Miomir Kostic

Harmonic distortion in electric power systems introduced by compact fluorescent lamps

The purpose of this paper is the investigation of the harmonic distortion introduced by the compact fluorescent lamps to the distribution systems. The results of some measurements on compact fluorescent lamps (CFL) and on self-ballasted fluorescent lamps (SBL) of various wattages are presented. Some of the most important electrical characteristics (voltage, current and power factor) were measured by a data acquisition system. The harmonic spectrum and the total harmonic distortion (THD) of the lamps were calculated using Fourier analysis of the recorded current waveforms. The measurements were performed with supply voltage other than the nominal one in order to determine the dependence of the THD variation upon the mains supply voltage. From these measurements, conclusions concerning the problem of harmonics are drawn.

Advantages and disadvantages of the use of compact fluorescent lamps with electronic control gear

The paper presents a comprehensive analysis dealing with the behaviour and economics of electronic compact fluorescent lamps. The economic analysis, based on the results of the test concerning the lifetime and the lamp lumen maintenance factor of electronic compact fluorescent lamps, and conducted using the cost-discount method, showed an obvious advantage for lamps of this type compared with incandescent ones. The strategic importance of the mass use of electronic compact fluorescent lamps, as well as serious power quality implications it can cause to the network, are explained in detail. Possible solutions of this problem are also presented.

A modified CIE mesopic table and the effectiveness of white light sources

Since practical application of the recently developed CIE mesopic system assumes the development of new measurement devices, recommendations and software for road lighting design, this paper presents a corrected photopic luminance table, which enables lighting designers to use the existing design procedures and measurement methods until all of these tasks are accomplished. It is also shown that there are numerous reasons for the practical application of the CIE mesopic system, although only photopic vision is involved in on-axis object recognition. Using the corrected photopic luminance table, an analysis is conducted regarding the potential electricity and cost savings when applying white light sources, which are more visually effective in the mesopic range.

Light-emitting diodes in street and roadway lighting – a case study involving mesopic effects

The paper considers the justification for the application of light-emitting diode (LED) technology to urban lighting. The results suggest that LEDs are convenient for architectural lighting and deserve to be considered for use in ambient lighting. The recently developed Commission Internationale de l’Eclairage (CIE) mesopic system enabled the inclusion of mesopic effects into a comprehensive techno-economic analysis, which dealt with efficiency, maintenance and financial aspects of the use of LEDs in street and roadway lighting. It is concluded that the average energy savings when using LED instead of high-pressure sodium (HPS) luminaires amount to 19–26% for single-sided, staggered and opposite layouts, although they are frequently negligible if mesopic effects are not included. The total costs of the LED lighting solutions, even including mesopic effects, are 1.36 to 6.44 times higher than those of the comparable HPS lighting solutions. Therefore, LEDs are questionable for street and roadway lighting.

An Algorithm for Estimating the Grounding Resistance of Complex Grounding Systems Including Contact Resistance

In cases where the grounding system is buried in soils characterized by poor contact with the electrodes (e.g., karst and sandy terrains), the contact resistance frequently represents a dominant component of the total grounding resistance. In such cases, estimation of the grounding resistance by conventional formulas given in the literature is useless, because they do not take into account the contact resistance. An algorithm for estimating the total grounding resistance of complex grounding systems, with the contact resistance included, was developed and presented in this paper. The algorithm is applied to a grounding system of a typical 110-kV transmission line tower used in the Serbian transmission power system. Simple formulas by which the total grounding resistance of the analyzed grounding system can easily be calculated are also derived. The obtained results are validated using 3-D finite-element method (FEM) modeling and a practical method from the literature. It was shown that the total grounding resistances determined by the proposed algorithm deviate less than 4% from those obtained by FEM calculations. Since the proposed algorithm is general and can be applied to any grounding system, it represents a powerful tool for estimating the grounding resistance in an early stage of the design process.

Comparison of electronic and conventional ballasts used in roadway lighting

Although manufacturers recommend light-emitting diode technology for all types of urban lighting, it is likely that high-pressure sodium lamps will be used for roadway lighting for many years. The purpose of this paper is to establish whether electronic ballasts represent a better solution for such lamps than electromagnetic ballasts. Special attention was devoted to the fact that electronic ballasts allow considerably higher voltage drops. However, taking into account the earth-fault protection demands, it is shown that electronic ballasts provide only a modest possibility to increase the length of the street lighting section. The techo-economic analysis showed that, owing to the high prices and shorter life of electronic ballasts, conventional electromagnetic control gear still represents a better choice from the financial point of view.

