Backup Protection Device Design And Implementation For Subway Network

With the development of economy the transportation is also getting more crowded as the population in city is getting higher. Subway has become an important way to solve this problem. With the increase in the construction of the subway, passengers also increase, which requires higher power supply reliability. Medium voltage ring network is the main source of underground energy with great significance, but the protection scheme of medium voltage ring network still has many deficiencies. For example, the differential protection as main protection can only protect the ring cable between two substations, and the protection of bus switchgear can only be achieved by backup definite time overcurrent protection and residual overcurrent protection, and a time differential between upper and lower levels exists in definite time overcurrent protection, which may lead to a malfunction of breakers.To solve these problems, current selection trip protection is used to replace the original backup protection scheme. After a detailed analysis of the feasibility, reliability and speedy backup protection device are analyzed and designed. The hardware consists of four cards, which are acquisition card for the exchange amount, digital input and output card, CPU card and power card. And each card has been introduced in detail.IED model has been established based on IEC 61850 and part of the modeling table has been presented. Software for protection devices were developed On CCES platform, and the flow chart of the main program has also been showed, and protection procedures have been described in detail and shown in the flowchart.Model of medium voltage ring network for subway has been implemented in RTDS and complete test program has been given. The result shows that the subway network backup protection devices can be operated quickly and reliably.