Decision theory process for making a mitigation decision on harmonic resonance in power systems

Includes bibliographical references.Decision analysis is a scientific tool that is traditionally applied in business and not to electrical engineering decisions. The reason for this research is to show how to use decision analysis to make a decision on the size of a power factor correction capacitor to be installed in an end-user plant in an electrical power system, that has the potential for harmonic resonance. How to make a decision as to whether or not mitigation is needed is also researched. The two-stage decision theory process, developed by management scientists, to assist decision makers on making a decision when uncertainty, risk and certainty situations-exist, is reviewed in this thesis. To understand the application of decision theory, worked examples are included to improve understanding and to provide a foundation for the new work introduced. The addition of capacitors to a harmonic carrying system can result in resonance. Harmonic levels can be magnified well above accepted limits and this can cause damage to system components, especially capacitors. Recognizing and correcting a harmonic resonance problem before disastrous consequences arise is essential for system designers. Traditionally, when considering harmonic resonance, power factor correction capacitors are sized heuristically and a power factor of 0.95 is taken as a starting point. Usually, a harmonic analysis software package is used and a frequency scan study is conducted to generate a resonance curve. Resonant points are then compared to the harmonics in the system. If there is coincidence, the technique of de-tuning is applied to overcome overlapping and to choose the capacitor size. For utilities to maintain system efficiencies at acceptable levels, they encourage end-users to use a capacitor size so that the power factor has a value greater than 0.9 and as a rule of thumb, correction is not done to unity. This traditional technique is subjective and lacks decision structure. A new three-stage decision theory process for making a harmonic resonance mitigation decision in an end-user plant is developed. Two new indices are developed to assist in making the decision. The first index assesses the severity of resonance and the second is used to make a mitigation decision. In Stage 1, a quantitative model is developed to structure and represent the decision problem with the harmonic resonance severity index as the objective function. The model uses a fixed capacitor based on full load rating as this represents the worst case. In Stage 2, Utility Theory is used as the decision criterion to select the most desirable capacitor size. In Stage 3, the mitigation index is applied to assess if mitigation is needed or not for the chosen capacitor. Three case studies, based on deterministic models are conducted and they demonstrate the effectiveness of this newly developed decision theory process

Power system harmonic field measurements PC simulations and standards

Includes bibliography.The research covered three main objectives: Application of PC based harmonic penetration packages and a comparison of their simulation results. Investigation and comparison of the IEEE, IEC and ESKOM power system harmonic standards. Measurement of harmonics in two industrial networks and the application of the results to the regulatory limits provided by the standards. The research makes use of two packages and uses parameters from an industrial network. Case studies were conducted using the same parameters so that the results obtained from each package could be compared. The standards have been individually investigated to determine each method for controlling harmonic distortion. The three standards have also been compared. Harmonic field measurements were conducted in industrial networks so that the limits imposed by the standards could be compared with real life operating conditions

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Hospital admission and emergency care attendance risk for SARS-CoV-2 delta (B.1.617.2) compared with alpha (B.1.1.7) variants of concern: a cohort study

Background: The SARS-CoV-2 delta (B.1.617.2) variant was first detected in England in March, 2021. It has since rapidly become the predominant lineage, owing to high transmissibility. It is suspected that the delta variant is associated with more severe disease than the previously dominant alpha (B.1.1.7) variant. We aimed to characterise the severity of the delta variant compared with the alpha variant by determining the relative risk of hospital attendance outcomes. Methods: This cohort study was done among all patients with COVID-19 in England between March 29 and May 23, 2021, who were identified as being infected with either the alpha or delta SARS-CoV-2 variant through whole-genome sequencing. Individual-level data on these patients were linked to routine health-care datasets on vaccination, emergency care attendance, hospital admission, and mortality (data from Public Health England's Second Generation Surveillance System and COVID-19-associated deaths dataset; the National Immunisation Management System; and NHS Digital Secondary Uses Services and Emergency Care Data Set). The risk for hospital admission and emergency care attendance were compared between patients with sequencing-confirmed delta and alpha variants for the whole cohort and by vaccination status subgroups. Stratified Cox regression was used to adjust for age, sex, ethnicity, deprivation, recent international travel, area of residence, calendar week, and vaccination status. Findings: Individual-level data on 43 338 COVID-19-positive patients (8682 with the delta variant, 34 656 with the alpha variant; median age 31 years [IQR 17–43]) were included in our analysis. 196 (2·3%) patients with the delta variant versus 764 (2·2%) patients with the alpha variant were admitted to hospital within 14 days after the specimen was taken (adjusted hazard ratio [HR] 2·26 [95% CI 1·32–3·89]). 498 (5·7%) patients with the delta variant versus 1448 (4·2%) patients with the alpha variant were admitted to hospital or attended emergency care within 14 days (adjusted HR 1·45 [1·08–1·95]). Most patients were unvaccinated (32 078 [74·0%] across both groups). The HRs for vaccinated patients with the delta variant versus the alpha variant (adjusted HR for hospital admission 1·94 [95% CI 0·47–8·05] and for hospital admission or emergency care attendance 1·58 [0·69–3·61]) were similar to the HRs for unvaccinated patients (2·32 [1·29–4·16] and 1·43 [1·04–1·97]; p=0·82 for both) but the precision for the vaccinated subgroup was low. Interpretation: This large national study found a higher hospital admission or emergency care attendance risk for patients with COVID-19 infected with the delta variant compared with the alpha variant. Results suggest that outbreaks of the delta variant in unvaccinated populations might lead to a greater burden on health-care services than the alpha variant. Funding: Medical Research Council; UK Research and Innovation; Department of Health and Social Care; and National Institute for Health Research

