A successful development and implementation of the dq-axis components and the wavelet packet transform (WPT)-based hybrid technique for power transformer protection is introduced in this paper. In this approach, the high-frequency subband contents of the dq-axis components of the differential current is extracted using the WPT. This characterization helps to provide enough information to efficiently detect and discriminate internal faults from inrush currents in power transformers. This hybrid method provides accurate information with only one level of the WPT of the dq-axis components of the differential current for power transformer protection. A real-time experiment is carried out for different normal and abnormal operating conditions, such as inrush and internal faults for different cases of loading, to test the efficacy of the proposed algorithm. The experimental results show fast, accurate, and reliable responses to all different types of disturbances that may occur in power transformers.Index Terms-Digital differential protection, magnetizing inrush current, power transformers, synchronously rotating reference frame dq, wavelet packet transform (WPT).
This paper presents a proposed technique of virtual-flux direct power control (VF-DPC) as the improvement in control method from the basic of conventional direct power control (DPC) for front-end three-phase pulse width modulated (PWM) in ac-dc converter. Three sensors in order to measure the three phase input voltage have been eliminated in the proposed method of virtual flux (VF) regarding from the estimation technique. Theoritical principles of VF-DPC are discussed in this paper. The steadystate performance of VF-DPC and conventional DPC are evaluated and presented in this work to estinguish for the excellent performance. It is shown that the VF-DPC exhibits the several advantages, particularly in providing low total harmonic distortion with almost sinusoudal of input current and unity power factor (pf) operation under balanced three phase voltage supply. The simulation results from both methods through Matlab simulation have demonstrated the outstanding performance of the new proposed control technique from VF-DPC.
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