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Oslo, Norway

Vanfretti L.,Statnett | Sevilla F.R.S.,KTH Royal Institute of Technology
IEEE PES Innovative Smart Grid Technologies Conference Europe | Year: 2015

This paper presents a three-layer voltage stability index computed using time-series obtained from dynamic simulations. The proposed index provides the distance with respect to voltage and power limits. Voltage, active and reactive power signals, which are determined using time series from dynamic simulations, are used to compute the index. The methodology assumes that no other information about the system (model) is available. A set of 3 different simulations at different loading levels and a given contingency are required to calculate the index. In the first layer, a two-element vector indicates if a power or a voltage limit was violated. In the second layer, a vector is used to specify which power and voltage loading level was violated and finally, in the third layer a matrix is used to retrieve precise information about which power and voltage limit has been violated in pre- or post-contingency. The index can analyze simultaneously different buses. The proposed index is illustrated using synthetic data and then tested using timedomain simulations on the KTH-Nordic32 system. © 2014 IEEE. Source


Gustavsen B.,Sintef | Runde M.,Sintef | Ohnstad T.M.,Statnett
IEEE Transactions on Power Delivery | Year: 2015

A 420-kV gapped-core five-legged variable shunt reactor is modeled in the frequency range 5 Hz-10 MHz based on frequency sweep measurements and curve fitting using rational functions. Comparison with time-domain measurements at reduced voltage shows that the model can accurately predict the transient behavior of the shunt reactor, both for impinging overvoltages and circuit-breaker transient recovery voltages. Among the observations is that mutual coupling between the phases leads to a beat phenomenon in the reactor voltage following disconnection. Representing the shunt reactor by an LC parallel circuit leads to unrealistic results for steep-fronted incoming waves and high-frequency oscillating overvoltages, and for the attenuation of the transient recovery voltage following disconnection. © 2015 IEEE. Source


Lelekakis N.,Monash University | Wijaya J.,Monash University | Martin D.,University of Queensland | Susa D.,Statnett
IEEE Electrical Insulation Magazine | Year: 2014

Utilities need to understand the aging of paper insulation in order to prolong the life of transformers. If the paper becomes severely degraded, it loses its mechanical strength and thus its ability to insulate the windings. © 2006 IEEE. Source


Kishor N.,Aalto University | Haarla L.,Aalto University | Turunen J.,Statnett | Larsson M.,ABB | Mohanty S.R.,Motilal Nehru National Institute of Technology
IET Generation, Transmission and Distribution | Year: 2014

Using wide area monitoring systems (WAMS) offers a possibility for an integrated measurement-based and model-based control, which suits to the operation of large electric power system (EPS), along with online analysis. This study presents studies on fixed-order controller design through model identification approach with use of synchronous measurement data. Firstly, in the study, the coherent generator in each area of large EPS is determined by the mutual information theory. Then, state-space two-input two-output model is identified for the generator that has highest participation factor and thus referred as coherent generator. The model identification algorithms; least-square, instrumental variable and subspace state-space based generalised Poisson moment function are used. Next, WAMS level model is identified between the input controllable variable and speed deviation difference of coherent generator of each area. Finally, a local controller (decentralised) in each coherent area and a centralised controller at WAMS level between two coherent areas are designed by optimisation of the several design functions; H∞ norm, H2 norm, spectral abscissa and complex stability radius, as much as possible. These controllers feed supplementary control signal in addition to one fed by local conventionally tuned power system stabiliser. The centralised controller at WAMS level is demonstrated to stabilise the speed deviations of each generator between any two areas in the large EPS. The study is investigated with different input signal variables; ΔVref, ΔPm excited by different pattern of disturbances. © The Institution of Engineering and Technology 2014. Source


Gustavsen B.,Sintef | Hoidalen H.K.,Norwegian University of Science and Technology | Ohnstad T.M.,Statnett
Electric Power Systems Research | Year: 2014

High-voltage cables with paper-oil based insulation are still widely used in electric power systems. One issue with EMTP-type modeling and simulation of such cables is that the permittivity of the insulation is frequency-dependent, thereby contributing to the dispersion of traveling waves. This frequency dependency is not taken into account in currently available EMTP-type programs. This paper presents field measurements from step voltage excitations on three different oil-filled cables with steel armoring. The waveforms are compared to EMTP-type simulations, demonstrating significant deviations from the measured waveforms. The frequency-dependency of the permittivity is next taken into account using a formula obtained by Breien and Johansen, and the modeling and simulation procedure is repeated. Inclusion of the frequency-dependency is shown to bring the simulation results much closer to the measured waveforms. © 2014 Elsevier B.V. Source

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