Fault Location and Incipient Fault Detection in Distribution Cables

A set of fault location algorithms for underground medium voltage cables, two incipient fault detection schemes for distribution cables and a state estimation method for underground distribution networks are developed in this thesis. Two schemes are designed to detect and classify incipient faults in underground distribution cables. Based on the methodology of wavelet analysis, one scheme is to detect the fault-induced transients, and therefore identify the incipient faults. Based on the analysis of the superimposed fault current and negative sequence current in time domain, the other scheme is particularly suitable to detect the single-line-to-ground incipient faults, which are mostly occurring in underground cables. To verify the effectiveness and functionalities of the proposed detection algorithms, different fault conditions, various system configurations, real field cases and normal operating transients are examined. The simulation results have demonstrated a technical feasibility for practical implementations of both schemes. Based on the methodology of the direct circuit analysis, a set of location algorithms is proposed to locate the single phase related faults in the typical underground medium voltage cables. A large number of complex nonlinear equations are effectively solved to find the fault distance and fault resistance. The algorithms only utilize the fundamental phasors of three-phase voltages and currents recorded at single end, normally at substation. The various system and fault conditions are taken into account in the development of algorithms, such as effects of shunt capacitance, mutual effects of metallic sheaths, common sheath bonding methods and different fault scenarios. The extensive simulations have validated the accuracy and effectiveness of the proposed algorithms. In order to extend the proposed fault location algorithms to underground distribution networks, a state estimation algorithm is developed to provide the necessary information for the location algorithms. Taking account of the complexity and particularity of cable circuits, the problem of the state estimation is formulated as a nonlinear optimization problem that is solved by the sequential quadratic programming technique. The simulation studies have indicated that the proposed fault location scheme incorporating with the state estimation algorithm can achieve good performance under different load and fault conditions

Underground distribution cable incipient fault diagnosis system

This dissertation presents a methodology for an efficient, non-destructive, and online incipient fault diagnosis system (IFDS) to detect underground cable incipient faults before they become catastrophic. The system provides vital information to help the operator with the decision-making process regarding the condition assessment of the underground cable. It incorporates advanced digital signal processing and pattern recognition methods to classify recorded data into designated classes. Additionally, the IFDS utilizes novel detection methodologies to detect when the cable is near failure. The classification functionality is achieved through employing an ensemble of rule-based and supervised classifiers. The Support Vector Machines, designed and used as a supervised classifier, was found to perform superior. In addition to the normalized energy features computed from wavelet packet analysis, two new features, namely Horizontal Severity Index, and Vertical Severity Index are defined and used in the classification problem. The detection functionality of the IFDS is achieved through incorporating a temporal severity measure and a detection method. The novel severity measure is based on the temporal analysis of arrival times of incipient abnormalities, which gives rise to a numeric index called the Global Severity Index (GSI). This index portrays the progressive degradation path of underground cable as catastrophic failure time approaches. The detection approach utilizes the numerical modeling capabilities of SOM as well as statistical change detection techniques. The natural logarithm of the chronologically ordered minimum modeling errors, computed from exposing feature vectors to a trained SOM, is used as the detection index. Three modified change detection algorithms, namely Cumulative Sum, Exponentially Weighted Moving Averages, and Generalized Likelihood Ratio, are introduced and applied to this application. These algorithms determine the change point or near failure time of cable from the instantaneous values of the detection index. Performance studies using field recorded data were conducted at three warning levels to assess the capability of the IFDS in predicting the faults that actually occurred in the monitored underground cable. The IFDS presents a high classification rate and satisfactory detection capability at each warning level. Specifically, it demonstrates that at least one detection technique successfully provides an early warning that a fault is imminent

Comparative detection and fault location in underground cables using Fourier and modal transforms

