DEPENDENCIES OF CURRENT HARMONICS OF SOME NONLINEAR LOAD DEVICES ON RMS SUPPLY VOLTAGE

The paper deals with the determination of current harmonic dependencies of some nonlinear load devices on the rms supply voltage. These dependencies are based on the laboratory experiments that include the variations of rms supply voltage in relatively wide ranges. The experiments were performed on some representatives of nonlinear load devices. Both current harmonic amplitudes and their angles are recorded during the voltage changes, and corresponding dependencies on rms voltage are obtained by curve fitting. The results are related to actual devices that are typically used in residential load sector. The obtained dependencies are the indices of potentially significant effects of rms voltage variation on current harmonics in low voltage installations

LOAD MODELLING AT LOW VOLTAGE USING CONTINUOUS MEASUREMENTS

The paper presents the results of load modelling at low voltage level of transformer station (TS) 10/0.4 kV/kV supplying predominantly residential load. Necessary data are obtained from recording device and measuring information system for continuous measurements permanently installed in concerned distribution network. Identified parameters of static exponential load model are classified according to day periods and days of the week, and statistically analysed in order to obtain reliable parameter estimates. These are compared with literature data for the same, residential load class. Possibilities for further application of described load modelling procedure are listed

The influence of capacitor banks on transformer load current

This paper deals with the influence of capacitor banks used for reactive energy compensation on total load current of 10/0,4 kV/kV distribution transformers. The analysis regards distribution area of Leskovac which comprehends town Leskovac and nearby settlements. Differently from previously published references that treat excessively reactive energy consumption, the value of reactive power on low voltage side of transformer taking into account the presence of capacitor banks is observed primarily in this paper. Both theoretically possible cases are restated on the basis of measurements: the compensation is adequate or inadequate. The cases of insufficient compensation and overcompensation are regarded to be inadequate compensation. The adequate compensation is achieved when reactive power oscillates around 0 kvar. The special case of adequate compensation, called conditionally adequate compensation, is introduced. For all four cases that describe reactive energy compensation, the calculation results of relative change of low voltage transformer current in the presence of capacitor banks, in comparison to the current without installed banks are presented

Application of Meteorological Variables for the Estimation of Static Load Model Parameters

This paper presents a novel approach for estimating the parameters of the most frequently used static load model, which is based on the use of meteorological variables and is an alternative to the commonly used but time-consuming measurement-based approach. The presented model employs five frequently reported meteorological variables (ambient temperature, relative humidity, atmospheric pressure, wind speed, and wind direction) and the load model parameters as the independent and dependent variables, respectively. The analysis compared the load model parameters obtained by using all five meteorological variables and also when the meteorological variables with the lowest influence are omitted successively (one by one) from the model. It is recommended based on these results to use the model with the maximum accuracy, i.e., with five meteorological variables. The model was validated on a validation set of measurements, demonstrating its applicability for the estimation of load model parameters when the measurements of electrical variables for parameter identification are not available. Finally, load model parameters of the analyzed demand were estimated on the basis of only ambient temperature, and it was found that such a linear model can be used with a similar accuracy as the models with up to four meteorological variables

