摘要:

In order to predict the noise level of a synchronous machine the paper develops equations to represent the permeance and m.m.f. variation at the stator bore. From these two equations expressions are derived which give the force variation causing vibrations in the core. The method for calculating the amplitude of, and number of nodes associated with, any particular harmonic is given. From this the loudness of the noise in decibels is obtained. Six examples are given of the application of the method to actual machines, on five of which the comparison is made between the results predicted by calculation and those obtained in service. Good agreement is obtained between calculation and observation, and it is thus possible to draw certain conclusions concerning the factors which influence the generation of open-circuit noise, in particular the objectionable noise at about slot frequency in synchronous machines. The paper shows that there are six such factors, namely(a) The stator permeance harmonics caused by the presence of the stator slots.(b) The rotor m.m.f. harmonics caused mainly by the shape and configuration of the rotor poles.(c) The pole pitch of force harmonics.(d) The frequency of the noise which depends on the number of poles and the number of slots.(e) Peripheral velocity of the noise harmonic.(f) Moment of inertia and natural frequency of the stator core.For noise to be generated, factors (a) and (b) must both be present in combination with one or more of the remaining factors. If required the method can also be used to calculate the noise spectrum over a range of frequencies. It is shown that, theoretically, skewing of the stator or rotor may reduce or eliminate open-circuit noise in a machine, but that practical difficulties restrict its field of application.

DOI:10.1049/pi-a.1960.0112

出版商:IEE    

年代:1960

数据来源: IET

摘要:

An earlier paper has described the basic steps which led to a practical form of 8/10-pole induction motor, of good performance, having only one stator winding. The principle on which this speed-changing motor was based has been given the name of ‘pole-amplitude modulation’. Since the publication of the original account of it, the principle has been further developed, and a number of improvements in the method have been devised and tested in practice on several new forms of 8/10-pole motor. This paper discusses the theory and tests on these new machines, which are of interest both in themselves and for the further light which they throw on the principles of pole-amplitude modulation. The tests were completely successful, and this type of machine is now in the repertory of several manufacturers as an established industrial product.

DOI:10.1049/pi-a.1960.0113

出版商:IEE    

年代:1960

数据来源: IET

摘要:

The paper outlines the main differences between motor and generator operation and considers the excitation of generators, in particular when provided by system capacitance. Results are given of tests on machines to ascertain the practical effects of uncontrolled excitation and switch-in currents. Information is given about some advantages arising from the absorption of reactive current produced by long transmission lines and the reduction in voltage drop on lines delivering power.The equipment necessary for control, protection, starting and synchronizing is described, as well as technical matters concerned with drying out windings and checking phase rotation.Three typical schemes are described and a list of existing and planned installations is given.An Appendix deals in more detail with the theoretical values of the equivalent circuit, torque and power factor, as well as circle diagrams.

DOI:10.1049/pi-a.1960.0114

出版商:IEE    

年代:1960

数据来源: IET

摘要:

Investigations show that a satisfactory classification of insulating materials with respect to their resistance to deterioration and breakdown by surface discharges in air is given by time-to-breakdown tests using simple rod and plate electrodes. It is necessary to circulate dry air over specimens to avoid the formation of semiconducting films, and comparison should be made only between specimens of similar thickness. The discharge resistance of most materials is reduced by increasing the ambient temperature or by applying mechanical strain. Results of tests on thin films and sheets of several polymers and on both glass and paper laminates of 1–3 mm thickness are given.Recommendations for standard tests for comparing the discharge resistance of materials are given in the Appendices.

DOI:10.1049/pi-a.1960.0117

出版商:IEE    

年代:1960

数据来源: IET