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Bi, Suzhi. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 113-119). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Improving the functioning and the safety of the electrical grids is a topic of great concern, given its magnitude and importance in today's world. In this thesis, we focus in these two subjects. In the first part, we study undetectable cyber-physical attacks on power grids, which are attacks that involve physical disruptions, including tripping lines and load modifications, and sensor output alterations. We propose a sophisticated attack model described under the full Alternating Current (AC) power flow equations and show its feasibility on large grids from a test cases library. As counter-measures, we propose different defensive strategies that the network's controller can apply under a suspected cyber attack. These are random, simple and fast procedures that change the voltages across the network and aim to unmask the current status of the system, assuming that the attacker cannot react against their randomness. Secondly, with access to data collected through Phasor Measurement Units (PMUs) by a power utility in the United States, we perform statistical analyses on the frequency and voltage time series that have been recorded at a rate of 30 Hz. We focus on intervals of time where the sampled data shows to be in steady-state conditions and, with the use of appropriate signal processing filters, we are able to extract hidden anomalies such as spatio-temporal correlations between sensors and harmonic distortions.

Electric power systems are among the most complex man made systems on the world. Most of the time, they operate under quasi-steady state. With the ever increasing load demand and the advent of the deregulated power market recently, the power systems are pushed more often to operate close to their design limits and with more uncertainty of the system operating mode. With the increasing complexity and more interconnected systems, power systems are operating closer to their performance limits. As a result, maintaining system security and facilitating efficient system operation have been challenging tasks. Transmission systems are considered the most vital components in power systems connecting both generating/substation and consumer areas with several interconnected networks. In the past, they were owned by regulated, vertically integrated utility companies. They have been designed and operated so that conditions in close proximity to security boundaries are not frequently encountered. However, in the new open access environment, operating conditions tend to be much closer to security boundaries, as transmission use is increasing in sudden and unpredictable directions. Transmission unbundling, coupled with other regulatory requirements, has made new transmission facility construction more difficult. Unfortunately these transmission lines are frequently subjected to a wide variety of faults. Thus, providing proper protective functions for them is essential. Generally the protection of Extra High Voltage (EHV) and Ultra High Voltage (UHV) transmission lines are carried out by the use of distance relays in view of the fact that they provide fast fault clearance and system coordination. Transmission line relaying involves detection, classification and location of transmission line faults. Fast detections of faults enable quick isolation of the faulty line from service and hence, protecting it from the harmful effects of fault. Classification of faults means identification of the type of fault and faulted line section, and this information is required for finding the fault location and assessing the extent of repair work to be carried out. Accurate fault location is necessary for facilitating quick repair and restoration of the line, to improve the reliability and availability of the power supply. Generally, the protection system using conventional distance relaying algorithm involves three zones. The first zone (Z1) of the relay is set to detect faults on 80%90% of the protected line without any intentional time delay. The second zone (Z2) is set to protect the remainder of the line plus an adequate margin. Second zone relays are time delayed for 1530 cycles to coordinate with relays at remote bus. The settings of the third zone (Z3) ideally will cover the protected line, plus all of the longest line leaving the remote station. Z3 of a distance relay is used to provide the remote backup protection in case of the failure of the primary protection. Since Z3 covers an adjacent line, a large infeed (outfeed) from the remote terminal causes the relay to underreach (overreach). Thus, a very large load at the remote terminal may cause distance relays to mal-operate. Settings for conventional distance relays are selected to avoid overreach/underreach operation under the worst case scenarios. Studies of significant power system disturbances reported by North American Electric Reliability Council (NERC) indicate that protective relays are involved, one way or another, in 75% of the major disturbances and the most troublesome ones are backup protection relays. With their limited view of the interconnected network based