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Hydraulic units often come across condition changes such as start-up, normal stop and load rejection. Load rejection transient process (LRTP) is one of the running conditions which make the unit and water diversion system in worst operation state. It has great influence on the safety and stability of hydraulic units. A new method called SE-ICNA which is based on Internal Characteristic Numerical Algorithm (ICNA) and static efficiency (SE) iteration is proposed. The analysis of rotating speed rising ratio (RS-RR) and pressure rising ratio (P-RR) in LRTP is mainly discussed for hydraulic unit security assessment. The correctness and rationality of SE-ICNA can be verified by means of Transient Process (TP) analysis on medium and small units within the scope of different water levels. Verification examples proved that this method has an excellent performance for hydraulic unit security assessment in low water level conditions. A conclusion is made that the proposed SE-ICNA method can well assess the security of small hydraulic units in low head conditions. [ABSTRACT FROM AUTHOR]

An energy analyzing method called the Impact Energy Model (IEM) is introduced to assess and diagnose the rub–impact fault of a rotor system. The main purpose of the model is to indicate the probability of rub–impact or the severity level of the fault. Utilizing the nonlinear predictive energy, an effective quantitative evaluation index IEM is obtained from the model. Some work has been done elsewhere to partly demonstrate the IEM through experiments. In this paper we mainly discuss the variation of the IEM index with the speed ratio Ω at different levels of damping ratio ξ. The stagnation point is discussed in detail which is important to the assessment for the probability or severity of a rub–impact fault. The influence of dynamic stiffness is discussed which may affect the assessment result of the IEM. Furthermore, a sensitive area of the rotor operating system is presented. The result shows that this sensitive area provides a reference for the operation and design of a rotor system. [ABSTRACT FROM PUBLISHER]