Gerd Balzer

Wind Energy Storages - Possibilities

The volatility of wind power can cause large problems for power systems operation. To remedy the disadvantages of wind power generation different storage technologies can be applied. In this paper technical and economical analysis of possible wind energy storages has been made. According to technical parameters the applicable technologies have been selected. Afterwards, for selected storages economical analyses which take into account different scenarios of investment and electricity prices have been made. Obtained results suggested compressed air energy storages, batteries and pump hydro storages as very good solutions for wind energy storage. Due to lack of suitable places in Germany a pump hydro storage solution is less feasible.

Offshore wind farms - VSC-based HVDC connection

Due to significantly higher and more constant wind speeds and the shortage of suitable sites for wind turbines on the land, offshore wind farms are becoming very attractive. The connection of the large offshore wind farms is possible with HVAC, classical HVDC and voltage source converter (VSC- based) HVDC technology. In this paper their main features will be given. From the economical and technical viewpoint, the type of connection depends on the size of the wind farm and on the distance to the connection point of the system. As very promising technology, especially from the technical viewpoint, the focus of this paper will be put on the VSC-based HVDC technology. Its main technical features as well as its model will be detailed. At the end, obtained simulation results for different faults and disturbances for one offshore wind farm connected with VSC-based HVDC technology will be presented.

Reliability model of large offshore wind farms

For investors of wind farms projects, it is indispensable to get reliable prognosis of the expected energy produced per year, taking into account technical failures and the stochastic characteristic of the wind. This applies especially for offshore wind farms with higher installation costs and difficult maintenance conditions. The repair of components located on sea may take many days or even weeks because of limited access caused by bad weather conditions. Additionally, transmission system operators which are providing the point of common coupling (PCC) have to know the impact of the wind farm on the reliability of the grid. In this paper a model for the probabilistic reliability calculation of the offshore wind farms as a whole and as a part of the entire system has been introduced.

Power fluctuation from a large wind farm

The planed increase of the offshore wind farm is significant and, therefore, their influence on the power systems. In this paper the influence of several factors such as wind farm size, wind pattern, wind speed and wind direction which impact the wind farm power output have been analysed. Different sizes of wind farms have been modelled and their effects on power output have been presented. Different wind patterns and different wind speeds have been considered. Also, the impact of wind directions has been analysed. The relation of different wind directions, i.e. wind rose and the power output has been investigated. The obtained results show a high dependence of the power output on the size and position of the wind farm as well as on the wind pattern. With the increase of the wind farm size the power output fluctuations from the whole wind farm reduce significantly

Energy storage design and optimization for power system with wind feeding

The electrical energy production from renewable sources has gained considerably in importance in the last years. A meaningful possibility of energy generation from renewable sources is the use of wind energy. The wind energy generation is weather dependent and load independent. Therefore, it can have a certain unreliability, which can cause the power fluctuations into the system. A possible solution for this problem can be the storage of wind energy. The use of sodium-sulphur (NaS) batteries is a meaningful backup method for large wind farms because of their excellent technical characteristics such as high energy density, high power density, high efficiency and long life times. For this paper a model, which calculates the optimal battery size for compensation of short-term forecast errors, are developed and the application of the battery systems is optimized.

Condition assessment and reliability centered maintenance of high voltage equipment

The reliability calculations point out the weak points or equipment of the system, so that maintenance measures should be efficient under the consideration of the restricted financial resources of the utilities. The principle of the system approach to apply the RCM strategy leads to the result which asset should be maintained or replaced. In the second part a new procedure to collect and assess the statistical data is presented to select the proper maintenance strategy. Furthermore, the usage of artificial intelligence (fuzzy logic) is described considering renovation strategies of complete substations. The total strategy leads to the result which equipment or substation of a system should be replaced first, second, and so on, with provided ranking of the maintenance activities.

Life cycle cost analysis of transmission and distribution systems

In the last years two topics are often in the discussion about energy supply companies. Special attention has been drawn by the topics of “Life-Cycle-Cost (LCC)” and “Risk Management” since the liberalization of the energy market in the late 90s of the last century. In Germany large parts of the 110 kV system were built up in the 60s and 70s, for this reason most of the assets increasingly reach their estimated life time. In this case, life cycle cost analysis offers a helpful methodology to compare different strategies like refurbishment, renewal or redesign. This paper presents the principle calculation of Life-Cycle-Costs on a complete 110 kV overhead transmission grid with air insulated substations. The results depict the main cost-driving and most important elements of the system. On this basis, different maintenance strategies have been examined with regard to their corresponding Life-Cycle-Costs.

Impact of the VSC HVDC Connection of Large Offshore Wind Farms on Power System Stability and Control

The impact of the wind power on the power system stability and control is already notable. With the increase of their power (single offshore wind farms will reach over 1000 MW) their impact will increase too. In this paper the use of voltage source converter HVDC transmission technology for the connection of the large offshore wind farms to the power system will be presented. The modelling of VSC HVDC and its control parameters and loops has been detailed. The impact of such connection on the power system stability and control has been analysed on a test power system.

Optimal location and control of shunt FACTS for transmission of renewable energy in large power systems

Shunt FACTS devices provide the possibility to control voltages and therefore to improve the security of the system. In order to use this possibility, the optimal location and the set values of the FACTS controllers have to be selected corectly. The singular analyses of the power system Jacobian matrix are applied to identify the optimal location of shunt FACTS devices in large power systems. Furthermore the application of Optimal Power Flow control is a possible method for choosing set values. In this paper a sensitivity index for the detection of sensor nodes is defined. Sensitivity analysis is used to determine the area on which the FACTS device has significant influence. And then only this limited area is included in the Optimal Power Flow control, because it is very difficult to include the entire system into the optimization process. Simulations are performed on an IEEE 57-bus system. Furthermore the objective function of Optimal Power Flow control is analyzed. This function consists of three components. A certain type of FACTS is not able to influence all these components. In this paper it is evaluated for which component the shunt FACTS devices are mainly responsible.

Optimal location of series FACTS devices to control line overloads in power systems with high wind feeding

The planned offshore wind farms in Germany are basically located in North region. For wind integration in Germany, establishing new transmission lines and employing new technologies have become unavoidable. Establishing new transmission lines is very costly and difficult regarding enviromental condition. One of the solutions is the utilization of Flexible AC Transmission Systems (FACTS). This paper discusses a method for determining the placement of series compensation to control line overload in power systems with wind power penetration. By a sensitivity based method critical lines can be identified quickly and accurately, to obtain desired wind feeding into the system. Thyristor Controlled Series Compensator (TCSC) is applied for system stabilization as a typical FACTS devices. This method is applied to realistic scenarios in a test system, which simulates reduced 380 kV network of Germany. Simulation results showed that the proposed method is effective and can enhance the transfer capability margin of existing power systems.