Assessment of Power System Equipment Insulation Based on Distorted Excitation Voltage

Electrical insulation plays a critical role in high voltage power system equipment. The presence of electrical, thermal, and mechanical stresses imposed when they are in operation for a long time cause gradual degradation of the insulation. Therefore, regular condition monitoring and diagnostic testing of power system equipment are of paramount importance for the reliable operation of electricity supply networks and systems. The dielectric dissipation factor (DDF) measurement is one of the most common techniques for insulation assessment. From a traditional perspective, a pure sinusoidal voltage is used for excitation in the testing. However, the grid voltage nowadays in reality is often distorted with a waveform having multiple harmonic components. Generally, there are distorted voltages and currents generated due to the presence of non-linear equipment or components in the system. Thus, testing under distorted voltage with harmonics provides a more realistic diagnostic measurement as compared to traditional AC sinusoidal high voltage testing. This dissertation investigates the impact of harmonically distorted excitation on the dielectric dissipation factor of high voltage power equipment. A practical measurement method based on distorted excitation is proposed and tested on a reference capacitor-resistor test object. A theoretical and mathematical model is developed to quantify the impact of distortion on the DDF measured in contrast to the case of non-distorted excitation. It is established that for the same total RMS magnitude of the applied excitation, the DDF decreases with the increasing harmonic proportion in the applied voltage waveform. For validation, laboratory experiments and computer simulations were carried out, and data obtained were compared with the analytical results. The proposed technique is then tested on some real high voltage components (33kV dry-type current transformers). The results confirm the monotonically decreasing trend, but the pattern is more complex. The dielectric dissipation factor mathematical and electrical circuit model is implemented based on the polarisation loss. The theoretical formulation is implemented in a computer simulation using MATLAB Simulink to validate the results. In summary, the thesis provides useful diagnostic insights on the characteristics of the dielectric dissipation factor measurement under distorted excitation

On load core loss measurement and allied problems in highly fluxed transformer cores

Imperial Users onl

Investigations of power quality problems in modern buildings

This thesis was submitted for the degree of Master of Philosophy and awarded by Brunel University.This thesis presents the results of measurements made in a typical office building (Tower A) and a Residential building (Kilmorey Hall), all located in the campus of Brunel University, West London for period of one week. The collected data were statistically treated to establish the best period that characterizes the harmonic distortions and other disturbances in these buildings. The chosen period was considered as best to get the correct harmonic distortions in the day, and at a specific interval. One phase was also chosen to represent the others after some considerations. The frequency of measurement was also noted. All the data collected were evaluated based on the limits proposed by International Standards: European, IEEE, and G4/5 Recommendations. Comparisons of the collected data were made between these two buildings. For the purpose of this project, the statistical treatment of the collected data characterizing the voltage harmonics was considered. The period of 9am to 5pm on a week day (Tuesday 26th October) was best for Tower A as it had the highest loading pattern for the week. This is a day-load establishment, because it is an office building. The period for Kilmorey Hall was Monday 1st November between the hours of 6pm up to 11pm, being considered as wholly residential building. All readings were spaced at 8minutes interval for frequency of measurement. The methodology presented in this project is useful for quantification and qualification of the harmonic distortion of voltage and current. It is estimated that more than 30% of the power currently being drawn from the utility companies is now consumed by sensitive non- linear load, and still increasing, both industrially and commercially [20]. Non- linear load is steadily increasing in residential areas also. The effect of continuous overvoltage was also considered even though the overvoltage was within the International Standards. The result was proved to cause unnecessary and unwanted overconsumption. This could not be helping to reduce carbon emission. Effects of Compact Fluorescent Lamps with electronic gears (CFLs) were also investigated as a rising source of harmonic production in Modern buildings

Harmonics Impact a Rising Due to Loading and Solution ETAP using the Distribution Substation Transformer 160 kVA at Education and Training Unit in PT PLN

Harmonics is a result of the progress of the use of non-linear loads are used in homes and offices. On the other hand, the energy crisis triggered the increased use of Energy Saving Lamps (LHE), Computer, electronic power equipment that is the cause of harmonics that can interfere with the electrical distribution system including Distribution Transformer (TGD). By performing measurements in the TGD, it is known the existence of harmonic currents which can increase the losses on the TGD. In the measurements made on the TGD Education and Training Unit Lubuk Alung capacity of 160 kVA obtained that influence THDi (Total Harmonic Distortion) currents in the TGD (6.57%) while according to the standard (4%). Shrinkage of 1.22 years of age transformer (4.067%). By using ETAP simulation active capacitor installation of 60 KVAR and 1500 mH obtained THD decline to 8% by neutral currents down to 12 A. From the simulation results ETAP effective current of each phase down 6% while the neutral current down 64%. Transformer derating of these conditions can be avoided and the use of the load can be increased. The impact of harmonics on transformer resulting in transformer losses increased from 3,755 kW to 3.775 kW. The increase in transformer losses (0.16 %) led to decreased work efficiency transformer. This resulted in a decrease in the capacity of the transformer

