In today's 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.

Integration Issues of Distributed Generation in Distribution Grids

Exploring sustainability transitions in the electricity sector with socio-technical pathways

This paper describes the approach to developing transition pathways for a low carbon electricity system in the UK, being pursued in a major new research project The project aims (a) to learn from past transitions to help explore future transitions and what might enable or avoid them; (b) to design and evaluate transition pathways towards alternative socio-technical energy systems and infrastructures for a low carbon future; and (c) to understand and where appropriate model the changing roles, influences and opportunities of large and small 'actors' in the dynamics of transitions The paper describes the approach being taken, which builds on the work of Dutch researchers on transitions and transition management using a multi-level framework of niches, socio-technical regime and landscape It also outlines its application to the case of transition pathways to a regime dominated by local distributed electricity generation, including the evolution of the physical and institutional infrastructure changes, and the roles of actors, both large, eg multinational energy supply and distribution companies, national governments, major investors, and small, eg households, innovators and entrepreneurs

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Developing transition pathways for a low carbon electricity system in the UK

Distributed generation system operate with grid in islanding condition will damage equipment,affect the safe and stable operation of power system,even threaten the safety of line maintenance peopleTherefore,studying on distributed generation system in islanding condition has practical significanceThis paper presents an overview of islanding detection methods for distributed generation systemsThe paper classifies islanding detection methodsFinally,its study direction in the future is also looked ahead

Review of islanding detection methods for distributed generation

The integration of distributed generation (DG) sources can cause significant impacts on distribution networks, particularly the changes in magnitudes and directions of short circuit currents that may lead to false tripping or fail to trip over-current protection relays in the system. It is expensive and technically challenging to redesign/reconfigure and/or to replace the original protection system for a distribution network. If not appropriately handled, this issue can be a big hurdle before the wide use of DG. Based on the impact analysis of the number of DGs, their locations and capacities upon short circuit currents, this paper presents an optimal DG placement method to maximize the penetration level of DG in distribution networks without changing the original relay protection schemes. Genetic algorithm is used to find the optimal locations and sizes of DG in distribution networks. Simulation studies have been carried out on a three-feeder test distribution network and a widely used 33-node test system to show the effectiveness of the proposed method.

Relay Protection Coordination Integrated Optimal Placement and Sizing of Distributed Generation Sources in Distribution Networks

Nowadays the number of dispersed generators (DGs) is growing rapidly. This change will greatly influence power system dynamics. A distribution network, where DGs are connected to the grid, cannot be considered as passive anymore. Therefore, in the future it will not be possible to use simple equivalents of distribution networks for power system dynamic modelling, as it was done before. At the same time, the whole power system cannot generally be represented in a detailed manner for dynamic studies because of huge system dimension. Therefore special techniques have to be applied for aggregation and order-reduction of distribution networks with DG. A brief review of existing techniques is provided here, and the dynamic reduction using Hankel norm approximation is performed for a 10 kV distribution network, which includes DG of different types.

Dynamic equivalencing of distribution networks with dispersed generation using Hankel norm approximation

Nowadays, more and more lamp types are being used. Since different lamp types have different working principles, they also have different flicker responses. This paper shows the measurement results of different flicker responses for various types of lamps. These results prove that the UIE/IEC flickermeter, which has been used widely around the world for many years, cannot be used to advise on the flicker level of all lamp types. This is because of the fact that this flickermeter is based on a 230 V, 60 W or 120 V, 60 W incandescent lamp and can be used as reference only for this type of lamp or as reference to the standard. The UIE/IEC (International Union for Electricity Applications/International Electrotechnical Committee) flickermeter and the existing standards are therefore insufficient for other lamp types. This paper describes a proposal to improve the UIE/IEC flickermeter.

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Flicker responses of different lamp types

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

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Effect on DG on distribution grid protection

Electricity networks of the future : various roads to a sustainable energy system

SUMMARY Inordertohandleahighpenetrationof distributedgeneration(DG),theexisting passivedistributionsystemsneedtobecome moreactive.Inthesocalled active network (AN), powerflow management has developed to copewith bidirectional power flow and the intermittence of DGs. This paper proposes a method to better manage active power flows based on graph theory application and multi-agent system (MAS). While the power system isrepresented asa directed graph,the optimalpowerflow (OPF) isunderstoodas a minimumcostflowproblem that canbe solvedbythesuccessive shortest path algorithm. The algorithm is implemented in a distributed way and is supported by MAS. Simulations using a five sub-areas network show that the method is able to reach the optimal operation statewhile restraining powerflows within definedbounds. Furthermore, the method can also response changes in power generation cost, network configuration and load demand increase. Copyright # 2009 John Wiley & Sons, Ltd.

Jma Johanna Myrzik

Papers

Dynamic equivalencing of distribution networks with dispersed generation using Hankel norm approximation

Flicker responses of different lamp types

Effect on DG on distribution grid protection

Electricity networks of the future : various roads to a sustainable energy system

An application of the successive shortest path algorithm to manage power in multi-agent system based active networks