Luminous flux to input power ratio, power factor and harmonics when dimming high-pressure sodium and LED luminaires used in road lighting

This paper presents experimentally obtained luminous flux to input power characteristics of high-pressure sodium and LED luminaires used in road lighting, confirming that when applying dimming scenarios more percentage energy savings can be achieved by an LED than by a corresponding high-pressure sodium lighting installation. However, both workshop and field experiments showed that the tested LED drivers (of either standard or improved dimming characteristics) have the disadvantage of poor power factors (down to 0.67) at low light levels achieved by dimming. In addition, an increased presence of current harmonics and high values of the current total harmonic distortion were noticed at low light levels, representing another serious disadvantage of LED technology regarding power quality. The relevant electrical characteristics of commonly used LED drivers were analysed in detail and the reasons for the poor power quality when dimming LED luminaires were recognised. A new generation of LED drivers with a considerably narrower range of input (AC) voltage will allow acceptable power factors and limited emissions of current harmonics to be achieved in practically all lighting regimes.

Warm white versus neutral white LED street lighting: Pedestrians' impressions

The subjective impressions of pedestrians are necessary in order to decide on the appropriate colour of light to be used for street lighting. Therefore, a pilot project aimed to compare subjective evaluations of the sidewalk illumination under two street lighting installations, realised by LEDs of 3000 K (warm white) and 4000 K (neutral white), was recently conducted in Belgrade. Both installations had comparable sidewalk illuminances as well as other relevant photometric parameters. The evaluation was done through a questionnaire. A group of 139 (61 male and 78 female) respondents, all of them university students, was asked to grade both lighting installations for the sidewalk light intensity, the appearance of human faces, the colour of light and the colour rendering as well as the overall impression. According to the median values, the 3000 K LED installation was considered better than the 4000 K installation for all aspects assessed as well as the overall impression. Although the survey results convincingly showed a preference for 3000 K LEDs for this comparison, additional research is needed using a more representative sample of people and a wider range of locations before a definite conclusion can be reached.

A new procedure for determining the road surface reduced luminance coefficient table by on-site measurements:

Numerous measurements have shown that the standard R classes do not represent adequately many road surfaces used nowadays. Therefore, the construction of portable reflectometers intended for on-site measurements of road surface reflection properties has been given particular attention during the last decade. This paper presents a new procedure for the improvement of the accuracy of such a portable reflectometer. Optimally extrapolating the values of the 20 luminance coefficients (q), each measured by the portable reflectometer for a set of angles of observation (α = 5°–80°), the 20 q-values referring to α = 1° are calculated. This enables their comparison with the corresponding q elements from each of the 447 reduced q-tables derived from the available r-table database, obtained by using a precise laboratory reflectometer on a wide variety of road samples. Selecting the closest reduced q-table, the corresponding r-table and the actual average luminance coefficient can be determined. In order to validate the proposed procedure, which can also be applied to other similar portable reflectometers, measurements of the luminance and overall and longitudinal luminance uniformities were carried out on eleven road-lighting installations. They showed that the results obtained by this procedure deviate only slightly from those obtained using r-tables determined by the laboratory reflectometer.

The Impact of an Incomplete Overlap of a Copper Conductor and the Corresponding Terminal on the Contact Temperature

By using a specially designed apparatus, the impact of poor contacts caused by an incomplete overlap of a copper conductor and the corresponding terminal of the low-voltage electrical equipment on the contact temperature was tested. The poor contact was simulated using the electrodes of different cross-sectional areas, exposed to different loads. The most frequently used combinations of the contact materials, copper–copper, copper–brass, and copper–stainless steel, were analyzed. The considered percentage of the overlapping areas of the electrodes amounted to 100%, 50%, and 15%. The influence of all of these parameters on the contact temperature, the occurrence of a hot spot, the establishment of a series electric arc, and the contact resistance was analyzed in detail. It was shown that a reduced overlapping area is considerably more dangerous (as a cause of fire) in case of the copper–brass contacts than in case of the copper–copper contacts. However, the most dangerous are the copper–stainless steel connections. (Being the cheapest, the stainless steel terminals can still be found in low-quality sockets.) It was also shown that the copper–brass connections are characterized by the highest contact resistances, which occur when stable electric arcs are established. An example from our practice is presented in order to show the potential consequences of an incomplete overlap.