Paul Taklaja

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.

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.

Test setup for measuring medium voltage power cable and joint temperature in high current tests using thermocouples

Thermal aspects of power cable performance are an important field of research as power grids depend increasingly on the reliability of underground cable systems. Overheating is a possible cause of cable faults and it should be ensured that no part of the cable exceeds its rated operating temperature. A test setup was established in Aalto University to study the changes of temperature across different power cable layers in various cable operating modes. The setup also includes three different types of joints to identify differences in behavior during temperature change. Temperature measurement was achieved using thermocouples inserted into the cable and each of the joints: heat shrink joint, cold shrink joint and hybrid shrink joint. This paper discusses the structure of the test setup and the capacity of different tests available with the given setup.

AC-voltage performance of field aged glass insulator strings

This paper presents the AC-voltage withstand performance of field aged 110kV transmission line glass insulator strings investigated under different environmental conditions. Insulator strings were removed from two 110 kV lines, one located near a coastal area and steel mill industry and the other located inland next to a dump. AC-voltage withstand levels were tested and leakage currents across insulator strings were measured in dry, mist and wet conditions. Results suggest that the polluted insulators from the steel mill should be replaced whereas protective measures need to be applied to the insulators at the dump to mitigate bird-related problems.

Wet tests on naturally polluted glass and composite insulators

The study examines what type of bird excrement contamination will lead to insulators flashovers on the Estonian 110 kV overhead power lines. Wet tests made in laboratory with naturally contaminated glass and composite insulators show that traditional (insulators surface) contamination will not lead to flashovers and therefore most likely the flashovers are caused by highly conductive bird excrement streamers. The tests also show that using corona rings at composite insulators line end fittings, affects the occurring probability of partial discharge extent on wetted insulator.