The effect of inrush transients on pv inverter's grid impedance measurement based on inter-harmonic injection

This paper addresses a cause for false tripping of photovoltaic inverters with antiislanding protection based on impedance measurement with inter-harmonic injection. Earlier discussions about tripping problems happening when several devices are doing the measurement at the same time are supplemented with a problem caused by inrush transients of nearby devices. A series of experiments was conducted in the Power Quality laboratory of the TU/e, on a PV inverter which complies with the DIN VDE 0126 standard. Impedance measurement was done in parallel with the inverter and measurement results are presented. A criterion for false tripping caused by transients is explored. Also, influences of network impedance and grid harmonic pollution on false tripping were analyzed. In the end, some signal processing techniques are proposed to avoid this problem

ARPES kink is a "smoking gun" for the theory of high-Tc superconductors: dominance of the electron-phonon interaction with forward scattering peak

The ARPES spectra in high-Tc superconductors show four distinctive features in the quasiparticle self-energy. All of them can be explained consistently by the theory in which the electron phonon interaction (EPI) with the forward scattering peak dominates over the Coulomb scattering. In particular, this theory explains why there is no shift of the nodal kink at 70 meV in the superconducting state, contrary to the clear shift of the anti-nodal singularity at 40 meV. The theory predicts a ``knee''-like structure of the imaginary part of the self-energy, which is phonon dominated for $\omega \approx \omega^{(70)}_{ph}$, and shows linear behavior for $\omega > \omega^{(70)}_{ph}$ - due to the Coulomb scattering. Recent ARPES spectra give that the EPI coupling constant is much larger than the Coulomb one. The dip-hump structure in the spectral function comes out naturally from the proposed theory.Comment: 5 pages, 3 figure

Signatures of pressure induced superconductivity in insulating Bi2212

We have performed several high pressure electrical resistance experiments on Bi1.98Sr2.06Y0.68Cu2O8, an insulating parent compound of the high-Tc Bi2212 family of copper oxide superconductors. We find a resistive anomaly, a downturn at low temperature, that onsets with applied pressure in the 20-40 kbar range. Through both resistance and magnetoresistance measurements, we identify this anomaly as a signature of induced superconductivity. Resistance to higher pressures decreases Tc, giving a maximum of 10 K. The higher pressure measurements exhibit a strong sensitivity to the hydrostaticity of the pressure environment. We make comparisons to the pressure induced superconductivity now ubiquitous in the iron arsenides.Comment: 5 pages, 4 figures, submitted to Phys. Rev.

Voltage dip detection with half cycle window RMS values and aggregation of short events

This paper presents the results of the analysis on the 2 data window lengths adopted in instruments for the detection of voltage dips (sags). The first one is commonly applied which use one cycle window to calculate the RMS value of residual voltage, the other one uses half cycle window to calculate the RMS values. These two window lengths are compared analytically and based on a simulation in this paper. Thee short duration dips are emphasized as they lead to more differences. The different affectivee factors like residual voltage and phase angle jump are also discussed. A set of field measured dip data are analysed with these 2 methods and the results are given and compared.</p

On the Secular Behavior of Irregular Satellites

Although analytical studies on the secular motion of the irregular satellites have been published recently, these theories have not yet been satisfactorily reconciled with the results of direct numerical integrations. These discrepancies occur because in secular theories the disturbing function is averaged over orbital motions, whereas instead one should take into account some large periodic terms, most notably the so-called ``evection''. We demonstrate that such terms can be incorporated into the Kozai formalism, and that our synthetic approach produces much better agreement with results from symplectic integrations. Using this method, we plot the locations of secular resonances in the orbital-element space, and we note that the distribution of irregular satellite clusters appears to be non-random. We find that the large majority of irregular-satellite groups cluster close to the secular resonances, with several objects having practically stationary pericenters. None of the largest satellites belong to this class, so we argue that this dichotomy implies that the smaller near-resonant satellites might have been captured differently than the largest irregulars.Comment: 56 pages, 24 figures, accepted for publication in The Astronomical Journa

Assessment of voltage dips based on field measurements in MV networks

Voltage dip is considered as the PQ problem related to the highest financial losses for the customers. It occurs unpredictably mainly due to short-circuit faults in the networks. Network operators and customers want to know more about the occurrence and the potential impact of voltage dips. PQ monitoring is an essential tool for the assessment of voltage dips and it can ultimately contribute to the regulation of voltage dip events. In this paper, firstly the methods of voltage monitoring and voltage dips characterization are discussed. Voltage dip indices of six substations are presented in order to assess the occurrence, type and severity of dips that occur in typical Dutch MV networks. Finally, an approach, which is based on the disrupted loads because of a voltage dip event, is introduced and applied to the data at one substation in order to assess the quality of supply voltage and its implications for the end-users

An Extended Hosting Capacity Approach Including Energy Storage

This chapter proposes an evolved concept of ”hosting capacity” using the term of ”feasible region” for installing additional loads or generations. Through converting the grid model into a more compact one, ”hosting capacity region” not only is promising to further exploit the grid potential for power delivery, but also benefits grid operation feasibility investigation with concise formulas. Facing the derived hosting capacity, originally complicated energy storage optimization problems can be represented algebraically, which is more efficient and friendly for computer processing. Case study based on a 10.5kV Dutch grid has been implemented, eventually demonstrating the validity of relevant assessment and optimization methods

Regulation and Classification of voltage dips

The impact of voltage dips on industrial installations can be very high. However, regulation within the European Standard EN 50160 is not detailed as the cells within the general table are not filled. As there is no reference on the expected number of voltage dips, the responsibilities for network operator and customer are unclear. Therefore the customers face challenges to make analysis on required mitigation measures. The Dutch Regulator requested the network operators to prepare a proposal for a regulatory framework regarding voltage dips. This paper presents the initial proposal for the MV distribution network. Based on the effect of various types of voltage dips to the reduction of active-power for aggregated customers, voltage dip severity weighting factors are developed and used to build the proposal

Uncovering a pressure-tuned electronic transition in BiSrYCu2O8 using Raman scattering and x-ray diffraction

We report pressure tuned Raman and x-ray diffraction data of Bi1.98Sr2.06Y0.68Cu2O8 revealing a critical pressure at 21 GPa with anomalies in six physical quantities: electronic Raman background, electron-phonon coupling, spectral weight transfer from high to low frequency, density dependent behaviour of phonon and magnon frequencies, and a compressibility change in the c-axis. For the first time in a cuprate, mobile charge carriers, lattice, and magnetism all show anomalies at a distinct critical pressure in the same experimental setting. Furthermore, the Raman spectral changes are similar to that seen traversing the superconducting dome with doping, suggesting that the critical pressure at 21 GPa is related to the much discussed critical point at optimal doping.Comment: 5 pages, 4 figures, submitted to PR