Cost Optimization for Steam Turbine Control Upgrades

The basic principles of generating electricity from steam have not changed during the last 100 years. Consequently, current steam turbine design is similar to the one introduced to the market by BBC, ALSTOM, ASEA or GE about a century ago. Of course modern blade and valve design dramatically improves heat rate; new materials increase effective longevity of the turbine. Similarly, the basic principles of how to control a turbine are the same as many years ago. However, equipment being used now to operate and control a turbine is quite different than that of the time when the first steam turbine was put into commercial operation. It is common knowledge that the control system is technically aging much faster than the turbine itself. Steam turbines achieve an average service life of 40 years. There are many steam turbines still operating with originally installed control systems. These aging control systems installed 20–30 years ago are becoming unreliable and costly to maintain. For most power plant owners/operators it has become a necessity to modernize their originally installed mechanical/hydraulic control systems. This is particulary important now, due to the very competitive, deregulated power production business. Control system upgrades together with improvement of the steam path components will result in efficient operation of the power plant for an extended number of years for a fraction of the cost necessary to build a new power generation station. Several control upgrade solutions and options are available at substantial cost saving, without compromising safety requirements, flexibility and reliability of the power plant. Step by step modular upgrades, utilizing the majority of pre-existing equipment, using proven standard software modules and inexpensive PLCs (programmable logic controllers), applying 2 out-of-three 3 analog signal acquisitions for 2 out of 3, or 1 out of 2 protection — these are some ways of reducing the cost of plant modernization. This paper will discuss and document particular cases where the cost optimization concept was successfully implemented with positive results in the following areas: • High availability and reliability achieved; • Safety and flexibility of operation improved; • Maintenance cost reduced.