The trend of generating power at distribution voltage level, known as distributed generation, is ... more The trend of generating power at distribution voltage level, known as distributed generation, is thought to be the future of energy generation, as it is environmental friendly and brings many advantages especially for electricity consumers. The paper presents the study of a real Romanian weak distribution network; the microgrid, comprising a transformer and the associated feeders, supplies single- and 3-phase domestic customers and public lighting. Various penetration levels of photovoltaic generation are considered in order to understand the potential issues that could appear. Practically, single- and 3-phase PV panels of different rated power were placed at diverse locations, i.e. close to feeders' terminals, and transformer substation, respectively. The results showed that harmonic distortion and voltage profile are getting better, while voltage asymmetry is increasing but it remains in the allowed range; positive effects appear especially if the PV generators are located near the feeders' end, where the voltage level is quite low.
Unbalanced line currents produce unequal voltage drops on the three phases of the supply system. ... more Unbalanced line currents produce unequal voltage drops on the three phases of the supply system. Consequently, the phase-to-neutral voltages within the supply system will be unbalanced because the voltage at any point of a power system is the difference between the generated voltage and the voltage drops due to the load current. Due to the negative effects of unbalance currents and voltages, the necessity of studying the propagation phenomenon of this electric disturbance at different voltage levels becomes a pertinent aspect of power quality. This paper presents the propagation process of unbalance through the electric power system, upstream from the LV distribution level. Using the symmetrical components theory, transformers with different types of connections are studied thus conclusions are taken regards transformers influence on the unbalance propagation.
Daylighting has become a more important feature of recent constructions due to the sustainable de... more Daylighting has become a more important feature of recent constructions due to the sustainable design movement, and suitable lighting controls provide building operators with the means to manage the way lighting energy is used in buildings more efficiently. Unfortunately, classic control systems, based on continuous dimming present some difficulties to adjust their performances to the rapid changes in daylight. Therefore,
The paper presents a new technique to mitigate the voltage unbalance in LV distribution grids usi... more The paper presents a new technique to mitigate the voltage unbalance in LV distribution grids using distributed generation (DG). Usually, public LV networks supply many single phase consumers; in this case, the unbalanced line currents produce the unbalance of standard symmetrical supply voltage system. This voltage system negatively influences other three-phase loads operating in the same system, i.e. motors, transformers, capacitor banks etc. Consequently, the utility must guarantee to these consumers a balanced voltage system that; this condition can be obtained by using distributed generation. The paper contains aspects regarding the unbalance in LV distribution grids, distributed generation and analyzes the opportunity of involving DG in voltage unbalance mitigation.
The sustainable development concept has revived the interest for daylighting as any day lit area ... more The sustainable development concept has revived the interest for daylighting as any day lit area has very promising energy-saving opportunities; according to some specialists, the potential energy savings can exceed 40%. However, daylight is a dynamic source of lighting, i.e. the illuminance from the sky is not constant, and the variations in daylight can be quite large depending on season, location or latitude, and cloudiness. As a result, electric lighting control systems will be needed from time to time to adapt the lighting systems to changing lighting conditions. Classic control systems, based on continuous dimming present some difficulties to adjust their performances to the rapid changes in daylight and to occupants' preferences. Taking into account these aspects, fuzzy control could be a better solution. The paper analyzes the possibility to implement this new technique in daylighting control and presents the structure of a fuzzy controller proposed by authors; its operation rules and the influence on the imposed value of the illuminance level are also studied.
Modeling of electrical networks elements (electric lines and transformers) during steady state op... more Modeling of electrical networks elements (electric lines and transformers) during steady state operation is based on the following suppositions: a) supply voltage system is balanced; b) currents are sinusoidal and form a balanced system of phasors; c) network parameters are constant; d) running state is permanent and stationary. These hypotheses can be correctly applied for single-phase and positive sequence schemes. An accurate modeling of electrical networks supposes the consideration of power losses and non-linear and unbalanced loads, which cause a distorted unbalanced operation state of the distribution and transmission networks. Therefore, the electric lines and transformers models have to be made taking into account the skin and proximity effects, the hysteresis phenomenon, losses due to inrush currents in magnetic materials etc. Paper presents a method to estimate parameters of electric lines and transformers using fuzzy logic. The electric parameters are considered fuzzy number, hence the input linguistic variables, fuzzyfication and defuzzyfication methods, knowledge base and output variables are presented. A virtual instrument that was created to evaluate parameter values is also presented.
