摘要:

The safe operation of large power transistors in motor-drive applications often requires the use of snubber networks. The design of these networks depends upon the type of device being used and upon the circuit configuration. Some operating experience with a monolithic Darlington device is reported. The importance of controlling the switching losses in these devices by the use of snubber capacitors is indicated. It is shown that these capacitors produce side effects in a variable-voltage, variable-frequency inverter which can lead to overcurrent conditions in the transistors. These currents can be controlled by the use of snubber chokes. But the chokes, which are usually included primarily to limit reverse recovery currents in the free-wheel diodes, must be designed according to a different criterion to achieve this. It is suggested that ‘thermal feedback’ should be provided for power transistors in order that they may operate at a safe and stable temperature.

DOI:10.1049/ij-epa.1979.0012

出版商:IEE    

年代:1979

数据来源: IET

摘要:

During the last few years many vibrational problems have been encountered on synchronous and asynchronous machines. The torsional vibrations of a.c. generating sets on ships were so large that a vibrationless parallel operation became impossible. With asynchronous machines, lateral vibrations of the rotor disturbed the operation in such a way that the rotor soon touched the stator inner surface. In both cases the problem was caused by electromagnetic self-excited phenomena, in connection with the mechanical damping of the rotor.

DOI:10.1049/ij-epa.1979.0014

出版商:IEE    

年代:1979

数据来源: IET

摘要:

This paper gives the basic theory of the transient behaviour of protective current transformers with the equations for the primary fully asymmetrical short-circuit current, the transformed secondary current and the required flux density in the core when the secondary circuit is loaded with resistance and inductive reactance at different power factors ranging from cos ψ = 1.0 to cos ψ = 0.2. The design factorsMandMoare introduced and presented in numerical and graphical forms to be used for design relations and performance evaluation of current transformers. The limits for the three basic design parameters are shown, namely the minimum core cross-sectional area, the minimum number of secondary turns and the maximum burden that must be used if it is required from the c.t. to transmit the primary fault current without saturation for a specific length of time, up to 10 cycles, or if the saturation is to be avoided completely. The effects of residual flux, if present, are included.

DOI:10.1049/ij-epa.1979.0015

出版商:IEE    

年代:1979

数据来源: IET

摘要:

This paper is a summary of the Hunter memorial lecture, as given by Mr. H.S. Brown, of the British Steel Corporation in November 1978. The paper provides a comprehensive review of the use of electricity in the steel industry, from the processing of ore to the manufacture of specialised steel products. The systems aspect of modern steel making is emphasised with a survey of present-day control techniques and an assessment of the future role for microsystems.

DOI:10.1049/ij-epa.1979.0016

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The paper examines the characteristics of modern vacuum interrupters, as used in vacuum circuit breakers, and the parameters of plant which they typically control. The overall objective is to assist engineers in the application of vacuum circuit breakers.

DOI:10.1049/ij-epa.1979.0017

出版商:IEE    

年代:1979

数据来源: IET