An integrated programme for power systems simulation using personal computers (PC's)

Thesis (Masters Diploma (Technology)--Cape Technikon, Cape Town, 1993The research objectives were to: Formulate a training structure covering conventional power systems topics; Research existing PC based power systems software resources; Develop a structure for a PC based power systems course; Research the capabilities of the software resources chosen; Develop a structure for a modern PC based power systems course taking into account the capabilities and limitations of the selected software programs; Develop for the PC based power systems course, task orientated computer based laboratory set-ups. The set-ups provide: An introduction into the topics concerned; An explanation of the usage of each program applied, where usage means an explanation of the Input and Output Data of each program; User friendly simulation experiments. These set-ups, together with software programs and a personal computer integrate into a training programme and realize a power systems simulation course

Electrical energy losses and cost evaluation of HVDC and UHVDC transmission lines

10th Conference on the Industrial and Commercial Use of Energ

Multi-criteria analysis for the sizing and selection of circuit breakers in power systems

This paper presents a broader analysis approach which adds to the traditional fault analysis technique commonly used in industry to size and select circuit breakers required for the power system. The fault analysis has been simulated on a computer software program DIgSILENT PowerFactory for all fault conditions. The circuit breaker selection will be based on a Multi-Criteria Analysis which helps to evaluate the design to arrive at the most user preferred result. This approach is refined to incorporate user preferences with respect to the criteria so that the final design is representative of both the design specification and the concerns of the user. This broader newer approach has been shown by means of case studies to be effective

Design of a steinmetz symmetrizer and application in unbalanced network

The design of delta and star Steinmetz Symmetrizers and applications in unbalanced three phase 4-wire networks supplied from asymmetrical voltages are studied in this paper. Unbalanced current and harmonics shorten motor life spans. An unbalance factor (mi) is defined and harmonics are studied using Superharm (4-wire) models. Two case studies, 1 & 2 are conducted. Case 1 has 1A and 1B and Case 2 has 2A, 2B & 2C. Study 1A is a laboratory set-up used for measurements and in 1B a delta symmetrizer is applied and compared to hand and simulation results. A second network that includes a delta motor and a 4-wire star load (2A) is analyzed (mi, P, Q, PF and IN) and compared to when a star symmetrizer (2B) is applied. The impact of a VSD (2C) on the motor and neutral when the symmetrizer is applied is also analyzed. Findings on Symmetrizers are made

Efficiency of an alternating current transmission line converted into a direct current system

10th Conference on the Industrial and Commercial Use of Energ

Harmonic filter design to mitigate two resonant points in a distribution network

This paper investigates the usage of passive harmonic filters to mitigate harmonic distortions when two resonant points are present in a system caused by shunt capacitors used for power factor correction and bus voltage regulation. Six scenarios were investigated using DIgSILENT 14 Power Factory software. The investigations are with and without power factor correction and capacitors used to increase bus voltage. Passive harmonic filters are designed to reduce harmonic distortions at the point of common coupling (PCC) to fall within the IEEE 519 harmonic voltage and current limits caused by parallel resonance. The results of the case studies are analysed to evaluate the effectiveness of the filter design