Jma Johanna Myrzik

Integration Issues of Distributed Generation in Distribution Grids

In todays distribution grids the number of distributed generation (DG) units is increasing rapidly. Combined heat and power (CHP) plants and wind turbines are most often installed. Integration of these DG units into the distribution grid leads to planning as well as operational challenges. Based on the experience of a Dutch distribution system operators (DSO), this paper addresses several possibilities to handle grid planning issues. Effects on voltage control, grid protection, and fault levels are investigated and described. These aspects are illustrated with the aid of simulations on an existing distribution grid. It is demonstrated that in compact distribution grids voltage control problems and blinding of protection are not likely to occur and that false tripping and fault level have to be considered carefully.

Harmonic effects caused by large scale PV installations in LV network

In the next decade the amount of decentralized generators will significantly increase in the distribution networks. Among the sustainable energy sources, the research on photovoltaic generators has received much attention, especially the study of residential photovoltaic (PV) systems, which has potential of becoming a significant market. Measurements in a bungalow park in the Netherland with a high penetration of PV have shown a lot of harmonic distortions at the point of coupling. There harmonics are concerning resonances and the interaction of current harmonics generated by the inverters and the voltage harmonics coming from the grid. This paper, will study the influence of the current harmonics generated by photovoltaic systems connected to the low voltage network and the interaction with other non-linear loads and the network voltage. Basis for this simulation is a neighborhood in the Netherlands with around 96 houses. Simulations will show the effect of these harmonic currents generated by big amount of photovoltaic systems and common electronic loads and the interaction between them.

Coordination of voltage regulation in Active Networks

This paper give an introduction about the Active Network concept that can be managed by a multi-agent system (MAS). Voltage regulation, one of Active Networks services, is then presented. The autonomous voltage control within each feeder (Cell) can be deployed by a combination of active and reactive power supports of distributed generators (DG). The coordination voltage control defines the optimal tap setting of the on-load tap changer (OLTC) while comparing amounts of control actions in each Cell. The test results show that the voltage regulation in Active Network can help to integrate more DGs and mitigate voltage violation effectively. The optimal solution can be reached within a small number of calculation iterations.

Analysis of power quality performance of the dutch medium and low voltage grids

Modern installations have become sensitive to power quality (PQ) related problems because more sophisticated devices with non-linear operating characteristics are often used there. On the contrary, most of these devices produce emissions that could decrease the PQ level of the network. It is becoming an increasing problem for the network operators to maintain good voltage quality because of the interactions of customerpsilas loads with the grid. It is anticipated that the networkpsilas physical characteristics (e.g. short circuit power, grid impedance) can influence the PQ performance (harmonic distortion, flicker severity) in the distribution grid. In this paper, a typical modern medium and low voltage Dutch grid is described that is modelled in the analysis tool dasiaPower Factorypsila. The network is simulated to analyze grid impedance and short circuit powers at different parts of the network. Furthermore, the importance of grid impedance is analyzed in relation to PQ aspects at the customerpsilas point of connection.

Power flow management in active networks

This paper proposes a new method to manage the active power in the distribution systems, a function under the framework of the active network (AN) concept. An application of the graph theory is introduced to cope with the optimal power generation (DGs/Cells dispatch) and interarea power flows. The algorithm is implemented in a distributed way supported by the multi-agent system (MAS) technology. Simulations show how the method works in cases of optimal operation, congestion management, and power generation cost change.

