Chris O. Heyde

Vision 2020 — Security of the network operation today and in the future. German experiences

Nowadays the supply of electrical energy from dispersed generation units has an increasing significance. Hence, security related power system operation strategies have to be adapted to face the new situation. In this paper the security of power system operation from the industry and research point of view will be discussed. After presenting an overview about the current situation, the problems will be pointed out. The promising ongoing research topics which have the ability to help the network operators to manage the turn towards a sustainable power system that will allow for exploiting as much regenerative energy as possible by reaching the high standards of security will be described.

Voltage stability analysis as part of an online DSA system

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.

Stochastic Computation of Power System Security Level

Power network security can be disturbed in situations of high penetration of dispersed generation (DG). Such situations lead to bottlenecks in the power network, which is especially observed in the German power network. These bottlenecks can either be eliminated by network extensions or by the use of generation response (GR). The GR, realized in Germany through the so called network security management (NSM), restricts the generation power in cases of network parameter violations such as excessive thermal currents. In this paper, first the security level indices will be defined. Because load, wind- and sun power have a highly stochastic nature, stochastic simulation in the form of a sequential Monte Carlo simulation (MCS) is employed to calculate those indices. The CIGRE distribution system benchmark is chosen for testing the simulations. Both, an aggregated and the complete distribution system were used to calculate the occurrence of network parameter violations. The results will be compared and discussed. This paper finishes with a discussion and demonstration about the advantage of implementing the developed methodology in a professional power system simulator.

Dynamic voltage stability assessment using parallel computing

Dynamic voltage stability analysis demands a large amount of computing power because of the higher degree of model details and the longer simulated time span. In order to perform voltage stability analysis during operation - so called on-line dynamic voltage stability assessment - and to help the operator with the results to make the right decision, these analyses have to be performed rapidly within a pre-defined duration of, for example, 15 minutes. The stability analysis is mainly characterized by contingency simulations, which can be done in parallel by nature. In this paper the approach of dynamic voltage stability assessment is described and the parallelization process will be presented.

Stability studies of offshore wind farms

Wind energy is the most important type of renewable energy in Europe. The stability of system network operation with a large penetration of wind energy has become one of the most critical issues in the new structure of power systems with different types of generation. In this paper the HVDC and HVAC connection of the wind farm to grid is compared. The HVDC is more advantageous in maintaining the system stability. Nevertheless this study focuses on the HVAC connection of wind farms with regard to its lower costs and widely practical application. Based on the topology of the offshore wind farm Alpha Ventus, a simulation model is developed in software PSS/NETOMAC. Using this model the steady-state voltage and power factor at the wind farm connection point is analyzed and compared with the grid code requirement on reactive power exchange and voltage stability. The impact of the cable switching on voltage is investigated as well. The simulation results indicate that overvoltage will occur during cable switching if the cable is not sufficiently compensated, and the overvoltage will become more critical with as the operational voltage levels of the cable increases.

Network security management tool for distribution systems

In this paper a network security management tool, which is integrated in a power system simulator, has been introduced. The network security management (NSM) is used by network operators to avoid insecure network states due to high penetration of DGs. Especially in situations of low load and strong wind the operation parameters e.g. current or voltage can exceed the allowable values. The NSM tool introduced in this paper is performing new NSM algorithms within the power flow calculations. On the one hand, it can be used as an online application to support the network operator in his decisions using measurements and short time forecasts. On the other hand, by using the tool for long time simulations it can be used to optimize the NSM algorithms, to optimally plan network reinforcement and to predict the intensity of the NSM system on the profitability of the DG operators.

Renewable Generation and Reliability in the Electric Power NetworkZuverlässigkeit elektrischer Netze mit Energieerzeugung aus erneuerbaren Energien

Abstract Present day electric power systems in developed countries are characterised by very high reliability. In Germany the mean supply interruption time per year for the end customers is 23 minutes. How will this high quality of supply change with the increase of decentralised and renewable generation? Which measures are necessary to keep on this high reliability standard? This is one of the investigation goals in the E-Energy project Regenerative Modellregion Harz (RegModHarz). From a power system planning point of view it is possible to calculate some reliability indexes to evaluate the network structure. This methodology and some calculation examples will be given in part one of this paper. Further, taking into account the current experiences with power system operation, some necessary measures to support the secure power system operation with a high share of renewable generation, will be presented. The expected level of reliability in the future distribution power system will be analysed.