Differential relaying scheme for tapped transmission line connecting UPFC and wind farm

• A differential protection scheme using wavelet transform is presented.
• The scheme reliably distinguishes internal faults from external faults.
• The speed accuracy is within one cycle from the fault inception.
• Easy implementation.

This paper presents a differential relaying scheme for a tapped transmission line in presence of Unified Power Flow Controller (UPFC) and wind-farm together. The process starts at retrieving the fault current signal at the respective busses connecting the lines involving fault and pre-processing it using multi-resolution based Wavelet transform to derive third level approximate coefficients (CA3). Further the Discrete Fourier Transform (DFT) is used to compute the RMS value of the signal from the reconstructed signals expressed in terms of Wavelet approximate coefficients. Once the RMS value of the signal is estimated the operating (tripping) and restraining signals are computed for fault detection and classification in transmission lines including UPFC and wind-farm. The proposed scheme has been extensively tested on faulted conditions with wide variations in operating parameters and the test results indicate that it can reliably detect and classify faults including the ability to discriminate internal faults from external faults in transmission lines with a response time of less than two cycles from fault inception.