Manfred Sakulin

An earth fault distance location algorithm in compensated networks with additional estimation of the fault impedance and fault current

Earth fault distance protection with distance protection relays is common practice in solidly grounded networks. However, in compensated networks earth faults can cause big problems, because they do not extinguish themselves. To find the fault point is from high interest also in combination with network expansion [9]. In previous investigations the authors found that the classic algorithm of these distance protection relays principally can be used also for compensated networks, - however the accuracy of the distance calculation strongly depends on the network conditions [1],[2]. In this paper a new improved algorithm is developed. For this purpose an exact 3-phase mathematical simulation model of the investigated network is used to check the results of the improved algorithm. The simulations show, that this improved distance calculation provides very good accuracy up to earth fault transitions impedances of 1 kohm. Furtheron it is shown in the paper that the same algorithm can be used in 2-phase networks as well. With the implemented improvements the algorithm again allows earth fault transitions impedances of up to 1 kOhm. Finally, the simulation results are validated by real test data to verify the usability of this improved algorithm.

Measurement and analysis of neutral point currents in a 400-kV-network

Neutral point treatment is a very important topic for protection and network operation. For different reasons 400-kV AC-power networks are operated with direct grounding of the neutral point. One major part of electrical networks are transformers. In transmission systems, usually at least one transformer per substation is operated with direct grounded neutral point, thus allowing earth currents to enter the transformer. New transformers are designed for very low noise emissions. During commissioning of a new transformer, unexpected noise was noticed and saturation due to DC currents respectively very low frequency currents (below 1 Hz) was assumed to be the reason. In a current research project of Austrian Power Grid and Graz University of Technology measurements of the neutral point current were performed. Analyses of these measurements revealed several frequency components in the spectrum, including DC, slow variations below 1 Hz, 16.7 Hz from railway system, 50 Hz mains, harmonics and interharmonics. This paper gives a description of the measurement setup, highlighting the problem of recording small DC currents in the presence of high AC currents. Furthermore results from a neutral point current measurement in the Austrian 400-kV-grid are presented and discussed.

Cable Installation Limits in Earth Fault Compensated 110-kV-Networks

Forced use of cables in earth fault compensated networks increases the capacitances to ground in the grid so that the capacitive ground fault current ICE increases, which causes problems concerning arc extinction. The ground fault current (limited to 132 A due to standards in Austria) depends on detuning, damping, unbalance, harmonics, saturation, operating voltage, harmonic resonances, and the distribution of the line inductances and capacitances (within the grid). A new grid calculation program was developed by TU Graz which allows to calculate the expansion limits of earth fault compensated networks under consideration of the harmonic contents in the fault current. Concerning the determination of these limits existing formulae are adequately adapted. The calculated results have been verified in real network experiments. Technical measures for further operation of the grids are investigated

Optimal Sizing of Biomass-Fired Organic Rankine Cycle CHP System with Heat Storage

A novel methodology for Optimal Sizing of Biomass-Fired Organic Rankine Cycle (ORC) Combined Heat and Power (CHP) System with Heat Storage is presented in this paper. The ORC technology received a lot of attention recently, especially for medium scale applications (e.g. district heating) where market potential is substantial. Another push for the technology is provided in the context of recent EU regulations to tackle the rising environmental problems, i.e. the 20-20-20 directive, which should provide another boost for the use of renewables in electric power systems. In this study, the simulation of the operation of a biomass fired ORC CHP system is discussed first, where the dispatch of the plant is optimized to maximize the profits from electricity and heat sales. Based on the optimal dispatch values, an economic evaluation is carried out to determine the feasibility of the proposed scheme for investment purposes; this evaluation is based on calculations of modified internal rates of return for a realistic scenario. Lastly, an optimization procedure for optimal sizing of the generation architecture with heat storage is convolved with the optimal operation and economic evaluation models, to achieve maximal rates of return on the ORC CHP investment. The results of the present studies demonstrate that the heat storage is not economically feasible in the assumed setup making profits from increasing the flexibility and thus utilization of the ORC CHP operation. Furthermore, the results show favorable economic parameters for the ORC CHP setup without the heat storage for annual heat demands higher than 5 GWh and biomass prices lower than 17 EUR/MWh.

Policies for reasonable system integration of renewable energy sources in Austria

The fight against climate change and the high import dependency on fossil fuels has led the European Union (EU) to a reinforced renewable energy strategy. Primary aims till 2020 are to reduce CO2-emissions about 20%, to increase the share of renewable energies to 20%, to improve the energy efficiency about 20% and to use about 10% of biofuels. In order to fulfil these ambitious targets especially energy efficiency, efficient use of energy resources and avoidance of energy wastings are an imperative prerequisite. This must be demanded also in the field of renewable energy sources - CO2 neutrality can never be an apology for wastefulness. Especially, the system integration of renewable resources must be carefully selected. Not only electricity generation, also feeding-in of biogas into the gas grid must become eligible for funding. Further aspects like transport, impacts on environment, provision of infrastructure and a stable funding system must be considered.

