Speed and security improvements of distance protection based on Discrete Wavelet and Hilbert transform

•Distance relay algorithm based on Discrete Wavelet and Hilbert transform is developed.•Speed and security of distance relay algorithms are assessed.•Distance relay assessment based on fault records from transmission networks.

In order to maintain power system stability, modern transmission networks demand a high fault detection speed. At the same time, a high level of protection security is required, since each protection maloperation might lead to a system blackout and high economic loss. The protection speed and security represent conflicting requirements fundamentally limited by the Heisenberg's Uncertainty Principle. Traditional line protection approach relies on fundamental frequency phasor estimation based on Discrete Fourier Transform. There are also various Discrete Wavelet Transform algorithms, typically based on Daubechies wavelet families, which may be used to estimate phasors. In this paper wavelet families other than Daubechies are evaluated as methods for estimating phasors. Two new algorithms based on Reverse Biorthogonal mother wavelets are presented and compared to the previous solutions. The protection speed and security are evaluated via a very demanding test formed on the basis of several thousands of fault simulations, as well as on 60 fault records from 400 kV and 220 kV transmission networks.