Marco Fleckenstein

Congestion management with a Unified Power Flow Controller in a 380 kV transmission network

Transmission System Operators (TSO) in Germany have to adapt their network to the new circumstances, such as the strong supply of offshore wind farms in areas with weak load. The input power has to be transported to other areas, originating higher workload of overhead lines. Utilization is subject to the impedance of the individual overhead lines. This leads to an uneven distribution of the load. With the use of Unified Power Flow Controller (UPFC), the utilization of overhead lines is set efficiently. This can especially help in case of outages from assets to ensure the N - 1 criterion. In this paper the influence of UPFC on the availability of the transmission network during a peak load-strong wind scenario is shown.

Grid services with PV-converters in distribution systems

The most affected parts of the electrical power system in Germany are the distribution grids due to the rapid expansion of renewable energies. Most of these micro power plants e.g. photovoltaic systems feed into the low (LV) and medium (MV) voltage level. The voltage stability in these levels is thus much more complex and is partially violated in moments of strong feed-in. To reduce this negative impact the directive VDE-AR-N 4105 was specified that PV-inverters must provide reactive power instead of pure active power. This directive should however only be the beginning. In a smart grid, the asset inverter should be used much more intensively. In this paper it is demonstrated by power flow simulations with the data of a real distribution grid including PV-system feed-in that there are more possibilities but providing the reactive power for the distribution and voltage stability. It is illustrated that the use of the complete apparent power of the inverter is a more appropriate way to obtain the stationary stability of distribution grids. With this strategy in addition, the power loss can be influenced in LV- and MV-level and the power factor of the feed-in of the HV/MV-supplying transformer can be adjusted.

Outage cost oriented maintenance strategies of outgoing feeders in transmission systems

The near-perfect performance of the 380 kV transmission network is one of the major reasons in the highly reliable electrical energy supply in Germany. But due to the sustained cost pressures for transmission system operators the operational expenditures must be reduced in order remaining competitive. A changeover from a usual time-oriented to a risk-based maintenance is more and more often on the agenda. In this paper a method is presented which generates risk-based maintenance strategies for overhead lines and their connecting outgoing feeder in a German 380 kV extra high voltage transmission system with the target operative risk costs reduction. The origin of this strategy is the determination of the importance of the different routes for an unrestricted functionality of the transmission system. This method takes into account standard as well as log-normal distributions of age-dependent reliability behavior of the assets, bay configurations and different load conditions of the transmission network in the 380 kV level. Furthermore a Monte Carlo simulation is used for creating combinations of financial and technical data. Finally, an extreme clipping of extraordinary combinations is performed with the value at risk method.

Risk-based asset replacement in EHV transmission networks

The developed method of risk-based asset replacement consists of the three major parts: availability & reliability calculations, asset risk determination with a Value at Risk (VaR) method and the multiple choice knapsack optimized replacement strategy developer. The transmission network availability & reliability calculations are carried out with multiple load flow scenarios which cover all typical load states during a year of the investigated transmission system. The developed VaR-method includes a Monte Carlo simulation to generate and concentrate an amount of input values to one key figure per asset. The individual outage rates and costs which depend on the time of failure occurrence are taken into account by the VaR determination. The multiple choice knapsack optimized risk-based replacement strategy developer determines the decision which activity is chosen for the individual asset and the reliability & availability of the overall transmission network and minimum investment costs as target figures. This two-dimensional optimum is found with the branch-and-bound algorithm of Sinha and Zolters. The three different opportunities are immediately replacement, refurbishment or inspection with a change to a corrective replacement. The transition from a standard to a risk-based replacement strategy allows a significant budget reduction while keeping transmission system reliability & availability. The assets providing an increased risk in the network due to their age-related behavior and location in the transmission network are determined and get a higher priority for exchange. Thus, the major assets are replaced more quickly and due to the corrective replacement strategy the costs are reduced for the less important assets.

Risk assessment of power wheeling in extra high voltage transmission systems

Power wheeling can have an intensive impact on the reliability and availability of the transmission network that is utilized with it. The extended risk for the transmission system network should be considered by fixing the operation charge for the customer. With the method presented in this paper, the increased risk of disturbances, which are caused by asset outages in the 380 kV level, on feeds of the power plants and the supply of customers in the network area can be clearly identified with a self-developed method which uses a Value at Risk (VaR) analysis. For the presentation a transmission network model is used, which represents the main network of a German transmission system operator (TSO). The illustrated scenario for the application of the developed method consists of a power wheeling operation (PWO) with a transmission capacity of 1 GW, which is carried out from the northernmost to the southernmost coupling points of the transmission network.

Energy storage system in the medium-voltage network

The distribution network in Germany is due to the rapid expansion of renewable energies the most affected part of the electrical power system. The behavior of the load flow in the medium and low voltage levels, especially through the feed of photovoltaic systems, is completely changing. The power supply from the overlaid voltage levels is subject to stronger fluctuations, which are mainly depending on weather conditions. The consequence is that higher power gradients can be expected at the supplying transformer. These can in turn be mastered by only a few types of power plants or be carried out very costly. With the use of central energy storage (CES), these power fluctuations are smoothed. Depending on the size of the storage peak shaving or even load leveling can be achieved. In this paper, the application of a central storage is presented in a rural distribution network, which has a high penetration of photovoltaic systems. The fluctuating feed of these solar power plants is considered with a measuring data set of several years which has a resolution of quarter-hour values. The centrally installed storage system has been simulated with different storage sizes. For the determination of results load flow calculations were performed with load profiles for a whole year in a quarter-hour resolution.

Multicriteria maintenance planning for disconnectors in extra high voltage transmission systems

Maintenance of equipment in the extra high voltage level in Germany is not condition-based but it is performed at fixed time intervals and with the same quality. The ever increasing utilization of the transmission network by means of decentralized supply of renewable energy is changing the demands of the system. Simultaneously, the transmission system operators (TSO) are forced to be more cost effective to keep operating expenses constant. Therefore, the budget needs to be limited so that a maximum profit for the conservation of the reliability of high voltage network is achieved. One possibility for the efficient planning of maintenance is the introduction of additional criteria. In this paper, criteria are presented that can assist in the operational maintenance of center break disconnectors. On the basis of reliability calculations the influence that these additional factors or their combination can achieve is shown by use of a grid system.