Potential analysis and further aspects of renewable energy sources in Austria

Climate Change as well as the growing import dependency - especially of the European Union - afford stringent measures. The new energy strategy of the EU sets challenging goals particularly regarding the future share of renewable energies. Especially the electricity production from renewable energies is of special interest because questions concerning storage and system integration are more difficult than for the heat and biofuel sector. The paper shows the present situation in Austria concerning the electricity production from renewable energies and summarizes the potential situation given in the literature. Special focus is set on the field of biomass and biogas and aside an estimation of the current potential the aspect of feeding biogas in an existing pipeline-system is discussed.

Ausbaugrenzen der Verkabelung und zukünftige Möglichkeiten zum weiteren Ausbau gelöschter Netze

Im vorliegenden Beitrag wird eine Methode zur Berechnung der Kabelreserve in oberschwingungsbehafteten gelöschten Netzen entwickelt. Durch Netzerweiterungen und vermehrten Einsatz von Kabeln steigen die Erdschlussströme, so dass Probleme mit der Einhaltung der zulässigen Grenzen des Erdschlussreststroms entstehen. Die auftretenden Oberschwingungsspannungen und die daraus resultierenden Oberschwingungserdschlussströme sind die maßgeblichen betriebs- und ausbaubeschränkenden Parameter. Resonanzen können zusätzliche Einschränkungen bedingen. Abschließend werden die derzeit möglichen Maßnahmen zur Erweiterung des Netzausbaus im Falle des Erreichens der Löschgrenze aufgezählt.In this article a method for the computation of the cable reserve in harmonic-afflicted compensated grids is developed. By grid expansions and increased use of cables the capacitive earth fault currents rise. As a result the residual ground fault current rises which causes problems concerning the permitted limits. The arising voltage harmonics and the resulting harmonic earth fault residual currents are the relevant expansion-limiting parameters. Resonances can cause additional restrictions. Finally, the possible measures for further expansion of grids are mentioned.

Calculation of voltage dips in meshed grids

Knowing the network parameters and the failure statistics of a network, the number of dips per year and the distributions of remaining voltages and dip durations can be estimated. Two approaches have been chosen by the authors: using a Monte-Carlo-method, the remaining voltages for random failure locations in the network are calculated. The simulation can be done for an arbitrary number of years, the number of dips per year is taken from the fault statistics. Using the second method, the calculation of the remaining voltage is performed for failures in every node of the network. The results are weighted according to the failure probability of each node. The dip duration is derived from the networks protection system. These methods have been applied to a real network. The results are compared with a 2-years-measurement in the network. Furthermore the rating of an appropriate dynamic voltage restorer is discussed.

Zuverlässigkeitsanalyse elektrischer Energieübertragungsnetze

ZusammenfassungZur Zuverlässigkeitsanalyse elektrischer Energieversorgungsnetze stehen heute deterministische und probabilistische Verfahren zur Verfügung. Das (n−1)-Kriterium erlaubt in seiner ursprünglichen Form lediglich eine einfache Ja/Nein-Aussage, jedoch keine quantitative Beurteilung der Versorgungssicherheit. Es wird daher eine quantitative Bewertungsmethode für das (n−1)-Kriterium entwickelt, die es erlaubt, dieses Kriterium zum Vergleich unterschiedlicher Netzausbauvarianten in einer flexibleren Form anzuwenden, ohne auf die Einfachheit und klare Aussage desselben zu verzichten.AbstractReliability analysis in electrical transmission networks can be done with the aid of heuristic and probabilistic methods. The heuristic (n−1)-criterion in its basic form allows only a yes/no-decision about the question if an electrical energy system is sufficiently reliable or not. Therefore, a new method of a quantitative rating for the (n−1)-criterion is shown in this report. With this method it is possible to compare different network solutions in a more flexible way, without losing the advantages of the simplicity and the clear facts of the (n−1)-criterion.

Reduction of the Net Losses in Distributed Networks

For loss reduction In distributed networks a multiplicity of possibilities exist. The use of cables instead of overhead lines as well as larger diameters of the lines lower the arising losses in distribution networks. Likewise a more even load profile leads to a reduction of losses, so that in the consequence primary energy, costs and CO2-emissions can be saved. Unbalances through asymmetrical loads arise particularly within the low-voltage grids and they are responsible for substantial losses compared with the situation of symmetrical load conditions. In this paper investigations are presented, which show that considerable loss reductions can be obtained by decentralized compensation. For the computation of the losses in urban distribution networks a model is developed. The parameters (standardised load profiles, number and kind of typical consumers, line data etc..) can be varied. Results of model computations are presented.