Showing papers on "Harmonics published in 1980"

Reactive Power in Nonsinusoidal Situations

Abstract: Reactive power is interpreted as a time-domain reciprocating flow of energy, with a formulation that is valid for any periodic waveforms It is shown that the current can be resolved into orthogonal components, and that the current and power components can be measured with practical instrumentation

Theory and Simulation of the Gyrotron Traveling Wave Amplifier Operating at Cyclotron Harmonics

Abstract: An analytical expresion for the efficiency of the gyrotron traveling wave amplifier is derived for the case of nonfundamental cyclotron harmonic interaction. It scales the efficiency with respect to the modes and parameters of operation. This relation, together with a general linear dispersion relation, also derived in the present paper, gives the characteristics and optimum operation conditions of the gyrotron traveling wave amplifier.

Harmonics in multiple convertor systems: a generalised approach

Abstract: This paper describes a method which has been developed (and used) to calculate the harmonics associated with systems containing a large number of convertors and other sources of harmonics, e.g. steel mills or large h.v.d.c. convertor stations. The method used is a steady-state (frequency-domain) analysis in which each convertor can be individually described in detail. The effect of the a.c. system impedance and harmonic filters is catered for by using an iterative procedure. By this method, voltage harmonics and unbalances caused by, for example, arc furnaces, system impedance, system unbalances, transformer saturation, firing unbalances and the effect of firing angle and load, can all be fully represented to give a final level of harmonic current injection into the a.c. system, or the voltage distortion of the a.c. busbars. The multiconvertor aspect of the problem, involving different convertor transformer phase shifts, is handled using a transformer/convertor matrix method. This method is therefore useful in examining new and planned extensions to existing systems to check whether they meet the requirements of standards, (such as Electricity Council recommendation G5/3).

Harmonic reduction in d.c.-ripple reinjection

Abstract: A d.c.- ripple reinjection principle is described which reduces the harmonic content produced by static convertors. It is shown by theory and experiment that, using this principle, a six-pulse convertor configuration can be made to operate as a twelve-pulse convertor from the point of view of a.c. and d.c. system harmonics. The reinjection circuit includes a feedback convertor in series with the d.c. output. This convertor provides automatic adjustment of the reinjected current as the load changes and improves the efficiency of the overall system.

Rectifier Harmonics in Power Systems

Abstract: The effect of rectifier harmonic currents on power systems is described. Rectifiers and inverters require nonsinusoidal waves of current. These current waves are made up of a number of sine waves which are harmonics of the fundamental wave. These harmonic currents can excite resonant circuits causing them to ``ring'' and produce large oscillating currents. Criteria as to possible problem areas are discussed and illustrated with case studies. Examples of application of filters to ``trap'' these harmonic currents are included.

Pole-amplitude modulation, pole-changing electric motors and generators

Abstract: A pole-amplitude modulation (P.A.M.) three-phase, pole-number changing machine having star-connected and delta-connected stator winding components, thereby providing additional means for reducing m.m.f. harmonics in the resultant three-phase field. Pole-number changing is effected by reversing the star-connected winding component relatively to the delta-connected component. A design method defines relationships between alternative pole-numbers and stator slot number, and slot-spacing between star- and delta-connected components.

Harmonic generation in organ pipes, recorders, and flutes

Abstract: A simplified treatment is given of the mechanism of sound production in musical instruments driven by air jets, which is sufficiently explicit that semiquantitative predictions can be made about the effects of certain variables upon the harmonic structure of the sound produced. In particular it is found that the amplitude of the even harmonics, generally, and of the second harmonic, particularly, is quite critically dependent upon the offset of the pipe lip from the symmetry plane of the jet. A completely symmetrical relationship (zero offset) reduces the generated amplitude of the second harmonic by a large factor. Experimental results with an adjustable organ pipe are found to confirm these predictions. The implications of these results for the voicing of organ pipes and recorders and for subtle tonal variation in flute playing are briefly discussed.

