A reliability model of a power distribution network with reference to petrochemical and gas-to-liquid plants

[摘要] The interruption cost for one hour of a petrochemical plant is 33 times higher than that ofthe average interruption cost for industrial plants across all industries. In addition to thehigh cost of loss of production, interruptions to the operations of petrochemical and gas-toliquidplants pose safety and environmental hazards. Thus it is necessary to betterunderstand the reliability requirements of petrochemical and gas-to-liquid plants.This study investigated the reliability of electrical distribution networks used inpetrochemical and gas-to-liquid plants compared to those used in other industrial plants. Amodel was developed that can be used to establish the adequacy of the reliability of adistribution network in terms of the components and network topologies used. This modelwas validated against data that had been collected by the IEEE and applied to an actualpetrochemical plant.Over 19 years' worth of data regarding the trips that have occurred on the distributionnetwork of an existing petrochemical plant was collected and manipulated in order tocalculate the reliability indices associated with the equipment used to make up thisRecommended Practice for the Design of Reliable Industrial and Commercial PowerSystems.The cost of loss of production and the capital costs associated with increased reliabilitywere calculated for a section of the existing petrochemical plant. The reliability associatedwith different network topologies that could possibly be used to supply power to thissection of the plant were modelled using an appropriate software package. The resultingtotal cost of ownership over the life of the plant associated with each topology was thencalculated in order to establish which network topology is the most appropriate forpetrochemical and gas-to-liquid plants.It was concluded the components that affect the reliability of an industrial distributionnetwork are different to those that affect a utility distribution network. These componentswere listed and compared. It was found that the reliability indices that were calculated forthe components that affect the reliability of a petrochemical plant were similar to thoseprovided by the IEEE. 17 out of 20 of the indices that were calculated were within therequired factor of deviation. Generally the failure rates of components used inpetrochemical plants were very similar to those given in the IEEE Gold Book, while theMTTR's for the components used in petrochemical plants were found to be slightly betterthan those given in the IEEE Gold Book. The effect of network topology was found to be significant, with small changes in thetopology of a network resulting in large variations in the reliability of the network. It wasalso found that the most appropriate type of network topology to use in the design of theelectrical distribution network of a petrochemical plant is the dual radial network. This isthe most conservative of the commonly used network topologies and is the one that iscurrently used in the existing plant that was studied.Due to the high cost of loss of production in petrochemical plants it was established thatany incremental improvement in the reliability of the dual radial network would bebeneficial to the total cost of ownership of such a plant. Such incremental improvement ofthe reliability of the distribution network could be cost effectively achieved by adopting aconservative maintenance strategy and the establishment of a conservative sparesinventory. Before this study was undertaken, there was no literature around the reliability of electricaldistribution networks that focused specifically on petrochemical and gas-to-liquid plants.This study produced a set of reliability indices and a model that electrical engineers canuse in the reliability analysis of petrochemical and gas-to-liquid plants. Furthermore itshows that, because the cost of loss of production in petrochemical plants is so high, themost conservative distribution network design and maintenance philosophies shouldalways be used.distribution network. These reliability indices were compared to those given by the IEEE

[发布机构] University of Pretoria