Sigurd Hofsmo Jakobsen

Identification of observables for future grids - The framework developed in the ELECTRA project

The main subject of this paper is the classification and identification of observables for present and future grids. In order to make an inventory of present and potentially new observables, a systematic classification and identification of observables for future grids is conducted. After first introducing some fundamental definitions for observables, observables are further classified by the characteristic time scale where they are used in the physical power system. For actual use in control loops, observables must be part of so-called “Control Triples” consisting of control aim, observable, and system input signal. A survey of existing and potential Control Triples was conducted among partners in the European ELECTRA project, resulting in a spreadsheet inventory. The main findings are presented and a few major observability needs for realising the so-called “vertical integration” of control schemes reinforced by “horizontal integration” of distributed control schemes in the future grid.

Modelling of corrective actions in power system reliability analysis

Consequence analysis, including the modelling of corrective actions, is an important component when performing power system reliability analyses. Using an integrated methodology for power system reliability analysis, we investigate the impact of different modelling choices for the consequence analysis on estimates for the energy not supplied. These investigations corroborate the large impact modelling assumptions for corrective actions have on the resulting reliability indices. We have also identified other features of the consequence analysis, such as islanding and distributed slack, that can be important to take into account. The findings and the underlying structured approach contribute to improving the accuracy of power system reliability analyses.

An open data repository and a data processing software toolset of an equivalent Nordic grid model matched to historical electricity market data

This article presents an open data repository, the methodology to generate it and the associated data processing software developed to consolidate an hourly snapshot historical data set for the year 2015 to an equivalent Nordic power grid model (aka Nordic 44), the consolidation was achieved by matching the model׳s physical response w.r.t historical power flow records in the bidding regions of the Nordic grid that are available from the Nordic electricity market agent, Nord Pool. The model is made available in the form of CIM v14, Modelica and PSS/E (Siemens PTI) files. The Nordic 44 model in Modelica and PSS/E were first presented in the paper titled “iTesla Power Systems Library (iPSL): A Modelica library for phasor time-domain simulations” (Vanfretti et al., 2016) [1] for a single snapshot. In the digital repository being made available with the submission of this paper (SmarTSLab_Nordic44 Repository at Github, 2016) [2], a total of 8760 snapshots (for the year 2015) that can be used to initialize and execute dynamic simulations using tools compatible with CIM v14, the Modelica language and the proprietary PSS/E tool are provided. The Python scripts to generate the snapshots (processed data) are also available with all the data in the GitHub repository (SmarTSLab_Nordic44 Repository at Github, 2016) [2]. This Nordic 44 equivalent model was also used in iTesla project (iTesla) [3] to carry out simulations within a dynamic security assessment toolset (iTesla, 2016) [4], and has been further enhanced during the ITEA3 OpenCPS project (iTEA3) [5]. The raw, processed data and output models utilized within the iTesla platform (iTesla, 2016) [4] are also available in the repository. The CIM and Modelica snapshots of the “Nordic 44” model for the year 2015 are available in a Zenodo repository.

Interruption costs and time dependencies in quality of supply regulation

Customer interruption costs depend not only on customer characteristics and interruption duration, but also on the time of interruption. Time-dependent costs are incorporated in the Norwegian quality of supply regulation. New cost data are proposed from 2015. This paper demonstrates the importance of taking the time dependencies in the interruption cost and the time-dependent correlation with other parameters into account. Ignoring these time dependencies may lead to wrong cost signals in the quality of supply regulation. A time-varying reliability model is used to investigate the influence of time dependencies and the impact of changing the cost data for a small example network with different customer sectors. It is shown that ignoring the time-dependent correlation leads to underestimation of the expected annual interruption costs.

Vector fitting for estimation of turbine governing system parameters

With the introduction of more and more renewables into the power system both the inertia and the primary frequency reserves are expected to decrease. It is therefore a growing concern that the frequency quality will deteriorate. One way of mitigating these problems may be a more detailed monitoring of the generators providing the primary reserves. A promising approach for monitoring the generators is to identify turbine governing system parameters using system identification. This will allow for estimating the droop and the bandwidth of the governor, parameters that are important for the primary control. Furthermore, if this can be reliably done on ambient data, updated estimates of these parameters can be obtained relatively fast. In this paper we will look into how vector fitting can be used for this purpose. The algorithm possesses some interesting properties for automatically constructing models from ambient data. How this can be done will be presented together with results obtained using real data from the Norwegian power system. A simple criterion for reducing the obtained model order is also proposed.

Contingency screening starting from probabilistic models of hazards and component vulnerabilities

The need to analyze high-impact low-probability events on power systems, due to natural and man-related threats calls for comprehensive approaches to security assessment, which exploit the concept of risk. The paper describes a probabilistic approach and a tool, developed in the EU research project AFTER, aimed at selecting the most critical contingencies to be analyzed in depth, starting from short-term probabilistic models of incumbent natural or man-related threats and from component vulnerability curves in an integrated power and ICT system. A fast estimate of the contingency impact is obtained by using topological metrics. Results on a realistic power system include the sensitivity analyses of different contingency selection options, and the verification of the performances of the estimated impact metrics for screening purposes.

Enhanced method for reliability of supply assessment - an integrated approach

A comprehensive analysis of reliability of electricity supply to end users requires a unique set of models, methods and tools. Of special significance are long term power market models for predicting future operating states (generation and load patterns) and more detailed network simulation models for analysing consequences of contingencies. This paper describes an integrated approach for reliability of supply analysis, assessing reliability and interruption costs down to the specifics of different kinds of end users at different delivery points in the network model. Furthermore, the effects of power system protection, temporal variation of parameters, and corrective actions as part of the consequence analysis, are taken into account in the presented integrated approach. The results are illustrated through a case study on a realistic hydro dominated four-area meshed test system.