Effect of Induction on Control/Signal Cables on Shunt Capacitor Bank Protective Schemes

Power factor correction is the main application for shunt capacitor units in the power system. The advantage of improved power factor is reduced line and transformer losses, improved voltage profile, reduced maximum demand, and improved power quality. The capacitors are installed in a distribution system on pole-mounted racks, substation banks, and high voltage (HV) or extra-high voltage (EHV) units for bulk power applications. Capacitors have many applications in power systems: they can be used in series to compensate the inductance of transmission lines to transmit more power. They can also be used as surge capacitors, starting motors, and static VAR compensators. Capacitor banks installed in power substations are vital in the sense that they provide the reactive power needed for the power system, which in turn improves the voltage profile in the system. There is always the option of grounding the banks or leaving them ungrounded. Each of the above configurations has its own advantages and disadvantages; to name a few, ungrounded banks are slightly more expensive compared to grounded banks as the neutral point needs to be insulated up to system basic insulation level; whilst grounded banks are prone to inject high-frequency transients (e.g., switching, ground faults) into the ground mat. This study is intended to address the recent incident in a high-voltage substation which led to the explosion of a capacitor bank. The study goes on to suggest grounding as a method to prevent such incidents. Furthermore, the effects of grounding and induction on control/signal cables as well as protecting relays are investigated

Ground fault current: Calculation of magnitude and its distribution in the neutral and ground paths

This thesis focuses on the ground fault current distribution and presents a method that enables a high accuracy in its calculation: starting from the model based on multi-conductor representation developed in Matlab, simulations are carried out to analyse which parameters influence the current distribution. These simulations, applied even on the portion of a real network, are also carried out on the commercial software Neplan and OpenDSS to validate the model

The effect of soil resistivity on the LV surge environment

Student Number : 0418388R - MSc(Eng) research report - School of Electrical and Information Engineering - Faculty of Engineering and the Built EnvironmentDue to the high soil resistivities and high frequency of lightning strikes in South Africa, the background theory about the effect of soil resistivity on the LV surge environment is important, but the present local and international standards do not give reasonable explanations for this effect. The previously published experimental results and research results related to this effect were investigated. From these investigations, it can be shown that the soil resistivity can affect surge generation, surge propagation and surge attenuation significantly. Also, soil resistivity plays a main role in the lightning surges caused by both direct strikes and indirect strikes, which can cause severe damage to the LV distribution system. Soil resistivity also has a significant impact on the resistance of an earth electrode

System data communication structures for active-control transport aircraft, volume 2

The application of communication structures to advanced transport aircraft are addressed. First, a set of avionic functional requirements is established, and a baseline set of avionics equipment is defined that will meet the requirements. Three alternative configurations for this equipment are then identified that represent the evolution toward more dispersed systems. Candidate communication structures are proposed for each system configuration, and these are compared using trade off analyses; these analyses emphasize reliability but also address complexity. Multiplex buses are recognized as the likely near term choice with mesh networks being desirable for advanced, highly dispersed systems

Contributions to Modeling and Simulation of HVAC Cables Using Field Test Results

RÉSUMÉ L'intérêt pour les câbles de transmission de puissance a augmenté au cours des dernières années avec des projets ayant lieu partout dans le monde. Cette tendance a motivé le développement de modèles de câble plus précis utilisés dans la simulation des transitoires électromagnétiques. Cette thèse aborde les différents domaines d'action associés à la modélisation et à la simulation des câbles à haute tension en courant alternative. Le premier champ d'action est la validation de modèles de câbles pour la simulation de transitoires électromagnétiques. La validation est basée sur des essais disponibles en tenant compte des différents paramètres et équipements. L’approche typique pour l'analyse des résultats d’essais consiste à extraire l'atténuation et la vitesse de l’onde ainsi que l'impédance caractéristique et à comparer ces valeurs à ceux du modèle. Cette approche permet de vérifier qu’un modèle de câble est précis, mais ne donne pas des indications sur les sources de divergence lorsque les résultats de l’essai et de la simulation ne sont pas en accord. Cette thèse présente une nouvelle approche pour la validation d'un modèle de câble pour la simulation des transitoires électromagnétiques, basée sur des résultats d’essais sur le terrain. L'innovation consiste à extraire les paramètres par unité de longueur du câble à partir des formes d'onde mesurées, plutôt que d'extraire seulement l'atténuation, la vitesse et l'impédance caractéristique. Ces données supplémentaires fournissent une base additionnelle pour l'analyse des résultats de l’essai et de la simulation. Le deuxième champ d'action de cette thèse est l'étude du phénomène de décharge naturelle des câbles. Bien que très peu d’essais de décharge se trouvent dans la littérature, ce phénomène est un sujet important pour les ingénieurs qui réalisent des tests sur des câbles à haute tension et pendant des travaux d'entretien. Récemment, le sujet de décharge a été le sujet de nouvelles considérations par certains gestionnaires de réseaux qui utilisent les câbles pour réguler la tension du réseau. Cette thèse contribue à l’étude des caractéristiques de décharge des câbles de type ‘papier imprégné d’huile sous pression’ à 275 kV.----------ABSTRACT The interest towards power transmission cables has increased in the recent years with projects taking place all over the world. This trend has motivated research for better understanding of phenomena associated with cables as well for more accurate cable models used in the simulation of electromagnetic transients (EMTs). This thesis addresses the different fields of action associated with the modeling and simulation of HVAC cables. The first field of action is the validation of cable models for the simulation of EMT’s. The most reliable validation method is based on comparison with field test results performed on actual cable system. Typically, the analysis of field test results consists of extracting the wave attenuation, velocity and surge impedance and comparing to those of the cable model. Although this approach allows verifying the cable model, it gives little insight into the sources of divergence when field test and simulations do not agree. This thesis presents a new method for validating a cable model for simulation of EMT’s based on surge field test results. The innovation consists of extracting per-unit-length (PUL) cable parameters from the measured waveforms, rather than simply extracting attenuation, velocity and characteristic impedance. This approach provides a broader base for analyzing field test and simulation results. The second field of action is the study of cable natural discharge. Although very few test results of cable charging and discharging can be found in the literature, this phenomenon is a matter of concern to cable engineers particularly when performing tests and during maintenance work. Recently, the charging/discharging phenomenon has received renewed consideration from utilities when using high-voltage (HV) cables for voltage control during periods of light load which requires nightly switching of cables. This thesis investigates discharging characteristics of 275 kV POF cables based on field and laboratory tests. The factors affecting the phenomenon, i.e. cable capacitance, leakage resistances of cable insulation and external insulators, are identified and typical values are provided. From these values, the time required to discharge a cable to safe voltage limits (25 V according to IEC 60479-1) is calculated. A correction factor to account for the impact of relative air humidity on the leakage resistance of external insulators is proposed. The results of this study can be applied to the design of cable protections and to evaluate the need for special discharge equipment

