Icelandic Power System Research Articles

Out-of-Step Protection Based on Discrete Angle Derivatives

This paper presents an out-of-step protection algorithm based on angle derivatives, which makes use of wide-area measurements and can be applied on arbitrary tie-lines in electrical power systems. The developed algorithm uses PMU measurements that are taken at both ends of a transmission line. Based on the changes of the electrical quantities in the power system, the algorithm detects unstable system conditions. Thus, the developed solution is settingless and can be easily applied where an out-of-step condition is expected. The concept is deployed by using an industrial controller and tested by conducting numerous hardware-in-the-loop simulations. Additionally, recorded data from actual out-of-step events in the Icelandic power system are used to validate the developed algorithm. The performance of the implemented method is compared against the traditional impedance-based out-of-step protection methods. The results confirm that the proposed algorithm detects out-of-step conditions more reliably and faster than the traditional impedance-based solutions.

Probabilistic Resilience Analysis of the Icelandic Power System under Extreme Weather

This paper presents a probabilistic methodology for assessing power system resilience, motivated by the extreme weather storm experienced in Iceland in December 2019. The methodology is built on the basis of models and data available to the Icelandic transmission system operator in anticipation of the said storm. We study resilience in terms of the ability of the system to contain further service disruption, while potentially operating with reduced component availability due to the storm impact. To do so, we develop a Monte Carlo assessment framework combining weather-dependent component failure probabilities, enumerated through historical failure rate data and forecasted wind-speed data, with a bi-level attacker-defender optimization model for vulnerability identification. Our findings suggest that the ability of the Icelandic power system to contain service disruption moderately reduces with the storm-induced potential reduction of its available components. In other words, and as also validated in practice, the system is indeed resilient.

Estimation of Power System Inertia From Ambient Wide Area Measurements

This study presents a method of estimating the effective inertia of a power system from ambient frequency and active power signals measured by phasor measurement units. Most importantly, we demonstrate that inertia can be estimated from ambient measurement data, not only from disturbances. This leads to the possibility of monitoring inertia in a close to continuous manner in the time scale of minutes or tens of minutes. The method allows the system to be divided into a number of areas and the effective inertia of each area to be estimated as a separate quantity. In principle, inertia is estimated by observing the dynamics between changes in active power and resulting frequency deviations during normal operation of the system. The method is based on applying system identification on these measurements and extracting inertia values from identified models. Efficacy of the method is demonstrated on results of real measurements from the Icelandic power system.

A model for optimal scheduling of hydro thermal systems including pumped‐storage and wind power

This study describes a model for optimal scheduling of hydro thermal systems with multiple hydro reservoirs. Inflow to hydropower reservoirs, wind power and exogenously given prices are treated as stochastic variables. Power flow constraints are included through a linearised power flow model. A linearised representation of start-up costs for generating units and pumps is provided. The model is well suited for medium- and long-term hydro thermal generation scheduling and has the capability of capturing detailed system constraints by using a fine time resolution. The presented model is tested on a realistic representation of the Icelandic power system, considering some potential future system extensions.

Optimal short term operation of a purely hydroelectric system

The short-term production scheduling problem for a purely hydroelectric system can be simplified so that the power production and water can be managed separately. This approximation is possible when plants have large daily reservoirs with fixed or controllable heads. The model described by the authors optimizes the hourly power production of a system of hydroplants by minimizing losses in turbines and waterways, while maintaining production to meet load. The problem is inherently of the mixed integer nonlinear type, but an algorithm has been developed to solve it in two stages by linear programming (LP). The model has been tested with data from an existing purely hydroelectric system, the Icelandic power system being the model system. Results indicate considerable savings in water usage from large seasonal reservoirs. These results also indicate the feasibility of installing the model in a control center computer when conditions are similar to the model system. >