Baoshan Iron & Steel (Baosteel for short) is one of the largest and most modernised iron and steel complexes in China. Baosteel has established its status as a world-class steel producer with comprehensive advantages in reputation, talents, innovation, management and technology. According to 'Guide to the World Steel Industry', Baosteel is ranked among the top three most competitive steel producers globally. Baosteel is also believed to have the most potential for an iron and steel enterprise in the future.
The company specialises in producing high-tech and high-value-added steel products. Meanwhile, it has become the main steel supplier to industries of automobile, household appliances, container, oil and natural gas, exploration, and pressure vessel. Baosteel exports its products to over 40 countries and regions including Japan, South Korea, and countries in Europe and America.
Shanghai Baosteel Group's number 2050 hot mill plant has four step heating furnaces processing 5 million tons of slab heating per year. Citect provided the energy control system in this plant.
Server redundancy
Under normal conditions, the primary I/O server is responsible for all data communication with the MODCELL control stations. At a regular time interval, the secondary I/O server checks whether the primary server's communication connection with the MODCELL is functioning as normal. If the communication is not functioning normally, the secondary server triggers the hardware alarm to inform maintenance personnel of the problem. The secondary I/O server also regularly checks the primary I/O server's running status. If the primary server is not functioning properly, the secondary server automatically takes over the primary server's I/O functions. When the primary I/O server resumes its normal functionality, I/O control is automatically passed back to it. Consequently, under normal circumstances, the secondary I/O server does not store the MODCELL data, which greatly reduces the communication load on the MODBUS network. Through the system's specialist program, MODCELL variables and parameters that experience changes are automatically copied to the secondary I/O server, thereby ensuring the data's consistency and integrity.
Communication path redundancy
The primary I/O server and the secondary I/O server are both connected to the MODCELL control stations via completely separate communication paths. If the primary server's connection to the MODBUS is blocked, the secondary I/O server will immediately start communicating with the control station that the primary server cannot communicate with. The secondary server will continue to do this until the primary server's communication link is restored.
Preserving consistent data
In order to decentralise the workload of the system and ensure the system's efficiency during the design of the hot-mill control system, Citect adopted I/O and other open control service principles. The primary I/O server acts as the redundant alarm, report and trend server, whilst the secondary I/O server is the primary alarm, report and trend server. Under normal running conditions, CitectSCADA operating stations only request alarm, report and trend information from the secondary I/O server. The internal system automatically carries out data replication between the two servers, hence preserving data consistency. Should the secondary I/O server suffer a fault, all report, alarm and trend information requests are redirected to the redundant primary I/O server. The difference between this method and communication redundancy is that, even if the secondary I/O server returns to normal, information requests from operating stations will still be directed to the primary I/O server unless the operating station is restarted or the primary I/O server also suffers a fault. This is done so that the system does not need to continually check whether the primary information server is functioning normally, hence avoiding excessive system checks.
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