*Laboratory, Bench, and Full-Scale Researches of Strength, Reliability, and Safety… DOI: http://dx.doi.org/10.5772/intechopen.88306*

due to the interaction between the stator and the rotor at the blade frequency, as well as the loads caused by Karman vortices. Special attention should be paid to resonance phenomena, when the proximity of the natural frequencies of the elements of hydro turbines and the frequencies of external influences occurs.

The level of resource exhaustion is determined by the results of special calculations. These calculations consist in determining the time *t* or the number of loading cycles *N* as a function of amplitudes *σ<sup>a</sup>* and average values *σ<sup>m</sup>* of the loading cycle, defect sizes *l*, characteristics of the mechanical properties of materials (conditional yield strength *σ*0.2, temporary fracture resistance *σb*, fatigue limit *σ*1, destructive deformations *εf*), and safety factors for stresses *nσ*, for a number of cycles *nN* and for size of defects *nl*. The results of the calculations usually defined the fatigue diagrams of the main elements of hydro turbines, the residual resource, and the probability of failure at a given operating time.

The main elements of hydraulic turbines requiring the design justification of the resource are an impeller, a turbine shaft, a turbine cover with fastening elements, a shoulder blade of guide, and other elements. Calculation justification is carried out on the basis of data on operating modes, acting loads, defects, and damages detected during the diagnostics [9].

One of the main stages of resource assessment is the determination of external loads for equipment components and the corresponding internal stresses. Despite the great interest of this topic and the significant achievements of recent years, the problem of correctly describing the dynamic behavior of hydro turbine under partial power conditions and during transients has not been fully resolved. With this in mind, it is becoming a more common method of computational modeling [10]. These methods are based on mathematical models that include three main elements: geometric model, model of external loads, and model of boundary conditions. The accuracy of each model can have a decisive influence on the results of numerical experiments, including the issues of resource estimation [8].

The main problems of estimate resource for hydro turbines today are:


The trends in the development of hydro turbine resource assessment methods at the present stage are characterized by the following circumstances:


It should be emphasized that the approach outlined requires statistical information on all parameters, which is included in the calculations. Particular attention should be paid to characteristics of mechanical properties, parameters of stressstrain states, and structural damage. Such information can be obtained by

conducting large volumes of tests and experimental studies. At the same time, the most preferable are methods and means allowing to evaluate the determining parameters (stresses, deformations, sizes of defects), taking into account the pecu-

**3. Computational models and experimental evaluation operational state**

The main source of the most severe HPP accidents and disasters are damage and destruction of hydro turbines. Therefore, the problem assessing resource, diagnosing damage, optimizing the operating modes of hydro turbines, and timing of repair works takes a special place in ensuring HPP safety. Until recently, the hydro turbine resource received little attention, since it was assumed that the hydraulic turbines have sufficient strength for long-term safe operation. However, the statistics of failures of hydro turbines shows [6, 7] that large safety margins do not guarantee

The hydro turbine resource must be justified taking into account the peculiarities of the loading modes and damage accumulation processes. With this in mind, the interest in assessment of the resource of hydro turbines is steadily growing. This

• An increase in the number of powerful hydro turbines that have fulfilled the

• Operating modes of hydro turbines with a high level of power variation

• Constantly increasing design requirements for efficiency, maneuverability,

• The use of new methods and means of technical diagnostics, indicating the

• The emergence of new perspectives for studying the behavior and state of hydro turbines based on the achievements of experimental and computational

The main factors that reduce the life of hydro turbines are fatigue, corrosionfatigue and cavitation damage, degradation mechanical properties of materials, and redistribution of stress and strain fields in the most loaded local zones. Fatigue damages are caused by a complex loading spectrum of hydro turbines, containing components with different frequencies. Low-frequency loads (with a frequency below or equal to rotation frequency) are dangerous the high amplitudes that cause formation and development of cracks in the most loaded zones. High-frequency components have small amplitudes, but the number of cycles can reach 10<sup>9</sup>

which ultimately also leads to the formation and development of cracks. A significant danger is represented by "start-stop" cycles, in which parasitic vortex structures, hydraulic shocks, and flow instability zones with nonoptimal flow around the blades arise. The most dangerous are the loads caused by water pressure pulsations

–1010,

presence of defects and damage not previously detected

liarities of the micro- and macrostructure of structural materials.

**of hydro turbines**

*Probability, Combinatorics and Control*

long-term safe operation of hydro turbines.

standard operating time

technologies

**42**

and reliability of hydro turbines

is facilitated by the following circumstances [8]:

4.Predicting the growth of cracks in the process of operating time for the purpose of determining the optimal time between repairs

This complex of methods and means is used in diagnosing the technical condition of hydro turbines with over standard operating life. Such work was carried out at the abovementioned hydropower stations in recent years. The main attention was focused on the most loaded structures: the impeller, the turbine shaft, the turbine

The systematization and classification results of nondestructive testing showed

• Corrosion fatigue cracks of the base metal and fatigue cracks of welded joints

that the main defects of the impeller blades of hydro turbines are:

*Laboratory, Bench, and Full-Scale Researches of Strength, Reliability, and Safety…*

cover, and the blade of guide.

*DOI: http://dx.doi.org/10.5772/intechopen.88306*

• Cavitation erosion

• Corrosion damage

**Figure 3.**

**Figure 4.**

**Figure 5.**

**45**

*Cracks in metal of impeller blades.*

• Technological defects of welds

*Corrosion damage and cavitation damage metal of impeller blades.*

*Internal defects of impeller blades, detected by ultrasound tomography.*


Thus, the problem of calculation and experimental evaluation operational state of hydro turbines has a number of unsolved or difficult tasks that require in-depth basic research on the nature of the stress-strain state of hydraulic units, features of damage development mechanisms, and degradation of mechanical properties of materials.
