An Over-Current Protection Scheme For Metro Medium Voltage Ring Network Based On IEC61850

Nowadays, the metro is widely used in an Urban Rail Transit System due to its high-speed, convenience and environmental protection. Alternating current medium voltage ring network is served as the metro power supply system that is essential for the normal operation of the metro. For relay protection of the medium voltage ring network, current differential protection using optical fiber communication channel is commonly used as the primary protection with high quick-action and selectivity. However, it could only protect the ring line using the currents obtained from both sides, and it cannot serve as backup protection for adjacent’lines. Therefore, overcurrent protection and zero sequence overcurrent protection are used as backup protection of cables in ring network and primary protection of bus protection. For overcurrent protection, the time limit for outlet side of the main substation is about1.5s and the time set for the substation is cooperated progressively with each other with a time range of0.25-0.3s. In this case, if over6substations are contained in a large ring network power supply sections or a small power supply sections, this protection is hard to meet the requirements for selectivity.To solve the shortage of medium voltage ring protection, a network protection is introduced and constructed using GOOSE fast trip and bar atresia. In this protection, cable protection, bus protection, and malfunction intertripping logic are constructed for the metro substations of the35kV medium voltage ring network. In this paper, a model is built based on IEC61850protocol to realize line protection device, abstracted information model of intelligent terminal model, and a communication method based on virtual terminals and dataset.In this paper, Chengdu Metro No.1medium voltage network is taken as an illustration for the logic of the proposed protection. First, Opnet Modeler Software is used to build the topology of communication network and the maximum transmission delay of the corresponding network is proved to be0.82ms. Second, cable protection, bus protection and feeder protection logic are simulated in Matlab/Simulink. Then the corresponding logic is masked together to construct the protection device model and this model is used to build a simple ring network model. Under the consideration of single and double power supply, this model has been used to simulate single-phase-to-ground faults, two-phase faults and three-phase faults. The functions of fast tripping and bar atresia as well as the protection logic are tested successfully. In this paper, the quickaction, reliability, selectivity, sensitivity of protection scheme is validated. Therefore, the protection logic and scheme based on the GOOSE selection jump mechanism are reasonable.