Modelling and aggregation of loads in flexible power networks

The power system research community and industry acknowledge the importance of accurate load modelling for power system studies, however, many still use typical representation of static loads by the constant impedance/current/power load models, while dynamic loads, if represented, are usually modelled with an induction motor (IM) model. The last systematic update of load models was performed in the mid 1990s, since when significant changes have occurred in the structure, type and composition of loads at all network buses. General inadequacy of currently used load models was highlighted in several unsuccessful attempts to reproduce the behaviour observed in recent blackouts during the corresponding “post-mortem” simulations and analysis. Over the last several years, there has been a renewed interest in both industry and academia for load modelling due to appearance of new types of loads, offering increased efficiency and controllability. Different types of modern non-linear power electronic loads are now responsible for a significant part of the total demand in almost all load sectors. Furthermore, there are currently no appropriate load models available for the correct representation of various directly connected and inverter-interfaced micro and small-scale distributed generation technologies, which, in some of the future network scenarios, may strongly impact real and reactive power demands and behaviour in future network scenarios, as they would be installed in large numbers. In a response to this renewed interest in load modeling, CIGRÉ Study Committee C4 established, in late 2009, the Working Group (WG) C4.605: “Modelling and Aggregation of Loads in Flexible Power Networks”. The WG started work in February 2010 with the aim to: i) provide a critical and updated overview of existing load models and their parameters for power system studies at all voltage levels, and identify types of loads and load classes for which adequate load models are presently missing; ii) provide a comprehensive overview of existing methodologies for load modeling, with a critical overview of component based and measurement based approaches, clearly identifying their advantages and disadvantages; iii) develop a set of recommendations and step-by-step procedures for load model development and validation, using either component based or measurement based approaches, or their combination; iv) develop load models for all typical devices and classes of customers for which there are no existing models and recommend their typical parameter values and ranges; v) provide recommendations on developing equivalent static and dynamic models of networks with significant amount of distributed generation, including equivalent models of micro-grids and active distribution network cells

CIGRE WG C4.605 : “Modelling and aggregation of loads in flexible power networks”

none22The power system research community and industry acknowledge the importance of accurate load modelling for power system studies, however, many still use typical representation of static loads by the constant impedance/current/power load models, while dynamic loads, if represented, are usually modelled with an induction motor (IM) model. The last systematic update of load models was performed in the mid 1990s, since when significant changes have occurred in the structure, type and composition of loads at all network buses. General inadequacy of currently used load models was highlighted in several unsuccessful attempts to reproduce the behaviour observed in recent blackouts during the corresponding “post-mortem” simulations and analysis. Over the last several years, there has been a renewed interest in both industry and academia for load modelling due to appearance of new types of loads, offering increased efficiency and controllability. Different types of modern non-linear power electronic loads are now responsible for a significant part of the total demand in almost all load sectors. Furthermore, there are currently no appropriate load models available for the correct representation of various directly connected and inverter-interfaced micro and small-scale distributed generation technologies, which, in some of the future network scenarios, may strongly impact real and reactive power demands and behaviour in future network scenarios, as they would be installed in large numbers. In a response to this renewed interest in load modeling, CIGRÉ Study Committee C4 established, in late 2009, the Working Group (WG) C4.605: “Modelling and Aggregation of Loads in Flexible Power Networks”. The WG started work in February 2010 with the aim to: i) provide a critical and updated overview of existing load models and their parameters for power system studies at all voltage levels, and identify types of loads and load classes for which adequate load models are presently missing; ii) provide a comprehensive overview of existing methodologies for load modeling, with a critical overview of component based and measurement based approaches, clearly identifying their advantages and disadvantages; iii) develop a set of recommendations and step-by-step procedures for load model development and validation, using either component based or measurement based approaches, or their combination; iv) develop load models for all typical devices and classes of customers for which there are no existing models and recommend their typical parameter values and ranges; v) provide recommendations on developing equivalent static and dynamic models of networks with significant amount of distributed generation, including equivalent models of micro-grids and active distribution network cells.mixedJ. V. Milanović; J. Matevosiyan; A. Borghetti; S. Ž. Djokić; Zhao Yang Dong; A. Halley; L. M. Korunović; S. Martinez Villanueva; Jin Ma; P. Pourbeik; F. Resende; S. Sterpu; F. Villella; K. Yamashita; O. Auer; K. Karoui; D. Kosterev; Shu Kwan Leung; D. Mtolo; S. Mat Zali; A. Collin; Yizheng XuJ. V. Milanović; J. Matevosiyan; A. Borghetti; S. Ž. Djokić; Zhao Yang Dong; A. Halley; L. M. Korunović; S. Martinez Villanueva; Jin Ma; P. Pourbeik; F. Resende; S. Sterpu; F. Villella; K. Yamashita; O. Auer; K. Karoui; D. Kosterev; Shu Kwan Leung; D. Mtolo; S. Mat Zali; A. Collin; Yizheng X