Translated Abstract
Large oil-immersed power transformer, as one of the most significant and costly electrical equipment of electric power system, plays a very important role in high voltage transmission and distribution system, and its security and reliability have a straight impact on the safety and stability of power system. It is well acknowledged that, under the circumstance of limited level of the apparatus design and manufacture, a better maintenance technique is the optimized way of promoting its security and life extension. Accordingly, Condition Based Maintenance (CBM) is universally popularized and becomes the trend of equipment maintenance and asset management for the following outstanding advantages: (a) comparatively accurately assessing transformer’s current condition (b) contributing to maintenance strategy making (c) avoiding equipments under-maintenance or over-maintenance, therefore a great deal of workload and expenditure being well saved (d) redounding to transformer’s lifetime extension (e) promoting reliability and lowering operating risk. Even though, however, as the transformer is one of the most complicated facilities and its fault and aging mechanism are still not totally clear, needing for further research, the present assess system and techniques for transformer CBM are still deficiently capable of accurately evaluating its actual condition for limited operational time span and lack of enough experiences.
This thesis summarizes the newly development and achievement of CBM for transformers, domestically and abroad, and addresses their separate advantages and disadvantages. Further, Heath Index (HI) methodology for CBM of transformer is developed. The methodology combines not only online and offline field test data, but also inspection and history load information, to establish assess system. Moreover, to deal with the disadvantage that the results obtained by present CBM system remain constant in a certain period, lots of research work on the relationship between operational parameters, load and oil temperature for instance has been done in this thesis. And the dynamic assess factor based on relationship between load and oil temperature is proposed, aiming to obtain its better real time condition.
Nowadays, as the increasing competition in the electric power market, the operational risk evaluation technology gains more concerns than ever. Not only transformer’s condition, namely fault probability, but also its profound impacts being well considered, the thesis brings in Fault Model and its Effect Analysis (FMEA) to anatomize transfomer’s all sorts of faults and corresponding effects, aiming at helping to figure out what to do in maintenance strategy. After conducting the status assessing procedure of target transfomer with four categories, and their corresponding reliability index and economic index are both calculated, which help to attain an opitimized maintenance strategy. It is believed that, under the condition of a controllable and acceptable system reliability, a maintenance plan which costs lower and gains higher can be expected to obtain. The methodologies developed by this thesis are proved to be useful through initial calculation and are expected to contribute to better maintenance strategy making.
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