Vol 53, No 4 (2019)

Russian experience in constructing an impervious element in the form of a clay-cement concrete diaphragm wall in the body of earth dams is presented. The characteristics of the technology of constructing the wall and its performance in the dam body are examined. The requirements imposed on the wall material, properties, and characteristics of its deformation are analyzed and the need to take into account its creep is shown. The results of a field investigation of a forcefully collapsed segment of the wall are presented. Practical recommendations are given.

Bearing assemblies in many respects determine the operating reliability of turbine generator units. Experience in operating a number of hydropower plants indicates that these assemblies remain a problem and require redesigning. This article describes the authors’ technical developments in modernizing bearings and experience in their implementation, showing the reliability and effectiveness of the proposed solutions.

The question of determining flow depth at the end of a ledge during free {flow into the atmosphere} was examined. The velocity-distribution law in the end cross-section of the channel is proposed. The results of depth calculation are compared.

The effectiveness of the use of accumulation basins ordinarily used for river sediment to reduce the rate of silting of the reservoirs of hydroelectric power plants situated on mountain rivers is considered. The investigation is performed by methods of numerical hydrodynamic simulation based on the two-dimensional Saint-Venant equations and a new model of sediment transport that takes into account the fractional composition of the sediment. Using as an example a concrete reservoir located on a mountain river, it is shown that it is extraordinarily important to take into account the heterogeneity of the soil in the process of solving these types of problems. A combination of the annual hydraulic flushing of reservoirs and mechanical removal of soil from the accumulation basins together assure the required useful volume throughout the entire service life of the hydroelectric plant, though it requires the annual removal of up to 40% of the sediment discharge of the river.

It is proven that the magnitude of the extrusion gap (dicontinuity of the depression curve) is obtained from the solution for establishment of the Boussinesq boundary problem for a solitary flow rate. The boundary problem of nonstationary filtration is reduced to the Crocco typical boundary problem.

An analysis of the hydraulic system of the natural circulation loop of the waste-heat boilers of combined-cycle gas turbine units is performed. It is demonstrated that the standard method of hydraulic calculation of steam boilers based on an evaluation of the reliability criteria of the hydraulic system and the thermal regime of the evaporator tubes is incorrect. The existence of loop-wide hydraulic persistence of flow in the low-pressure evaporator in natural circulation caused by elevated resistance of the steam-outlet tubes is demonstrated for the first time. Recommendations are given for increasing the reliability of the hydraulic system of the low-pressure evaporator loop and selecting an optimal combined water and chemical regime to prevent erosion wear of the metal of the inner surface of the evaporator tubes.

To assess the effect of engagement in power and frequency control on the level of wear of the steam-turbine power units, a method for calculating the remaining life based on the equivalent operation time is proposed. By using a power-generating unit equipped with the K-300-240 turbine as an example, a number of equivalent hours of turbine operation were calculated reflecting the engagement of the power unit in the rated primary frequency control and automated secondary power and frequency control. The effect of the loading rate of the steam-turbine power units, operating in the rated and sliding steam pressure modes, on the level of equipment wear within various ranges of power increase was studied.

The causes of change in the slope of the cross beams of steam-turbine foundation are considered. It is shown that changes in the slope of a cross beam can be caused by the mechanical action of the turbine cylinders through the external bearing housing or by nonuniform heating of the faces of the cross beam. It is proved that the friction force between the bearing housing and the foundation frame cannot cause a considerable (several-fold exceeding the design value) change in cross-beam slope observed in some turbines. It is shown that a rotation of the bearing housing around the turbine axis in the horizontal plane causes plastic deformations in the joint between the bearing housing and the guiding longitudinal keys, which leads to an off-design increase in the torque applied to the cross beam.

The problem studied here is important because of the need for an efficient technology for monitoring the state of the wire in a span based on combined software and hardware for analyzing the technical state of the wires in 110 kV overhead electrical transmission lines in order to obtain a comprehensive estimate of the effect of external climatic factors owing to wind and ice loading, as well as the amount of thermal elongation of the wires owing to the effect of current flow. An analysis of the instantaneous state of the wires and their limiting mechanical strength makes it possible to evaluate the effectiveness of measures for preventing accidents and lessening the undersupply of electrical power to final consumers. Visualizing the instantaneous parameters of the wire in a span of an overhead electrical transmission line will make it possible to reduce the time needed to undertake steps to prevent emergencies. The algorithm for monitoring the state of wires in overhead lines is based on information about the existing values of the longitudinal and transverse angles obtained with sensors that are installed directly on the wire in an electrical transmission line.

Questions related to attempts to increase the efficiency of control of the vibration state of the stator in turbogenerators with tangential design of the elastic suspension of the core are discussed. Results of a theoretical study of the influence of the rigidity of the base supports of the frame of the turbogenerator and of features of the mounting of the active steel to the intermediate cradle on the vibratory state of the elements of the stator are discussed. Problems related to assessing the vibration state of the core on the basis of the level of vibration of the frame are considered. Measures to improve the procedure used to monitor the vibration and technical state of a stator are proposed.

The information bases of algorithms for protecting the stator of a generator operating on busbars from single-phase-to-ground faults (SPGFs) are investigated. The information bases of algorithms in which the effective values of the components of zero-sequence higher current harmonics and differential currents are studied. It is shown that higher harmonics in the current of the SPGFs of the generator stator are divided into three groups, the harmonics of each of which have the property of individuality, manifesting itself in the original character of dependence of their level on the location of the SPGFs. The information content of harmonics of one group enrich the information value of other harmonic groups, increasing protection sensitivity and selectivity. It follows from an analysis that the most promising direction of development of algorithms for protection against SPGFs is the use of components of higher current harmonics.