Substation Area Differential Protection Study Of 500kV Wujia Substation Transformer

As network communication technology of intelligent substation maturing,it has been possible to maximumly share the whole station information in the intelligent substation,which provided the condition for the study about the area protection.In this paper,the program of substation area differential protection of 500 k V Wujia substation transformer is studied.Based on the centralized collection and analysis of the whole substation information,the substation area differential protection can be seen as the centralized reserve protection for the entire substation.With the side busbar of the transformer in the substation as the protecting border,the substation area differential protection can show the short circuit with any type in the protection area or inside the transformer.The substation area differential protection can also provide the fast and sensitive reserve protection for sampled data exceptions of all conventional protection configurations.With these functions,the substation area differential protection could replace complicated side switch failure united jumping of the main transformer,which is still be widely used now.In this paper,with ratio brake differential protection as the fundamental,the two main transformers and the connected electronic instruments in Wujia substation are divided into various differential areas,such as big differential area or small differential area.By calculating the short current in various differential areas during the short circuit in the substation,the implementation principle of the transformer substation area differential protection has been illustrated.Besides it,the conductive possibility of the transformer substation area differential protection designing is proved by the fault simulation calculation,which is based on the parameters of the electronic instruments in the Wujia substation.In addition,the influences to substation area differential protection by the transformer magnetizing inrush current in the electronic system and the disconnection of the current loop of the substation area differential protection are also discussed.At last,the recognition methods to these negative influences are made andthe preventive solution are provided,which are differential speed protection preparation and disconnected atresia differential protection logic.Based on the centralized collection and analysis of the whole substation information,the collection and control to the electrical quantity and switch numbers by the substation area differential protection should be done through the internet.Therefore,the request of the substation area differential protection to the reliability and rapidness of the data transmission through the internet is very constrict,which need to be conducted under the optical fiber ethernet.In order to keep the reliability of the substation internet,the Wujia substation electronic instruments were divided into process layer,spacer layer and station control layer according to the IEC61850 standard.Besides it,MMS,GOOSE and SV internets were designed.To keep the reliability of the conduction internet and reduce the network hardware investments,the networking solution was optimized by GOOSE and SV common internet configuration and the VLAN planning technology.At last,by testing the transmission delay and lost frame rate between process layer and spacer layer of Wujia substation with internet monitor instruments,the common internet configuration was proved to fulfil the requirements of the Wujia substation conductions.Because of the various of the substation running type,the transformer substation area differential protection need to automatically adapt the power grid running type and adjust the action strategy.To do so,the sub-gate and close gate locations of the substation electronic instruments were collected to identify the power grid running type.The coordination mechanism of the transformer substation area differential protection to three frequently phenomena in substation was also discussed,such as the exit of any load branch,busbar isolation knife double cross and the exit of any transformer groups.In this paper,by associating the 500 k V Wujia substation project,the theory analysis and calculation of the transformer substation area differential protection were investigated,as well as the common internet configuration planning and the coordination mechanisms with electronic system running type.Based on the results,the principle and the internet optimize planning of the transformer substation area differential protection was proved to be possible.