Harmonic Reduction in Inverters by Use of Sinusoidal Pulsewidth Modulation

Abstract: This paper presents a new technique for harmonic reduction in inverters using sinusoidal pulsewidth modulation. In this inverter, the output wave with sinusoidal pulsewidth distribution can be kept in maximum degree of symmetry, and so it offers excellent harmonic control in comparison with any other modulation technique. Detailed analysis shows that the harmonics lower than the ninth (or the thirteenth) are all less than one percent of the fundamental component when the number of pulses per half cycle is over seven (or nine). These results are confirmed by the theoretical data obtained from the natural sampling, and the experimental observations for single-phase full-bridge sinusoidal pulsewidth modulated (SPWM) inverters. It is concluded that by the use of this new technique it is quite easy to design an inverter with a distortion-free sinusoidal output.

Forced Vibrations in an Unsymmetric Piecewise-Linear System Excited by General Periodic Force Functions

Abstract: This paper discusses forced vibrations in an unsymmetric piecewiselinear system excited by general periodic force functions. The system has no damping. The superharmonic resonances up to the second order are analysed by means of a perfect Fourier series method. As the simplest example, the exciting forces are assumed to be of even function with the second higher harmonics only. The theoretical resonance curves are computed by a digital computer and are compared with the results obtained by an analog computer. They show a fairly good agreement.

Harmonic generation in free molecules

Abstract: A molecular theory of harmonic generation in free molecules is developed using the principles of quantum electrodynamics. A Cartesian tensor formalism is employed and emphasis is placed on the rotational average which is required to account for the random molecular orientations in the pump beam. It is demonstrated that even harmonics are forbidden to all orders of the multipolar interaction Hamiltonian and in the appendix a new relation involving the rotational average of an arbitrary rank Cartesian tensor is presented.

Modulated structure of thiourea [SC ( N H 2 ) 2 ]

Abstract: To verify the condensation of higher-order harmonics of the soft mode in incommensurate phase, group-theoretical consideration and detailed structure analysis have been made of the incommensurate phase of thiourea. The group-theoretical consideration shows that extinction rules observed by neutron diffraction imply condensation of even-order harmonics. An analysis based on a four-dimensional space group also confirms the condensation of the second-order harmonics.

Second harmonic generation from pulsed copper vapor laser radiation

Abstract: An investigation was made into second harmonic generation, in an ADP crystal, of pulsed copper vapor laser radiation. The dependence was found of the conversion efficiency on the average excitation radiation power. The maximum conversion efficiency was 8.5%. Thermal self-interaction effects were found to be the principal factor limiting the attainment of high average powers at the second harmonic frequency.

Modes of vibration and sound radiation from tuned handbells

Abstract: Although handbells can vibrate in many different modes, only the two modes of lowest frequency are normally tuned by the bellcrafters. The frequency of the second mode is generally tuned to be three times that of the first. Each of these modes also radiates sound at twice the modal frequency, however, so that the radiated sound spectrum includes the second and sixth harmonics as well as the first and third. The amplitude of the second harmonic partial is proportional to the amplitude of the fundamental, and a similar relationship relates the sixth harmonic to the third. The first and third harmonics are radiated most strongly at right angles to the bell axis; the second and sixth harmonics are maximum along the axis. Small asymmetries in the bell often create warble due to beats between the two components of a split modal doublet. The tonal quality of a handbell depends upon the clapper strike point, the hardness of the clapper, and the force of the blow in addition to the design and construction of the bell itself.

An Analysis of the Harmonic Impedance of a Saturated Induction Machine

Abstract: Design of inverters for use with induction motors requires a knowledge of the impedances of the machine to harmonics of the supply frequency. This paper presents an harmonic equivalent circuit and describes how its parameters may be obtained. It shows that, when the harmonic current magnitudes and relative phase angles are such as to produce phase modulation of the rotating field, the harmonic magnetizing inductance is equal to the fundamental saturated magnetizing inductance. When the current harmonics produce amplitude modulation of the rotating field, the harmonic magnetizing inductance is equal to the incremental slope of the fundamental magnetization curve at the point of operation. Measurements made with phase currents having controllable harmonic content are presented to corroborate the theory.

