摘要:

If the values of the 2psteps of equal durationT/2p, generating an alternating signal whose period isT, are chosen in order to eliminate all the harmonics whose order is between 2 andp, Y.H. Ku's transformation of a 3-phase balanced system of such signals gives components of periodT/2p, whenpis equal to three or a multiple of three. Only one-2pth of T is necessary to study the supply of a load as it is shown in the case of an asynchronous motor.

DOI:10.1049/piee.1977.0113

出版商:IEE    

年代:1977

数据来源: IET

摘要:

The paper describes a control system in which a cycloconvertor is connected between the secondary winding of a 3-phase induction motor and the a.c. mains supply to give variable-speed subsynchronous and supersynchronous operation. Considerations of power flow in the secondary circuit show that for stable operation the cycloconvertor must be controlled from a frequency signal source synchronised to the secondary e.m.f. A secondary e.m.f. signal generator is described which produces the necessary control signal and provides a means of power-factor control. A simple model is proposed in which the cycloconvertor appears as a current source in the secondary circuit of the machine. Experimental results are presented showing smooth operation below, through and above synchronous speed with either driving or braking torques.

DOI:10.1049/piee.1977.0114

出版商:IEE    

年代:1977

数据来源: IET

摘要:

The paper presents a method of numerically integrating a system of differential equations based on an idea of orthogonal approximation of functions. Here, block-pulse functions are chosen as the orthogonal set. The method gives piecewise constant solutions with minimal mean-square error and is computationally similar to the familiar trapezoidal rule of integration. Design of piecewise constant controls or feedback gains for dynamic systems can be simplified following this approach.

DOI:10.1049/piee.1977.0119

出版商:IEE    

年代:1977

数据来源: IET

摘要:

Precision measurements of losses in low-loss liquid dielectrics at microwave frequencies may be performed by means of a bridge method described by Lynch and Ayers. The paper describes modifications to such a bridge in order that measurements may be made over a range of temperatures. Results are presented for the temperature variation of loss angle at X-band in two very low-loss materials (cyclohexane and cycloheptane). The errors arising in the measurements are analysed; the overall likely error in the determination being ±(1μrad or 2.4%).

DOI:10.1049/piee.1977.0120

出版商:IEE    

年代:1977

数据来源: IET

摘要:

By considering the variation between runs comprising a given experiment, between the average results of independent experiments and between the extrapolated results of different experimental methods, some assessment of the systematic and random errors to be expected in high-frequency dielectric measurements is obtained. The liquid investigated is chlorobenzene as this has good chemical properties, possesses a rigid molecule and has been extensively investigated over a wide frequency range by other workers. Our results show that the random errors are frequency dependent but have average values of ±1.5% for α and ±0.1% fornbut that the systematic errors may reach as much as ± 3% for α and ± 0.6% fornin the difficult regions. By combining data over a wide frequency range one may arrive at continuous curves whose estimated errors are ±1% for α and ±0.2% forn.

DOI:10.1049/piee.1977.0121

出版商:IEE    

年代:1977

数据来源: IET

摘要:

A simulation technique is described to generate both transient and steady-stateB/Hcharacteristics including hysteresis. The basic linear model is defined by three constant parameters, and, by refining these parameters to be nonlinear functions, the accuracy of representation is then improved. Additional features to improve the modelling technique for recoil characteristics are discussed. Good agreement was obtained between predicted and measured values for a wide range of materials.

DOI:10.1049/piee.1977.0122

出版商:IEE    

年代:1977

数据来源: IET

摘要:

Samples of grain-oriented 3¼% silicon iron have been tested for magnetostriction when magnetised at 90° to the rolling direction, and the effects of tensile stress have been observed. These tests were performed on coated and decoated samples, and included the effect of magnetic annealing. From variations in magnetostriction, an assessment has been made of the internal stresses in the materials, and a stress equivalent for magnetic annealing has been deduced. The influence of the coating has been considered in the light of the various stresses which it sets up, both on the magnetostriction and magnetic-annealing processes. A comparison has been made of the differing contributions of the coating to the performance of conventional and highly oriented silicon iron.

DOI:10.1049/piee.1977.0123

出版商:IEE    

年代:1977

数据来源: IET

摘要:

Uniform-field electric-strength measurements on a range of fluorocarbon vapours are reported. The fully fluorinated compounds were examined over a temperature range of −40°C to temperatures just below the respective boiling points and for gap spacings in the range 1.5–5 mm. The electric strengths and breakdown distributions are interpreted in terms of the ionisation and attachment processes taking place. The utilisation of the exceptionally good dielectric properties of these materials when operated as evaporative coolants/insulants is discussed.

DOI:10.1049/piee.1977.0124

出版商:IEE    

年代:1977

数据来源: IET