摘要:

A transmission-line treatment has been used to explain the variation of capacitance and dissipation factor of cylindrical porous-anode bodies as a function of frequency due to the distributed resistance of the electrolyte within the pores. A correction has been determined to account for the effect of the ends of the cylindrical body. An effective resistivity is determined from experimental results which is a function of rhe volume of either the solid or liquid electrolyte and is also a function of the proportion of closed pores. A packed-sphere model is used to indicate the effect of the mean metal-particle size. The theory is applied to experimental results on a tantalum electrolytic capacitor.

DOI:10.1049/piee.1970.0291

出版商:IEE    

年代:1970

数据来源: IET

摘要:

A new method of connection for 3-phase windings is described. It is shown that a conventional 60° phase-spread winding can be subdivided into two components, one of which is connected in delta and the other in star, the two winding components being connected in parallel to a 3-phase supply. Theoretically, the new principle is only applicable where the number of slots per phase is infinite, but it is demonstrated that entirely satisfactory results can be achieved with reasonably small numbers of armature slots. Simplicity of construction is considered to be very important, and, in each of the windings discussed, all the coils are identical and carry currents of equal magnitude. Theoretical examination shows that the new method gives a higher fundamental spread factor than for a conventional 3-phase winding, and a superior m.m.f. waveform, as well as providing a means of reducing the effective number of turns in series per phase. The theoretical studies were verified by tests on a 3-phase squirrel-cage induction motor.

DOI:10.1049/piee.1970.0293

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The voltage equations of the slip-ring motor including the multiple armature reaction, i.e. the primary, secondary and tertiary armature reaction, are derived and presented in matrix notation. The theory put forward is valid for integral-and fractional-slot windings. With integral-slot windings and equal numbers of phases in the stator and the rotor, the current and field harmonics are neither influenced by delta connection nor by parallel branches of the winding (unlike the squirrel-cage motor). A system ofncomplex equations, for which, in general,n= 14, …, 30 suffices, is used to determine thenunknown stator-and rotor-current harmonics. The field harmonics, losses, torques etc. are obtained from the current harmonics. As an illustrative example, the system of simultaneous equations withn= 18 is solved for a 4-pole 70kW motor having 48 stator 36 rotor slots. The magnitudes and frequencies of the stator-and rotor-current harmonics for several coil pitches and slot skewings are given, and the resulting flux-density harmonics in the air gap are determined. The results are compared with measurements and are in agreement with them.

DOI:10.1049/piee.1970.0294

出版商:IEE    

年代:1970

数据来源: IET

摘要:

A modified method of power-system transient-stability assessment is presented and shows that, although they were previously considered to be negligible, the inclusion of the effects of variations of rotor angular velocities can have an influence on the stability as great as that of other factors (such as the voltage regulator saturation, flux decay and machine damping) which it is already considered worthwhile to incorporate in system calculations. The present study, although limited to treating synchronous machines as being frequency-dependent, can be extended to other power-system units, and it points to the need for a reassessment of the role of transient frequency deviations in transient-stability studies.

DOI:10.1049/piee.1970.0295

出版商:IEE    

年代:1970

数据来源: IET

摘要:

Theoretical steady-state power/rotor-angle expressions are derived for a salient-pole synchronous machine with hysteresis in the field and armature members represented by idealised elliptical flux-density/magnetising-force characteristics. It is shown that the effect of hysteresis may be represented in an equivalent machine simulation by modified unequal values of direct and quadrature axis effective armature resistance. The displacement angle between m.m.f. and flux is measured by different methods, and, for a reversal of rotor angle movement, an approximate method is described to represent a recoil line on the power/angle characteristic. Predicted and measured characteristics are in close agreement and show that the effect of hysteresis is to increase the steady-state-stability limit.

DOI:10.1049/piee.1970.0296

出版商:IEE    

年代:1970

数据来源: IET

摘要:

For devising a general guidline on lightning protecting of distribution substations connected to overhead lines through cables, the surge voltages at both ends of the cable are derived for various types of incident lightning surges. The substation is represented by an open-circuited cable, which would result in surge voltages at the cable terminations equal to, or more severe than, the surge voltages for practical installations. The results are used to assess:(i) whether protective devices are needed(ii) when they are needed, whether surge diverters at one end of the cable provide adequate protection.Attention is paid to the surge strength of the line insulation, as on it depend the types of incident lightning surge to be used in devising general guidelines.

DOI:10.1049/piee.1970.0298

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The optimal control of continuous-time linear multivariable systems with finite- and infinite-time quadratic performance is investigated using the maximum principle. The time-varying optimal-control law is shown to be related to the matrix Riccati differential equation, and a solution is obtained in terms of the components of the transition matrix associated with the linear system of 2ndifferential equations in thenstate variables and thenadjoint variables. The time-varying transition-matrix formulation is also used to develop a solution of the steady-state matrix Riccati and associated Lyapunov equations. The infinite-time optimal-control solution is derived in terms of partitioned eigenvector components related to the stable modes of the augmented system, and the technique is shown to be similar in principle to the method previously developed for reducing the order of a set of matrix differential equations by neglecting high-order modes. The results are also shown to be related to the solution of the algebraic Riccati equation and are used to develop an eigenvector solution for the Lyapunov equation. The techniques are extended to consider the optimal control of the linear system containing input derivatives. Results are obtained for the optimal control of a 1st- and 2nd-order linear system and for a 6th-order model representing the dynamics of a superheater system. The various techniques available for obtaining a solution of the linear optimal-control problem, namely the recurrence-type control algorithm based on dynamic programming, the eigenvector solution of the steady-state Riccati equation and the solution obtained by numerical integration of the time-varying Riccati equation, are compared.

DOI:10.1049/piee.1970.0300

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The problem of deriving a sufficient condition for a given nonlinear system with a high-frequency input to be asymptotically stable is considered. It is suggested that the dynamics of the disturbed motion of the nonautonomous system can be approximated to sufficiently well by applying the concept of the so-called ‘modified nonlinearity’. The system so obtained is in a form to which the theorem of Popov is applicable and provides a sufficient condition for the approximate nonautonomous system to be asymptotically stable. The results of this approach for systems with high-frequency sinusoidal and random input signals are examined. Some numerical examples are also presented to illustrate the simplicity of the method and also its usefulness.

DOI:10.1049/piee.1970.0301

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The properties of (pointwise-state) controllability and observability are generalised to apply to systems not in state-space form. A standard form is given for system matrices in second form, and for transfer-function matrices, and is shown to be unique. The standard form is used to analyse the controllability and observability (as generalised) of cascaded systems.

DOI:10.1049/piee.1970.0302

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The current to a large (radius = 2.4 mm) negatively biased spherical probe in a flowing plasma (a propane/air flame) has been measured over wide ranges of plasma-ionisation density (3 × 1015to 1018m−3), probe bias (10–400V) and probe/plasma relative velocity (3–40m/s). Under these conditions, the sheath surrounding the probe is thin and the probe current is a function of the probe/plasma velocity. In consequence, the static continuum probe theory of Su and Lam, and the motionally dependent thick-sheath theory of Clemenets and Smy are both found to be in error by at least an order of magnitude. A thin relationship has been derived for the spherical probe which shows excellent agreement with the experimental data:I=12.13(με0)1/4(neevf)3/4V1/2rp5/4whereI= probe current, μ = ionic mobility, ε0= permittivity of free space,ne= ionisation density,e= electron charge,vf= flow velocity,V= probe bias andrp= probe radius (all in MKS units)

DOI:10.1049/piee.1970.0303

出版商:IEE    

年代:1970

数据来源: IET