• Energy Research

The variability of large scale wind power generation at high penetration levels has a significant impact on the secure and economic operation of onshore power systems. Grid bottlenecks, high gradients and wasting of wind energy can be avoided using local Energy Storage Systems (ESS) with dedicated power and capacity. The storage type considered in this study is an adiabatic compressed air energy storage (ACAES). This paper presents a comparison of different ESS applications aiming both to increase the profit of the power plant operator in selling the electricity into the electricity market and to support the intermittent electricity production of the wind park. This contribution presents the investigation methodology and discusses computation results for a region in Germany.

New data acquisition technologies, such as phasor measurement units (PMU), have been implemented in recent years to operate the power system with more reliability and control by improving the protection schemes like line differential protection or damping the inter-area oscillations. The present standard IEEE C37.118 only provides general information about the testing conditions and requirements, without giving any specifics.. To create the PMU data function for the applications and thereby make the power system more reliable, the appropriate PMU test standards have to be developed and disseminated. Future testing methods should ensure that units from different manufacturers are tested identically and function properly under different repeatable test scenarios and test stand set up conditions. This paper presents experiences from tests of PMU accuracy and calibration conducted in Europe and the USA, which will facilitate the development of future standards. The test stand itself and the test results from the various PMU manufactures are presented, compared and discussed in this paper, taking into account the standardization issues.

In this paper a voltage stability analysis is described, which is coupled with an online dynamic security and protection assessment system (DSA). The focus will lie on the calculated indices and their algorithms using time domain simulations. Because the online DSA collects information from four different modules, the voltage stability module, small signal stability module, the transient stability module and the protection module, the required information exchange between these modules is examined.

This paper presents in situ measurements of a newly developed current density measurement system for proton exchange membrane fuel cells (PEMFC). While the functional principle and technical evaluation of the measurement system were presented in a previous paper, this paper analyzes the influence of various operation parameters, including multiple start-stop operation, at the anode, cathode and cooling locations on the distribution and long-term development of the current density. The system was operated for 500 h over two years with long periods of inactivity between measurements. The measurement results are evaluated and provide additional information on how to optimize the operation modes of fuel cells, including the start and stop of such systems as well as the water balance.

This paper presents the application of eigenvalue analysis for the investigation of the harmonic distortion level in a low voltage distribution system. This analysis is used to describe the sensitivity of the distribution system's nodes to the harmonic distortion. The measurement made in the studied system are presented and discussed with a special emphasis on distribution system's sensitivity to harmonic distortion. The theoretical approach is then proved by a comparison between the measurement results and the eigenvalue analysis of the modeled system.

A newly developed measurement system for current density distribution mapping has enabled a new approach for operational measurements in proton exchange membrane fuel cells (PEMFC). Taking into account previously constructed measurement systems, a method based on a multi layer printed circuit board was chosen for the development of the new system. This type of system consists of a sensor, a special electronic device and the control and visualization PC. For the acquisition of the current density distribution values, a sensor device was designed and installed within a multilayer printed circuit board with integrated shunt resistors. Varying shunt values can be taken into consideration with a newly developed and evaluated calibration method. The sensor device was integrated in a PEM fuel cell stack to prove the functionality of the whole measurement system. A software application was implemented to visualize and save the measurement values. Its functionality was verified by operational measurements within a PEMFC system. Measurement accuracy and possible negative reactions of the sensor device during PEMFC operation are discussed in detail in this paper. The developed system enables operational measurements for different operating phases of PEM fuel cells. Additionally, this can be seen as a basis for new opportunities of optimization for fuel cell design and operation modes.

Power transmission systems are being operated closer to their stability limits compared to twenty years ago. As a result, an increasing risk of blackouts combined with extremely high costs economically and socially is observed. To reduce this risk the personnel in the control rooms of the transmission system operators have to be assisted by a system, which assesses the dynamic state of security online. The system presented in this paper is designed to investigate the security with regards to voltage stability, transient stability and small signal oscillatory stability. The performance of the system is sufficiently high to be employed in the online environment of the control room.

Abstract PEM-fuel cells operated with hydrogen and air offer promising possibilities for the decentralised energy supply in stationary and mobile applications. But, there is still a remarkable need for more research for the optimisation of the single components even though the research, especially the development of membrane-electrode units and bipolar plates, has made considerable progress within recent years. This also applies to the definition of suitable test algorithms and parameters for recording the characteristics as well as long time tests. The investigations for single cells or stacks can thereby be subdivided into investigations in the stationary and the dynamic state. This paper shows a simplified approach for the evaluation and modelling of PEM-fuel cell stacks for the stationary state. Based on the definition of regression approaches for the dependence of several parameters the number of stack parameters is initially reduced to a sufficient number of values. The remaining parameters are used to form an energy model which can be combined with the energy models of auxiliary components like air compressors and sinus inverters [1] . Algorithms for recording the parameters still have to be defined. Therefore, the tests for the preparation of a set of characteristic curves can be very time consuming because of the multitude of variable parameters. This paper presents and discusses optimised measurement algorithms for the evaluation of PEM-fuel cell stacks to reduce this time exposure.

In recent years the energy consumption, decentralised feed-in, storage of renewable energies [1] and the power system complexity have grown rapidly worldwide. Hence, some electrical networks are already working at their stability limits because they were not originally designed for today's load. Consequently, the risk of power system instability has greatly increased. Therefore, protecting electrical networks from critical situations such as blackouts has become a very relevant issue in the network operation. The fast evaluation of the current network state, particularly its dynamic state, and the use of appropriate remedial measures in the control rooms play an important role in solving this problem. This paper describes the online Dynamic Security Assessment system for the prevention of power system instabilities and improvement of the electrical network state by applying remedial measures.

THE increase of stochastic renewable infeeds to transmission networks as bulk generation of large offshore windfarms or as distributed generation in distribution networks requires new strategies in the system operation. On one hand the transmission capacity of the power systems must be as high, as unplanned dynamics, caused by these infeeds, can be transported without producing system bottlenecks. Such dynamic energy transports occur sometimes over long distances and require operational coordination between different TSOs. On the other hand new indicators, describing the power system stability and the margins to stability limits must be developed and tested, which allow a prediction of the dynamic state of the power system if contingencies would occur.