1,721,014 research outputs found
Impact of uncertainties on resonant overvoltages following transformer energization
No full textA number of changes in the power system have increased the risk for more serious resonances in the harmonic frequency range. The changes also result in an increased uncertainty with regard to the frequency and damping of those resonances. Uncertainties could be related to variations with time, uncertain future developments in the grid, and the modelling of individual components. This article investigates uncertainties affecting resonant overvoltages caused by transformer energization. Several study cases investigating the impact of different uncertainties on resonances and resonant overvoltages, performed in PSCAD, are presented. The results show that some uncertainties may have a significant impact on the resulting impedance characteristics and on the resulting overvoltage levels.</p
Uncertainty analysis of stochastic dynamic line rating
No full textThis paper presents an uncertainty analysis of lines equipped with dynamic line rating (DLR) that are exposed to operational overloading. Multiple sources of uncertainties are taken in to account to model the line rating probabilistically. The superiority of dynamic rating above static rating is confirmed in this paper. However, it is shown in this paper that when the uncertainties in line rating are not considered, DLR can result in a high probability of undetected overloading. Based on assumptions for the uncertainties in relevant weather parameters, the probability of overloading is calculated for three different loading profiles of a line, for each hour during an eight-year period. Guaranteeing a low probability of overloading, with a deterministic dynamic rating, will require a large margin and result in many hours during which unnecessary measures against overloading will be taken. A stochastic dynamic rating, as introduced in this paper, allows for a more transparent and hour-by-hour trade-off between failure to take measures and unnecessary measures against overloading.</p
Impact of modelling of MV network and remote loads on estimated harmonic hosting capacity for an EV fast charging station
No full textThe ability of the distribution network to host electric vehicle (EV) charging might be limited by the harmonic voltages due to their harmonic emission. Network harmonic impedance seen from the point of connection of the charging station plays an important role in harmonic voltage calculation. In this paper, the hosting capacity is estimated for a fast charging station close to a distribution transformer considering different scenarios in terms of network modelling. Data from a typical Swedish distribution network is used, together with a one-month measurement of the emission from state-of-the-art EV charging. The hosting capacity using harmonic voltage limits is compared with the hosting capacity using the transformer rating. A stochastic approach is used for both. This paper shows that harmonic hosting capacity studies are needed; it shows that details of the distribution network must be included to get an accurate estimation of the harmonic hosting capacity; it also shows that a stochastic approach is needed for estimating the harmonic hosting capacity.Validerad;2023;Nivå 2;2023-04-11 (hanlid);Funder: Umeå Energi; Göteborg Energi research foundation</p
Impact of Uncertainties on Resonant Overvoltages
No full textA number of changes in the power system have increased the risk for more serious resonances in the harmonic frequency range. The changes also result in an increased uncertainty with regard to the frequency and damping of those resonances. Uncertainties could be related to variations with time, uncertain future developments in the grid, and the modelling of individual components. In this article, a distinction is made between discrete and continuous stochastic uncertainties. This article further investigates uncertainties affecting resonant overvoltages. Several study cases investigating the impact of different uncertainties on resonances and temporary overvoltages, performed in PSCAD, are presented. The results show that some uncertainties may have a significant impact on the resulting impedance characteristics and potentially on the resulting overvoltage levels.</p
Solar PV stochastic hosting capacity in distribution networks considering aleatory and epistemic uncertainties
No full textThis paper proposes a stochastic method, ''mixed aleatory-epistemic“, for estimating solar PV hosting capacity (HC) of low-voltage (LV) distribution networks. The approach treats the aleatory and epistemic uncertainties in a different way. The HC is estimated by applying the transfer impedance matrix, 'which is only calculated once', and the superposition principle to determine the voltage magnitude rise due to solar PV. By distinguishing between aleatory and epistemic uncertainties, the calculations are limited to the relevant hours (time-of-day or time-of-year) during which high solar PV production is expected. In this way, the random aleatory uncertainties (background voltage, solar PV production, local consumption) are modelled by their probability distributions during the selected time period. The distributions for the epistemic uncertainties (installed capacity per customer, number of customers with solar PV, phase to which single-phase units are connected) are created with simple models involving the interval value and possible occurrence. The stochastic approach proposed is applied to three LV distribution networks to illustrate the method. The results show that both types of uncertainties affect the HC. The need for distribution network planners to identify and distinguish between the types of uncertainties is emphasised.Validerad;2021;Nivå 2;2021-03-18 (alebob);Finansiär: Skellefteå Kraft Elnät; Umeå Energi AB</p
