Trond Toftevaag

Large-scale wind power integration and voltage stability limits in regional networks

When planning and developing large-scale wind power plants in areas distant from the main power transmission system, voltage control assessments and reactive power compensation are increasingly important. Voltage stability of the regional network may be a main limitation with respect to maximum rating and operation of the wind power plant Technical constraints in relation to wind power integration in weak grids may in general be associated with limited thermal capacity in parts of the grid and/or the adverse effect wind power can have on voltage quality and stability. In certain situations, however, local constraints regarding development of new transmission lines or upgrading of existing lines can make it interesting to utilise the existing lines to a level which in worst case may imply operation beyond the normal technical constraints of the system. In this work, challenges and opportunities arising from situations as described above are analysed, and viable measures to enable secure and acceptable operation of large wind farms in remote areas close to the thermal capacity and stability limits of the power system, are pointed out. The paper presents results from computer analyses of a simplified, yet realistic, electrical power system with wind power integration, illustrating possible solutions to achieve this.

Control concepts to enable increased wind power penetration

This paper addresses problems encountered in planning and operation of wind farms in areas with favorable wind conditions, but long distances to load centers and relatively weak transmission systems. The paper presents an overview of several control problems and challenges to he considered in order enabling increased wind power penetration. This includes control objectives related to voltage/reactive power control and active power control, including management of network constraints. Realistic examples are provided to illustrate proposed solutions with respect to coordinated control of wind farms and their interactions with the existing transmission and generation system. Results from computer analyses of a simplified, yet realistic, electrical power system model are used to illustrate two possible control concepts to achieve increased wind power integration. These are reactive power control and coordinated generation control.

The Potential of Integrating Wind Power with Offshore Oil and Gas Platforms

Offshore wind technology has developed rapidly and an offshore wind farm has the potential to power nearby offshore platforms in the future. This paper presents a case study of integrating a 20 MW wind farm which addressed the theoretical challenges of integrating large wind turbines into a stand-alone oil and gas platform grid. Firstly, the operational benefits of the 20 MW wind power integration were quantitatively assessed with regard to the fuel gas consumption and CO2/NOx emissions reduction. Secondly, the electrical grid stability after integration of the 20 MW wind power was tested by nine dynamic simulations that included: motor starts, loss of one gas turbine, loss of all wind turbines and wind speed fluctuations. Thirdly, the maximum amount of the wind power available for integration was identified by simulating critical operational conditions and comparing these to the governing standards. Integration of an offshore wind farm to an oil and gas platform is theoretically possible, but has not been proven by this study and many other operational and economic factors should be included in future feasibility studies.

External grid representation for assessing fault ride through capabilities of distributed generation units

The existing power systems are challenged as the share at MV distribution level of distributed generation is increasing. In order to ensure the security of operation and power quality in these grids, transmission and distribution power system operators have issued connection and operation guidelines related to integration of distributed generation. Some of these guidelines are designed to assess fault ride-through capabilities when dynamic connection studies are performed for distributed generation units. While most of the ongoing research have addressed especially the fault ride-through capabilities of the investigated generation unit when the most severe fault occur close to the point of common coupling, some research questions remain related to the adequacy of the representation of the external grid. This paper will compare several representations of external grid proposed by different authors for achieving more accurate results of fault ride-through capabilities of small scale hydro units.

Analysis of parallel operation of seigs with voltage based controller in mini-grid

This paper presents the analysis of simulation-results of a Mini-Grid system consisting of two SEIGs 0.46 MVA and 0.23 MVA and voltage based generator controllers in SIMPOW®. The typical test-cases include simulation of SEIG, with lead-lag controller and PI controller in Mini-Grid system, when subjected to ramping load (both active and reactive). The results show that the characteristics of the conductance controller have very little influence in operation of such system. Whereas, ramping of active and reactive power of the load, more than the rated capacity of the resistive shunt, has significant effect on the stability of the system. The simulations also show that the voltage dependency of the load has a significant influence on the dynamic stability of the system.

EQUAL-AREA CRITERION APPLIED ON POWER TRANSFER CORRIDORS

This paper presents a novel adaptation of the equal-area criterion. The adapted criterion provides a new possibility to study the stability criteria of critical power transfer corridors, supporting the specification of the secure power transfer capacity of the interconnected power system. Furthermore, the authors describe how the adapted equal-area criterion can be employed in the design of System Integrity Protection Schemes to prevent instability and mitigate consequences of extraordinary events. The concept is tested on the benchmark model IEEE Reliability Test System 1996.

Application of Linear Analysis in Traction Power System Stability Studies

Dynamic phenomena such as oscillations and instability in railway power systems have caused concern in the experts’ community during recent years. On several occasions, modern advanced electrical rail vehicles have been the source of low frequency power oscillations leading to an unstable power system due to lack of damping, and as a consequence operational problems. A method to study these phenomena is needed. Well known linear techniques based on small-signal analysis provide valuable information about the inherent characteristics of even non-linear single-phase power systems. This paper describes how a traction power system and its dynamical railway-related components are modeled in a commercially available power system analysis software and studied by linear analysis such as eigenvalues, participation factors and parameter sensitivities. This is used to gain knowledge about the interaction between the rail vehicles and the electrical infrastructure. Linear analysis is found to be a powerful tool in this respect provided that adequate models of the relevant components can be established in RMS mode. The results clearly indicate poor interaction.