Electrical Energy
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1000 MW Station upgrades to PLC-based auxiliary Control System
 | Spare parts inventory for converted systems reduced from $147,000 to $65,000 thanks to control equipment standardization |
I. CUSTOMER ENVIRONMENT / PROJECT CONTEXT
Customer profile:
Hoosier Energy, Bloomington, IN, serves 18 rural electric membership cooperatives distributing power in southern Indiana.
The former auxiliary controls at the two-unit, coal-fired, 1000 MW Merom Generating Station represented a mixed bag of technologies: relay-based, proprietary black box and proprietary chip to gate-based controllers and statement language programming. A few had early PLCs. No effort was made to coordinate the various systems when the station was built. Many of the systems were difficult to troubleshoot and poorly supported. Spares were expensive.
Customer objective and constraints:
Although the original controls never impaired station availability, they threatened to do so from time to time. This concern drove Hoosier Energy to replace the most troublesome systems first.
Objectives included:
- a coordinated system using standard control equipment to facilitate system maintenance and reduce the spare parts inventory,
- a control system designed and installed by the people who would operate and maintain it.
II. SOLUTION IMPLEMENTATION
Implementation methodology (main phases):
Believed unique for a station of this size, the planning, engineering, installation, and start-up of the replacement controls and networks were almost entirely performed by station personnel, supported by Schneider Electric.
Duration:
The upgrade of the late-1970's era controls occurred over a seven-year period, from 1991 to 1998.
Solution overview (services, products, systems, architectures...):
The controls conversion project totals 29 Modicon® PLCs and 23 PC-based operator stations, all residing on five Modicon Modbus Plus networks bridged together. The only original controls still in place are those for the boilers, turbines, burner management, and scrubber analog control and operator console.
The upgrade work was accomplished by Corie Biggs and Tony Cornelius, production engineers, with assistance from the Electrical Maintenance and the Controls and Instrumentation groups. During outages, additional electricians and technicians were assigned to projects as needed. Cornelius and Biggs developed the control and communications systems, wrote the programs, and prepared the operator screens.
Although different Modicon PLC models have been installed since the upgrade project began in 1991, all are fully backward and forward compatible. Every PLC resides on a network and can be programmed and maintained using Modicon Modsoft software and Modicon 984 conventions. The five 1.0 Mbps Modbus Plus networks already in service are bridged together, allowing them to operate as one large network. Fiber optic backbones eliminate lightning damage and electromagnetic interference, and permit communication lines to be routed in power cable trays.
When upgrading each system, long-standing problems such as a poor control strategy or lack of operator information were solved by adding more points. For example, the single status light that covered all four clamps on the rotary car dumper has been replaced with a separate status indication for each clamp. Other additions have included automatic start-up, improved interlocking, remote
monitoring, more sensors, etc.
III. RESULTS / ACHIEVEMENT
Customer benefits:
The in-house conversion resulted in numerous advantages:
- Expenditures for the conversion are estimated to have been only 1/3 to 1/2 the cost of retaining an engineering consultant and employing electrical contractors – approximately $200 per point.
- Station personnel have a sense of ownership over the new controls. They know how the systems work and can quickly troubleshoot and correct problems – a benefit lost when controls are parachuted into a plant.
- Control equipment standardization has reduced the spare parts inventory for converted systems from $147,000 to $65,000.
- Because the projects were developed and implemented without the time-consuming reviews and approvals typical of contract projects, considerable time was saved and headaches avoided during implementation. The people affected by the work did the work, and they made decisions quickly.
Customer testimonies (Verbatim):
Corie Biggs, Station Production Engineer:
"Hoosier Energy determined that a network of compatible PLCs would be the best upgrade approach. Installing a distributed control system would have been costly, required outside assistance, and made sense only if boiler and turbine controls were included." |  |
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Solution breakdown
- Process control: different Modicon PLCs
- Modbus Plus network
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