Determination of Harmonics of Converter Current and/or Voltage Waveforms (New Method for Fourier Coefficient Calculations), Part II: Fourier Coefficients of Nonhomogeneous Functions

Abstract: A new method of determining Fourier coefficients is described. The advantage of the method is the substitution of algebraic addition to replace the integration operation in Fourier analysis. The method is applicable to every periodic function that satisfies Dirichlet conditions. Several waveforms of converter voltages and currents are analyzed as examples for the method.

Instability in h.v.d.c. schemes at low-order integer harmonics

Abstract: A method is described which can be used to calculate the harmonics in convertor systems both with fmite a.c. and d.c. impedances. The method is used to investigate a type of instability in h.v.d.c. schemes which can only be shown if fmite a.c. and d.c. side impedances are used in calculations.

Mean-Field Theory of Peierls and Spin-Peierls Instabilities –Commensurability, Harmonics and Dimerized-State Pinning–

Abstract: Mean-field study of the Peierls instability is made at zero temperature with the electron occupation number varied over a wide range between half-occupancy and nearly zero-occupancy. Total energy of the system, order parameters and the lattice displacement pattern are calculated by taking account of all the accompanying harmonics. The lowering of the total energy per atom is shown to be very large in the neighborhood of the half- and 1/15-occupancies. The amplitudes of harmonics increase drastically as the electron number approaches the zero-occupancy. The spin-Peierls transition is also studied with an XY model. Although the effect of magnetic field on the spin-Peierls system has a close similarity to that of the electron number variation on the Peierls system, an important difference between them is pointed out on the pinning of a dimerized state.

Simulation of lower‐hybrid heating in a nonuniform plasma slab

Abstract: A computer simulation study of the excitation of lower hybrid waves by external sources and the associated plasma heating is presented. A plasma slab with a nonuniform density profile is modeled with a two and one‐half dimensional electrostatic particle code. Both a finite‐length electrostatic antenna and a single wave exciter are considered. The frequency is chosen so that a wave conversion layer exists in the plasma. It is found that a narrow sheath is formed at the plasma edge and the dominant effect is surface electron heating within that region. Ponderomotive force effects as well as the nonlinear generation of harmonics and subharmonics also occur. A low amplitude lower hybrid wave is observed to be excited by the sources and propatates to the wave conversion layer where it is absorbed.

Method of inspecting internal pressures in sealed containers

Abstract: A nondestructive method for inspecting internal pressures of sealed containers wherein a magnetic impulsive force is impinged upon a metallic surface of the container and the resulting vibration of the metallic surface is detected. The detected signal is applied to a plurality of band-pass filters from which the fundamental and harmonics are extracted. The two highest level signals extracted from the band-pass filters, designated the fundamental and a harmonic, are selected, which signals are analyzed by comparison to predetermined values for level and frequency and for their ratio of their levels with respect to one another. A judgment as to the integrity of the sealed container may be made based upon the deviation from the aforesaid predetermined values.

Polyphase ferroresonant voltage stabilizer having input chokes with non-linear impedance characteristic

Abstract: Power conditioning apparatus particularly suited for computer facilities and including non-linear input chokes connectible with line power. The outputs of the input chokes are serially, magnetically coupled through primary windings to pulse saturable reactors of a synthesizing network which includes a capacitor bank and operates to synthesize a sinewave output. Series tuned traps are coupled to the synthesizer network to avoid the development of harmonics above fundamental.

