Jaan Niitsoo

A review of the harmonic and unbalance effects in electrical distribution networks due to EV charging

For wide use of electric vehicles (EVs), there are different aspects of the electric power system to consider for making it ready for the increased load by battery charging. The topics include power production, peak load management, distribution transmission capacity but also distribution network power quality and many more. This paper presents an overview on the likely power quality impacts in the distribution networks associated with EV charging. Based on a literature review, focus is especially put on harmonics and load unbalance in the network. Most relevant papers observing these topics are presented summarizing their contribution. The power quality aspects in distribution networks discussed here are not often presented within analysis of permissible EV penetration levels. Harmonics or voltage unbalance and effects associated with these could introduce additional limits to the EV charging capacity for the distribution networks. Therefore the analysis on the EV charging influence on these power quality topics requires also high-priority discussions before drawing conclusions on the distribution networks capabilities.

Current harmonics of EV chargers and effects of diversity to charging load current distortions in distribution networks

Charging of electric vehicles (EVs) is expected to bring a healthy addition of load for the distribution networks. The residential networks where the EV owners would charge their vehicles after returning from daily activities would especially be subjected to high load increase. As EV charger is a powerful nonlinear load rather large harmonic currents can be present during the EV charging. This means a significant increase also to the current harmonics. Analysis of the quantities of the harmonic currents is necessary for guaranteeing the distribution network operation that would meet the power supply standards. In this paper, the EV charging measurement results are presented and analyzed with focus on the current waveform distortions. Different EVs are analyzed for the current harmonics present during the slow rate home charging. For the modeling of the EV charging loads in the networks, discussion is presented on the harmonic currents summing and cancellation effects. The results presented in the paper can be further used for modeling of the actual harmonic loads of the EVs in the distribution networks.

Harmonic levels of domestic and electrical vehicle loads in residential distribution networks

Purpose of the present paper is to provide the results of the study performed in order to assess current distortion of domestic and electrical vehicle (EV) loads and corresponding voltage distortion in the residential distribution networks. For the study harmonic current amplitudes and phase angles of different home appliances were measured and afterwards the corresponding models were composed in DIgSILENT Power Factory. The focus of the study was to analyse the characteristics of the residential distribution network with and without the EV charging. The results of the study showed an extensive harmonic distortion in residential load current and considerable voltage distortion at the substations busbar. The results presented in this paper are especially important when dispersed generation (DG) and EVs are going to be connected in bulk into the distribution networks.

Residential load harmonics in distribution grid

Purpose of the present paper is to provide the results of the study performed in order to assess current distortion of domestic loads and corresponding voltage distortion in the residential distribution networks. For the study harmonic current amplitudes and phase angles of different home appliances were measured and afterwards the corresponding models were composed in DIgSILENT Power Factory. The focus of the study was to analyse the characteristics of the residential distribution network with different amounts of real nonlinear loads. The results of the study showed an extensive harmonic distortion in residential load current and considerable voltage distortion at the substations busbar. The results presented in this paper are especially important when dispersed generation (DG) and electrical vehicles (EV) are going to be connected in bulk into the distribution networks.

Electricity consumption analysis and power quality monitoring in commercial buildings

The results of the analysis of the electricity consumption and power quality indicators in two office buildings are presented. It comprises electricity consumption and power quality during work days and weekends. The consumption data analysed is from a one year period and the power quality analysis is based on a one week measuring period. The aim of this analysis is to determine the current situation in these buildings in order to study the possibilities and limitations to implement different energy efficiency measures. In addition to the energy efficiency point of view, the problem is also addressed together with the power quality aspects.

Preventing Bird Streamer Outages Using Alternative Tower Configurations

This paper presents methods for mitigating the destructive impact of bird excrement contamination on 110 kV power lines. In addition to the typical retrofitting techniques (cover-ups and perch management), focus is mainly on reconfiguration and alternative tower designs aimed at eliminating streamer outages. Advantages and disadvantages of existing designs are assessed and novel ideas are presented by the authors.

Impulse characteristics of 24 kV overhead line pin insulators

One of the main characteristics of the distribution grid is the reliability of medium voltage overhead lines which can be improved by appropriate insulation coordination. This paper assesses common insulator types in Estonia. Old glass pin insulators and newly installed porcelain pin insulators were tested against different lightning overvoltages (impulse flashovers) in order to determine their volt-time characteristics. Test results show convincingly that the new porcelain pin insulators can be easily physically broken when stressed by lightning impulses. This can lead to the numeral increase of outages in medium voltage overhead lines in the distribution grid.

Analysis of electricity meters under distorted load conditions

Due to the rapid growth of non-linear loads in power systems in recent decades, harmonic pollution is becoming more and more serious. Energy measurement devices are commonly designed for working at sine wave. In this paper the results of an analysis on different electricity meters used in distribution network under different load conditions are presented. Study shows that error of energy meters reading depends on the type of the meter, harmonic distortion, reactive energy and direction of reactive power. Measured errors were higher than 6% under some conditions.

Modelling EVs in residential distribution grid with other nonlinear loads

Unregulated charging of electric vehicles (EVs) could impact load characteristics in distribution networks. Difficulties with power quality may appear in residential networks where the grid is weak. For providing greater capabilities to EV charging, the power quality aspects have to be considered in addition to the load increase analysis. This paper discusses the harmonic content of the EV charging load and the changing power quality indicators in the residential distribution network. Actual EV charging measurement results are presented and averaged current harmonic amplitude and phase angles values for EV charging load modelling are proposed. Results of different modelling scenarios are presented and analyzed. The results of the study showed an extensive harmonic distortion in residential load current and voltage distortion at the substations busbar. The results pointed out in the paper can be further used for modelling the actual harmonic loads of the EVs in distribution networks.

Electric field distribution in glass and porcelain pin insulators

Distribution grid reliability depends heavily on insulation coordination of medium voltage overhead lines (OHL). Adequate knowledge of OHL insulators is needed to improve distribution grid performance. This paper discusses the distribution of electrical fields in 24 kV pin-type porcelain and glass insulators. To visualize the electric fields affecting the insulators, computer simulations were conducted. The simulations results were compared to previously conducted lightning impulse puncture withstand tests. The comparison showed that the electric stress in the insulators was not sufficient to cause puncturing, but in the laboratory tests, puncture did occur in some insulators.