Thesis (M.S.)--University of Wisconsin--Madison. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 125-127).

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A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering, 2015 / Electrical utilities are tasked with managing large numbers of assets that have long useful lives and are fairly expensive to replace. With emphasis on medium voltage vacuum circuit breakers, a key challenge is determining when circuit breakers are close to their end-of-life and what the appropriate action at that point in time should be. Condition-based maintenance, intended to “do only what is required, when it is required,” has been reported as the most effective maintenance strategy for circuit breakers. This dissertation provides an overview, together with laboratory measurements, on non-intrusive technologies and analytics that could reduce maintenance costs, unplanned outages, catastrophic failures and even enhance the reliability and lifetime of circuit breakers by means of a real-time condition monitoring and effective failure prevention maintenance approach. The key areas of research are the condition assessment of the mechanical mechanism based on coil current signature diagnosis, degradation detection of the main interrupting contacts through thermal monitoring and interrupter vacuum integrity assessment based on magnetron atmospheric condition (MAC) testing. The information from test results allows both immediate onsite analysis and trending of key parameters which enables informed asset management decisions to be taken. / GS2016

For predictive maintenance of circuit breakers, a number of variables must be considered in order to assess the genuine working condition of a circuit breaker [CB]. This thesis selects vibration signatures obtained on the operating mechanisms and arcing chambers as a source of monitoring breaker conditions. The task of analyzing the behavior of a circuit breaker is perennial and difficult but the thesis has an attempt to tackle this problem. Experiments have been devised to monitor CBs; however, these have limitations details of which will be discussed. For example, each circuit breaker has its own unique vibration signature and the shape of the vibration may be different even though breakers confront similar problems. CBs have decades-long service life spans and failure rates are relatively low. Those that fail are not necessarily saved and there have been relatively few samples to base evidence upon. There are different vibration analysis algorithms available including Dynamic Time Warping [DTW], Resolution Ratio [RR], Discrete Envelope Statistics [DES], event time extraction, Chi-square based shape methods, and fractal theory. Some of these algorithms are based on acoustic properties of materials and rely on assessing extracted time component and the frequency components are extracted. This research applies multi-resolution analysis [MRA] to decomposed signals to in order to assess different sub-wave levels so that wave features may be captured and modeled. There are many ways to analyze the waves. This thesis uses optimizing fuzzy rules with genetic algorithm [GA] as the proposed method. The simuation part of the thesis uses spring performance as an example of how vibration signature analysis may be implemented. Spring vibrations are evaluated by two classification algorithms: Dynamic Time Warping [DTW] and multi-resolution analysis [MRA] with optimizing fuzzy rules with genetic algorithm [GA]. The first method is competent to identify the faulty cases from the normal ones by looking at the deviation of the vibration signature frequency content. In contrast, it is not capable to identify the degree of how bad it performs from looking at the frequency variation. For the second method, it is capable of not only classifying the abnormal cases from the normal cases, but also distinguishing the vibration signatures into different category so that the spring condition can be retrieved immediately. Fuzzy rules is capable of classify a new case to a category and genetic algorithm is an effective tool to minimize the applicable fuzzy rules. The accuracy of the identification is very satisfactory, which is over 90%. Consequently, the proposed algorithm is very useful for asset management purpose of breaker since the lifespan of the spring is known. Diagnostic technicians are able to make decision on the replacement scheme of the spring. There are some areas that this research uncovered that suggests further study is mandated. For example, there are other parameters that can be monitored and compared other than spring constant such as valve position in trip coil and close coil, acceleration parameter in changeover valves, damping in hydraulic cylinders and mechanical linkages, gas pressure in primary contacts and breaker resistance in line system.

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Interruption of DC is more challenging than that of AC because of the absence of DC zero-crossings. This thesis proposes an alternative counter-voltage (ACV) DC hybrid circuit breaker (DC-HCB). This DC-HCB can interrupt the DC up to 5 kA with the source voltage of up to 1 kV and it can meet the general requirements i.e., interrupting the DC within 5ms, and limiting over-voltages due to the CB operation. The existing/investigated DC circuit breakers, i.e., active mode DC-HCB and the traditional counter-voltage (TCV) DC-HCB are also investigated and compared with the proposed DC-HCB. The investigations are based on the time-domain simulation studies in the PSCAD/EMTDC. The studies show that the ACV DC-HCB is the preferred option to both the existing DC-HCBs. The main features of the proposed ACV DC-HCB include lower capacitance in the commutation path and the need for a smaller dielectric strength for the primary-path circuit breaker.

Thesis (M.S)--Florida State University, 2004. / Advisor: Dr. Hui Li, Florida State University, College of Engineering, Dept. of Electrical and Computer Engineering. Title and description from dissertation home page (viewed May 20, 2005). Includes bibliographical references.

The objective of this research project was to develop and implement a model for an A.C circuit breaker in the Electromagnetic Transients Program (EMTP). Various models for the arcing process were evaluated, and the modified Mayr equation was chosen for the model. Other equations were added to demonstrate the generality of the algorithm developed. Since the Electromagnetic Transients Program was not designed to accommodate directly elements whose resistance varies with time, such as an electric arc, several strategies for interfacing the model with the program were studied. The compensation method was selected, and was used for interfacing the circuit breaker model with the program. After implementation of the model, it was validated by comparing its performance with experimentally verified results reported previously. In order to render the model more practical, an auxiliary breaker parameter estimation routine was developed and tested. / M.S.