Stanislav Pejovic

Smaller Hydro, Higher Risk

Small or large hydropower plant design, construction and operation are complex tasks. Thousands of details must be well conceived and executed, and carefully coordinated for a project to achieve safe and economical operation that can be judged a social, technical and environmental success. Any hydroelectric installation, as a rule, should be designed using several stages. At each stage, all project documentation should be reviewed by independent reviewers selected and nominated by official authorities. Reducing the amount of analyses, without justification, or worse yet, neglecting the design procedures puts the project at risk. A collaborative effort at reducing this risk is thus advocated.

Standardization as Prevention of Fatigue Cracking of Hydraulic Turbine-Generator Shaft

Design, construction and operation of Hydropower plants are complex tasks. A large number of details must be carefully considered, coordinated and executed in order that the projects achieve safe and economical operation. Corrosion fatigue cracking of horizontal turbine-generator shafts has been thoroughly examined and discussed in the last twenty years. As a result of corrosion fatigue cracking, in most cases, catastrophic failures occurred. Excessive damages of vertical shaft couplings, discovered during turbine rehabilitation , have raised concerns regarding the value of nut guard application, as well those of corrosion damage rectification and repair techniques . Because of the consequences of shaft failure the following paper will provide the rationale for contribution to the respective standard.

Niagara Pump Generating Station proven functionality unique in Canada

Hydropower plant design, construction and operation are complex tasks. A large number of details must be carefully considered, coordinated and executed, in order that the projects achieve safe and economical operation. The Sir Adam Beck Pump Generating Station (PGS) is a six unit station commissioned in 1957. It has a production capacity of 174 MW and also provides regulation of the Sir Adam Beck 1 and 2 forebay level and crossover water level control. Originally constructed by the English Electric Company, this plant with its Deriaz units is unique within Canada and one of very few in the world. Ontario Power Generation (OPG) maintains and operates generating station (PGS) located in Niagara Falls. OPGs generating portfolio also includes a considerable nuclear component not amenable to rapid load changes. There are occasions when the load on the system falls below the available supply from these nuclear assets. OPG also has significant intertie capability with neighbouring utilities and sale of this energy is one of the methods by which this imbalance can be managed. Operating the PGS in the pump mode to supply additional load on the system is another means of managing the load/base generation mismatch. There are times when market conditions exist where these options are limited or not sufficient to balance the system load. At these times other more costly control measures must be implemented.

Nonreflective Boundary Design via Remote Sensing and Proportional-Integral-Derivative Control Valve

This paper develops the concept of a nonreflective (or semireflective) boundary condition using the combination of a remote sensor and a control system to modulate a relief valve. The essential idea is to sense the pressure change at a remote location and then to use the measured data to adjust the opening of an active control valve at the end of the line to eliminate or attenuate the wave reflections at the valve, thus controlling system transient pressures. This novel idea is shown here through numerical simulation to have considerable potential for transient protection. Using this model, wave reflections and resonance can be effectively eliminated for frictionless pipelines or initial no-flow conditions and can be better controlled in more realistic pipelines for a range of transient disturbances. In addition, the features of even-order harmonics and nonreflective boundary conditions during steady oscillation, obtained through time domain transient analysis, are verified by hydraulic impedance analysis in the frequency domain.

Smart design requires updated design and analysis guidelines

This paper reviews several cases where there is an obvious and important margin between the ideal of smart design and the practical reality which often makes due with obsolete guidelines, outdated recommendations and leads to expensive maintenance troubles. Stated alternatively, this paper is a plea for an attempt to better integrate high technology, experience, knowledge and economics so that both owner and human interests can be better supported and protected. To this end, several well-known plants (Sayano-Shushenskaya, Grand Coulee, Niagara Falls, Richard B Russell, Iron Gates 2, Jenpeg, Bajina Basta, Zvornik, to name a few) have been briefly analysed to clarify the crucial need for updated approaches. Of course, whether the plant is large or small, designing, constructing, operating and updating hydropower plants is a complex set of tasks. Any hydroelectric installation, as a rule, should be designed in several stages. At each stage, entire project documentation should be reviewed by independent reviewers. Reducing the number of analyses, or limiting their scope, with no clear justification except for an attempt to save a little on cost upfront, or worse yet, neglecting the design procedures, can put a project at risk. For a variety of reasons the continuity of knowledge and experience has been lost nearly everywhere. The paper argues that an organized and multidisciplinary transfer of experience is a priority task to be undertaken by the electricity sector. There is a clear need to plan, finance and implement various long-term initiatives; it is urgent that decisions to address this be made now to preserve the currently available knowledge and the almost 200-years of project experience.

Hydraulic Oscillation Analysis Using the Fluid-Structure Interaction Model

The paper presents a fluid transients analysis in hydraulic systems including fluid-structure interaction (FSI). The method is based upon an improved model, that takes into account gravitational and hydraulic resistive forces. The results of calculation applying the FSI model are compared to results obtained by simplified models and to those recently published.

Treatise on water hammer in hydropower standards and guidelines

This paper reviews critical water hammer parameters as they are presented in official hydropower standards and guidelines. A particular emphasize is given to a number of IEC standards and guidelines that are used worldwide. The paper critically assesses water hammer control strategies including operational scenarios (closing and opening laws), surge control devices (surge tank, pressure regulating valve, flywheel, etc.), redesign of the water conveyance system components (tunnel, penstock), or limitation of operating conditions (limited operating range) that are variably covered in standards and guidelines. Little information is given on industrial water hammer models and solutions elsewhere. These are briefly introduced and discussed in the light of capability (simple versus complex systems), availability of expertise (in house and/or commercial) and uncertainty. The paper concludes with an interesting water hammer case study referencing the rules and recommendations from existing hydropower standards and guidelines in a view of effective water hammer control. Recommendations are given for further work on development of a special guideline on water hammer (hydraulic transients) in hydropower plants.

Design Challenges in Hydropower Systems: Trade-offs and Difficulties in Operation

Hydraulic systems experience a variety of challenging conditions including hydraulic transients and oscillations. A long list of complex causes -- including extreme pressures and resonance -- can threaten power plants: the litany of failure is both long and painful, but also instructive. In fact, it is estimated that more than 50% of hydroelectric plants worldwide and other energy-related systems such as water transporting plants, water cooling system in nuclear and other thermal plants, oil pipelines, experience serious trouble or suffer severe operational constraints. We contend here that at least one problem is the presumption that comes from thinking that this is what a well known and used technology, and thus we have grown inattentive. Moreover, we argue that a vigorous and reflective design and review procedure, diligently applied, would be a great assistance not only for the quality of projects but also to assist the education of the next generation of experts. Specifically, we believe that an appropriate design, review, and trial operation procedure could have prevented many recent accidents and troubles.

Über die Strömung durch Turbomaschinen mit Potential im Meridianschnitt

ZusammenfassungZum Berechnen der Strömung durch die Schaufeln einer Turbomaschine wird ein neues Verfahren vorgeschlagen, bei dem man zunächst die radiale und die axiale Geschwindigkeitskomponente aus der Potentialströmung ermittelt, dann die hierzu passende Schaufelform berechnet und schließlich hiermit die tangentiale Geschwindigkeitskomponente der wirbelbehafteten Strömng erhält.