Essay Example on In recent years electricity market liberalization and environmental Concerns

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In recent years electricity market liberalization and environmental concerns factors that contribute to the renewed interest in distributed generation DG In liberalized markets it is important to adapt to the changing economic environment in the most flexible way DG technologies in many cases provide flexibility because of their small sizes J Driesen et al 2006 At present environmental policies are probably the major driving force for the demand for DG Environmental regulations force players in the electricity market to look for cleaner energy solutions Furthermore most government polices aiming to promote the use of renewables also results in an increased impact of DG technologies as renewables There has been an immense interest in incorporating DG into distribution networks in recent years DG definitions used in the literature Ackermann et al 2001 have proposed the following general definition for DG Distributed generation is an electric power source connected directly to the distribution system or directly to the customers facilities or both 



During the last decade the penetration of renewable energy based DG units has increased significantly Wind and solar are the natural renewable power choices for many countries and they have successfully integrated into existing electricity infrastructures DG units bring many new challenges for power system operators T Aziz et al 2011 needing to integrate these units into existing distribution system These challenges includes bidirectional power flow less inertial generation and unregulated intermittent behaviors These challenges mean that power quality is one of the key issues and DG units have a significant impact on the system and equipment in both steady state operation and in dynamic operation They affect reliability instability and safety for both customers and electricity suppliers Because of the close proximity of the DG units to loads and to their controllers in medium and low voltage networks dynamic interaction is a more complex issue than it is in large systems The impact of DG on power quality there are typically two majors concerns 



Thomas Ackermann et al 2002 namely voltage flicker and harmonics In distribution network the most common cause of flicker is a rapid variation of load current however not only load variation s cause flicker but also DG can directly or indirectly contribute to voltage flicker The main causes of flicker are i starting of a large DG unit ii sudden and large variations of the output of DG iii Interaction between DG and the voltage controlling equipment of feeder It is widely recognized that the presence of non linear components of power systems manifests in the appearance of harmonics The presence of harmonics in a power system is undesirable for a number of reasons some of which are i Harmonics increases power loss in both utility and customer equipment ii Sometimes harmonics may provoke malfunctionally of sensitive load or control equipment iii Harmonics having significant magnitudes can cause a reduction of lifetime of motors transformers capacitor banks and some other equipment Power electronics devices as used for DG might can cause harmonics If DG was not properly interfaced with the distribution network its presence may actually reduce the overall reliability of the distribution grid here all the aforementioned apples harmonics flicker and voltage regulation Hence assessing and responding to power quality issues are important tasks for accommodating the higher penetration of DG units and for the secure operation of the electricity system 



DG units embedded with different technologies and with different steady state and dynamic characteristics can improve power quality depending on how the challenges they pose are dealt with It can therefore be modern high power electronics technology can be used to solve the relevant power quality phenomena associated with DG high power electronics technology is the flexible ac transmission system FACTS on the one hand and Custom Power N G Hingorani 1995 is giving rise to a slew of forward looking enhancements for systems that transmit and distribute electricity The first allows a greater control of power flow and a secure loading of transmission lines to levels nearer to their thermal limits among other benefits The second applicable to distribution systems focuses on the reliability and quality of power flow The concept of Custom Power describes the value added power that electric utilities and other service providers will offer their customers in the future


The improved level of reliability of this power in temis of reduced interruptions and less variation will stem from an integrated solution to present problems of which a prominent feature will be the application of power electronic controllers to utility distribution systems and the Custom Power were envisioned as serving the distribution system The Custom Power concept is one off two strategic technological responses to the poor power quality presently surfacing in factories offices and homes The other response is the development of complementary individual end user equipment running on low power and low voltage Today the action in advanced power electronics is shifting expectations for reliability into an entirely new dimensionThe emerging expectations of the Custom Power concept are that power supplied by utility systems should have virtually no or far fewer brief disturbances caused by lightning faults switching and other events Even though these disturbances are cleared within at most a few seconds they disrupt the operations of utility customers In fact many utilities have set up Custom Power teams to address this issue The success of the approach to some extent involves the overall enhancement of the distribution system through other advancements that are under way


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