Utilisation of line surge arrestors to improve overhead HVAC and EHVDC line performance under lightning conditions.

Doctoral Degree. University of KwaZulu-Natal, Durban.In high lightning areas, lightning strokes play an important role in the performance of overhead EHV AC and DC lines. A single lightning stroke, that terminate on the earth wire and/or tower can lead to back flashovers. This flashover depends on factors such as conductor type, tower, soil resistivity and magnitude of the stroke. The flashover across the insulator and the resultant fault current surge will propagate along the line, until it is extinguished or the breaker operates. This movement of the surge currents tend to damage and reduce the life span of associated equipment such and circuits breakers, insulators, transformers and impact network performance adversely. Furthermore, this operation of the protective devices leads to power interruption to consumers on that network, and loss of production, thus negatively impacting the economy. This thesis investigates the incidences of network failure due to lightining strokes occuring on Eskom HVAC network as well as HVDC networks, considering soil resistivity, tower footing resistance and factors that influence the earthing resistances. Tower footing resistance needs to be kept uniform and as low as possible to extinguish the surge across the tower and hence reducing the back flashovers across the insulator under lightning conditions. Theoretical simulations were conducted on the different methods that are available to improve the tower footing resistance values. A case study was undertaken to ascertain the tower footing resistance of an 88kV Eskom line. The crows earthing configuration was then utilized to reduce the footing resistance to a value less than 30 ohms, using line surge arrestors (LSA) which are devices that can drain power surges to ground, if placed adequately and in sufficient numbers. Furthermore the thesis determines the relationship between the magnitude of the lightning stroke, the tower top voltage, tower footing resistance and hence the back flashover voltage that would appear on the line, which would lead to power interruptions. Surge arrestors were modelled using MATLAB software. The required number of surge arrestors per phase is thus determined that is required to drain the surge current down to earth., thus preventing power interruptions. EHV AC and DC cases studies are simulated and results are presented snd discussed.Publications listed on page iii

Power system applications of fiber optics

Power system applications of optical systems, primarily using fiber optics, are reviewed. The first section reviews fibers as components of communication systems. The second section deals with fiber sensors for power systems, reviewing the many ways light sources and fibers can be combined to make measurements. Methods of measuring electric field gradient are discussed. Optical data processing is the subject of the third section, which begins by reviewing some widely different examples and concludes by outlining some potential applications in power systems: fault location in transformers, optical switching for light fired thyristors and fault detection based on the inherent symmetry of most power apparatus. The fourth and final section is concerned with using optical fibers to transmit power to electric equipment in a high voltage situation, potentially replacing expensive high voltage low power transformers. JPL has designed small photodiodes specifically for this purpose, and fabricated and tested several samples. This work is described

Power quality and electromagnetic compatibility: special report, session 2

The scope of Session 2 (S2) has been defined as follows by the Session Advisory Group and the Technical Committee: Power Quality (PQ), with the more general concept of electromagnetic compatibility (EMC) and with some related safety problems in electricity distribution systems. Special focus is put on voltage continuity (supply reliability, problem of outages) and voltage quality (voltage level, flicker, unbalance, harmonics). This session will also look at electromagnetic compatibility (mains frequency to 150 kHz), electromagnetic interferences and electric and magnetic fields issues. Also addressed in this session are electrical safety and immunity concerns (lightning issues, step, touch and transferred voltages). The aim of this special report is to present a synthesis of the present concerns in PQ&EMC, based on all selected papers of session 2 and related papers from other sessions, (152 papers in total). The report is divided in the following 4 blocks: Block 1: Electric and Magnetic Fields, EMC, Earthing systems Block 2: Harmonics Block 3: Voltage Variation Block 4: Power Quality Monitoring Two Round Tables will be organised: - Power quality and EMC in the Future Grid (CIGRE/CIRED WG C4.24, RT 13) - Reliability Benchmarking - why we should do it? What should be done in future? (RT 15