Remarks on Spatial Distribution of Long Period Variations in the Geomagnetic Field over European Area

Abstract: Geomagnetic observatory data were analysed to obtain the spectral amplitudes and phases of the 27-day variation and its harmonics over a network of mostly European observatories, but extended to global scale by including some suitably distributed geomagnetic stations on other continents. The spectral amplitudes, estimated by different methods, were subjected to spherical harmonic analysis by expanding the geomagnetic potential function into a series of spherical harmonics up to the 2nd order and by calculating the corresponding coefficients. The contours of the H and Z components were then calculated to analyse their latitude-longitude dependence over European area. The moduli of electromagnetic response functions estimated from global data for individual harmonics were compared with the results obtained previously for European data only. The distribution of deviations of (Z/H) ratios defined by differences between the actual data and the theoretical fits were investigated. Using the theoretical basis of electromagnetic induction in stratified conductors, we estimated the depths of a perfect substitute conductor at those depths from characteristics of the 27-, 13-, and 9-day variations.

Beamed microwave power transmitting and receiving subsystems radiation characteristics

Abstract: Measured characteristics of the spectrum of typical converters and the distribution of radiated Radio Frequency (RF) energy from the terminals (transmitting antenna and rectenna) of a beamed microwave power subsystem are presented for small transmitting and receiving S-band (2.45 GHz) subarrays. Noise and harmonic levels of tube and solid-state RF power amplifiers are shown. The RF patterns and envelope of a 64 element slotted waveguide antenna are given for the fundamental frequency and harmonics through the fifth. Reflected fundamental and harmonic patterns through the fourth for a 42 element rectenna subarray are presented for various dc load and illumination conditions. Bandwidth measurements for the waveguide antenna and rectenna are shown.

Electromagnetic flowmeter system

Abstract: An electromagnetic flowmeter system whose electromagnets are excited by a direct-current source through switching means operating at a predetermined drive frequency to generate a pulsatory current establishing a magnetic flux field in the flow tube through which the fluid to be measured is conducted. The fluid intercepting this field induces a pulsatory voltage in the metering electrodes mounted at diametrically-opposed positions on the tube. The electrode voltage is applied to an analyzer which includes a sampling switch operating in synchronism with the drive frequency to extract pulses from the electrode voltage during the magnetic flux steady state intervals thereof. These pulses, which are rich in harmonics, are fed through a filter that selects one of the harmonics to yield a harmonic signal which is demodulated to produce an output signal free of disturbances.

Short-range doppler radar

Abstract: In a Doppler radar system for measuring the velocity of a vehicle, such as an automobile, in order to lessen interference with external electric wave appliances, such as radios and televisions, caused by transmitting microwaves, one of the higher harmonics generated from a mixer diode driven by the fundamental waves of a local oscillator is selected by a filter for transmission and is used as the transmission output wave, whereby the power of the transmission waves is remarkably reduced in comparison with the mixer driving power.

Higher order modes in non-sinusoidal volume phase holograms

Abstract: It is shown with the aid of analytical approximations and numerical calculations that the amplitudes of higher order modes in a volume phase hologram (thick phase grating) are only marginally affected by harmonics in the permittivity modulation.

Static compensator for fluctuating load power supply circuits - is typically for arc furnaces and has thyristors in antiparallel to absorb reactive power (BR 23.12.80)

Abstract: The thyristor based static compensation is for fluctuating load reaction power drawn from an AC distribution network. The load is typically an arc furnace where short and open circuit conditions rapidly succeed each other. The compensation circuit is intended to cope with rapid transients and to work in conjunction with normal more slowly reacting regulation circuits. The arc furnace etc.(1) is connected directly across the supply (4) and has an associated filter bank (5) across it removing harmonics. The compensator proper has a shunt capacitor bank (6) matching the reactive power handling capability of the circuit and a thyristor reactive power absorbing circuit (7). The thyristors are fired as a function of a reactive power sensor (11) output fed from the supply and a subtraction circuit (12), the sensor having a series active filter (13).