Power and Energy Losses in Medium-Voltage Power Grids as a Function of Current Asymmetry—An Example from Poland

Abstract

In connection with the growing requirements regarding the quality and continuity of energy supply and the dynamic development of renewable energy sources, the need for a thorough analysis of factors affecting power and energy losses and the effectiveness of the MV network increases. One of the biggest challenges in managing power networks is the problem of load asymmetry. Load asymmetry can lead to numerous adverse phenomena, such as increased power losses, deterioration of the quality of energy supplied, and an increased risk of network failure. Despite various research on this issue, there is still a need for a more accurate understanding of mechanisms leading to the development of methods of minimizing these phenomena. The relationships describing power losses in lines and power transformers are widely known. However, most published analyzes assume the same load on each phase. If the asymmetrical load of the line already appears, such analysis is not based on the data of actual lines and applies to a homogeneous line with equal load along its entire length. Therefore, the authors decided to modify the method of calculating power losses so that they can be determined in a branched line loaded in many points, with knowledge of the current flowing into the line, its length, and the number of acceptances. This method allows for the determination of power losses in an innovative way, taking into account line load asymmetry. The use of relationships commonly available in the literature to determine power losses leads to errors of 5.54% (compared to the actual, measured losses). Taking into account both the asymmetry and multi-point loading in the method proposed by the authors allows us to limit this error to 3.91%. To estimate the impact of asymmetry on power losses in lines and power transformers, the authors performed field tests in the selected medium voltage power network. The increase in power losses determined on their basis caused by the asymmetry of the load currents obtained values from 0.03% to 4.78%. Using generally known methods of reducing asymmetry, these losses can be avoided, and therefore the energy transmission costs may be reduced, and the greenhouse gas emissions might be lowered.