Waveshape Detection Technique to Supervise Transformer Differential Protection

One of the areas of concern that greatly affects the reliability of a power transformer protection includes the failure of the protection scheme to discriminate between a fault and a non-fault condition which can result in either the tripping of a transformer when there is no fault or the failure to trip the transformer under genuine fault conditions. The inability of a protection scheme to detect internal faults can lead to abnormal overheating in turn leading to premature failure of the transformer. To improve the reliability of the power transformer protection with regards to protection maloperation, this article investigates the performance of the waveshape detection technique which operates in the time domain to improve transformer protection maloperation associated with harmonic measurement in the transformer differential current. A MATLAB model was developed to demonstrate how the waveshape detection algorithm can be used to improve transformer differential protection maloperation challenges associated with pure inrush conditions and transformer energization onto a fault. The second harmonic blocking scheme is evaluated in MATLAB and used as a reference to assess the effectiveness of the waveshape detection technique. The results obtained show that the shortcomings of the traditional harmonic blocking schemes can be alleviated by the waveshape detection technique.