摘要:

The motorised dental handpiece is now firmly accepted as a low-speed rotary dental instrument. Factors affecting the design and acceptability of this instrument are considered in conjunction with a determined specification. Motor gearing, case temperature and control are considered. Experimental data from a handpiece designed according to material presented are compared with data from other rotary hand-held instruments.

DOI:10.1049/ij-epa.1978.0012

出版商:IEE    

年代:1978

数据来源: IET

摘要:

This paper deals with the various causes of motor overheating likely to be encountered with standard motors and starters, and what protection can reasonably be provided. There is no simple and cheap answer to this problem; nor will any form of protection deal with a motor which is unsuitable for its task.

DOI:10.1049/ij-epa.1978.0013

出版商:IEE    

年代:1978

数据来源: IET

摘要:

Modern industry requires more and more fully automatic electrical drives, and the actual control equipment is digital and/or analogue. Usually d.c. motors are used, and for this purpose a.c. to variable d.c. power conversion is required, but recently squirrel-cage motor drives have sometimes been favoured and, for this purpose, a.c. to variable-frequency a.c. power conversion has been developed. In order to improve efficiency and reliability of automatic drive systems, their planning and construction demands extensive knowledge of control theory, and, quite often, more than one feedback loop will be applied. The direct mathematical treatment of the transient behaviour of the closed-loop system and application of the root locus approach is discussed in the present paper, using various types of compensation and smoothing devices.

DOI:10.1049/ij-epa.1978.0014

出版商:IEE    

年代:1978

数据来源: IET

摘要:

The paper develops a method of predicting the electrical performance of arc furnaces. The technique is based on a power chart derived from an equivalent phasor diagram. Comparisons with other methods of prediction and with practical observations are made. An approximate form of the operating chart is also presented which is applicable to systems having a low resistance/reactance ratio.

DOI:10.1049/ij-epa.1978.0015

出版商:IEE    

年代:1978

数据来源: IET

摘要:

The synchronising performance of a 125 MVA synchronous compensator with solid salient poles is studied, and it is shown that, by using a 2-axis mathematical model, predictions of the starting and synchronising performance may successfully be made. The conditions for minimum supply-system transients when pulling into step at reduced voltage, and the subsequent transfer to rated voltage are investigated. A proposal is made for an alternative arrangement in which these operations are performed simultaneously, and this is shown to reduce the severity of the supply transients. Previous studies which considered the synchronising of a synchronous motor with a constant load torque are found to be invalid in the compensator application.

DOI:10.1049/ij-epa.1978.0016

出版商:IEE    

年代:1978

数据来源: IET

摘要:

This paper describes a positive-feedback situation which arises due to interaction between the constant-power input characteristic and the input-filter impedance characteristic, in a d.c. chopper controller. The limiting condition for convergent oscillation is predicted and confirmed by practical measurements on a 250 A, 400 V chopper.

DOI:10.1049/ij-epa.1978.0017

出版商:IEE    

年代:1978

数据来源: IET