The modern power systems are supplying a increasing number of non-linear loads like: power electr... more The modern power systems are supplying a increasing number of non-linear loads like: power electronics, arc furnaces, arc discharging light sources etc. These loads are harmonics and interharmonics sources. Interharmonics represent electrical components that are not synchronized with the systems fundamental frequency; due to this fact, they have a more destructive impact on power system elements than harmonics. International organizations
Abstract—Curricula for power engineering programs have undergone substantial change in the past y... more Abstract—Curricula for power engineering programs have undergone substantial change in the past years as modern techniques for analysis and design of power systems find their way,into these courses. The paper presents a laboratory controller, implemented as a virtual instrument that mimics a real fuzzy logic controller for a boiler system in a thermal power plant. The instrument is dedicated to
Interharmonics represent those electrical signals whose frequencies are not integer multiples of ... more Interharmonics represent those electrical signals whose frequencies are not integer multiples of the supply fundamental frequency. They correspond to electrical components that are not synchronized with the systems fundamental frequency; due to this fact, they have a more destructive impact than harmonics on the elements of the power system. International organizations like IEC and IEEE International Force Task Committee have
Power quality has become an important issue for electric power engineering. Nowadays, the distrib... more Power quality has become an important issue for electric power engineering. Nowadays, the distribution electric networks have unbalanced operating regimes, mainly produced by the great number of single-phase loads. Unbalanced line currents produce unbalanced voltage drops on the three phases of the supply system. Consequently, the voltage system within the supply network will become unbalanced. Voltage unbalance influences different components of the electric networks: the effects on the motors are the growths of losses, supplementary heating, and finally, the motors life is shorted. In the distribution and transmission electric networks the main effect of the unbalanced currents is the existence of additional power losses. Taking into account the above mentioned aspects, it is necessary to study the propagation of unbalance through the electric power system, upstream from the LV distribution level. By using the symmetrical components theory, transformers with different types of connections were studied, and their influence on the unbalance propagation was analyzed. A numerical example is presented for the propagation of unbalance from the secondary side of a transformer with Yzn connection to its primary side.
The trend of generating power at distribution voltage level, known as distributed generation, is ... more The trend of generating power at distribution voltage level, known as distributed generation, is thought to be the future of energy generation, as it is environmental friendly and brings many advantages especially for electricity consumers. The paper presents the study of a real Romanian weak distribution network; the microgrid, comprising a transformer and the associated feeders, supplies single- and 3-phase domestic customers and public lighting. Various penetration levels of photovoltaic generation are considered in order to understand the potential issues that could appear. Practically, single- and 3-phase PV panels of different rated power were placed at diverse locations, i.e. close to feeders' terminals, and transformer substation, respectively. The results showed that harmonic distortion and voltage profile are getting better, while voltage asymmetry is increasing but it remains in the allowed range; positive effects appear especially if the PV generators are located near the feeders' end, where the voltage level is quite low.
Unbalanced line currents produce unequal voltage drops on the three phases of the supply system. ... more Unbalanced line currents produce unequal voltage drops on the three phases of the supply system. Consequently, the phase-to-neutral voltages within the supply system will be unbalanced because the voltage at any point of a power system is the difference between the generated voltage and the voltage drops due to the load current. Due to the negative effects of unbalance currents and voltages, the necessity of studying the propagation phenomenon of this electric disturbance at different voltage levels becomes a pertinent aspect of power quality. This paper presents the propagation process of unbalance through the electric power system, upstream from the LV distribution level. Using the symmetrical components theory, transformers with different types of connections are studied thus conclusions are taken regards transformers influence on the unbalance propagation.
Daylighting has become a more important feature of recent constructions due to the sustainable de... more Daylighting has become a more important feature of recent constructions due to the sustainable design movement, and suitable lighting controls provide building operators with the means to manage the way lighting energy is used in buildings more efficiently. Unfortunately, classic control systems, based on continuous dimming present some difficulties to adjust their performances to the rapid changes in daylight. Therefore,
The paper presents a new technique to mitigate the voltage unbalance in LV distribution grids usi... more The paper presents a new technique to mitigate the voltage unbalance in LV distribution grids using distributed generation (DG). Usually, public LV networks supply many single phase consumers; in this case, the unbalanced line currents produce the unbalance of standard symmetrical supply voltage system. This voltage system negatively influences other three-phase loads operating in the same system, i.e. motors, transformers, capacitor banks etc. Consequently, the utility must guarantee to these consumers a balanced voltage system that; this condition can be obtained by using distributed generation. The paper contains aspects regarding the unbalance in LV distribution grids, distributed generation and analyzes the opportunity of involving DG in voltage unbalance mitigation.
