Lidija Korunovic

International Industry Practice on Power System Load Modeling

Power system load modeling is a mature and generally well researched area which, as many other in electrical power engineering at the present time, is going through a period of renewed interest in both industry and academia. This interest is fueled by the appearance of new non-conventional types of loads (power electronic-based, or interfaced through power electronics) and requirements to operate modern electric power systems with increased penetration of non-conventional and mostly intermittent types of generation in a safe and secure manner. As a response to this renewed interest, in February 2010 CIGRE established working group C4.605: “Modelling and aggregation of loads in flexible power networks”. One of the first tasks of the working group was to identify current international industry practice on load modeling for static and dynamic power system studies. For that purpose, a questionnaire was developed and distributed during the summer/autumn of 2010 to more than 160 utilities and system operators in over 50 countries on five continents. This paper summarizes some of the key findings from about 100 responses to the questionnaire received by September 2011 and identifies prevalent types of load models used as well as typical values of their parameters.

Processing of load parameters based on Existing Load Models

The paper specifies the most frequently used load models. These load models are presented, discussed and correlated with the corresponding low voltage equipment and devices, as reported in existing literature. Load model parameters are statistically analysed, including dispersion of their values. Additionally, the paper presents analysis of load model parameters used at higher voltage levels, based on the responses of 41 transmission system operators and utilities in Europe, which participated in a survey initiated by CIGRE Working Group C4.605.

Measurement and analysis of neutral conductor current in low voltage distribution network

This paper presents measurement results of neutral conductor current in low voltage network in the region of city of Niš, Serbia. The influence of load unbalance and nonlinear loads on neutral conductor current is analysed. Load current harmonics have strong influence on rms value of neutral conductor current in the network that supply commercial load.

Calculations and analysis of induction motors impact on short-circuit current

The paper gives a qualitative and quantitative analysis of induction motors impact on the current of a three-pole short-circuit. The transient process in the system is described by Parks model of an induction motor. These results are used for checking the simplified engineering calculation. On the example of the thermal power plant with its self-consumption, a comparative analysis is made of calculation results. The paper also tests the behaviour of induction motors during change of voltage at their connection due to faults in the network. The motor behaviour is thereby tested in the direct environment of the faults location. It has been established that in cases of longer duration of faults, these induction motors unload the fault location and therefore reduce the total fault current.

Efficient nonintrusive distinguisher of small nonlinear electrical loads

The work contributes to the identification of small nonlinear appliances which are hardly distinguished by existing noninvasive load monitoring methods. It improves the steady load monitoring by introducing distortion power as an additional parameter to the widely used Harts algorithm based on measurement of active and reactive power. The results show that the method efficiently distinguishes the variety of nonlinear appliances whose usage is fast growing nowadays. Furthermore, this approach is advantageous in comparison with other approaches, which use three parameters to precisely identify the appliances, due to its simplicity. Namely, distortion power can be easily determined using only smart meters and thus no any additional measuring equipment is required.

The analysis of typical seasonal load duration curves of low-voltage consumers

The paper presents some typical daily load curves formed by averaging data collected by the system for remote energy meter reading in time period longer than two years. Data from nearly 7000 energy meters at low–voltage consumers are processed, statistically reliable daily load curves are obtained and their characteristics are listed. Typical load duration curves of months belonging to winter and summer season are formed on the basis of daily load curves and depicted in the paper. These seasonal load duration curves of different load classes at low voltage are mutually compared. The influence of different number of working days, Saturdays and Sundays on monthly load duration curves is discussed, and corresponding load factors and loss factors for winter and summer months are statistically analysed.

Some power quality indices in distribution network of city of Niš

This paper presents the results of power quality research in low voltage distribution network of the second biggest city in Serbia, Niš. The research is based on the measurements in transformers stations 10/0.4kV that supply different load classes and that are located in different parts of the city. Power quality indices - total and individual harmonic distortions, unbalance factor and rms voltage variation are analysed and compared with IEEE Standard 519 and EN 50160 limits. The results are grouped and discussed according to load classes that considered transformer stations supply.

The analysis of load parameters influence on distribution network calculation results

This paper considers the problem of radial middle-voltage distribution network calculation. The influence of different load types on voltage, load flow and power loss calculation results has been especially researched. Also, AVR influence on network condition has been examined. Calculation results are illustrated on a IEEE test network.