1,721,162 research outputs found
Analysis of the dc link current spectrum in voltage source inverters
No full textA general expression for the spectrum of the dc-link current of single- and three-phase voltage source inverters is presented to predict the amplitude and frequency of the harmonic components produced by balanced and unbalanced loads, defining positive, negative and zero sequence components. The computation is developed using the switching functions approach, relating the output voltage waveform to the absorbed dc-link current; so, the method may be applied also to measured waveforms, when no analytical expression is available. The method is extended also to the general case of non sinusoidal load currents. The spectrum of the dc-link current for several inverter modulations (deterministic and random modulations) is calculated and considerations on the harmonic distortion and dc-link filter requirements are presented
Discussion of “Series expansion for line series impedances considering different specific resistances, magnetic permeabilities and dielectric permettivities of conductors, air and ground”
No full textMeasuring and Analyzing Power Quality in Electric Traction Systems
No full textPower Quality phenomena in a broad sense, stationary and transient, are considered focusing on railway applications: dc and ac traction lines are considered, identifying the main sources (fixed, like substations, and moving, like vehicles), their characteristic emissions, how they propagate and combine along the traction lines and back to the three-phase ac supply lines. The analysis covers the railway standards applicable to the traction line and the industrial standards applicable to the ac feeding lines. The peculiarity of railway applications, that is the presence of moving distorting loads interconnected by a non-ideal transmission line and characterized by variable operating conditions and by the superposition of multiple sources with different dynamics, requires specific processing, analysis and visualization methods, that are addressed by means of examples based on real data
An active analog filter architecture ensuring unity-gain and low sensitivity
No full textThe proposed architecture features an independent setting of filter poles,
while ensuring a constant unity gain. The unity gain simplifies the cascaded connection
of filter blocks and avoids the increase of voltage swing for subsequent cascaded
blocks observed with other filter architectures. Only the input Operational Amplifier
must meet more demanding requirements (in terms of bandwidth and open-loop
gain), while the other units are voltage follower units with the possibility of using a
video buffer to cope with a demanding load capability. Performances are much better
than or comparable to other known filter architectures
Distribution of the traction return current in AC and DC electric railway systems
No full textThe problem of the determination of the real distribution of the return current in electric railway traction systems is considered. One or more conductors (depending on the specific supply system) are purposely set up to carry the traction return current flowing from the rolling stock axles back to the supply (i.e., substation); yet, part of the return current flows through signalling conductors (disturbing current) and through the earth, depending on the value of the electric parameters of the system, on the circuit arrangement, and on the relative position of the supply, the rolling stock, and signalling devices. The amplitude (as a percentage of the total return current) of the disturbing current may be high enough to cause interference to signalling. This work investigates the behavior of the return current in ac and dc electric railway systems, on the basis of a reference system for the variation of the most important electrical parameters. The definition of the transfer function between the return current and the signalling circuit variables is an important element for the compatibility analysis between train detection systems, rolling stock and infrastructure, to promote the cross-acceptance of rolling stock in Europe and abroad
Assessment of Electromagnetic Emissions from Synchronous Generators and its Metrological Characterization
No full textA specific class of electrical machine, i.e., synchronous
generators, with a broad application for energy production
is considered. The electromagnetic emissions are evaluated on the
results of several measurement campaigns, accompanied by their
metrological characterization; signal-to-noise ratio, uncertainty,
reproducibility, and repeatability are evaluated in different operating
conditions, measuring positions, and generators under tes
Variability and uncertainty of Track Circuit band-pass modeling for interference evaluation
No full textWhen evaluating track circuits (TCs) interference, the latest normative approach indicates the use of band-pass filters that emulate the TC receiver response. The rms value of the output, when compared to the interference limit, indicates whether a specific signal might create interference or not. The implementation of the filter has some degrees of freedom and needs thus to be characterized in terms of added uncertainty to the interference evaluation process. The latter is relevant to safety, strictly related to the incorrect assignment of the status of the track section monitored and protected by the TC itself. When giving a definitive answer about the immunity of a specific TC and the compatibility with the tested rolling stock, it is thus necessary to completely evaluate the uncertainty associated to the chosen model and to the related signal processing operations, even if – it is recognized – their influence may be considered of second order with respect to infrastructure and rolling stock non-idealities
Direct Measurement of Power Quality over Railway Networks with Results of a 16.7 Hz Network
No full textOn the measurement of the stray capacitance of single layer air solenoids
No full textLow stray capacitance solenoids are air solenoids, possibly single layer, with significant turn-to-turn
spacing. The problem of the correct estimation of the stray capacitance is relevant both during design and to
validate measurement results. The expected value is so low that any stray capacitance of the external instruments
is relevant; a simplified method is proposed that doesn’t perturb the stray capacitance of the solenoid under test.
The method is based on the resonance with an external capacitor and on the use of a linear regression technique
A Magnetic Field Probe with MHz Bandwidth and 7 decades Dynamic Range
No full textThe design process of a general-purpose high-
performance instrument for magnetic field measurements is
presented. Demanding requirements have been extracted from
standards, regulations, and the literature in some fields of appli-
cation [e.g., human exposure and industrial and military electro-
magnetic compatibility (EMC)], consisting of a frequency range
of 1 Hz to 400 kHz, an approximately seven-decade dynamic
range with impact on designed voltage levels and internal noise,
an output signal format, and postprocessing algorithms. The
experimental characterization of the prototype is also reported,
showing that the frequency response of the instrument is extended
up to the megahertz range. The comparison of the instrument’s
performances with those of commercial products and published
equipment confirms the extremely good performances
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