Effect on DG on distribution grid protection

Up till recently past electric power systems were characterized by centralized production units, a high voltage transmission grid for the bulk energy transmission and medium and low voltage distribution grids to bring the energy to the consumer. Traditionally no generation sources were connected to the distribution grid, however, this has changed significantly the past decade. Nowadays various types of small generation sources, better known as distributed generation (DG), are connected to the distribution grid. Due to CO2 reduction goals many of the small units integrated in the distribution grid are renewable energy sources, such as wind turbines, small scale hydro plants and photovoltaic panels but also high efficient non-renewable energy sources, such as small Combined Heat and Power (CHP) plants are implemented. Connection of DG not only alters the load flow in the distribution grid but can also alter the fault current during a grid disturbance. Most distribution grid protective systems detect an abnormal grid situation by discerning a fault current from the normal load current. Because DG changes the grid contribution to the fault current, the operation of the protective system can be affected. This is reported in (Deuse et al., 2007; Doyle, 2002; Kauhamieni & Kumpulainen, 2004), however, in these papers the protection problems are discussed in general terms. In this chapter a detailed analysis of possible protection problems is given. It starts with an analytical description of fault currents in distribution grids including DG. With the aid of the analytical equations the effect of DG on the fault current is studied and key parameters are identified. This chapter also provides an equation to calculate the location where the DG-unit has the most effect on the grid contribution to the fault current. During the design stage of the protective system for a distribution feeder including DG this equation can be applied to determine if protection problems are to be expected. The application of the derived equations are demonstrated on a generic test feeder. An overview of all possible protection problems is presented and a classification of the protection problems is given. Furthermore these protection problems are linked to the theoretical background which is discussed in the beginning of the chapter. In this part of the chapter solutions for the possible protection problems are presented as well as new developments in protective systems which enables a further integration of DG in distribution grids. 5

Photovoltaic energy in power market

Photovoltaic (PV) penetration in the grid connected power system has been growing. Currently, PV electricity is usually directly sold back to the energy supplier at a fixed price nd subsidy. However, subsidies should always be a temporary policy, and will eventually be terminated. A question is raised whether grid-connected PV generation will be more beneficial by making biddings in power markets than by supplying at a fixed price. An economic model of profit maximization for PV generation when joining power markets is proposed to answer the question. A simplified model is applied to simulate a case study of PV biddings in the Amsterdam Power Exchange (APX) spot market, using PV generation data from a standardized neighborhood PV installation. A Monte Carlo method is used to calculate penalty costs due to over-predicted irradiation. Also a Monte Carlo simulation is applied to survey a number of random imbalance capacities and corresponding prices within a Gaussian distribution by repeating the calculation loop. The sensitivity for prediction errors is examined by simulations with different unpredictability levels of solar irradiation. The outcome of the simulations is a value for the difference between the two revenues of PV generation when joining power markets and when supplying at a fixed price.

Effects of Further Integration of Distributed Generation on the Electricity Market

Environmental concern leads to legislation to stimulate the further integration of renewable energy in the Dutch electricity supply system. Distributed generation is suited for the integration of renewable energy sources. Furthermore it can be used to generate both heat and electricity in a more efficient way using muCHP. Unfortunately, the additional integration of distributed generation has some negative consequences for the organisation of the electricity market. Programme responsible parties have to set up E-programmes which describe trade amongst them. Due to the higher unpredictability and uncontrollability of distributed generation, the E-programmes tend to be less accurate. This results in imbalance between supply and demand of electricity which has to be settled by the transmission system operator. This leads to extra costs for the programme responsible parties which could finally result in a drawback for the integration of renewable energy sources. Therefore market based solutions have to be created.

Participation of distributed generation in balance Management

Distributed generation is not yet considered to participate in balance management in power systems. Low marginal costs and poor predictability make them less attractive for this application. However, further integration of distributed generation will make participation in balance management a necessity both for down regulation as well as up regulation. The potential of different distributed generators to participate in balance management is analysed. Economic and regulatory boundaries are discussed, as well as improvements to create incentives for distributed generators to participate.

Provision of ancillary services for balance management in autonomous networks

The main hypothesis underlying the work presented in this paper is that the future power system will rely on large amounts of distributed generation (DG) with large percentage of renewable energy based sources. Consequently, this system will be characterised by significantly increased uncertainties on generation side and therefore, its behavior in time will be more difficult to control. This paper discusses the current methods for balance management. Furthermore it considers the limitations and presents a novel approach for balance management in a future situation.