Options in generating unit controls for small hydro facilities

The small hydro unit controls should be designed to have greater reliability than the average availability rate of a hydro unit as determined by the Electric Power Research Institute (EPRI). This rate was determined by a 1983 EPRI Hydro-power Reliability Study as 94.8%. Two methods in which this high availability rate can be ensured in the unit control system is by furnishing a system with redundant PLC's, or by furnishing a single PLC with a manually operated control system for back-up. In addition, it is desirable in most cases to have speed governing capability. The authors focus on the advantages and disadvantages of a redundant PLC control system.