on their locally measured inputs, conventional backup protection relays generally take actions to protect a localized region of the network without considering the impact on the whole network. Relay mal-operations or unintended operations due to overload, power swing, and relay hidden failure are the main factors contributing to the blackouts. Most of the problems are associated with relays tripping too many healthy lines. Since a relay makes the decision automatically to remove a component from the system according to its internal mechanism, the relay mal-operation or unintended operation can make an effective influence on the system stability. Approaches to reduce the relay misbehavior need to be identified. Real time monitoring tools to assess the relay misbehavior are needed, providing the system operator, the accurate information about unfolding events. Existing transmission line protection scheme still has drawbacks. Advanced fault analysis mechanism to enhance the system dependability and security simultaneously is desirable. Relay settings play a significant role in major blackouts. So correct settings should be calculated and coordinated by suitable studies. Attempts are to be made to employ highly accurate AI techniques in protective system implementation. The research work focussed on developing knowledge based intelligent tools for the improving the transmission system security. A process to obtain knowledgebase using SVMs for ready post-fault diagnosis purpose is developed. SVMs are used as Intelligent tool for identifying the faulted line that is emanating from a substation and finding the distance from the substation. The approach uses phasor values of the line voltages and currents after the fault has been detected. The approach is particularly important for post-fault diagnosis of any mal-operation of relays following a disturbance in the neighboring line connected to the same substation. This may help in improving the fault monitoring/diagnosis process and coordination of the protective relays, thus assuring secure operation of the power systems. The approach based on SVMs, exploits the first part of this goal. For comparison, a classifier and regression tools based on the RBFNNs was also investigated. The RBFNNs and SVM networks are introduced and considered as an appropriate tool for pattern recognition problems. Results on a practical 24Bus equivalent EHV transmission system of Indian Southern region and on IEEE39 bus New England system are presented to illustrate the proposed method. In a large connected power network, the number of generators are more in number and their set patterns number will be large. As the line flows are sensitive to generator set patterns, it is difficult to consider all the combinations of generators while simulating the training and testing patterns as input to SVMs. To simulate the training and testing patterns corresponding to possible changes in line flows to meet the load in the present deregulated environment, line flow sensitive generators set to be identified/merit-listed. In this regard, to identify the most sensitive generators for a particular line of interest, a method from the literature is adopted and developed a software program based on the graph theory concepts. Case studies on generator contributions towards loads and transmission lines are illustrated on an equivalent 33bus system, a part of Indian Northern grid with major part of Uttar Pradesh and also with an equivalent 246bus system of practical Indian Southern grid. A distance relay coordination approach is proposed using detailed simulation studies, taking into account various operating conditions and fault resistances. Support Vector Machines as a pattern classifier is used for obtaining distance relay coordination. The scheme uses the apparent impedance values observed during fault as inputs. SVMs are used to build the underlying concept between reach of different zones and the impedance trajectory during fault. An improved performance with the use of SVMs, keeping the reach when faced with different fault conditions as well as line flow changes are illustrated with an equivalent 246bus system of practical Indian Southern grid and also with an equivalent 265bus system of practical Indian Western grid. A strategy of Supportive System is described to aid the conventional protection philosophy in combating situations where protection systems are mal-operated and/or information is missing and provide selective and secure coordination. Highly accurate identification/discrimination of zones plays a key role in effective implementation of the region-wide supportive system. This typically requires a multiclass SVM classifier to effectively analyze/build the underlying concept between reach of different zones and the apparent impedance trajectory during fault. Different multiclass methods are compared for their performance with respect to accuracy, number of iterations, number of support vectors, training and testing time. The performance analysis of these methods is presented on three data sets belonging to the training and testing patterns of three supportive systems for a region, part of a network, which is an equivalent 265bus system of practical Indian Western grid.

