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Abstract
Transformers may be damaged due to either internal or external fault conditions. Internal faults includes turn to turn faults (shorts between turns) or between turns and the core of the transformer or the transformer tank, whereas the effects of these faults depends mainly on their positions on the winding. External faults refer to those circumstances that happen outside the transformer itself and may affect the transformer condition remarkably. Different factors can participate in these situations such as external transmission faults, high operating temperatures, lightning (surges), overloading, lack of Cleanliness …. etc. The aim of this thesis is to propose a novel winding fault detector for power transformer protection based on its electromagnetic equations. Unlike other similar algorithms, the proposed method depends on the available measurements at the transformer terminals. The core of the proposed detector is based on electromagnetic equations of parameters which can be derived directly from open- and short-circuit tests, resulting in a practical, reliable and versatile fault detector for power transformers.
A detailed modeling of power transformer faults is presented. The auxiliary routine BCTRAN of the EMTP is employed to generate the transformer parameters from the standard test data. Then, a method to alter the generated parameters to account for the power transformer internal faults, turn to-earth, and turn-to-turn faults is outlined. A proposed simplified equation to estimate the leakage factor is introduced. A step by- step development of an example for deriving a winding fault model of a practical power transformer with full test data is given and investigated.
The internal fault simulation results was verified and corroborated using an experimentally laboratory transformer connected to DS1003 DSP sub-system.
The proposed protection scheme employs the measurable voltage and current signal quantities at both primary and secondary sides of the transformer to discriminate the normal and abnormal operating conditions from the faulty conditions.
The main features of this scheme were examined using the experimental laboratory transformer associated with the DPS sub-system. The results revealed that the detector can successfully discriminate all internal faults in the transformer winding including ground faults, phase faults, turn-turn faults and high impedance faults.
The universality of the proposed scheme was justified by investigating its performance with different sizes of power transformers covering a wide range of their power ratings. All applied test results corroborate the superior performance of the proposed method.