Reliability assessment of autonomous power systems incorporating HVDCInterconnection links

Dialynas, EN

dc.contributor.author	Dialynas, EN	en
dc.date.accessioned	2014-03-01T01:44:50Z
dc.date.available	2014-03-01T01:44:50Z
dc.date.issued	1996	en
dc.identifier.issn	02721724	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/24500
dc.relation.uri	http://www.scopus.com/inward/record.url?eid=2-s2.0-33747360436&partnerID=40&md5=e6fd50a301b904a14965cfdce4afad2f	en
dc.title	Reliability assessment of autonomous power systems incorporating HVDCInterconnection links	en
heal.type	journalArticle	en
heal.publicationDate	1996	en
heal.abstract	Tho electrical power systems that are not connected with neighbouring systsmsface specific problems related to their management and are known as "" island systems"" . The installation of the most economic size of generating unit for reinforcing the overall capacity of the system may not bo possible without taking into account the security and reliability aspects. The interconnection with neighbouring systems is generally considered as an alternative planning reinforcement scheme. HVdc transmission links have found increasing use during the last two decades since they have proved to be a suitable and economic alternative scheme for tho interconnection of island systems. One of the major advantages of these links is that they allow the island systems to continue to have a separate operating procedure for control of frequency and voltage. A reliability assessment of these power systems may be conducted applying tha probabilistic modeling and evaluation techniques that have been developed and published to analyze composite generation and transmission systems. However, these techniques do not sufficiently take into account the respective design and operational parameters of the island systems. The actual configuration of a HVdc interconnection link depends on the various features and operating practices of the two systems connected and contains a significant number of components. Such practices involved are the switching arrangements available in outage conditions and the maintenance procedures of the system components. An important parameter of system design is the rating of the interconnection link taking into account the current technology in HVdc links and the rating of the generating units existing in the island system. The loading profile on the interconnection link is expected to normally follow a cyclic pattern throughout the day following the shape of the system demand curve. Alternatively, the loading profile can be preset to one or more fixed values during the respective time period. After a decision is taken to connect an island system with another power system using a HVdc interconnection link, another step may be necessary to be conducted in the planning process of certain systems where there will exist surplus generating capacity. It becomes necessary to determine which generating units need remain in the system while all the remaining ones will be removed. There are many factors and criteria influencing this decision process but the most important one is the reliability performance of the various load-points in the system. For this reason, it is necessary to conduct a reliability assessment of the composite generation and transmission system by taking into account the existing interconnection link and the various generating units decided to remain in the system. The operating practices of these units must follow the dispatching principles in daily system operation and in outage conditions. In certain systems, generating units located within the network, are in standby or parallel operation and can supply the load of neighbouring load-points during outage conditions causing major problems in the area concerned. For economical reasons, these units can be considered that they may operate for a limited number of hours each day due to the respective staffing arrangements. The purpose of this paper is to present an improved method for assessing the overall reliability performance of autonomous power systems that may or may not contain HVdc interconnection links. This is a hybrid method based on a Monte-Carlo sequential simulation approach which incorporates an analytical approach for the reliability modeling and evaluation of HVdc transmission links. The basic steps of the developed method are the following: 1) Input the appropriate data required for the analysis. 2) Perform a reliability analysis of each HVdc interconnection link and obtain the equivalent capacity outage table of its output node. If the link has either a paralleled monopolar or bipolar configuration, assume that one pole is on outage, modify the link configuration and obtain the respective equivalent capacity outage table of the output node. 3) Perform a reliability analysis of the composite generation and transmission system applying a specially developed Monte-Carlo simulation approach and obtain the respective reliability indices for the load-points under consideration and for the entire system. For this analysis the following specific system features must be considered: The output node of each Hvdc interconnection link is considered to be an equivalent generating unit having multiple states. The effect of maintenance outages is taken into account by considering that, during the respective scheduled time periods, the configuration of the link is different and it is represented by the respective equivalent capacity outage table. A generating station is assumed to be available only during its respective operating times according to its staffing arrangements (1, 2, 3 shifts) and the scheduled maintenance procedures. Each HVdc interconnection link has two alternative operating modes. The first mode assumes that the link is treated as an equivalent generating unit with a specific priority order and its output level is determined by the system generation requirements and the priority order of all the units available in each time period concerned. The second mode assumes that the loading profile of the link follows a prespecified pattern which can only be violated when either the link is not available or the generating capability of the system is not sufficient. 4) Evaluate an appropriate set of reliability indices for each load-point being analyzed and the entire system. When a Hvdc interconnection link is included in the analysis, evaluate the following additional indices: Average annual energy produced by the generating units of the system (AEG) in Gwh/year - Average annual energy supplied through the HVdc interconnection link (EGHVDC) in Gwh/year • Frequency of events occurred when the Hvdc interconnection link is not capable to transmit the demanded load (FCHVDC) - Average period of the above events (TCHVDC) in hours • Average annual energy not supplied during the above events (ECHVDC) in Gwh/year • Frequency of events occurred when the power supplied through the Hvdc interconnection link is greater than that defined by the respective loading profile (FPHVDC) • Average period of the above events (TPHVDC) in hours • Average annual energy supplied during the above events (EPHVDC) in Gwh/year 5) Evaluate an additional set of system indices quantifying the health of the generation and transmission system under study. The functionality of the system is identified as being healthy, marginal or at risk. The principles of the power system health analysis were extended so that they can be easily incorporated into a Monte-Carlo simulation approach. For this purpose, two alternative techniques were developed for evaluating the probabilities of the system being in the health and marginal states. The method developed has been implemented efficiently into the self-sufficient and easy to use computer program RANIPS which can be used for analyzing alternative system configurations and establishing the impact of various system parameters. The data required for both the autonomous system and the HVdc interconnection links are inputted in a very simple way considering the respective one line diagram and operating features. Furthermore, the paper presents the results obtained from the analysis of a system whose configuration was based on the power system of a Greek island planned to be connected with the interconnected power system of the Greek mainland. A number of alternative case studies were conducted that demonstrate the increased information that can be gained from the use of the method developed.	en
heal.journalName	IEEE Power Engineering Review	en
dc.identifier.volume	16	en
dc.identifier.issue	1	en
dc.identifier.spage	68	en
dc.identifier.epage	69	en