Text in English, with English, Afrikaans and Zulu summaries / This study was conducted owing to the protracted problem and challenges that unauthorised electrical connections pose to electricity utilities. This study sought to contribute to the combating of unauthorised electrical connections in KwaZulu-Natal, South Africa, which has never before been studied in this manner. Considerable revenue is stolen from utilities because of unauthorised electrical connections, by-passing of electrical meters and tampering with electricity networks. This contributes to public safety risks, fatalities, property damage and overloading of electrical networks. This in turn causes transformer and electricity network overload and power supply failure, prolonged unplanned power cuts, loss of jobs, food security risk, serious poor economic development, damaged electrical infrastructure, loss of revenue, electricity disruptions, electric shock, and the burning of dwellings. This leads to the interruption of supply to legal and compliant customers, all with disastrous effects. It is therefore difficult to manage the supply and demand of electricity under these circumstances, more especially in this period when South Africa faces a tight electricity supply. In this dissertation, the international and national perspectives reveal the nature and extent of unauthorised electrical connections. It was explored how unauthorised electrical connections are presently being combated and what specific security measures may be implemented to enhance the combating of unauthorised electrical connections. A case study design was used to investigate in greater detail the opinions, views, perceptions and experiences of the targeted interviewees using interviewing, site observation and case docket analysis. This design guided the use of specific sample groups, procedures and techniques used for data collection and analysis. The design and development of the different data collection instruments and the piloting of the instruments were implemented to ensure validity, reliability, accuracy and trustworthiness of the collected information. The study produced findings to assist electricity utilities to better manage this phenomenon. Recommendations were formulated to assist stakeholders to improve their roles in the combating of unauthorised electrical connections. / Hierdie studie is uitgevoer na aanleiding van die uitgerekte probleem en uitdagings van onwettige elektrisiteitsverbindings vir elektrisiteitsvoorsieners. Hierdie studie poog om by te dra om onwettige elektrisiteitsverbindings in KwaZulu-Natal, Suid-Afrika te beveg; dit is nog nooit tevore op hierdie wyse ondersoek nie. Beduidende inkomste word van diensmaatskappye gesteel as gevolg van onwettige elektrisiteitsverbindings, die wat elektriese meters omseil en met elektrisiteitsnetwerke peuter. Dit dra tot openbare veiligheidsrisiko's, fataliteite, skade aan eiendom, en oorlading van elektrisiteitsnetwerke by. Dit lei weer tot oorlading van transformators en elektrisiteitsnetwerke, gebrek aan kragvoorsiening, verlengde onbeplande kragonderbrekings, werksverlies, voedselsekuriteitrisiko, ernstige swak ekonomiese ontwikkeling, skade aan elektrisiteitinfrastruktuur, verlies aan inkomste, elektriese skok, en huise wat afbrand. Dit lei tot die onderbreking van voorsiening aan wetlike en inskiklike klante met rampspoedige gevolge. Dit is dus moeilik om voorsiening en vraag na elektrisiteit in hierdie omstandighede te bestuur, veral in hierdie tyd wat Suid-Afrika drukkende elektrisiteitvoorsiening beleef. In hierdie verhandeling onthul die internasionale en nasionale perspektiewe die aard en mate van onwettige elektrisiteitsverbindings. Dit was ondersoek hoe onwettige elektrisiteitsverbindings tans beveg word en watter spesifieke veiligheidsmaatreëls geïmplementeer kan word om die bevegting van onwettige elektrisiteitsverbindings te bevorder. Die gevallestudie-ontwerp is gebruik om die onderhoudgewers se menings, sienings, perspektiewe en ervarings