Lauri Kütt

Parameters Identification and Modeling of High-Frequency Current Transducer for Partial Discharge Measurements

Rogowski coil (RC) is a low-cost, air-cored, and flexible induction sensor for nonintrusive condition monitoring and thus can be used in a variety of applications. In this paper, a lumped parameter model of RC is presented and an experiment-based methodology is developed to determine its parameters. The performance of the RC is analyzed for detection and measurement of high-frequency (pulsed) signals such as partial discharge (PD) current pulses. A simple and efficient technique of numerical integration is adopted to avoid the conventional type of expensive and complex design analogue integrators. RC is modeled and simulated in the alternative transient program-electromagnetic transient program environment. The designed coil is tested to measure PDs in the laboratory. Simulated and experimental performance of RC is compared with a high-frequency current transformer. This comparison shows a good match and, hence, validates the design of RC for PD applications.

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.

Analysis of power consumption and losses in relation to supply voltage levels

This paper is focused on the effects of active and reactive power consumption and losses depending on voltage level variations around the normal (rated) voltage level. Supply voltage variations from rated voltage affect both power consumption and losses in the network. Focus is put on load response to the voltage change, while motor-type and mixed residential load is observed. Relations between voltage variation and load power consumption are suggested. Comparisons based on literature as well as classical theory and on-site measurements are presented.

Harmonic load of residential distribution network — Case study monitoring results

The non-linear loads in domestic applications are becoming more common as the power electronic converters are being implemented more widely. This can lead to more significant load current distortions. This paper is presenting a case study results to describe the expected harmonic distortions and to provide models to estimate their magnitudes during day for different times of year. The results presented are from a residential area low-voltage network, which is also providing the heating power for the households. The discussion is presented about the daily harmonic current profiles, which are presented to vary to great extent, harmonic to harmonic and for the different times of the year. The daily profiles of the harmonics with more stable characteristics are described using daily patters trend models.

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.

An improved technique to determine the wave propagation velocity of medium voltage cables for PD diagnostics

Investigation of wave propagation characteristics for high frequency pulses is an important aspect for the partial discharge (PD) diagnostics in medium voltage cables. Precision in determining the electromagnetic wave propagation velocity in the cables determines the accuracy of developing cable model and localization of partial discharge initiation site. It has been observed that commonly used time domain reflectometry (TDR) and time difference of arrival (TDA) methods pose certain limitations while finding out the propagation velocity of the cables. This can cause serious inaccuracy during localization of PD faults. This paper presents an alternative quarter wave length (QWL) method in frequency domain to measure the propagation velocity. It is based on transmission line model of the cables and eliminates the practical limitations of TDR and TDA techniques. The comparative assessment of these methods is presented based on experimental measurements. The comparison asserts the improved performance of proposed technique. This improved technique can be used to enhance the diagnostics capability for power networks.

Magnetic sensor coil shape geometry and bandwidth assessment

There are quite many scientific examples out there regarding on-line measurements of fast pulses and fast partial discharge phenomena [1] [2] [3] using magnetic sensor coils. In these examples, most attention has been paid on the results obtained with specific design of magnetic sensor. There is though a lack of actual design consideration of the sensor regarding its target bandwidth and sensitivity. In current paper the focus is put on the design aspects of such a magnetic loop sensor. Geometrical shape of the magnetic sensor loop is considered and coils with different shapes are put into tests to determine their real parameters.

Analyses of supply voltage quality, power consumption and losses affected by shunt capacitors for power factor correction

This paper is focused on active power consumption and losses in industrial and commercial facilities, depending upon supply voltage quality parameters. The shunt capacitors for power factor correction affect directly supply voltage level and harmonic distortions of supply voltage and current and hence affect power losses in industrial facilities, particularly in induction motors. In the paper practical measurement methods are described for estimating power losses when power factor correction capacitors are used. The impact of capacitors upon supply voltage level and harmonic distortions is discussed. Measurement results of voltage and current harmonics spectrum in industrial 0,4 kV power systems are shown.

Reactive power compensation for spot welding machine using thyristor switched capacitor

High-power industrial spot-welding machines make use of transformers that have very high reactive power consumption. Simple reactive power compensation schemes cannot be used however, because of the cyclic nature of the spot welding transformer operating. This paper describes the development of a simple reactive power compensator solution for the spot-welding machines. Focus is also put on the transformer saturation and current transients that can emerge from deployment of such reactive power compensation methods.