This paper describes three different ways of transformer modeling for inrush current simulations. The developed transformer models are not dependent on an integration step, thus they can be incorporated in a state-space form of stiff differential equation systems. The eigenvalue propagations during simulation time cause very stiff equation systems. The state-space equation systems are solved by using A- and L-stable numerical differentiation formulas (NDF2) method. This method suppresses spurious numerical oscillations in the transient simulations. The comparisons between measured and simulated inrush and steady-state transformer currents are done for all three of the proposed models. The realized nonlinear inductor, nonlinear resistor, and hysteresis model can be incorporated in the EMTP-type programs by using a combination of existing trapezoidal and proposed NDF2 methods.
COBISS.SI-ID: 17118486
The investigation was aimed at magnetically-nonlinear dynamic model of a single-phase transformer, where the effects of dynamic hysteresis losses are accounted for by a simplified model. Such a modelling could be applied when analyzing the transient operating conditions or the impact of nonlinear and unbalanced loads on the transformer operation in power systems.The inverse form of the Jiles-Atherton hysteresis model was applied for the hysteresis losses of a transformer defining. The original Jiles-Atherton model can be applied when more accurate hysteresis models are required, however, at the cost of increased model complexity and required computational effort. Apart from that the main drawback is impossible application of such a modelling, when some of the input parameters are unknown. On the other hand the simplified hysteresis model does not increase the required computational effort substantially. Both methods have been modified in such a way that they can be used when the magnetizing curve of the iron-core material is not available, whilst the magnetically-nonlinear characteristic of the entire device can be determined experimentally. The aforementioned characteristic can be given in the form of an approximation polynomial or in the form of a look-up table.
COBISS.SI-ID: 17030166
This paper describes a new approach to maintenance of high voltage devices in switchyards that is based upon upgraded Reliability Centered Maintenance (RCM). In addition to periodical maintenance, the Slovenian Transmission System Operator (TSO) ELES also uses an application that enables RCM. On the basis of multi-year monitoring of maintenance strategic maintenance concept was developed, which takes into consideration not only well known indices of technical condition and importance, but also indices of risk and environment. The new approach is demonstrated on the example of 400 kV switchyard of 400/220/110 kV Podlog substation before and after its overhaul
COBISS.SI-ID: 16611862
This paper describes ensuring safe working conditions for workers performing electrical installation work and maintenance on overhead lines within the vicinity of high voltage. Due to harsh operating conditions and the necessity of ensuring uninterrupted electricity supply, it is sometimes necessary to replace a conductor on a double-circuit overhead line with one circuit for normal operations. In such cases, there is a high-risk of conductor swing that may cause contact with the phase conductor of the adjacent energized circuit. The presented special sliding grounding clamp has been designed and constructed in order to carry the fault current to ground. It enables a good flow of the current from the drawn conductor and, thus, protects the workers from excessive step and touch voltage on the working site. The sliding grounding clamp has been constructed, and tested in practice. It has also been granted a Slovenian national patent.
COBISS.SI-ID: 17047574
The roof surfaces within urban areas are constantly attracting interest regarding the installation of photovoltaic systems. These systems can improve self-sufficiency of electricity supply, and can help to decrease the emissions of greenhouse gases throughout urban areas. Unfortunately, some roof surfaces are unsuitable for installing photovoltaic systems. This presented work deals with the rating of roofsurfaces within urban areas regarding their solarpotential and suitability for the installation of photovoltaic systems. The solarpotential of a roofćs surface is determined by a new method that combines extracted urban topography from LiDAR data with the pyranometer measurements of global and diffuse solar irradiances. Heuristic annual vegetation shadowing and a multi-resolution shadowing model, complete the proposed method. The significance of different influential factors (e.g. shadowing) was analyzed extensively. A comparison between the results obtained by the proposed method and measurements performed on an actual PV power plant showed a correlation agreement of 97.4%.
COBISS.SI-ID: 16262934