In this research, we create a single-phase to ground synthetic fault by the simulation of a three-phase cable system and identify the location using mathematical techniques of Fourier and modal transforms. Current and voltage signals are measured and analyzed for fault location by the reflection of the waves between the measured point and the fault location. By simulating the network and line modeling using alternative transient programs (ATP) and MATLAB software, two single-phase to ground faults are generated at different points of the line at times of 0.3 and 0.305 s. First, the fault waveforms are displayed in the ATP software, and then this waveform is transmitted to MATLAB and presented along with its phasor view over time. In addition to the waveforms, the detection and fault location indicators are presented in different states of fault. Fault resistances of 1, 100, and 1,000 ohms are considered for fault creation and modeling with low arch strength. The results show that the proposed method has an average fault of less than 0.25% to determine the fault location, which is perfectly correct. It is varied due to changing the conditions of time, resistance, location, and type of error but does not exceed the above value

Partial discharge pulse propagation in power cable and partial discharge monitoring system

Partial discharge (PD) based condition monitoring has been widely applied to power cables. However, difficulties in interpretation of measurement results (location and criticality) remain to be tackled. This paper aims to develop further knowledge in PD signal propagation in power cables and attenuation by the PD monitoring system devices to address the localization and criticality issues. As on-line or in-service PD monitoring sensors commonly comprise of a high frequency current transformer (HFCT) and a high-pass filter, the characteristics of detected PD pulses depend on the attenuation of the cable, the HFCT used and the filter applied. Simulation of pulse propagation in a cable and PD monitoring system are performed, based on analyses in the frequency domain using the concept of transfer functions. Results have been verified by laboratory experiments and using on-site PD measurements. The knowledge gained from the research on the change in pulse characteristics propagating in a cable and through a PD detection system can be very useful to PD denoising and for development of a PD localization technique

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

The concept of leadership and constitution of a country from the Islamic and Malay archipelago perspectives according to Taj Al Salatin manuscript

The concept of leadership has been present eversince the dawn of time, with scholars steering broad studies from various directions and viewpoints, which were then formed into literary works. In the Malay Archipelago, Taj al-Salatin manuscript (1603M) is extensively recognised as a masterwork that emphasised leadership qualities from the Islamic viewpoint. This study was conducted to recognise the author’s notions on Islamic leadership in the context of Malay Archipelago, using descriptive method by analysing the manuscript. The results revealed that leaders and leadership are deliberated, as a decree from Allah SWT. Good rulers must be competent, with higher knowledge and morals than their followers. Taj al-Salatin presents the indication that rulers should exercise Tasawwuf, which among its practises take account of unceasing self reminder of death, rejecting desires and lust, and prioritising remembrance of Allah. In his manuscript, Bukhari al-Jauhari presents the idea, optimism and the notion of “rulers are perfect beings”, which personifies the concept of Tauhid and espouses noble character for universal civilisation. A ruler of a country should at all times stand on the grounds of good moral standards and the people are led towards generating a peaceful, thriving and blissful nation

Electrical Characterization of Arcing Fault Behavior on 120/208V Secondary Networks

Arcing faults have been a persistent problem on power systems for over one hundred years, damaging equipment and creating safety hazards for both utility personnel and the public. On low-voltage secondary networks, arcing faults are known to cause specific hazards collectively called "manhole events", which include smoke and fire in underground structures, and in extreme cases explosions. This research provides the first comprehensive attempt to electrically characterize naturally occurring arcing fault behavior on 120/208V secondary networks. Research was performed in conjunction with the Consolidated Edison Company of New York, whereby a single low-voltage network was instrumented with thirty high-speed, high-fidelity data recording devices. For a nominal one year period, these devices collected detailed, high-speed waveform recordings of arcing faults and other system transients, as well as statistical power system data, offering new insights into the behavior of arcing faults on low-voltage networks. Data obtained in this project have shown the intensity, persistence, and frequency of arcing faults on low-voltage networks to be much higher than commonly believed. Results indicate that arcing faults may persist on a more-or-less continuous basis for hours without self-extinguishing, may recur over a period of hours, days, or weeks without generating enough physical evidence to be reported by the public or operate conventional protective devices, and may draw enough current to be observed at the primary substation serving the network. Additionally, simultaneous fault current measurements recorded at multiple locations across the network suggest the possibility of using multi-point secondary monitoring to detect and locate arcing faults before they cause a manhole event