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Power-mains transients from connection of resistive loads and a possible capacitive mitigation
No full textThe voltage transient disturbances produced in the power mains by the connection of resistive loads are analyzed theoretically and experimentally. The effect of a series inductance is included in the circuit model. A fast unidirectional (exponential) waveshape that reduces the instantaneous phase-to-neutral voltage is demonstrated. Differential- and common-mode components are separated, and the basic quantitative formulas are given.
An additional interesting case is analyzed, i.e., the switching of resistive loads when a capacitor is installed across the line on the mains side of the switch. The presence of such a capacitor results in the appearance of double-exponential transients that are considerably smoothed with a maximum rate of change reduced by orders of magnitude in comparison with the case without the capacitor. Low capacitance values are shown to be adequate to give substantial smoothing, and this technique appears suitable to mitigate the rate-of-change related effects of the resistive-load switching. To that purpose, a quantitative analysis is given with simple design equations.
The analytical derivations are based on a three-wire circuit representation of the power line described in a previous paper. This different application and the agreement with the experimental results confirm the reliability of that lumped-constant model for the analysis of the low-frequency disturbances
A notch-filter network for wide-band measurements of transient voltages on the power line
No full textA voltage probe to measure powerline disturbances in a broad frequency range in the presence of high-amplitude transients is described. Design options and experimentally verified performances are shown. The design is based on the sharp suppression of the fundamental ac power frequency by means of an RC notch filter, whereas all other frequencies are passed from a very-low - 3-dB limit of 300 Hz (or even lower) to a very-high upper limit of 1 GHz (or higher). The intrinsic high-frequency limitations of the lowfrequency notch circuit are overcome by means of a coordinated parallel high-frequency path. The combination of the two is capable of the extremely wide frequency response (in excess of 6 decades) with an excellent flatness, within ± fractions of a decibel in the passband. In addition to the basic bandwidth requirement, this voltage probe also satisfies the important requirements of a high-linearity (large transients) and low-phase distortion (high fidelity of reproduction in the time domain). The other performance parameters (such as in-band attenuation, input impedance, power frequency rejection, power dissipation, and dimensions) are equal to or better than those of the relatively narrow bandwidth voltage probes currently specified in the standards and regulations. The design lends itself to reproducible and reliable realization with ordinary components and with little need to resort to practical tricks or tweaking. Design variations are offered for possible simplified circuits with reduced performance. © 1989 IEE
A classification of the power-line voltage disturbances for an exhaustive description and measurement
No full textA classification and related terminology is suggested for the description of voltage disturbances on AC power lines. The current usage in the technical literature and in industrial and instrumentation applications has been incorporated. The disturbances are classed into two categories: waveshape disturbances and superimposed disturbances. The waveshape disturbances are further differentiated according to the type of voltage variations (over- or under-voltages) which are in turn subdivided according to a limit in time duration. The superimposed disturbances are subdivided into persistent and transient types. The former are present as a continuous voltage variation, for an extended period of time, and can be further subdivided into coherent, having a definite frequency spectrum, or random, having a continuous frequency distribution. A persistent random disturbance can be described as stationary or nonstationary, according to whether its spectrum has a statistically constant or nonconstant power density. Experimental examples of transient disturbances are presented and discussed in the light of the proposed terminology and of the physical phenomena (characteristics, origin, propagation, coupling, natural oscillations) involved
Analysis of errors in transient disturbance measurements using high-pass probes
No full textTransient disturbances conducted on the mains are increasingly recognized as important events. Time-domain treatment is essential for the analysis of these transients, which are distinct from other disturbances (cw), where a simpler frequency-domain technique can usually be applied. Transients are measured using a wide variety of devices with a known transfer function (voltage probes, current probes, baluns) to couple the disturbed conductor to the measuring apparatus. All these devices introduce errors due to their transfer function. Most measuring devices are shown to be accurately represented by a single analytical model consisting of a first-order or second-order high-pass network, thus permitting accurate analytical and numerical determination of the output waveform for the more interesting input waveforms, i.e., unidirectional transients (double exponentials) or ringing transients (damped sines and cosines). The distortion at the output results in errors of the more common parameters used to specify the disturbances, namely, peak value, average rate of rise, integral of the squared voltage, impulse strength, and undershoot. These parameters are computed and shown in graphical form, permitting evaluation of the errors simply on the basis of the knowledge of the cut-off frequency of the probing network and of the characteristics of the input transient. Simplified asymptotic treatment is also offered for the determination of the output waveshape for early times and late times. The early-time error is shown to be proportional to the integral of the input signal, and the late-time output waveshape corresponds to the impulse response of the probing network. The above results permit a simple treatment of complex waveshapes. Experimental verification confirms the analytical and numerical predictions. © 1990 IEE
The role of dispersion in fast wavefronts of power-mains disturbances
No full textThe analysis presented relates the transient voltage rate of change to the power main (PM) line attenuation and dispersion (mainly dielectric) characteristics. The initial discontinuity produced by a load connection or disconnection is modified on propagation along the PM line. Attention is confined to differential-mode transients. The response of the line to an ideal step is analyzed to derive limits for the rate of change of the wavefront. The approximate 10 to 90% rise time is derived and FFT computations have been performed for confirmation, as a function of distance along the line from the excitation point. Attention is confined to the incident wave
An analysis of the transients injected into the power mains by inductive-load disconnections
No full textA theoretical and experimental analysis of the transients injected into power mains by inductive load disconnections is presented. The theoretical analysis is based on highly simplified equivalent circuits including actual components, parasitic elements, and equivalent low-frequency and high-frequency representations of the power-main line. A three-wire line (phase, neutral, and safety ground) is considered, permitting the analysis of differential- and common-mode aspects of the phenomena. Experimental results and computer simulations confirm the predictions of the analysis
High-frequency and low-frequency components of the capacitive switching transients in power mains
No full textLow-frequency transients and impedance in the power mains considering line loading
No full textProtection against the transients originated by the connection or disconnection of loads in the power mains is of fundamental importance for the electric energy quality, The knowledge of the parameters of the disturbances and of the characteristics of the mains lines is essential for the mitigation of the unwanted phenomena and for the design of protection measures, This paper offers a lumped-constant analysis of the influence of the network loads on the transient waveshapes, and on the impedance seen when looking into the mains, The complex problem involving two loads and two line sections is reduced to a simplified model permitting analytical treatment with the consequent possibility of prediction and of extraction of the important features. The simplifying assumptions are 1) the line losses are low, and 2) the distance between the loads involved in the transient is short with respect to the total line length, The approximation limits are pointed out and the experimental validation demonstrates excellent agreement, Only the more significant case involving capacitive loading of the line is worked out in detail, Other cases of interest also involving resistive-inductive loading have been treated and are here delineated in summary
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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