Networking of power system relays
As a tool of information and data communication, computer network has become the technical pillar of the information age, which has changed the appearance of human production and social life. It has a profound impact on various industrial fields, but also provides a strong means of communication for various industrial fields. So far, except differential protection and pilot protection, all relay protection devices can only reflect the electrical quantity at the protection installation site. The role of relay protection is also limited to the removal of fault components, reducing the scope of the accident. This is mainly due to the lack of powerful means of data communication. The concept of system protection has been put forward in foreign countries, which mainly refers to automatic safety devices at that time. Because the role of relay protection is not only limited to the removal of fault components and limiting the scope of the accident (which is the primary task), but also to ensure the safe and stable operation of the whole system. This requires that each protection unit can share the data of operation and fault information of the whole system, and each protection unit and reclosing device coordinate actions on the basis of analyzing these information and data to ensure the safe and stable operation of the system. Obviously, the basic condition to realize this kind of system protection is to connect the protection devices of main equipment in the whole system with computer network, that is to realize the networking of microcomputer protection devices. This is entirely possible under the current technical conditions.
For general non system protection, the realization of computer networking of protection devices also has great benefits. The more system fault information can be obtained by relay protection device, the more accurate the fault nature, fault location and fault distance detection are. It has been a long time to study the principle of adaptive protection, and some achievements have been made. However, in order to realize the self-adaptive protection to the operation mode and fault state of the system, more system operation and fault information must be obtained. Only when the protection is networked can this be achieved.
For some protective devices, the reliability of protection can also be improved by realizing computer networking. In 1993, Tianjin University proposed a distributed bus protection principle for 500kV EHV multi circuit bus of the Three Gorges Hydropower Station in the future, and initially developed this device. The principle is that the traditional centralized bus protection is divided into several bus protection units (the same as the number of circuits of the bus to be protected), which are installed on the protection screen of each circuit. Each protection unit is connected by computer network. Each protection unit only inputs the current flow of the circuit, which is converted into digital quantity, and then transmitted to the protection of all other circuits through the computer network Unit, each protection unit calculates the bus differential protection according to the current of the circuit and the current of all other circuits obtained from the computer network. If the calculation result proves that it is the bus internal fault, only the circuit breaker of this circuit will be opened to isolate the fault bus. In case of external fault of bus bar, each protection unit is calculated as external fault and does not act. The principle of distributed bus protection based on computer network has higher reliability than the traditional centralized bus protection principle. Because if a protection unit is disturbed or misoperated due to calculation error, it can only trip the circuit by mistake, and it will not cause the malignant accident that the whole bus bar is cut off. This is very important for the system hub with extra high voltage bus in the Three Gorges power station.
It can be seen from the above that the performance and reliability of protection can be greatly improved by the networking of microprocessor-based protection devices, which is the inevitable trend of the development of microprocessor-based protection.