C.J. Renedo

Energy potential of waste from 10 forest species in the North of Spain (Cantabria).

In this work, the waste from 10 forest species of Cantabria have been characterized from the point of view of energy. The studied species were the waste of: Eucalyptus globulus, Eucalyptus nitens, the hybrid E. globulusxE. nitens, Eucalyptus viminalis, Eucalyptus smithii, Eucalyptus regnans, Eucalyptus gunni, Fagus sylvatica, Quercus robur and Pinus radiata. The leaves were the tree part with the greatest NCV (net calorific value) in all the species. The best results were obtained for the leaves of E. smithii (24.5 MJ/kg), F. sylvatica (22.8 MJ/kg) and E. nitens (22.5 MJ/kg), at minimum moisture. Values around 65,000 MJ per hectare and year were obtained for the Eucalyptus spp., and 47,000 MJ per hectare and year for the P. radiata. The economic-environmental analysis revealed that the use of the forest waste for energy production would mean an approximate annual income of 8 Meuro and would fix the annual CO(2) emitted by the Cantabrian industries at 78%.

Total harmonic distortion decomposition depending on distortion origin

The total harmonic distortion (THD) ratio is a well-known parameter that characterizes the distortion degree at a specific point of the grid. In this paper, a decomposition of the THD will be presented in order to determine the responsibility of the distribution company and the electrical energy consumer for the harmonic distortion measured at the point of common coupling (PCC). For this study, the power quantities proposed in the new Standard IEEE 1459-2000 and developed by L. Czarnecki were considered. The algorithm of the decomposition will be implemented on a measurement platform based on a digital signal processor (DSP). The general structure of the system-hardware and software-are also discussed. Finally, the apparent powers, defined by both L. Czarnecki and the IEEE Standard, are also compared for single-phase and three-phase systems.

Thermal-fluid characterization of alternative liquids of power transformers: A numerical approach

The transformers lifespan depends importantly on its refrigeration. Mineral oils perform this work in the majority of the power transformers. However, this type of coolant has two main drawbacks: low biodegradability and low ignition point. Several alternative liquids are being developed in order to overcome these drawbacks. This paper compares their thermal-fluid behavior with a mineral oil by means of several parameters, such as temperature, flow rate, fluids velocity, convective heat transfer coefficient (h) and the cooling criterion (P). These are calculated using the numerical results of the simulation of a 3D-model of a Low Voltage Winding that belongs to a power transformer with ONAN cooling. The software COMSOL Multiphysics has allowed the simulation of the geometry using a physical model in which buoyancies and viscous forces are the only considered establishing the natural convection. As a result of the comparison, it is clear that the mineral oil is the best coolant liquid. Among the alternative liquids, silicone oil would be the second best coolant fluid, followed by the synthetic and natural esters, respectively. On the other hand, it seems to be clear that the 3D simulations can be used to compare properly the cooling capacities of the liquids.

Effects of voltage sags on different types of ballasts for 150-W HPS lamps

Nowadays, energy efficiency is a hot topic in a very demanding environment. In this way, improvements in lighting applications, which is a significant point of energy consumption, could be very much welcomed. Electronic ballast may serve to this goal since they are focused on achieving energy savings, reduction in the utility line harmonic content and reactive power, as well as on implementing dimming control and some other parameter of interest in lighting applications. On the other hand, power quality problems are very common in our power system and any new electric device should be designed taking into account these events. One of the typical problems in electrical distribution systems are voltage sags. These have a great incidence on the electrical equipment connected to the network in the same area. The sags cause more damages than the rest of disturbances because these have a greater frequency of occurrence. In this work, the effects of voltage sags on several 150-W high- pressure sodium lamps combined with two different types of electronic ballast have been studied. One of the ballasts supplies the required voltage to minimize the reactive component in the resonant inverter, while the other regulates the power supplied by the utility line to be constant in long term, the resonant inverter being also in open loop at constant switching frequency providing the short term stability. The results of these electronic ballasts will be compared with those obtained with the traditional electromagnetic ballast. The influence of the lamp age will be also considered in the approach. The final goal of this study is to improve the performance of the ballast prototypes under voltage sags.

