Research On Issues Of Digital Of Power Systems

During past decades, Information & Communication Technology (ICT) has gotten extensive application in electric power systems. The ICT has brought profounding changes in operation, dispatching, controlling, and management of power system, and brought forward Digital Power Systems (DPS). The thesis carries out research on data transmission and indepth applications in electric power systems. The outputs of the thesis are listed as follows.A prototype of Wide Area Current Differential Protection System (WACDP) based on network communication is proposed. Graph theory based expert system has been developed to coordinate primary and backup current diffenential protection zones. Relay agents can be utilized to carry out primary and backup current differential protection. Its application over substation automation systems using IEC 61850 protocol combining Publisher/Subscriber mechanis has been discussed.Since Electriconics Instrument Tranducers (EITs) are much cheaper than traditional electromagnetic instrument transducers, they can be equipped with redundancy. The redunant measurements of EITs are available via communication network within a substation automation system using IEC 61850 protocols. Pattern identification and rule-based approaches are proposed to identify the fake measurement. The former identify fake measurement with all measurements of the substation while the latter identify fake measurement with redundant measurements and expert experience to prevent mis-operation of protection system due to fake measurement.Data compression technologies, such as curve fitting and sampling/interpolation, are proposed to transmit power system dynamics in existing SCADA. The power system dynamics can be compressed to an acceptable volumn to be transmited over existing communication channels. Thereafter, the system dynamics can be reconstructed with the compressed data. The sampling/interpolation can also be utilized to facilitate tranimitting compressed systems dynamics in Wide Area Measurement System.Analysis on fault data of four power grids in south China unveiled Self-Organized Criticality (SOC) in time series of power systems fault. Since cascading outage, precipitation related extreme climate (thunder storm, hurricanes, storm, ice storm) and other events (land slide, wild fire) contribute much to power system fault, it is speculated that the power system fault derives its SOC from cascading outage and SOC of precipitation related extreme climate and other events. The speculation is consistent to the power systems fault burst out in 2008 ice storm in China.It is pointed out that the main impact of global warming upon electric power systems arise from extreme climate since intensity and frequency of extreme climate will increase notably with enhanced global surface temperature. Whereas, global warming should not be blamed alone for frequent blackout due to extreme ice storm. Precipitation following power law distribution seems conflict to the presumption that ice accretion following lognormal distribution hold in design criteria of overhead transmission lines. Therefore, the risk of overhead transmission line undergo structural failure during ice storm is much higher than expected. It is pointed out that by allocating maintenance resource to vulnerable section based on analysis on spatial and temporal biased distribution of power system fault, the system reliability during extreme climate can be enhanced efficiently and cost effectively.