Greet Vanalme

Sensitivity of personal computers to voltage sags and short interruptions

This paper discusses the sensitivity of personal computers (PCs) to voltage sags and short interruptions on the basis of the extensive test results. Existing standards and previously published works are reviewed, and a description of a used testing procedure is presented. The following tests were performed: sensitivity to rectangular voltage sags with ideal and nonideal supply characteristics, and sensitivity to voltage sags caused by the starting of large motors. The results obtained emphasize the importance of clear definition of the malfunction criteria for this equipment.

Analysis of the neutral conductor current in a three-phase supplied network with nonlinear single-phase loads

This paper describes what factors (i.e., load and supply) have an important effect on the neutral conductor current. It is shown that an asymmetry up to 10/spl deg/ or an unbalance of 10% in the power supply has only a minor effect on the RMS value of the neutral conductor current. An unbalance in load conditions increases the neutral conductor current. Harmonics in the power supply voltage highly affect the RMS value of the neutral conductor current.

Simulation of losses in LV cables due to nonlinear loads

Companies active in distribution or transmission of electrical energy know the power losses in their HV and MV cables. Users have no idea of the magnitude of the cable power losses in their electrical installations. Nevertheless cable power losses can be a significant part (3%-5%) of the total power consumption. Nonlinear loads (ASD, CLF, IT-equipment,...) are often installed with the aim of rational energy use. However, one is not aware of the increase of cable losses due to the nonlinear load. A software tool is developed in order to enable companies to simulate the supply system losses of their present or future electrical installation in an easy way, including the use of both active or passive filter systems. In this paper the power losses in LV cables are analyzed, including the impact of nonlinear loads. A simple model is proposed in order to calculate power losses in a quick way. The model uses an equivalent resistance, taking into account frequency dependency by means of a correction factor only dependent on the conductor cross section and not on the current harmonic spectrum. The model is validated by experiments. Deviations less than 5% are found. Because of the suitability of the model for a wide range of harmonic spectra, power losses can be easily calculated with sufficient accuracy without the knowledge of the current harmonic spectrum. The paper also includes a sensitivity analysis of parameters influencing cable losses and some practical recommendations to reduce cable losses.

Analysis of the neutral conductor current in a three phase supplied network with nonlinear single phase loads

This paper describes which factors (i.e. load and supply) have an important effect on the neutral conductor current. It is shown that an asymmetry up to 10/spl deg/ or an unbalance of 10% in the power supply has only a minor effect on the RMS-value of the neutral conductor current. An unbalance in load conditions increases the neutral conductor current. Harmonics in the power supply voltage highly affects the RMS-value of the neutral conductor current.

Influence of harmonic currents on cable losses for different grid configurations

Nowadays, both industrial and residential consumers use power electronics with the aim of rational use of energy or the implementation of distributed generation. However, power electronics may cause harmonic currents. Since cable losses are function of the rms current, harmonic currents will increase cable losses. This contribution analyses the influence of the current harmonic spectrum on low voltage cable losses. Grid configurations are discussed with the aim to optimize cable joule losses in case of nonlinear load conditions.

Modelling and sensitivity analysis of the thermal behaviour of cables for different current conditions

Asymmetry, unbalance and nonlinearity of loads affect the current distribution in both phase and neutral conductor cores in three phase power supply systems. Especially in cases of nonlinear single phase loads the neutral conductor can be loaded with an excessive current. Consequently, cable temperature, which is directly related to the power dissipation, is highly affected. Applying a maximum insulation temperature as boundary condition, the power conducting capacity of LV-cables will substantially be affected by asymmetry, unbalance and especially nonlinearity of loads. Physical cable parameters with respect to both thermal resistance and cable geometry were analyzed in order to determinate the most relevant influencing parameters. The temperature distribution in the cable section is thermally calculated and is subsequently simulated, using 2D finite element modelling. Finally, measurements of the cable temperature are performed verifying the simulation results.

Analysis on the increased losses in supply systems due to voltage drop and voltage distortion

Non linear load currents generate increased losses in supply system elements, such as transformers, cables, capacitor banks, harmonic filters etc. Due to the interaction between these elements through grid impedance and voltage distortion, it is not sufficient to consider the losses in the separate elements to optimise the energy efficiency of the entire supply system. Only the overall energy loss of the supply system is of interest. A simulation tool is developed and used to compare supply system configurations, with respect to total losses.