P. Allenbach

High-Order Modeling of Hydraulic Power Plant in Islanded Power Network

Numerical simulations of the transient operation of an islanded power network subject to load rejections are performed. The islanded power network case study consists of a 1-GW hydroelectric power plant featuring four generating units, a long penstock, and a surge tank connected to four 1.3-GW thermal power plants and passive consumers. The modeling of every network component is described and special care is paid to the modeling of the hydroelectric power plant. In particular, the high-order modeling used for these investigations enables the detailed simulation of water hammer, mass oscillations, and nonlinear hydraulic characteristics of the turbines interacting with the electrical components of the network. Moreover, the stability analysis of the systems is performed for different load conditions and the damping performances of a power system stabilizer IEEE PSS2B are investigated.

Investigation of Control Strategies for Variable-Speed Pump-Turbine Units by Using a Simplified Model of the Converters

This paper presents the modeling, simulation, and analysis of the dynamic behavior of a fictitious 2 × 320 MW variable-speed pump-turbine power plant, including a hydraulic system, electrical equipment, rotating inertias, and control systems. The modeling of the hydraulic and electrical components of the power plant is presented. The dynamic performances of a control strategy in generating mode and one in pumping mode are investigated by the simulation of the complete models in the case of change of active power set points. Then, a pseudocontinuous model of the converters feeding the rotor circuits is described. Due to this simplification, the simulation time can be reduced drastically (approximately factor 60). A first validation of the simplified model of the converters is obtained by comparison of the simulated results coming from the simplified and complete models for different modes of operation of the power plant. Experimental results performed on a 2.2-kW low-power test bench are also compared with the simulated results coming from both complete and simplified models related to this case and confirm the validity of the proposed simplified approach for the converters.

A fully modular tool for small-signal stability analysis of hydroelectric systems

In electrical systems, the small-signal stability analysis method is usually applied to synchronous machines by using the Park representation (d, q-components). This paper presents the generalization of a different approach for this method, based on a, b, c phase variables. This approach is essential to software systems using phase variables as state variables and its generalization yields a small-signal stability analysis tool which is fully modular. Two test cases are presented to showcase the application of this approach to elements such as synchronous machines, automatic voltage regulator (AVR), power system stabilizer of type IEEE PSS2B, penstock, Francis turbine and speed regulator.

Influence of the Francis Turbine location under vortex rope excitation on the Hydraulic System Stability

Hydroelectric power plants are known for their ability to cover variations of the consumption in electrical power networks. In order to follow this changing demand, hydraulic machines are subject to off-design operation. In that case, the swirling flow leaving the runner of a Francis turbine may act under given conditions as an excitation source for the whole hydraulic system. In high load operating conditions, vortex rope behaves as an internal energy source which leads to the self excitation of the system. The aim of this paper is to identify the influence of the full load excitation source location with respect to the eigenmodes shapes on the system stability. For this, a new eigenanalysis tool, based on eigenvalues and eigenvectors computation of the nonlinear set of differential equations in SIMSEN, has been developed. First the modal analysis method and linearization of the set of the nonlinear differential equations are fully described. Then, nonlinear hydro-acoustic models of hydraulic components based on electrical equivalent schemes are presented and linearized. Finally, a hydro-acoustic SIMSEN model of a simple hydraulic power plant, is used to apply the modal analysis and to show the influence of the turbine location on system stability. Through this case study, it brings out that modeling of the pipe viscoelastic damping is decisive to find out stability limits and unstable eigenfrequencies.

On the hydroelectric stability of an islanded power network

Islanded power networks comprising a small number of large power plants are subject to perturbations leading to important transients, and, hence need high performance governors. The design of these governors requires a detailed model of the system. This is even more important in the case of hydroelectric power plants featuring surge tank and long penstock. For a complete understanding of the dynamic behavior of the system, the model must also take into account the interaction with the electrical power network. This paper presents such a modeling for a 1 GW hydroelectric power plant and the use of an efficient method for the governor parameter determination. Assessment of the governor performances is carried out for different power ratios between hydroelectric and whole network

Forced response analysis of hydroelectric systems

At off-design operating points, Francis turbines develop cavitation vortex rope in the draft tube which may interact with the hydraulic system. Risk resonance assessment by means of eigenmodes computation of the system is usually performed. However, the system response to the excitation source induced by the cavitation vortex rope is not predicted in terms of amplitudes and phase. Only eigenmodes shapes with related frequencies and dampings can be predicted. Besides this modal analysis, the risk resonance assessment can be completed by a forced response analysis. This method allows identifying the contribution of each eigenmode into the system response which depends on the system boundary conditions and the excitation source location. In this paper, a forced response analysis of a Francis turbine hydroelectric power plant including hydraulic system, rotating train, electrical system and control devices is performed. First, the general methodology of the forced response analysis is presented and validated with time domain simulations. Then, analysis of electrical, hydraulic and hydroelectric systems are performed and compared to analyse the influence of control structures on pressure fluctuations induced by cavitation vortex rope.

HIL Simulation of a mixed islanded power network with external DSP regulator

The present paper describes the implementation of an industrial regulator in a real time Hardware-In-the-Loop simulation of a mixed islanded power network including precise models of the hydraulic system. The studied network is composed of three different types of electrical power generation systems and a consumer.

Modeling and Numerical Simulation of a Complete Hydroelectric Production Site

For many years the EPFL Laboratory for Electrical Machines develops SIMSEN, a numerical software package for the simulation in transient and steady-state conditions of electrical power systems and adjustable speed drives, having an arbitrary topology. SIMSEN is based on a collection of modules, each corresponding to one system component (machines, converters, transformers, control devices, etc.). This contribution presents the extension of SIMSEN to the hydraulic components of a hydroelectric power plant including pump-turbine, valve, penstock, surge tank, gallery, reservoir, etc. The basic idea is to define for each hydraulic component an equivalent electric component which can be introduced in the existing electric version of SIMSEN. Doing this, it becomes possible to use the modularity of the electric version to define the complete topology of the hydroelectric power plant and the connected electrical network. This extension enables numerical simulations taking precisely into account the interactions between the hydraulic and the electric parts of the system during transients. It is therefore useful for transient and stability analyses as well as for the design optimization.

Hardware-in-the-Loop Simulation Software for Regulator Tests and Optimization

This paper presents a real-time extension, called SIMSEN-RT, of the simulation software SIMSEN. SIMSEN-RT allows carrying out hardware-in-the-loop (HIL) simulations of power systems using hardware regulators. It can therefore be used to fine-tune regulator parameters or to test the regulator behavior in different operating conditions (emergency shutdown, islanded operation, etc.). SIMSEN-RT runs on a standard PC and needs no expensive hardware. As it is based on an existing simulation tool, hardware regulators can be tested in any power system configuration. SIMSEN RT will be used by Voith Siemens Hydro for HIL tests of turbine governors and voltage controllers.

Coordination of a turbo-generator protections through power-system simulation software SIMSEN

The correct coordination of the electrical protections of a synchronous generators is a difficult task, especially those based on impedance. Usually, these protections are set according to the recommendations of the main standards and manufacturer guides. However, the validation of the settings is difficult to obtain, since there is no commissioning test to evaluate the correct selectivity. In this paper, the use of SIMSEM power-system simulation software is proposed to evaluate the settings of a turbo-generator. Firstly, three electrical protections based on impedance characteristics are described. Secondly, a case study is presented with some simulations results. Finally, the advantages of using this procedure in the engineering process of power plants.