Detection of internal fault from external fault and inrush current in power transformers based on combination of VMD and ELM

Power transformers are one the most expensive and important equipment of power systems that play an important role in the continuous supply of electrical energy. Therefore, their protection has a significant impact on network reliability and stability. The differential protection scheme equipped with harmonic restraint is used for detection of transformer internal faults. But, current transformer (CT) saturation would have undesirable effect on its performance. In some cases, the CT saturation during internal fault can lead to even harmonics which can prevent the relay from sending trip signal. Moreover, the CT saturation due to DC offset of inrush current can result in relay maloperation. In this paper, a new feature is extracted from differential current based on VMD analysis. This feature as well as differential and bias magnitudes are used for detection of internal faults from other operating conditions. In the proposed method, different classifier such as ANN, PNN and ELM have been used as classifier core. The obtained results show that the proposed the combination of VMD and ELM can correctly detect all internal faults even with severe CT saturation.