ELEKTRICITETSLÄRA

Current Research Projects

Hydro Power

Cooperation between Uppsala university and Luleå university of technology

Project Leader:: Docent Urban Lundin, Uppsala universitet
Researchers: Dr. Arne Wolfbrandt, Dr. Per Sundqvist, Uppsala universitet. Prof. Jan-Olov Aidanpää, Professor. Michel Cervantes, Stefan Nilsson, Luleå tekniska universitet.
Adjunct professors Adj. Prof. Niklas Dahlbäck, Vattenfall Uppsala universitet. Adj. Prof. Thommy Karlsson, Norconsult
Ph.D. students: Birger Marcusson Uppsala universitet, Jose Perez Uppsala universitet, Linn Saarinen, Uppsala universitet

 

Throughout history, the mechanical power of flowing water has been used to grind grain, saw lumber and produce iron. In modern hydropower plants, the potential energy of a volume of water is converted to electrical energy with a high efficiency via a turbine and a generator. Today, hydroelectric power accounts for about one fifth of the world power supply and is by far the most important renewable energy source on the planet. While the growth rate in hydropower generating capacity has been quite modest in Western Europe and North America during the last decade, the hydropower business is on the other hand flourishing on other continents, Asia in particular, following the exploitation of new sites.

Kraftverk Generator

Porsi hydropower plant (Lule River).
Foto: Alstom

Cross-sectional view of a
hydropower generator.

 

Up until the 1960’s, hydroelectric power plants accounted for almost 100 % of the Swedish electrical power production. Today the hydropower share of the total national annual production of electrical energy is 45 – 50 % depending on the precipitation conditions during the previous year. The major large scale hydropower development in Sweden took place during the 1940-60’s. A continued development of the remaining undeveloped rivers in the north of Sweden was postponed due to widespread protests from the public. The major point of upset was the impact on the local environment following the construction of large hydropower dams. Four ”national rivers” (Kalix River, Pite River, Torne River och Vindel River) are protected by a strong environmental legislation prohibiting further development.  

From a system perspective, hydropower generating stations, due to their excellent regulation properties, also play an important role in keeping an entire AC power system at a stable point of operation. The power fed into and taken out of an AC power grid should at all times be equal, otherwise the operating frequency will change. Since the amount of power generated in hydropower stations can be altered quickly and easily, hydropower stations are as a rule the first generating units where regulatory actions are performed to keep the system frequency constant. Moreover, hydropower units are expected to take an even greater regulatory responsibility in the future, following the anticipated increased introduction of wind power plants of unpredictable generation characteristics in the power system.
Today, the activity within the Swedish hydropower business is mostly limited to  refurbishments and maintenance work. In 2003, a study addressing the improvement potential of existing hydropower plants was conducted at Uppsala University in collaboration with Luleå Institute of Technology. The study recognized that many existing hydropower units can be made more efficient than they are at present and that better turbines and generators is a key concern. Partly as a result of the outcome of the study, the Division for Electricity at Uppsala University was asked to start conducting research on hydropower generators by representatives from the Swedish Hydropower Centre (SVC).

The research activities within the hydropower group mainly concerns the development and validation of computer analysis software tools that can be used to study hydropower generators during disturbed operation and various transient or fault conditions. Furthermore, the group works with modeling of phenomena related to the dynamic interaction between hydro generating stations and the power grid. The main goals of the research is to provide better insight on operational conditions that might be harmful for the hydropower units and choice of suitable parameterization of regulators. Also, the research program is a part of an national effort to maintain and develop the competence within this technology branch.   

Experiments will soon become natural complement to the theoretical research activities of the Hydropower Group. In 2007, a 185 kVA 12-pole synchronous generator was donated to the Hydropower Group by GE Energy Kristinehamn and this machine will form the back-bone in a planned experimental setup.

FEM-bild
Magnetic fieldlines in one pole-pitch of a cross section of a hydro power generator.

 

Cooperation

SVC

The research on hydropower generators at the Division of Electricity is funded by the Swedish Hydropower Centre, SVC (http://www.svc.nu).

Ongoing Projects


Influence of an Unbalanced Magnetic Pull on Generator Performance

When the rotor of a generator is not exactly centered inside the stator, the radial magnetic force density will be larger in areas where the air gap is smaller. Consequently, a net radial pull force -  the Unbalanced Magnetic Pull (UMP) - arises. This force causes extra wear on the bearings of the hydropower unit and may in some cases also cause undesired vibrations.

Luftgap

In this project we study the forces that arise due to static and dynamic eccentricities (constant and varying air gap irregularity) with special emphasis on the influence of iron saturation.

Contact: Dr. Urban Lundin, Senior Researcher

Study of the Influence of Damper Circuits on Generator Performance

In large synchronous machine the rotor poles are commonly equipped with short-circuited damper bars. When the rotor field and the armature field are not revolving synchronously, currents are induced in these bars. The interaction between these currents and the magnetic field provides a force that damps out field speed deviations. In this project, we try to do accurate predictions of the amplitude and the general appearance of damper bar currents. A detailed study of these currents makes it possible to better appreciate the damping effect during rotor oscillations and how the damper bar currents affect magnetic unbalance forces.

Contact: Dr. Urban Lundin, Senior Researcher

Interaction between Hydropower Generators and the Power Grid

In this project we study the impact of transient load changes and faults occurring in the power grid on single generating units. The primary tool to perform such an analysis is a 2D finite element software which contains a detailed field model of the generator completed with circuit equations that describe the surrounding local grid. Important state variables such as currents, voltages, flux densities and power losses are tracked in time-stepped simulations. The goal is to qualitatively estimate to what extent grid faults are responsible for the unusual wear that is sometimes encountered in generators during revision work. Also, we are interested in finding out if there are any particular operational modes where the generator is more sensitive for absorption of grid transients.

Contact: Martin Ranlöf, PhD Student