An on-line cavitation monitoring system for large Kaplan turbines

Cavitation erodes hydro turbines and reduces their performance. As cavitation varies with the operating condition and the service time of turbines, an on-line monitoring system for water turbines (TrbMAU) is developed. Both audible sound (20Hz similar to 20 kHz) and ultrasound (50 kHz similar to 300 kHz) are continuously monitored. The signal characteristics such as standard deviation, noise level and frequency compositions are evaluated. The evaluation results are stored in database in association with the operating condition donated by water head and wicket gate opening (or power output). According to the frequency characteristics, the sound emitted by cavitation is distinguished from the others such as water flow sound and mechanical sound. The cavitation intensity on different water head and power has been traced out. The degree of cavitation erosion is estimated according to the cavitation intensity at a fixed operating condition such as rated power and designed water head. The TrbMAU has been put into service in Gezhouba Hydro Power Plant. The application results are presented.