Sharmistha Bhattacharyya

Harmonic current pollution in a low voltage network

Modern household customers use many power electronic based devices for their daily usage. Those devices emit harmonic current pollutions and eventually increase harmonic voltage distortion level in the network. In the future network, the background harmonic pollution in the MV and upstream networks could increase with the integration of more distributed generations. Thus, the harmonic related problem will increase in the network and therefore should be considered seriously. With the distorted supply voltage, most of the devices produce even more harmonic current pollutions. In this paper, three typical households are modeled with their various connected devices. Each device is tested in the laboratory to find out its harmonic current emission spectrum for different grid voltage conditions. Also, harmonic current spectrums are measured in the laboratory at each of the three house models terminal. Further, harmonic simulation is done on a typical low voltage network in which several household customers are connected and the above measured harmonic spectrums of households are used in the analysis. Harmonic current emission levels at different points of the network are calculated. Those values are compared with the laboratory measurements and also with the available standard limits. This analysis gives an overview of harmonic current emission level at different installations of a low voltage network.

Analysis of power quality performance of the dutch medium and low voltage grids

Modern installations have become sensitive to power quality (PQ) related problems because more sophisticated devices with non-linear operating characteristics are often used there. On the contrary, most of these devices produce emissions that could decrease the PQ level of the network. It is becoming an increasing problem for the network operators to maintain good voltage quality because of the interactions of customerpsilas loads with the grid. It is anticipated that the networkpsilas physical characteristics (e.g. short circuit power, grid impedance) can influence the PQ performance (harmonic distortion, flicker severity) in the distribution grid. In this paper, a typical modern medium and low voltage Dutch grid is described that is modelled in the analysis tool dasiaPower Factorypsila. The network is simulated to analyze grid impedance and short circuit powers at different parts of the network. Furthermore, the importance of grid impedance is analyzed in relation to PQ aspects at the customerpsilas point of connection.

Assessment of the impacts of voltage dips for a MV customer

Voltage dips problems often cause large financial losses to sensitive industrial and commercial customers. Worldwide many industrial customers, connected to the high and medium voltage networks, often complain about voltage dips to their network operators. A voltage dip problem becomes critical in case of the incompatibility between the power supply and the immunity of the connected devices at customers installation. Improving the networks supply performance to reduce voltage dips would lead to huge amount of investment; whereas a process outage at a customers installation often involves significant amount of financial losses. Therefore, an optimized solution is to be found out based on the networks yearly dip statistics and the sensitivity of the customers installations to restrict this problem. In this paper, an industrial customer connected to a typical MV network is considered. The annual voltage dip frequency of the Dutch network is estimated and its impact on the considered customer is analyzed. Further, a methodology is proposed to define responsibilities of the different parties involved to minimize voltage dip problems.

Harmonic current interaction at a low voltage customer's installation

The increased use of power electronics and switching devices in the electricity network have changed the operational environment of the power system. These devices have non-linear voltage-current characteristics and produce harmonic currents, and consequently distort the voltage waveform. A low voltage domestic customer can have mixed loads that consist of linear and non-linear loads such as home appliances and lighting devices. In the PQ laboratory of TU/Eindhoven, the harmonic fingerprints of various household devices are measured. A LV household customers installation, consisting of various home appliances, is simulated in the network analysis tool ‘Power Factory’. The measured harmonic fingerprints of the connected devices are fed in to this software to perform harmonic simulations. The simulation results give the total harmonic current distortion level at the installation and the combined harmonic current interaction effects of different household devices. Furthermore, a case study is done to evaluate the total current harmonic distortion level at a customers installation when the grid voltage is polluted with a specific order of harmonic (such as the 5th harmonic). This is expected to be a typical futuristic scenario when many non-linear devices would be connected in the network and would distort the supply voltage.

Estimation of the planning levels for flicker in the Dutch networks

The electricity grid operator should supply a voltage at a customers installation according to the requirements of the standard EN50160 or national grid code. In contrast, no present grid codes specify clearly the responsibility of the customers regarding power quality (PQ) at their installations. The voltage flicker is one of the most irritating PQ problems on which the Dutch grid operators get many complaints. It often happens that flicker is generated because of the customers own or neighboring customers loads. Therefore, the standard should specify a limit for the customers about the flicker emission at their installations. The new technical report IEC/TR 61000-3-14 indicates a method to estimate the flicker emission limit for various customers in the low voltage (LV) network. In this paper, an analysis is done on a model Dutch network to estimate a LV customers maximum share of flicker emission into the network. Also, the most appropriate planning level value of flicker at different voltage levels in the Netherlands is suggested.

Impacts of modifications of standards on the power quality measurement results

Power quality (PQ) standards are needed to achieve coordination between the characteristics of the quality of a networks power supply and the requirements of the end use equipments. The European standard EN50160 is a reference for the voltage supplied in medium and low voltage European grids. In the recent years, many discussions are done among regulators, network operators and industrial partners to improve this standard. In 2009, the last revision of this standard was approved and a number of modifications are given regarding the supply voltage related parameters. In this paper, a brief analysis is done to find out the implications of those changes to the existing networks voltage supply characteristics. Five years PQ measurement results of the Dutch networks are used as a reference case and are evaluated based on the new values given in the final draft of the EN50160 standard and the existing Dutch Grid Code.

Integrated approach for power quality requirements at the point of connection

Given the nature of electricity, every party connected to the power system influences voltage quality, which means that every party also should meet requirements. In this field, a sound coordination among technical standards (system-related, installation-related and product-related) is of paramount importance. Further, characteristics of currents (e.g. inrush currents, harmonic currents) should be explored as well their interaction with the voltage. This is also influenced by the impedance of the grid provided by operators. In order to clearly identify responsibilities for voltage quality disturbances on the point of connection (POC), voltage and current requirements have to be available at the POC. Presented in this paper is the relation between inrush currents, flicker severity levels and grid impedances in the low voltage grid. Furthermore maximum harmonic currents at the POC in low voltage grids are determined by using these grid impedances.