Petr Toman

Comparative Studies of Diphenyl-Diketo-Pyrrolopyrrole Derivatives for Electroluminescence Applications

Four different derivatives of diphenyl-diketo-pyrrolopyrrole (DPP) with alkyl side groups were synthesized to increase their solubility. Quantum chemical calculations revealed that the substitution influenced molecular geometry and subsequently modified absorption and photoluminescence spectra. The theoretical results were confirmed by experimental characterization. With increasing phenyl torsion the vibrational structure was less pronounced and larger Stokes shift was observed. Simultaneously, the molar absorption coefficient decreased as the deformation increased. On the other hand, the measured fluorescence quantum yields were modified only slightly. This indicates the possibility to prepare soluble derivatives without loss of quantum yields and to use these materials for construction of efficient and stable electroluminescent devices. Furthermore, the electroluminescence of the thin layer devices based on the soluble low molecular DPPs were characterized and discussed.

Interharmonic - Flicker Curves of Lamps and Compatibility Lever for Interharmonic Voltages

The aim of the paper is to describe procedures for systematical determination of immunity of lamps to supply voltage variations caused by interharmonics. The curve of lamp immunity is presented as an interharmonic magnitude versus interharmonic frequency curve and is called interharmonic-flicker curve. The interharmonic-flicker curves of lamps are determined by utilizing a modified concept for measurement of a lamp gain factor in frequency domain and by utilizing the published limits on voltage flicker. Another described method for establishing the interharmonic-flicker curves of lamps is the method based on measuring the luminous flux flicker curve which is defined by utilizing the published limits on voltage flicker as well. Further a complex measured data file of interharmonic-flicker curves in various combinations of discharge lamps (fluorescent lamps and high intensity discharge lamps) and ballasts are pointed. Measured and compared combinations include various types of discharge lamps, various wattages, modes of operation of the ballast and its specific designs and dimensioning of circuit elements etc. Finally, determined interharmonic-flicker curves of chosen lamps are used for proposal approach how to revise the compatibility level for interharmonic voltages relating to flicker.

Possible Solutions to Problems of Voltage Asymmetry and Localization of Failures in MV Compensated Networks

The compensated networks are affected by the phase capacity asymmetry of wiring, which causes the unbalancing of the phase voltages in the tuned condition of the arc-suppression coil. In the especially unfavourable cases this effect reduces the possibility of network operation with the tuned arc-suppression coil. The operation with the arc-suppression coil out of tune is accompanied by higher values of the fault currents during the ground faults and the natural frequency of the course of recovery voltage in the network after switching off or interrupting the ground fault. These disadvantages can only be removed by efficient elimination of the phase asymmetry. The new methods of eliminating the phase capacity asymmetry allow for controlling the phase asymmetry size (its reduction as well as its possible increase), they keep it within a specified tolerance band (Uo value in the tuned condition of the arc-suppression coil is typically maintained at levels from 1% to 4% of the network voltage phase value). The new methods of elimination of the phase capacity asymmetry have favourable effects on the network operation during the ground fault and do not reduce the protecting elements sensitivity to high-ohm ground faults. By improving the accuracy of the arc-suppression coil tuning the safety of the compensated networks operation can be enhanced. The other properties of the whole system of phase capacity asymmetry elimination designed to increase the compensated networks operation safety, to improve the reliability of ground- fault protections and to locate the fault areas, can be fully utilized

The method of the additional earthing of the affected phase during an earth fault and its influence on MV network safety

The paper deals with the description and analysis of the method of the additional earthing of the affected phase used for the elimination of the fault current during an earth fault in a compensated network. The efficiency of this method is strongly influenced by the fault location and resistance and, in some cases, its application can lead to deteriorating the situation at the point of the fault and thus to increasing the risk of dangerous touch voltage. The paper analyses the results of the simulations of selected fault cases where the negative influence of the additional earthing of the affected phase on the fault current magnitude (and therefore on the occurrence of the dangerous touch voltage at the point of the fault and in the neighboring LV network) can be expected. All the theoretical conclusions and assumptions were consequently verified by experiments in a real distribution network. Their results were then used in the final part as a basis for proposing the measures to apply the method in MV distribution networks.

