessive wear. The paper illustrates, by reference to a 125 tonne furnace, the method of assessing the optimum operating currents and power factors and the effects of differing powersupply systems. The importance of a low-impedance power system is illustrated, and the possibility of being unable to use the maximum furnace power without excessive refractory wear is noted. The particular problems of connecting arc-furnace loads to electrical supply systems are reviewed, and consideration is given to the problem of voltage flicker. The use of compensators is discussed with reference to existing installations, in which strong supplies from the supply-authority system are not economically available. The furnace operating characteristics, which indicate the optimum points of working, have to be checked on commissioning, and the paper outlines the test procedures. The optimum points for each type of charge and steel can be assessed only during their actual production. The importance of proper recording of relevant data is stressed, and reference is made to the use of computers and automatic power-input controllers.

DOI:10.1049/ij-epa.1978.0004

出版商:IEE    

年代:1978

数据来源: IET

摘要:

Two outstanding events have had a profound effect on UK earth-leakage practice: the introduction of highly sensitive residual-current earth-leakage devices at the beginning of the 1960s, and the prohibition of the use of water-supply pipework as the sole earthing electrodes of installations in the 14th edition of the IEE Wiring Regulations, 1966. The advent of 20–30 mA protection aroused considerable scepticism because of fears that it would be subject to nuisance tripping; in practice, this has only rarely been experienced, but unfortunately mistakes have occurred in the application of both high and medium-sensitivity residual-current earth-leakage devices. This paper, based principally on practical experience, has been written with the object of increasing the interest in and greater general understanding of this vitally important subject, and is mainly confined to applications for standard 415 and 240 V supplies.

DOI:10.1049/ij-epa.1978.0005

出版商:IEE    

年代:1978

数据来源: IET

摘要:

The paper introduces a new type of bidirectional shaded-pole motor, which retains the use of single-turn copper shading rings. The experimental results obtained from a prototype of the new motor are presented and compared with those obtained from a more conventional bidirectional shaded-pole motor that has wound shading coils on both tips of each salient pole. It is shown that the new type of motor can be made to be fully reversing rather than simply reversible.

DOI:10.1049/ij-epa.1978.0006

出版商:IEE    

年代:1978

数据来源: IET