Application of EMD and STFT Methods in Analysis of Energization of an Unloaded Overhead Line Under Different Operating Conditions

Maintaining of voltage conditions recommended by EN 50160 Standard is ultimate aim related to power quality. This issue gets an additional importance in era of modern power systems and smart grid environments. Occurrence of voltage whose magnitude exceeds the highest voltage level recommended for proper electrical equipment operation is known as overvoltage. Switching operation such as line energization can cause this type of disturbance. The paper deals with switching overvoltages occurred during energization of an unloaded overhead transmission line under different operating conditions. Namely, this process can be performed under normal or fault conditions. The latter means that some kind of fault has occured along the line and exists at the moment of energization. Switching overvoltages have to be analyzed not only from the aspect of magnitude, but also from the aspect of the existing harmonics in the harmonic spectrum. Accordingly, the Empirical Mode Decomposition and Short time Fourier Transform were used. The obtained results were compared to the calculated ones. In this way, one may get characteristic harmonics values which occur during the energization process, what would make a worthwhile contribution related to recognition of operating conditions during energization. Also, a conclusion about applied methods efficiency is drawn.