A novel Instantaneous Power-based Differential Protection (IPDP) for transformers is presented in this paper. The instantaneous power, gathering the voltage and current information, discriminates between internal fault and external fault, inrush current, sympathetic inrush current, overexcitation, and ultrasaturation with and without CT (Current Transformer) saturation. The proposed method relies on the waveshape properties of the instantaneous power signal. A high-resolution time-frequency analysis (TFA) technique, namely Second-Order Transient-Extracting transform (STET), is used for the discrimination purpose. Furthermore, the STET technique results are examined in a Hardware-in-the-Loop (HIL) test using Raspberry Pi (R-Pi) to evaluate the real-time speed of the proposed algorithm. This real-time manipulation results in the internal fault and other transient phenomena distinction time to be 14 ms. The proposed method does not require transformer parameters and various operating conditions of the power system and is entirely immune against noise. The usefulness of the proposed method is evaluated through numerous simulations as well as experimental implementation. Two experimental setups are considered for ensuring the practicality of the proposed method. The first one is a laboratory setup for capturing real-world transformer internal fault and inrush current waveforms. The second one includes a relay and CT tester, namely, Vebko Amirkabir AMT105 relay tester and a laboratory CT for determining the CT saturation test.
