A STUDY ON IMPROVING POWER SUPPLY CAPABILITY FOR 500/220KV POWER SYSTEM IN JIANGSU PROVINCE

摘要

This paper reviews the development courses of 500kV bulk transmission system in Jiangsu Province,China, and their corresponding 220kV interconnected sub-transmission systems. Each developmentcourse which has its unique and specific characters is focused and studied. With the development of500kV transmission system into mature, a number of 220kV sub-transmission systems, among which aredirectly and electrically disconnected via 220kV lines or circuit breakers in operation but are electricallyinterconnected via 500kV system, are formed mainly due to the reason of decreasing system fault levelbelow the limits of circuit breaker. Such isolated 220kV sub-transmission system is defined as the IslandGrid (IG) in this paper.The purpose of this paper is to study the capability of power supply of IG system as well as the keyfactors, such as transformer impedance, influencing the capability based upon three typical models of500kV/220kV IG system structure. Further more, the conclusions of study will be used to help ussignificantly increase economic system scale and efficient with the accepted security and/or reliabilitystandard set by Regulator, especially in the case of the severe constraints of land resources and corridorsto construct new transmission lines and substations.The IG system generally comprises of the power sources, such as 500kV main transformers and thegenerators connected to 220kV IG, the connected distribution systems which are regarded as the loads inthe study, and the tie-lines to the neighbor IGs which are disconnected during the normal conditions andcan be interconnected if the said IG is in contingency due to the outages of 500kV main transformer orlarge generator in order to maintain again the power supply capability and the security and/or reliabilitystandard.The conclusions of this study are successfully and practically applied in Jiangsu power systemplanning and the transmission system expansion project development. A project commissioned inNanjing, capital of Jiangsu Province, is that two 500kV substations were expanded and renovated withhigh impedance transformers, and the interconnected 220kV IG system was maintained without the gridstructure modification.