650 MW混流式水轮机转轮应力测试研究

Measurement and research of stress level on runner blade of a 650 MW Francis turbine

频繁启停、低负荷运行等不利工况给混流式水轮机的安全稳定运行带来了直接的威胁,由此长期积累的疲劳损害和裂纹影响了转轮寿命。本文介绍了应力测试的基本原理,讨论了应力现场测试在测点和设备布置方面的关键点,并在一台650 MW混流式水轮机上开展了转轮叶片的应力测试及研究。测试结果表明,叶片在开机过程中承受了很大的动应力,极易导致裂纹的产生。在不同负荷范围内,水轮机的水力稳定性与叶片应力水平及特征密切相关,是制约混流式水轮机安全运行范围的重要因素之一。为保证水轮机的安全运行和长期服役,需优化现有的开机过程,并尽量使水轮机在当前水头对应的最优负荷区运行,降低转轮应力以保证运行安全。

Francis turbine has to face variable operation conditions,such as low heads,low loads,frequent start-ups and stops,etc.Fatigue crack on the runner blade may occur and threat the operation safety of prototype turbine.The basic principle of stress measurement is introduced in this paper,and key points of measurement location and device arrangement are discussed accordingly.Measurement results of stress level on runner blade of a 650 MW Francis turbine show that,severe stress is detected during start-up of test machine which may lead to fatigue cracks.On specific load ranges,stress level and characteristic strongly relate to the hydraulic stability at these loads,which is one of the limitations for wide-range operation of Francis turbine.To ensure the operation safety and service life of runner,the start-up progress must be improved,and the Francis turbine must operate within the nominal operation ranges at specific heads to reduce the stress level.