摘要:

The paper presents the results of an investigation into the Laws relay type of limited-motion rotary servoactuator. Laws's prediction relations based on magnetic equivalent circuits of the actuator are examined, extended and presented in SI units. Quantitative comparisons between predictions and test results for a large actuator recently designed for an industrial application are discussed. Design aspects are outlined, and the use of the finite-element technique for dealing with highly saturated designs is illustrated.

DOI:10.1049/ip-b.1990.0001

出版商:IEE    

年代:1990

数据来源: IET

摘要:

Steep-fronted voltage transients produced by switching operations are a major source of insulation failure in machine windings. Determination of the severity of these transients is essential if machine insulation systems are to be designed correctly. However, the severity of these transients varies widely depending upon plant parameters and system configurations. Consequently, there is a need to establish, in general terms which plant parameters and system configurations lead to particularly severe transient conditions. Computer studies have been carried out to examine what factors determine the severity of switch-closing transients in a cable-connected motor system supplied from a complex source. The source-side network included full representation of the busbar and its section, multiple cable connections and facilities for transformer of infinite busbar primary supply. The load-side network included the motor cable and a ladder-network representation of the motor winding. The Fourier transform method was used for the solution method so that frequency-dependent variables of the cables could be fully incorporated in the solution. The studies were based on a single-phase system representation simulating first-pole-to-close conditions. Busbar lengths and configurations were found to be of fundamental importance in defining transient severity. Short-busbar lengths and parallel-busbar configurations gave rise to particularly severe transients. The effect of increasing the number of cables connected to the busbar was found to be not as severe as expected, due to the presence of the short-busbar subsections in between the cables. Stray capacitance local to the motor-controlling switch, although not usually taken into consideration in such studies, was found to be a factor of some importance. Motor cable length and motor parameters were found to be of lesser importance.

DOI:10.1049/ip-b.1990.0002

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The operation of a class-E-derived single-ended parallel-resonant convertor is examined both theoretically and practically. The convertor topology is produced from the electric-circuit dual of the class E convertor by the addition of a diode in antiparallel with the switching transistor. The resulting convertor exhibits zero-current-switching characteristics. A fundamental-frequency analysis of the convertor is presented which defines the limits of zero-current switching and the convertor conversion characteristics. Experimental results from a prototype convertor are presented.

DOI:10.1049/ip-b.1990.0003

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The AC-supply voltage waveforms on offshore oil platforms can be heavily distorted during drilling operations. The harmonic and commutation distortion is caused by the drilling rectifiers which drive large DC motors. This paper examines a method of analysing these disturbances, especially the commutation spikes which appear on the high-voltage busbars (the point of common coupling)and are spread throughout the platform supplies. The analytical method uses proprietary CAD software and equivalent-circuits to analyse the waveforms using a time-domain approach. The tool thus developed is used to show directly how the drilling and platform parameters will affect the waveshapes. The effects of firing angle, rectifier rating, platform short-circuit levels and cable capacitance amongst others are discussed. It is also shown that variable-speed drives will have a similar effect. The consequence of sharing generation between platforms is illustrated, as is the use of damper circuits to reduce the commutation spikes.

DOI:10.1049/ip-b.1990.0004

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The paper considers some of the developments that have taken place over the last few years in the field of synchronous machines of unusual geometry. The advances, in common with improvements in conventional drives, have only been possible because of developments in power electronics and materials. In the field of industrial drives, the linear induction motor with its simple variable voltage controller is established as a worthwhile product. Several manufacturers enjoy steady sales. Linear synchronous motors are a comparatively new development in this field; they have the virtue of considerably higher force production but require a variable frequency supply. However, in small sizes, power integrated circuits have become available that can be used to power the machines as brushless DC drives. A tubular version using permanent magnet excitation is described. In the area of transportation it is evident that, in the schemes under investigation, the linear synchronous motor is beginning to dominate the position. The most developed high speed systems use long-stator synchronous machines. However, short-stator versions are also under investigation, and the paper describes some recent studies. The development of disc brushless alternators is also described. In these machines the excitation winding is located on the same side of the airgap as the AC winding. A demonstration of the use of the new ‘high’-temperature superconductors, which uses a double disc form of these machines, is outlined.

DOI:10.1049/ip-b.1990.0005

出版商:IEE    

年代:1990

数据来源: IET

摘要:

Calculations of induced voltage in metallic lineside cables have traditionally been made using simple methods based upon the explicit solution of transmission line equations. These methods were developed about 40 years ago with an emphasis on lead-sheathed cables which were in continuous contact with the ground. The paper reviews the limitations of the classical approach and concludes that in-secton induced voltages are significantly overstated by this approach. An alternative computer-based approach is presented which is more appropriate for modern cables, with insulated outer sheaths, which are normally earthed by discrete earth-rod connections along the cable. This new approach, which is illustrated with reference to CAD techniques developed for autotransformer and booster-supplied AC railways, should permit a more realistic and economic approach to specifying screening requirements for copper cables. Examples of the use of the developed software for assessing induced voltages in the recently electrified 2 × 25 kV North Island Main Trunk in New Zealand are also presented.

DOI:10.1049/ip-b.1990.0006

出版商:IEE    

年代:1990

数据来源: IET