Sudden Load Rejection Research Articles

Effects of Hydro Power Plant Releases on Navigation Conditions in the Lower Lock Approach

Waterways are usually designed as multipurpose structures and perform a number of functions in addition to transport. A very common use is the generation of electricity in hydropower plants, water withdrawal for users and flood protection. On canalized rivers, increased attention must be paid to the design of the layout of the individual structures within the barrage. This paper deals with the optimization of barrage layout with respect to the interaction of navigation and hydropower use of the waterway. The navigation conditions below a power plant can be significantly affected by peak operation or by sudden load rejection. These phenomena can generate a negative surge wave with very adverse effects on navigation. In addition, special attention should be paid to the current conditions in the lower lock approach area and the guard wall that separates the lock approach from the weir and the power plant should be optimised. Appropriate design of operational and structural measures can significantly increase the traffic capacity of a waterway. The research was conducted as part of project no. DG18P02OVV004 within a support programme for applied research and experimental development of national and cultural identity, funded by the Ministry of Culture of the Czech Republic.

Transient-state analysis of hydropower plants with cross-flow turbines

Transients in hydropower plants can result in serious disturbances in a plant operation and damage of mechanical and civil components. The best way to prevent such adverse outcomes is to conduct a transient-state analysis using a mathematical model of the hydropower plant system. Based on the collected data on 270 hydropower plants with cross-flow turbines, regression equations were derived that relate a cross-flow turbine specific speed, rated speed, runner diameter and runner width to the rated turbine head and discharge. The obtained equations were used to estimate the turbine performance characteristics using available unit hill charts of three different cross-flow turbines. Finally, the estimated performance characteristics were used to form the boundary condition ‘cross-flow turbine’ within the unsteady 1D mathematical model. The model was validated through case studies by comparing calculated and measured changes in the turbine speed and inlet pressure, induced by sudden load rejection. The difference between the calculated and measured peak pressures was up to 5% during the most critical period, that is, from the moment of load rejection up to the guide vanes closure. In the case of turbine speed, the difference between the peak values was less than 10% in the same period.

Simulation and experimental illustration of vibration at load rejection in a continuously overloaded large hydrogenerator

Large hydro generators are usually overloaded at various situations such as the period when excess water is available and when excess inflow is to be discharged. The period may have extended to many weeks under exigent conditions e.g. six weeks in case of a 1000 MW hydropower plant (HPP) located at northern region, India at 20% overload. All the performance related parameters including vibrations were observed during commissioning except runaway speed test at load rejection. At overloads, if there is a sudden load rejection the vibration transients will be even more severe due to drop in current and internal impedance. Hence this paper aims to analyze the vibration signature of large synchronous generator (SG) when operated at overloads and subjected to sudden load rejection. The substantiation of the factual model of 250 MW hydro generating units (HGU) replicating the case plant has been simulated using SIMSEN software. Apart from case report and simulative validation an experimental verification is also conducted with a prototype model of 2.2 kW SG. This paper provides the feasibility to operate the SG's 20% beyond its rated load as designed with proper maintenance and safety carried out by plant operators.

Transient hydrodynamic analysis of the transition process of bulb hydraulic turbine

In this paper, a semi-implicit method for solving pressure coupled equations used to calculate the flow field, and dynamic mesh were employed to simulate the three-dimensional dynamic turbulent flow of whole flow channels, in start transition process and runaway transition process of bulb hydraulic turbine. In above processes, the transition process of pressure field and flow field were realistically modeled and simulated, which reflects the influence of water flow state, after passing through guide vanes on the inflow of the runner blades, and reveals the flow field variations in the transition process. The numerical results show that: during the start transition process, with the increase of guide vane opening, the flow circulation produced by water flowing through the guide vanes becomes smaller; therefore, the rotational acceleration of the runner decreases and the rotational speed value reduces. In the runaway transition process, the hydraulic turbine operating with load has a sudden load rejection and then, the hydraulic turbine rotational speed is rising with the guide vane closing, leading to pressure pulsations and severe vortex phenomenon, which will cause significant vibrations of swings.

Synchronous and asynchronous generators frequency and harmonics behavior after a sudden load rejection

This paper describes load rejection tests, done at two hydro power plants in Sweden, one equipped with synchronous and the other with asynchronous generators. During the tests voltages and currents are digitized, recorded and thereafter off-line processed. By this, in the processing of distorted and fast parameter-varying voltages and currents the powerful estimation technique, the Newton type algorithm, is applied. It was intended to investigate the frequency changes and the distortions of the measured signals. The transient processes at both generators are compared. In particular, the frequency changes after the instance of load rejection are investigated and discussed from the signal processing and physical nature point of view.

Synchronous and Asynchronous Generators Frequency and Harmonics Behavior after a Sudden Load Rejection

This paper describes load rejection tests done at two hydro power plants in Sweden, one equipped with synchronous and the other with asynchronous generators. During the tests, voltages and currents are digitized, recorded, and thereafter offline processed. By this, in the processing of distorted and fast parameter-varying voltages and currents, the powerful estimation technique, the Newton type algorithm, is applied. It was intended to investigate the frequency changes and the distortions of the measured signals. The transient processes at both generators are compared. In particular, the frequency changes after the instance of load rejection are investigated and discussed from the signal processing and physical nature point of view.

One Problem, Many Solutions—Transients in Open Feedwater Cycles

The author examines the historical development of the awareness of the problem created by the effects of sudden load rejection on the boiler feed pumps operating in open feedwater cycles and of the many different solutions subsequently proposed to deal with this problem. The relative merits of these solutions are examined from the points of view of the effect of their respective assumptions on the reliability and on the practical and economic aspects of the resulting installation. Finally, the author considers whether the use of protective controls may not, in the end, be the most practical approach to solving this problem.