Health indexes for power transformers: a case study

Proper operation of power transformers is critical to ensuring transmission and distribution of electrical power. Most transformers have an electrical insulation system based on oil and paper. The state of the insulation system is the major factor influencing the state of the transformer. During service the dielectric materials within the transformer deteriorate, and small concentrations of impurities such as water, carbon monoxide, carbon dioxide, and furan compounds accumulate in the oil. Since it is easy to obtain oil samples from power transformers, the information most commonly collected by transformer fleet managers relates to the physical and dielectric properties of the oil. These properties include dielectric strength, dissipation factor, color, interfacial tension, and concentrations of dissolved gases, furans, acids, and moisture. Using these properties it is possible to determine whether a transformer has developed certain specific faults, e.g., partial discharges, arcing, sparking, overheating, etc. On the other hand, various health indexes have been proposed to characterize the general condition of a transformer [1]-[3]. The factors taken into account in these indexes vary, and are given different statistical weightings depending on their influence on the general condition of the transformer. In this article we evaluate the condition of a fleet of operating power transformers, using two recently proposed health indexes, and compare the results.

Effects of Flicker on Different Types of 150-W High-Pressure Sodium Lamps and Ballasts

The limits of the severity of flicker caused by voltage fluctuations is defined in Europe by the standard CENELEC EN 50160. Under normal operating conditions, flicker level will not exceed the long term severity Plt=1 during 95% of the time in one week. This threshold was originally established considering that a lamp with tungsten coiled coil filament of 60 W and 230 V that is gas-filled produces a flicker perceivable by 50% of the population when it is supplied with a voltage that verifies Plt=1. Other light sources like fluorescent lamps and discharge lamps with ballasts exhibit a different behavior under the same supply conditions. This means that the flicker meter should be different for each type of illumination technique ir order to provide accurate information about flicker phenomena. At the same time, lamp age also plays an important role in flicker generation. In this research work, a test system and a methodology able to measure the optical fluctuation produced by different types of lamps and ballast is presented. This experimental platform allows to obtain a correlation between voltage flicker levels and optical flicker perception. It can be considered the first step in the definition of new lamp models. This work also shows that age lamp has a significant correlation with flicker generation.

Aging assessment of dielectric vegetable oils

The combination of a dielectric solid (paper) and a dielectric liquid (mineral, vegetable, or silicone) is the most commonly used insulation system in power transformers because of the favorable dielectric properties of these insulations and the high heat capacity of the oil, which allows for cooling. It is known that temperature is the main parameter in determining the aging of these insulations and, therefore, the lifetime of a power transformer.

Evaluation of Energy Meters' Accuracy Based on a Power Quality Test Platform

Abstract Is it advisable to replace ferraris based meters with electronic meters? The permanence of the electromechanical meters currently in use is often justified on the grounds of their long working life and low price. However, it is well known that they are highly sensitive to external conditions and that many factors can lead to miscalibration. This work attempts to clarify some key points in order to answer the previous question. It reviews the operating principles of energy meters. The behavior of watt-hour meters under nonsinusoidal conditions is also studied. The disturbances considered were harmonics, unbalance and main frequency variations.

Comparison of flicker sensitivity in HPS lamps

The European standard CENELEC EN 50160 establishes that the severity of flicker caused by voltage fluctuations, under normal operating conditions, will not exceed the long term severity Pu = 1 during 95% of the time in one week. This threshold was originally established considering that a lamp with tungsten coiled coil filament of 60 W and 230 V that is gas- filled produces a flicker perceivable by 50% of the population when it is supplied with a voltage that verifies Pu = 1. Other light sources like fluorescent lamps and discharge lamps with ballasts exhibit a different behavior under the same supply conditions. This means that the flickermeter should be different for each type of illumination technique. A test system and a methodology able to measure the optical fluctuation produced by different types of lamps is presented. This experimental platform allows to obtain a correlation between voltage flicker levels and optical flicker perception. It can be considered the first step in the definition of new lamp models and the specification for new electronic ballast design.

Numerical analysis of the hot-spot temperature of a power transformer with alternative dielectric liquids

The assessment of two vegetal oils as coolant in Low Voltage Winding of a power transformer with zigzag cooling have been analyzed. These dielectric fluids cooling performance has been compared with a typical mineral oil. To make the study, a 2D-axisymmetrical model of a power transformer has been developed to perform a numerical analysis using a Finite Element Method based software, COMSOL Multiphysics®. Some values are obtained in order to establish the comparison, such as hot-spot temperature or hot-spot factor. Moreover, the influence of the increase of the number of passes of the cooling circuit on the hot-spot temperature has been evaluated for all liquids and compared with the initial design. Results obtained in this work show that the hot-spot temperature is lower for the vegetal oils in the initial design. Furthermore, an increase in the number of passes affect more positively to the mineral oil since similar values of the hot-spot temperature for all liquids are obtained. Values of the hot-spot factor indicates that higher number of passes leads to lower efficient cooling circuits owing to the increase of the pressure drop although the hot-spot temperature decreases.