摘要:

One of the proposed synchronisation systems for a large-scale p.c.m. transmission and switching complex uses independent oscillators at each station, which are phase-locked to the average phase of all the incoming lines. This paper derives a simple analogue to the system which allows a sufficient stability condition to be stated by inspection. The effect of parameter changes upon the equilibrium frequency is discussed, and a detailed discussion of the initial conditions shows that, for a 2-oscillator system, there are two stable-equilibrium frequencies that the system may reach. The Appendix contains rigorous proofs of the more intuitive statements in the paper.

DOI:10.1049/piee.1968.0305

出版商:IEE    

年代:1968

数据来源: IET

摘要:

The theory of resistiven-port networks has attracted considerable interest during the last decade. This is due, partly, to the fact that results obtained in analysis and synthesis of resistive networks have been applied to many other engineering problems. The field of applications covers all such systems which can be modelised by nets whose branch characteristics may be expressed by real numbers, e.g. communication and probabilistic nets, switching networks etc. In the paper, general equivalence theory of resistiven-port networks is studied. A parametric representation of the whole class of equivalent resistiven-ports corresponding to a given short-circuit admittance matrix is derived. An algebraic-geometric interpretation of this representation is given and some properties pertinent to its continuity and differentiability and to the connectedness of the domain of realisability are then obtained. A special discussion is devoted to certain distinguished subclasses of equivalent resistiven-ports. The results obtained here reveal the internal symmetry inherent in the whole family of equivalentn-ports.

DOI:10.1049/piee.1968.0306

出版商:IEE    

年代:1968

数据来源: IET

摘要:

Propagation tests indicate that the skywave field strength from a medium-frequency broadcasting transmitter can be reduced by 16dB on paths to the north at midlatitudes in the southern hemisphere, when vertically polarised transmission is replaced by orthogonal transmission. The reduction is observed to vary with time and path bearing, the variation with time being such that, during any one night, the median reduction is a maximum when the field strength is high, and a minimum when the field strength is low. Short-term variations are considered to be consistent with a small variation in the limiting polarisation of the ionosphere, and with ray deviations from the most direct path. Long-term variations are considered to be due to changes in the nondeviative absorption from night to night. The observed change in improvement factor with path bearing is in agreement with that expected for the transmitting-aerial configuration. Implementation of this system awaits the development of suitable transmitting aerials.

DOI:10.1049/piee.1968.0307

出版商:IEE    

年代:1968

数据来源: IET

摘要:

A novel method, that of finite elements, for the solution of Helmholtz's equation is suggested. Various 2- and 3-dimensional problems are solved using this method, and the results are compared with more conventional techniques, particularly the finite-difference method, which it may be regarded to supersede. The ease with which various boundary conditions may be handled is discussed and illustrated. Nonhomogeneous configurations present no difficulty, nor do they require any special formulation.There is considerable scope for the further development of the technique, which has, until now, been applied mainly to the solution of Laplace or Poisson equations.

DOI:10.1049/piee.1968.0308

出版商:IEE    

年代:1968

数据来源: IET

摘要:

It is shown that the nonquadrature, tapped-quadrature and shaded-pole forms of single-phase induction motor can be equivalent to a conventional quadrature motor having a common line impedance. It follows that a single equivalent circuit can be used to determine the performance of each form of motor, provided that appropriate values are employed for the circuit elements in each case. In consequence, the same arrangement of a given type of analogue computer can be used to predict the performance of all three special forms of single-phase motor, as well as the conventional quadrature motor. Further, in contrast to some existing equivalent circuits, the presented circuit has the advantage of direct representation of the actual supply currents taken by each form of motor without any transformation of the supply voltage.

DOI:10.1049/piee.1968.0309

出版商:IEE    

年代:1968

数据来源: IET

摘要:

The problem of travelling electromagnetic waves in multiregion induction machines at power frequencies is examined. Using the concept of surface impedance, a method is derived whereby equivalent circuits can be established in a systematic manner. A method of determining levitation force from a knowledge of the equivalent circuit is developed. Calculation of input and output power is simplified using the approach outlined. The ferromagnetic portions of the multiregion system are assumed to have constant permeability.

DOI:10.1049/piee.1968.0310

出版商:IEE    

年代:1968

数据来源: IET

摘要:

The paper presents an analytical and experimental study of the additional losses which occur in induction motors supplied with nonsinusoidal waveforms. Measurements on an inverted induction motor are used to show the importance of losses due to skew-leakage and end-leakage fluxes, and to verify the methods developed for calculating these components. Computed losses are compared with test results obtained on a variety of machines and supply waveforms, and the agreement is shown to be consistently good. The manner in which the losses are related to the machine design and to the supply harmonic content is described.

DOI:10.1049/piee.1968.0311

出版商:IEE    

年代:1968

数据来源: IET

摘要:

Depending on the choice of design parameters, an induction machine can produce a cogging torque sufficiently high to give rise to locking at standstill. It is noted that the commonly used method of analysis of these torques, involving permeance waves, is strictly incorrect, and its use in conjunction with the ‘overlap’ method is inaccurate. The way in which cogging torques arise is discussed in terms of the energy associated with the magnetic field in the machine. A new method is described by which this torque variation can be determined from simple equations. Experiments on machines confirm the results of the analysis.

DOI:10.1049/piee.1968.0312

出版商:IEE    

年代:1968

数据来源: IET

摘要:

Earlier papers have discussed the air-gap flux-density distribution in inductor alternators and have verified the theory by measurement. It is the aim of this paper to show that, with a knowledge of flux-density distribution, it is possible to predict the load performance of these machines from the open-circuit curve—an easily calculable starting point.First, the measured open-circuit voltages are compared with those calculated from previous knowledge of the flux-density wave, which in turn has earlier been compared with that calculated from air-gap geometry. By taking the correct components of armature reaction, it is shown that the voltage at any load point can be obtained by combining these with the open-circuit flux distribution, to obtain a resultant flux distribution, and hence voltage. This involves the intersection of generalised curves, expressing the vector-diagram geometry, with the special curve for the particular machine, expressing the open-circuit-voltage/field-current relation. Examples of this method are given both for the experimental machine and for a much larger commercial alternator, and are shown to predict the load curves under widely varying conditions.

DOI:10.1049/piee.1968.0313

出版商:IEE    

年代:1968

数据来源: IET

摘要:

In the design of synchronous salient-pole generators and motors, current formulas for the output coefficient express this constant in terms either of the apparent power, speed, length of stator core and gap diameter or of the magnetic and electric loading. The paper develops an analysis in which the output coefficient is expressed as a function of the dimensions of the stator core, the magnetic loading and the electric loading related to the temperature rise of the stator winding, in terms of the thickness of insulation and slot dimensions. The output of the rotor is derived as a function of the pole pitch and height of pole. It is shown that there are two optimum values of the mean flux density in the air gap, and that there is also an optimum value of the electric loading, defined as a function of the width of slot. It is also shown that, for a stator designed in accordance with this analysis, there is one value of the height of rotor pole required to accommodate a field coil to establish the m.m.f. required to balance the armature reaction. The theory is illustrated by a series of curves calculated from the parameters of an existing large hydroelectric generator. It is further shown that the overall dimensions and cost could possibly have been reduced by the application of the principles established in this paper.

DOI:10.1049/piee.1968.0314

出版商:IEE    

年代:1968

数据来源: IET