Protection performance study for secondary systems with IEC61850 process bus architecture

摘要

Following the introduction of the microprocessor into the power system protection field, modern microprocessor based numeric relays have developed very rapidly in the last 20 years, and modern power system protection schemes are virtually all based on microcomputers technology. The International Electro-technical Commission (IEC) recently launched the standard IEC61850, “Communication Networks and System in Substation”, which is having a major impact on the structure of new protection systems and schemes. In itself it describes the concepts for sub-station communications covering protection, control and metering functions. However, although it is going to have a major impact on the power systems communications, it will also influence the design of future protection systems. There will also be a host of other opportunities and advantages that can be realised. These include easier upgrading, refurbishment and replacement of sub-station protection. They also provide for greater use of general purpose Intelligent Electronics Devices (IEDs), self-healing systems, and plug and play type facilities. The Ethernet based communication network for data transfer between process level switchyard equipment and bay level IEDs, the process bus, is defined in IEC61850 Section 9-2. This process bus facilitates the communication of two types of real-time, peer-to-peer communication messages. Generic object-oriented substation event messages, the GOOSE messages and the data sample values, SVs which include the measured currents and voltages. Although this standard describes the message structures and the timing requirements, it does not describe the process bus topology. This work describes different LAN topologies that can be used in the design of process bus for protection systems. It considers the implications of the different structures on the operation of the protection scheme and how these relate to the operational strategy of different operators. It provides an assessment of the data handling capabilities of the system and how the demands of the protection system can be met. Several potential problem areas are identified and analyzed. The probabilistic nature of these systems is discussed and the implications explained. It also provides an insight into the implementation of the alternative topologies and their performance when applied to a transmission line feeder protection and transformer protection. The digital substation and the implementation of IEC61850 are fundamental to the future of protection ‘relays’. There are many pointers to the potential directions that these systems will develop and the skills required for the protection engineers of the future. This project is seeking to overcome some of the ownership challenges presented by modern protection and control (P&C) devices, which have an inherent short life due to their dependence on modern electronics and software.