in meer besonderhede te ondersoek deur onderhoude, waarnemings en saakdossierontledings te gebruik. Die ontwerp het die gebruik van spesifieke steekproefgroepe, prosedures en tegnieke wat vir dataversamelings en -ontleding gebruik is, gerig Die ontwerp en ontwikkeling van die verskillende dataversamelinginstrumente en die bestuur van die instrumente is geïmplementeer om geldigheid, betroubaarheid, akkuraatheid en geloofwaardigheid van die versamelde inligting te verseker. Die studie se bevindings help elektrisiteitsdienste om hierdie verskynsel beter te bestuur. Aanbevelings is geformuleer om belanghebbers te help om hul rolle te bevorder in die stryd om onwettige elektrisiteitsverbindings te beveg. / Ucwaningo lwenziwa ngenxa yokubona inkinga egxilile neqhubekela phambili kanye nezinselele ezibangelwa ukuzixhumela ama-connection kagesi (i-elektrisithi) maqondana nezinkampani zikagesi. Ucwaningo belufuna ukufaka esivivaneni kudaba lokuvimbela ukuzixhumela kogesi ngendlela engekho emthethweni eKwaZulu-Natali, eNingizimu Afrika, yona okungakaze kwenziwe ucwaningo ngayo ngale ndlela. Kunengeniso eliningi lemali entshontshwa ngale ndlela kwizinkampani noma izinhlangano zikagesi ngoba kunokuzixhomela ugesi okungekho emthethweni, ukungasetshenziswa kwamamitha ogesi, kanye nokuphazamisa ama-network kagesi. Lokhu kubangela izingozi nokungavikeleki kubantu bonke, ukulimala, ukulinyazwa nokonakala kwempahla noma iprophathi kanye nokuthi ama-network kagesi agxisheleke nokucindezeleka ngokweqile. Kanti futhi lokhu kubanga ukuthi ama-transformer kanye nama-network kagesi acindezeleke ngokweqile nokwenza ukuthi isaplayi kagesi ihluleke nokufeyila, lokhu okubangela ukuthi kube nama-power cuts noma ukucishwa kukagesi okungahleliwe, ukulahleka kwemisebenzi, ingozi yokuphazamiseka kokuvikeleka kokudla, ukuthi ukuthuthuka komnotho kuphazamiseke kakhulu, ukulahleka kwengeniso lemali, ukuphazamiseka kokuphakelwa kukagesi, ukulinyazwa kwabantu ngokubanjwa ugesi, kanye nokusha kwemizi eshiswa ugesi. Lokhu kuholela ekutheni kuphazamiseke isaplayi kagesi kumakhastama akhokha kahle nenza izinto ngokulandela umthetho, lokhu okubanga imiphumela yezinhlekelele ezimbi. Ngakho-ke kuba nzima ukubhekana kanye nezinto zesaplayi kanye nokudingeka kukagesi ngaphansi kwalezi simo, ikakhulukazi lapho iNingizimu Afrika ibhekene nokuncipha noma izinga eliphansi lesaplayi kagesi. Kule dissertation isimo sikazwelonke kanye nesamazwe omhlaba, siveze inhlobo kanye nezinga lokuxhunyelwa kukagesi okungekho emthethweni. Kubuye kwabheka nokuthi ukuxhunyelwa kukagesi okungekho emthethweni kubhekwana kanye nokuvinjelwa kanjani, nokuthi yiziphi izindlela eziqondene ezisetshenziswayo zokuvikeleka ezingasetshenziswa ukuthuthukisa izinqubo zokuvimbela ukuxhunyelwa kukagesi nama-connection angekho emthethweni angavinjelwa kanjani . Kusetshenziswe idizayini ye-case study ukuphenyisisa ngokujulile imininingwane, imibono, izinqubo zokubheka isimo kanye nezipiliyoni zalabo obekuqondiswe kubo ama-interview ngesikhathi kwenziwa ama-interview, ukuyobheka ngamehlo esimo ezindaweni, kanye nokuhlaziya amadokhethi amacala ngokwenzekayo. Le dizayini yiyona eholele ekusetshenzisweni kwamasampuli amaqembu athize, izinqubo noma amaprosija athize kanye namathekniki athize asetshenzisiwe ekuqoqeni kwe-data kanye nohlaziyo lwayo. Idizayini nokwenziwa kwama-instrumenti okuqoqwa kwe-data ehlukene, kanye nokwenza ama-instrumenti okulinga noma e-piloting, kusetshenzisiwe ukuqinisekisa i-validity, ukuthembeka (reliability), ukuqondana ncamashi kwama-instrumenti (accuracy) kanye nokuqiniseka okubizwa ngokuthi yi-trustworthiness yolwazi noma i-infomeshini eqoqiwe. Ucwaningo, lukhiphe imiphumela yokusiza izinkampani noma izinhlangano zikagesi ekuphatheni kangcono le nkinga noma ifenominoni (phenomenon) yenkinga. Kwenziwe izincomo zokusiza ababambe iqhaza (stakeholders) ukuthuthukisa indima yabo ekulwiseni ukuxhunyelwa kanye nama-connection kagesi angekho emthethweni. / Criminology and Security Science / M. Tech. (Security Management)