Personal computers immunity to short voltage dips and interruptions

The paper is focused on the short voltage dips and interruptions in the public supply networks and their influence on the connected computer power sources. There is performed a comparison of the immunity classification by standard EN 61000-4-11 against proposed immunity classification, which is based on the disturbing influences in real supply networks. There are mentioned specifications of the essential phenomena, which have influence on the final limiting curve of immunity. Limiting curves of some types of electric equipments are measured and pointed.

Analysis of the power quality and the impact of photovoltaic power plant operation on low-voltage distribution network

In general, the power quality analysis is a very complex issue and it requires a long-term measurement in real distribution networks. Moreover, the voltage has to be within specific voltage tolerance for the low-voltage distribution network. In this paper the measurement of the low-voltage network after the connection of a small photovoltaic power plant is evaluated. Therefore, the influence on the changes of the voltage, flicker and total harmonic distortion by connected power plant under different operating states is described in the paper. The main task of the article is to present the results of the voltage quality measurements carried out in low-voltage distribution network.

IEC 61850 communication based distance protection

IEC 61850 is the standard for communication substation which determines new applications of protection based on peer-to-peer communications between multifunctional protection devices (IEDs). The GOOSE messages (Generic Object Oriented Substation Event) can be used to replace the hard wired control signals exchanged between IEDs for interlocking and protection purposes. The idea is that the implementation of high-speed peer-to-peer communications should be equal or better than what is achievable by existing technology. The paper focus on using IEC 61850 based protection relays and on possibility of modeling of this processes in Matlab.

Practical experience of using additional earthing of the faulty phase during a ground fault

The paper is focused on the operational experience with an automatic system for suppression of a fault current during a ground fault by the additional earthing of the faulted phase in a supply substation. Such system was experimentally installed in the Brno-Medlánky 110/22 kV substation. To verify the benefits of the system as well as to assess its possible failings, twenty-four experimental measurements based on a theoretical study were performed. During those experiments, low-resistance and arc ground faults were monitored in the urban and suburban part of the compensated network with a capacitive current of 300 A and 800 A. The results of the crucial experiments and the evaluation of the system functioning are summed up in the final part of the paper.

Solution of voltage asymmetry and reduction of outage time in MV compensated networks

The compensated networks are affected by the phase capacity asymmetry of wiring, which causes the unbalancing of the phase voltages in the tuned condition of the arc-suppression coil. In the especially unfavourable cases this effect reduces the possibility of network operation with the tuned arc-suppression coil. The operation with the arc-suppression coil out of tune is accompanied by higher values of the fault currents during the ground faults and the natural frequency of the course of recovery voltage in the network after switching off or interrupting the ground fault. These disadvantages can only be removed by efficient elimination of the phase asymmetry. The new methods of eliminating the phase capacity asymmetry allow for controlling the phase asymmetry size (its reduction as well as its possible increase), they keep it within a specified tolerance band (Uo value in the tuned condition of the arc-suppression coil is typically maintained at levels from 1% to 4% of the network voltage phase value). The new methods of elimination of the phase capacity asymmetry have favourable effects on the network operation during the ground fault and do not reduce the protecting elements sensitivity to high-ohm ground faults. By improving the accuracy of the arc-suppression coil tuning the safety of the compensated networks operation can be enhanced. The other properties of the whole system of phase capacity asymmetry elimination designed to increase the compensated networks operation safety, to improve the reliability of ground-fault protections and to locate the fault areas, can be fully utilized.

Utilization of Particle Swarm Optimization Algorithm for Optimization of MV Network Compensation

This article describes the possibilities of solving optimal distribution of capacitors by particle swarm optimization (PSO) used in parallel compensation of medium voltage (MV) distribution network. PSO is a suitable tool for solving combinatorial problems benefiting from low requirements for criterial function. An algorithm looks for such a parameter set-up that has a minimum price and a minimum level of the total power losses and a minimum cost of capacitors and minimum maintenance expenses, all of this under given limitations. Its functionality is demonstrated on the example of a power network.