The sustainable development concept has revived the interest for daylighting as any day lit area ... more The sustainable development concept has revived the interest for daylighting as any day lit area has very promising energy-saving opportunities; according to some specialists, the potential energy savings can exceed 40%. However, daylight is a dynamic source of lighting, i.e. the illuminance from the sky is not constant, and the variations in daylight can be quite large depending on season, location or latitude, and cloudiness. As a result, electric lighting control systems will be needed from time to time to adapt the lighting systems to changing lighting conditions. Classic control systems, based on continuous dimming present some difficulties to adjust their performances to the rapid changes in daylight and to occupants' preferences. Taking into account these aspects, fuzzy control could be a better solution. The paper analyzes the possibility to implement this new technique in daylighting control and presents the structure of a fuzzy controller proposed by authors; its operation rules and the influence on the imposed value of the illuminance level are also studied.
Modeling of electrical networks elements (electric lines and transformers) during steady state op... more Modeling of electrical networks elements (electric lines and transformers) during steady state operation is based on the following suppositions: a) supply voltage system is balanced; b) currents are sinusoidal and form a balanced system of phasors; c) network parameters are constant; d) running state is permanent and stationary. These hypotheses can be correctly applied for single-phase and positive sequence schemes. An accurate modeling of electrical networks supposes the consideration of power losses and non-linear and unbalanced loads, which cause a distorted unbalanced operation state of the distribution and transmission networks. Therefore, the electric lines and transformers models have to be made taking into account the skin and proximity effects, the hysteresis phenomenon, losses due to inrush currents in magnetic materials etc. Paper presents a method to estimate parameters of electric lines and transformers using fuzzy logic. The electric parameters are considered fuzzy number, hence the input linguistic variables, fuzzyfication and defuzzyfication methods, knowledge base and output variables are presented. A virtual instrument that was created to evaluate parameter values is also presented.
The modern power systems are supplying a increasing number of non-linear loads like: power electr... more The modern power systems are supplying a increasing number of non-linear loads like: power electronics, arc furnaces, arc discharging light sources etc. These loads are harmonics and interharmonics sources. Interharmonics represent electrical components that are not synchronized with the systems fundamental frequency; due to this fact, they have a more destructive impact on power system elements than harmonics. International organizations
Abstract—Curricula for power engineering programs have undergone substantial change in the past y... more Abstract—Curricula for power engineering programs have undergone substantial change in the past years as modern techniques for analysis and design of power systems find their way,into these courses. The paper presents a laboratory controller, implemented as a virtual instrument that mimics a real fuzzy logic controller for a boiler system in a thermal power plant. The instrument is dedicated to
Interharmonics represent those electrical signals whose frequencies are not integer multiples of ... more Interharmonics represent those electrical signals whose frequencies are not integer multiples of the supply fundamental frequency. They correspond to electrical components that are not synchronized with the systems fundamental frequency; due to this fact, they have a more destructive impact than harmonics on the elements of the power system. International organizations like IEC and IEEE International Force Task Committee have
Power quality has become an important issue for electric power engineering. Nowadays, the distrib... more Power quality has become an important issue for electric power engineering. Nowadays, the distribution electric networks have unbalanced operating regimes, mainly produced by the great number of single-phase loads. Unbalanced line currents produce unbalanced voltage drops on the three phases of the supply system. Consequently, the voltage system within the supply network will become unbalanced. Voltage unbalance influences different components of the electric networks: the effects on the motors are the growths of losses, supplementary heating, and finally, the motors life is shorted. In the distribution and transmission electric networks the main effect of the unbalanced currents is the existence of additional power losses. Taking into account the above mentioned aspects, it is necessary to study the propagation of unbalance through the electric power system, upstream from the LV distribution level. By using the symmetrical components theory, transformers with different types of connections were studied, and their influence on the unbalance propagation was analyzed. A numerical example is presented for the propagation of unbalance from the secondary side of a transformer with Yzn connection to its primary side.
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