摘要:

Energisation transients in distribution systems are of great concern to the users of equipment supplied by these systems. Such equipment is usually connected to the system by a length of cable. Consequently, the characteristics of the cable are required when any calculations are to be made on the magnitude and nature of such transients. In particular, and as far as high-speed transients are concerned, it is the wave-propagation characteristics of the cable that are of prime importance. Wave-propagation characteristics of the 3-core cables used in distribution systems are, however, difficult to obtain by analytical methods due to the complex geometry of the cable. It will be the purpose of the present work to derive the wave propagation characteristics of a typical 3-core, 3-phase distribution cable for use in transient studies and, in particular, high-speed transient studies. Numerical techniques are described for obtaining the series impedance and shunt admittance matrices from which the propagation characteristics are derived. Studies are made on representative cables and the effect that the various cable parameters have on the propagation characteristics are investigated and illustrated. The effect that the energisation source impedance characteristics have on the wave launched down the cable, and received, are also studied.

DOI:10.1049/ij-epa.1979.0001

出版商:IEE    

年代:1979

数据来源: IET

摘要:

When specifying the winding insulation of electrical machines it is necessary to know the electrical stresses to which the winding will be subjected. In the case of interturn insulation the most severe stresses are caused by steep-fronted voltage waves produced by circuit-breaker closure. To some extent such steepfronted waves are reduced in severity by the time they reach the machine terminals by distortion and attenuation in the cable connecting the machine to the circuit breaker. In the studies described the interturn voltages in the line-end coils of cable-connected machines are evaluated. The equivalent circuits for the machine winding, the cable, and the energising source are obtained and compounded into an equivalent circuit for the complete system. The interturn voltages in the line-end coils of the machine are obtained from solutions of this equivalent circuit. Studies are made with a number of different cable lengths and types, and for a number of energisation source representations. Single-pole and 3-pole simultaneous closure of the circuit breaker are considered. The use of series inductors at the circuit breaker, or shunt capacitors at the motor terminals, for reducing the severity of the interturn voltages is also investigated. The results obtained indicate that the type of cable insulation and the length of cable are both significant in influencing the magnitude of interturn voltages. Energisation source impedance has a large effect. Comparison of seriesinductance and shunt-capacitance methods of surge protection reveals that both methods are effective, but that both produce other unwanted effects.

DOI:10.1049/ij-epa.1979.0002

出版商:IEE    

年代:1979

数据来源: IET

摘要:

This is a general review of the present state of development of silicon rectifier equipment for the supply of d.c. for railway traction. Current general practice is described and reference is made to the latest developments, including compensators for paralleling double-bridge rectifiers, and capsule diodes.

DOI:10.1049/ij-epa.1979.0003

出版商:IEE    

年代:1979

数据来源: IET

摘要:

For an optimal design of switching in power electronics a precise and reliable concept of protection against periodic and transient surge voltages is required. The characteristics of the most important active protective devices – d.s.a.s.-Si overvoltage suppressors, b.o.v. zinc-oxide varistors and b.o.d. breakover diodes – that are used for this purpose are compared here. Calculation and appliction examples are given to demonstrate that each of these three devices has its own application areas and that they complement each other so as to offer an economic and technically optimal surge-voltage protection in every case. Design fundamentals for determining losses and the cooling system sometimes required are presented.

DOI:10.1049/ij-epa.1979.0005

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The revolving-field theory as applied to single-phase induction motors is extended to develop a concise yet comprehensive theory for asymmetric three-phase induction motors. Each phase is represented by its equivalent circuit, not only to allow for uneven direct transformer interactions, due to asymmetric locations of phase windings, but also to account for the different number of turns, wire size, winding factor etc. each phase may have. The accuracy of the theory was confirmed by actual measurements on symmetric and asymmetric three-phase induction motors. Computed and test data on some motors are included for illustration. It is also shown that the general three-phase development can be easily applied to determine the behaviour of two- and single-phase induction machines, a useful feature for unified computer-aided design, by eliminating one and two phase windings, respectively. Not only the procedural details for determining the performance of single- and two-phase induction motors are given, but comparisons of numerical and test results on some output entities are included as well. Though the comparisons among theoretical and test results are made on fractional horsepower motors, the types being built at Universal Electric, the author is certain that the development presented here is equally applicable to all sizes of induction motors.

DOI:10.1049/ij-epa.1979.0006

出版商:IEE    

年代:1979

数据来源: IET