Luigi M. Millanta

Power-line impedance and the origin of the low-frequency oscillatory transients

The three main issues discussed are the origin and characterization of flow-frequency transients, the determination of the impedance of power systems by deliberate switching of capacitors, and suggestions for remedies against these transients. The origin of low-frequency oscillatory transients is attributed to the connection of large capacitances across live wires of the distribution systems. Measurements based on the connection of capacitors of known capacitance across the line are demonstrated to be a natural, accurate, and reproducible means of probing the power-line impedance. This turns out to be constituted by resistance and inductance in the frequency range explored. A physically significant equivalent circuit can be derived, based on the consideration that the three-wire distribution system (phase, neutral, safety wire) consists of three mutually coupled loops. The measurement technique (V-terminal data) permits derivation of both common-mode and differential-mode components. Several conclusions are drawn on the basis of the results of the time-domain transient analysis. Essential quantities of the phenomenon (peak voltage, duration, spectral content) are derived, and corrective measures are suggested. >

The high-frequency behavior of the shield in the magnetic-field probes

Shielded loops are commonly used for magnetic-field emission and susceptibility experiments. The shield is demonstrated to play a role which changes from low to high frequencies. In the lower frequency range it operates as an electrostatic shield while at higher frequencies it carries the field-generating/sensing currents. The consequences are discussed for the probe equivalent circuit, terminal impedance and calibration, and the relevant formulas are given, along with the expressions defining the frequency limits. Experiments accurately confirm the shields HF behavior.

Analysis of the common-mode rejection in the measurement and generation of magnetic fields using loop probes

Radio frequency magnetic fields are measured using loop probes. Among the aspects of nonideal behavior, a dominant and elusive one is the unwanted response to common-mode excitation. Little attention has been given to this effect in literature and means for predicting its rejection in comparison to the (intentional) differential-mode response are not available. Formulas to describe the common-mode rejection are derived in this paper and the role of the physical quantities (mainly geometry and frequency) influencing this behavior is quantitatively discussed and made evident. Experiments and computations confirming the theoretical predictions are offered.

A notch-filter network for wide-band measurements of transient voltages on the power line

A voltage probe to measure power-line 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 to a very high upper limit of 1 GHz. The intrinsic high-frequency limitations of the low-frequency notch circuit are overcome by means of a coordinated parallel high-frequency path. The combination of the two is capable of extremely wide frequency response (in excess of 6 decades) with excellent flatness, within fractions of a decibel in the passband. This voltage probe also satisfies requirements of high linearity and low phase distortion. 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 standards and regulations. >

Circuit Loading in Radio-Frequency Current Measurements: The Insertion Impedance of the Transformer Probes

Considerable inaccuracy can be introduced in RF current measurements through loading effects from the transformer-type RF current probes. A physical model, which consists of a lumped impedance in series with the flow of the current under measurement, is obtained. The correlation between the loading (insertion) impedance and the geometrical and physical characteristics of the probe is clearly described through formulas that are useful for design purposes. The model is compared with those existing in the technical literature, and the main differences are highlighted and discussed. The theoretical predictions are experimentally confirmed. A direct application of the concepts discussed here to the improvement of the accuracy of the V/I -type vector impedance measurements is also shown. This paper is an extended version of the work by Carobbi and Millanta, including a more detailed description of mathematical derivations and experimental results and an updated list of references.

Power-mains transients from connection of resistive loads and a possible capacitive mitigation

The voltage transient disturbances produced in 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. The case of the switching of resistive loads when a capacitor is installed across the line on the mains side of the switch is analyzed. The presence of such a capacitor results in the appearance of double-exponential transients that are considerably smoothed with a maximum rate of change without the capacitor. Low capacitance values are shown to be adequate for giving substantial smoothing, and this technique appears to be suitable for mitigating the rate-of-change related effects of the resistive-load switching. The analytical derivations are based on a three-wire circuit representation of the power line described previously by the authors (1990). The reliability of that lumped-constant model for the analysis of the low-frequency disturbances is confirmed. >

Using the log-normal distribution in the statistical treatment of experimental data affected by large dispersion

There are situations in experimental work where large fluctuations of the measurand are experienced, either because of inherent variations of the observed quantity or because of the complexity of the system process leading to the output quantity. A large spread of the measured values around the center value results. It often appears to the experimenter that the spread of values around the mean is not symmetric, rather, values above the mean obtained by multiplying by a certain factor are approximately as likely as those obtained by dividing the mean value by the same factor. A log-normal distribution thus appears to be a candidate for a representation of the distribution of the observed quantity, at least as a simplifying assumption, when such distribution cannot be assumed a priori on the basis of physical reasoning. A system where large variations of the observed quantity result can be exemplified by the radiator-to-receiver transmission in the dominant presence of reflecting surfaces, such as in a screened room. Overall, large variations are often observed in EMC work, where we are usually faced with complex experimental or predictive processes. In the following, we describe the procedure through which the parameters of the log-normal distribution fitting a given set of experimental outcomes are obtained. This description is applied to the measured field distribution in a screened room.

Helmholtz coils: Static and frequency-dependent performance limitations

Summary form only given. The static performance of Helmholtz coils as used for magnetic-field calibration or susceptibility tests is analyzed with respect to useful field volume and sensitivity to mechanical imperfections. The frequency-dependent behavior is analyzed, and boundaries between quasi-static and high-frequency behavior are shown. The origin of the restrictive limits is discussed, and a lumped-element equivalent circuit is considered.<<ETX>>

A broad-band network for power-line disturbance voltage measurements

The authors discuss the design and realizations of a broadband network and its application to a voltage probe for monitoring the disturbance on the AC power line, including the very low-frequency components above the fundamental 50- or 60-Hz frequency. The circuit is capable of monitoring frequencies from a few hundred hertz to well beyond 200 MHz. The very large bandwidth is obtained by paralleling the basic step-skirt high-pass filter structure with a high-frequency pass-over branch. The basic characteristics such as inband attenuation, power-frequency rejection, impedance, and dimensions compare satisfactorily with existing voltage probes having much larger low-frequency cutoff. >

Results of isolated lower limb perfusion for loco-regional advanced/recurrent melanoma using borderline true hyperthermia plus additional bolus of melphalan. A critical analysis of homogeneous cases

This study was conducted to assess the safety and efficacy of our modified ILP treatment with borderline true hyperthermia and high melphalan concentration in stage III lower limb melanoma.