Time domain analysis of switching transient fields in high voltage substations

Switching operations of circuit breakers and disconnect switches generate transient currents propagating along the substation busbars. At the moment of switching, the busbars temporarily acts as antennae radiating transient electromagnetic fields within the substations. The radiated fields may interfere and disrupt normal operations of electronic equipment used within the substation for measurement, control and communication purposes. Hence there is the need to fully characterise the substation electromagnetic environment as early as the design stage of substation planning and operation to ensure safe operations of the electronic equipment. This paper deals with the computation of transient electromagnetic fields due to switching within a high voltage air-insulated substation (AIS) using the finite difference time domain (FDTD) metho

Assessing the contribution of harmonics at the point of common coupling in networks

Abstract: The presence of harmonics in voltage and current waveforms is a result of an increase in use of nonlinear loads in power systems. Utility and end users are in disagreement over who is responsible of polluting the Point of Common Coupling (PCC) and therefore poor power quality. Hence, there is a need for dedicated techniques of analysis to determine the contributions of harmonics between utility and customer...Ph.D. (Electrical and Electronic Engineering Science

Power Quality

Electrical power is becoming one of the most dominant factors in our society. Power generation, transmission, distribution and usage are undergoing signifi cant changes that will aff ect the electrical quality and performance needs of our 21st century industry. One major aspect of electrical power is its quality and stability – or so called Power Quality. The view on Power Quality did change over the past few years. It seems that Power Quality is becoming a more important term in the academic world dealing with electrical power, and it is becoming more visible in all areas of commerce and industry, because of the ever increasing industry automation using sensitive electrical equipment on one hand and due to the dramatic change of our global electrical infrastructure on the other. For the past century, grid stability was maintained with a limited amount of major generators that have a large amount of rotational inertia. And the rate of change of phase angle is slow. Unfortunately, this does not work anymore with renewable energy sources adding their share to the grid like wind turbines or PV modules. Although the basic idea to use renewable energies is great and will be our path into the next century, it comes with a curse for the power grid as power fl ow stability will suff er. It is not only the source side that is about to change. We have also seen signifi cant changes on the load side as well. Industry is using machines and electrical products such as AC drives or PLCs that are sensitive to the slightest change of power quality, and we at home use more and more electrical products with switching power supplies or starting to plug in our electric cars to charge batt eries. In addition, many of us have begun installing our own distributed generation systems on our rooft ops using the latest solar panels. So we did look for a way to address this severe impact on our distribution network. To match supply and demand, we are about to create a new, intelligent and self-healing electric power infrastructure. The Smart Grid. The basic idea is to maintain the necessary balance between generators and loads on a grid. In other words, to make sure we have a good grid balance at all times. But the key question that you should ask yourself is: Does it also improve Power Quality? Probably not! Further on, the way how Power Quality is measured is going to be changed. Traditionally, each country had its own Power Quality standards and defi ned its own power quality instrument requirements. But more and more international harmonization efforts can be seen. Such as IEC 61000-4-30, which is an excellent standard that ensures that all compliant power quality instruments, regardless of manufacturer, will produce of measurement instruments so that they can also be used in volume applications and even directly embedded into sensitive loads. But work still has to be done. We still use Power Quality standards that have been writt en decades ago and don’t match today’s technology any more, such as fl icker standards that use parameters that have been defi ned by the behavior of 60-watt incandescent light bulbs, which are becoming extinct. Almost all experts are in agreement - although we will see an improvement in metering and control of the power fl ow, Power Quality will suff er. This book will give an overview of how power quality might impact our lives today and tomorrow, introduce new ways to monitor power quality and inform us about interesting possibilities to mitigate power quality problems. Regardless of any enhancements of the power grid, “Power Quality is just compatibility” like my good old friend and teacher Alex McEachern used to say. Power Quality will always remain an economic compromise between supply and load. The power available on the grid must be suffi ciently clean for the loads to operate correctly, and the loads must be suffi ciently strong to tolerate normal disturbances on the grid