Svenska Kraftnat

Sundbyberg, Sweden

Svenska Kraftnat

Sundbyberg, Sweden
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Molin A.,KTH Royal Institute of Technology | Sandberg H.,KTH Royal Institute of Technology | Johansson M.,Svenska Kraftnat
2016 IEEE 55th Conference on Decision and Control, CDC 2016 | Year: 2016

This paper analyzes the joint impact of uncertainties in the input data on the power system state estimator. The approach is based on the sensitivity analysis of the estimated telemetry data with respect to the measurement data and the branch parameters with the main goal of locating relevant input components. In order to find relevant inputs, we analyze the normalized sensitivity matrix by sparse principal component analysis (PCA). The non-zero entries of the loading vectors related to the dominant principal components are considered to be the relevant inputs to the state estimator as they mainly contribute to the amplification of the estimated values. It turns out that PCA shows an elementary structure of the sensitivity matrix: All non-zero entries of a loading vector corresponding to a positive singular value belong either to the telemetry data or to the branch data. We show that this property is also valid for PCA with different sparsity-promoting constraints on the loading vector. The proposed analysis method is demonstrated by a numerical study. © 2016 IEEE.

Sidenvall P.,STRI | Gutman I.,STRI | Carlshem L.,STRI | Bartsch J.,STRI | Kleveborn R.,Svenska Kraftnat
2017 12th International Conference on Live Maintenance, ICOLIM 2017 | Year: 2017

There is an exponential growth in application of composite insulators during the last decade(s). They are especially popular for overhead line refurbishment and compact lines and these applications require higher demands on electric field grading. Two main criteria are used for the dimensioning of grading rings for composite insulators, the first one for the metal parts and the second for the housing of the insulator. If the second criterion is not fulfilled, deterioration of the surface could occur due to water induced corona. STRI has developed a test method to verify the second criterion on full scale products. This test method was repeatable and has been used by STRI with success in several practical applications. The goal of this paper was to verify further application of the test method internationally. Thus, for the evaluation of the reproducibility a Round Robin Test in five different laboratories was performed with very positive results. © 2017 IEEE.

Winter W.,TenneT TSO bv | Elkington K.,Svenska Kraftnat | Bareux G.,French Electricity Transmission Network | Kostevc J.,ELES
IEEE Power and Energy Magazine | Year: 2015

In the future a growing amount of power electronics will lead to a transition of the power system to a structure with very low synchronous generation. Due to large transit power flows and uncertainties, transmission systems are being operated under increasingly stressed conditions and are close to their stability limits. Together with the integration of large amounts of renewable generation with power electronic interfaces and the addition of high-voltage direct current (HVdc) links into the power system, these challenges will necessitate a review of the operation and control of transmission networks. This article will demonstrate the need for R&D performed by network operators and explain a set of challenges, focusing on three main areas: transmission grid operation in a new power system environment, the need to increase overhead line (OHL) utilization, and the impact of reduced inertia on power system frequency. © 2014 IEEE.

Zhu K.,KTH Royal Institute of Technology | Chenine M.,KTH Royal Institute of Technology | Nordstrom L.,KTH Royal Institute of Technology | Holmstrom S.,Svenska Kraftnat | Ericsson G.,Svenska Kraftnat
International Journal of Emerging Electric Power Systems | Year: 2013

Although there is a plethora of literature dealing with Phasor Measurement Unit (PMU) communication delay, there has not been any effort made to generalize empirical delay results by identifying the distribution with the best fit. The existing studies typically assume a distribution or simply build on analogies to communication network routing delay. Specifically, this study provides insight into the characterization of the communication delay of both unprocessed PMU data and synchrophasors sorted by a Phasor Data Concentrator (PDC). The results suggest that a bi-modal distribution containing two normal distributions offers the best fit of the delay of the unprocessed data, whereas the delay profile of the sorted synchrophasors resembles a normal distribution based on these results, the possibility of evaluating the reliability of a synchrophasor application with respect to a particular choice of PDC timeout is discussed.

Westerlund P.,KTH Royal Institute of Technology | Hilber P.,KTH Royal Institute of Technology | Lindquist T.,Svenska Kraftnat
International Journal of Industrial and Systems Engineering | Year: 2016

This paper presents a method that can be used to rank disconnectors in the electric power system, according to the condition of one of the most critical parts, the contacts. The temperature of the contacts can be continuously measured by a new type of infrared sensor. For the case study, 54 sensors were placed on six disconnectors together with reference sensors measuring the ambient temperature. The measured temperature at each contact is then regressed against the ambient temperature and the current through the disconnector. Both a linear and a quadratic dependency of the current are tested and the quadratic one explains the data best. The coefficient of the current serves as a measure of the condition of the contact. Then, it becomes possible to identify in which contacts the resistance has increased the most. As a consequence, it is possible to make better maintenance decisions for the disconnectors. Copyright © 2016 Inderscience Enterprises Ltd.

