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This multi-site paper manufacturing company produces folding box board and corrugated base papers. In this installation, INTERBUS helps control the operating costs of the in-house power generating facilities by networking all relevant data for the power system. Power is generated by two steam turbines and a gas turbine producing a total of 11.3 megawatts of power. The design objective of the energy management system was to avoid exceeding the 15-minute peak value fixed in a contract with the power supply company. Missing the mark of this objective would have translated into considerable premiums charged by the utility — premiums greater than the cost of the new energy management system, even if the maximum value was exceeded only once. CONTROL SYSTEM The PC-based process control system functions as the energy management system, supervising a PLC-equipped central station tied-in via Modbus. The INTERBUS network connects the site’s six buildings, each containing a data distribution cabinet with a patch field and INTERBUS coupler. All measured values, as well as the meter pulses for energy consumption and energy generation, are transmitted to the PLC via fiber optic cables. In addition to INTERBUS data, the fiber optic cabling also carries RGB signals. All data is transmitted to four CRTs in the individual buildings, sharing Ethernet data via the same fiber optic cabling used for INTERBUS. These four CRTs inform operating personnel by presenting energy states within the entire plant. The system enables operators to optimize energy consumption levels. SPECIAL CONCERNS In this installation, powerful and, therefore, cost-intensive drives move paper reels weighing several tons. The large number of powerful drives contaminate the company’s sites with strong electromagnetic fields. Thus, fiber optic cabling (already installed for networking the multiple sites) with INTERBUS was the only choice for the energy management system. Conventional networking methods would have been significantly more expensive in terms of cabling replacement and quantity, as well as for complementary surge protection and other protective measures.
To date, the INTERBUS-based energy management system has made it possible to maintain consumption levels below power utility’s 15-minute peak value, avoiding expensive utility premium costs — and meeting the company’s system design goal. INTERBUS also solved the problem of utilizing existing fiber optic cabling to transmit multiple streams of different data types: INTERBUS, Ethernet, and RGB. INTERBUS with fiber optic cabling inexpensively addressed electromagnetic interference concerns while also saving considerable costs as compared to recabling or extensive parallel wiring schemes. Lastly, INTERBUS supported the use of a PC-based system controlling PLCs, without locking the company into either one of these single control methods.
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APPLICATION OVERVIEW
RESULTS/BENEFITS SUMMARY