Limits set by component loadability on solar power integration in distribution networks
No full textThis paper proposes a deterministic and stochastic approach to quantify the hosting capacity that is often limited by the loadability limit of the cable cabinet or transformers due to customers with solar photovoltaics (PV) units. Distribution networks from two areas in Sweden supplying 309 MV/LV distribution transformers with 12,000 customers downstream have been studied. Using a deterministic model, a method is proposed and applied to assess the cable overvoltage against the loadability while considering the voltage rise margin. In addition, measurements have been applied to the methods and the loadability limits assessed. Illustrations for the concepts and important results for the guide to DSOs decision-making guide has been obtained. It is shown in the paper the hosting capacity anticipated at the end of a distribution network cable with a particular size is determined more often by the loadability at larger voltage rise margin and by overvoltage at smaller voltage rise margins. The results obtained for the data used show that the overload limit is exceeded more often for transformers than for cable supplying the cable cabinets at smaller solar PV sizes. For larger solar PV sizes, the feeder cable loadability limit is likely to be exceeded first before that of the transformers. The stochastic approach applied to the yields a small probability to exceed the hosting capacity and depend on the two epistemic uncertainties
A simplified static frequency converter model for electromechanical transient stability studies of 16 <sup>2</sup>/<sub>3 </sub>Hz railways
No full textWith increased share of Static Frequency Converters (SFCs) in 16 2/3 Hz railway grids concerns about stability have increased. Stability studies for such low-frequency railway grids are few, and models that describe SFC dynamics are especially few. This paper presents an open SFC model for electromechanical stability studies in the phasor domain, suited for 16 2/3 Hz synchronous railway grids. The developed and proposed SFC model is implemented in MatLab Simulink, together with grid and loads. Numerical studies are made, in which the proposed SFC model is validated against both measured RMS-phasor amplitude of voltage and current at the railway grid side of an SFC. The SFC model developed is able to reproduce the measured RMS voltage and current with an acceptable accuracy.</p
Deep learning for power quality
No full textThis paper aims to introduce deep learning to the power quality community by reviewing the latest applications and discussing the open challenges of this technology. Publications covering deep learning to power quality are stratified in terms of application, type of data, and learning technique. This work shows that the majority of the deep learning applications to power quality are based on unrealistic synthetic data and supervised learning without proper labelling. Some applications with deep learning have already been solved by previous machine learning methods or expert systems. The main barriers to implementing deep learning to power quality are related to lack of novelty, low transparency of the deep learning methods, and lack of benchmark databases. This work also discusses that even with automatic feature extraction by deep learning methods, power quality expert knowledge is still needed to implement and analyse the results. The main research gaps identified in this work are related to the applications of semi-supervised learning, explainable deep learning and hybrid approaches combining deep learning with expert systems. Suggestions for overcoming the present limitations are: providing a stronger collaboration among the grid stakeholders and academy to keep track of power quality events; proper labelling and enlarging of datasets in deep learning methods; explaining the end-to-end decision making of deep learning methods; providing open-access databases for comparison purposes.</p
Guidelines for monitoring power quality in contemporary and future power networks – results from CIGRE/CIRED JWG C4.112
No full textOn the Analysis of Voltage and Current Transients in Three-Phase Power Systems
No full textThis paper presents a method for analysis measurementsof voltage transients in three-phase systems. The method is based on the Clarke transform introduced in 1950 forcalculations of travelling waves along three-phase transmission lines. The proposed method also shows close similarities with the classification of three-phase unbalanced voltage dips into types C and D. After extracting the actual transient, e.g. by using a notch filter centered on the power-system frequency, the three signals are decomposed into seven components. From the relationbetween these seven components, the dominant component isidentified. The method is successfully applied to a number of measured transients. The paper also identifies the limitations of the method and gives suggestions for future work
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