Setreus J.,Svenska Kraftnat | Hilber P.,KTH Royal Institute of Technology | Arnborg S.,Svenska Kraftnat | Taylor N.,KTH Royal Institute of Technology
IEEE Transactions on Power Systems | Year: 2012

This paper presents a method to quantify and rank transmission system components by their importance for system reliability under different load scenarios. Each component is ranked by three separate importance indexes based on its expected outage rate and impact on: 1) system security margin; 2) load supply; and 3) generation units. By studying these three interests individually, a more complete view of the risks to system reliability can be assessed. The method is demonstrated on a detailed power system model (7000 components) of a significant part of the Great Britain transmission system at 400 and 275 kV. The results show how sensitive the component indexes are to the load scenario. The method provides an input for decision-making when planning maintenance and new investment and can be used as a complement to deterministic criteria. © 1969-2012 IEEE.

Sidenvall P.,STRI | Sundin N.,STRI | Gutman I.,STRI | Carlshem L.,Svenska Kraftnat | Kleveborn R.,Kleveborn Consulting
EIC 2014 - Proceedings of the 32nd Electrical Insulation Conference | Year: 2014

Two main criteria for the optimal design of corona/grading rings for composite insulation system include limit of E-field to avoid corona from a metal part and limit E-field to avoid water-induced corona on composite surface. At present only the first criterion is verified by the standard RIV test. This paper presents an innovative laboratory test method that can be used as a verification of the composite insulation system design to avoid water induced corona on the surface. Several approaches of producing water induced corona have been tested and evaluated. Pre-tests were performed on a small test object to optimize the different procedures. Tests were then performed on a full scale 420 kV composite insulator to verify the complete procedure. Different measuring techniques have also been evaluated. 3D calculation of the electric field for all tested structures has also been performed in Comsol software and compared to E-field criteria. Results from these calculations have also been compared with corona inception levels from the different tests and a good correlation was found. The innovative non-standard Water Drop Corona Induced test seems to be the best practical option for further development. © 2014 IEEE.

Sidenvall P.,HIGH-TECH | Gutman I.,HIGH-TECH | Carlshem L.,Svenska Kraftnat | Bartsch J.,Svenska Kraftnat | Kleveborn R.,Kleveborn Consulting
IEEE Electrical Insulation Magazine | Year: 2015

Historically, line composite insulators have been used with success in relatively clean environments mainly due to the simplicity of handling and better pricing than ceramic insulators. Voltage upgrading and compact design of overhead lines are new typical nisch areas for composite insulators. Hydrophobicity is a key parameter of composite insulators providing insulation performance much higher than ceramic insulators. However, the outstanding hydrophobic properties of composite insulators may be deteriorated not only due to dry-band activity in polluted areas but also due to continuous corona activity on the housing material itself or corona from the metal parts (fitting, grading/corona ring) onto the housing. In the worst case the insulator may suffer from erosion and other damages [1]. This puts higher importance on protecting the insulator from long-term aging. © 2015 IEEE.

Ericsson G.N.,Svenska Kraftnat
IEEE Transactions on Power Delivery | Year: 2010

The introduction of smart grid solutions imposes that cyber security and power system communication systems must be dealt with extensively. These parts together are essential for proper electricity transmission, where the information infrastructure is critical. The development of communication capabilities, moving power control systems from islands of automation to totally integrated computer environments, have opened up new possibilities and vulnerabilities. Since several power control systems have been procured with openness requirements, cyber security threats become evident. For refurbishment of a SCADA/EMS system, a separation of the operational and administrative computer systems must be obtained. The paper treats cyber security issues, and it highlights access points in a substation. Also, information security domain modeling is treated. Cyber security issues are important for smart grid solutions. Broadband communications open up for smart meters, and the increasing use of wind power requires a smart grid system. © 2010 IEEE.

Bengtsson T.,ABB | Roxenborg S.,ABB | Saha M.M.,ABB | Lindstrom P.-O.,Svenska Kraftnat | And 2 more authors.
19th Power Systems Computation Conference, PSCC 2016 | Year: 2016

This paper will review the Sub-synchronous oscillation phenomena and the interactions between the electrical power system and the mechanical turbine generator system. The paper present captured field data of sub-synchronous and super synchronous resonance at the generator terminals of a nuclear power plant and at a transmission sub-station from a field study during several years. It describes the relationship between sub- and super-synchronous currents and voltages, such as frequencies, dependencies, duration, time constants and magnitudes. From this study, a protection scheme has been devised that easily can be incorporated into a numerical relay using standard protection functions and a numerical multi-purpose filter. © 2016 Power Systems Computation Conference.

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