Evaluation of Penstock Tunnel Leakage with Instrumentation

摘要

Underground penstock tunnels at hydropower plants often have probable failure modes related to high external pressures resulting from leakage. Leakage of aging penstocks is a problem that must be monitored with an appropriate surveillance program using strategically placed instrumentation. When higher pressures than expected are observed around the penstock, an investigation and analysis must be performed to determine the cause, assess the threat, change operating procedures, and design a mitigation approach. Geotechnical instrumentation, typically vibrating wire piezometers installed in the vicinity of the tunnel is critical to identifying any problems or conditions of concern. This paper presents a case study of a pumped storage facility where penstock leakage was suspected and addressed with additional sensors, data collection, and analysis. Calculations determined restrictions on watering and dewatering rates of the reservoirs to preserve the penstock. This paper describes instrumentation planning, sensor installation, and data analysis methods used to evaluate leakage at penstock tunnels. Modeling of large urban areas also called for efficient run strategies to achieve reasonable computation times. Adequate terrain grid sizes and computational model time step that allowed enough spatial resolution were controlled by the Courant condition being between 0.45 to 1. Errors associated with volume conveyance within the two-dimensional flow area were below 0.7% for all models.