Research on wavelet packet decomposition based adaptive non unit transient current protection for EHV transmission lines

The reflection and refraction of fault-generated wave is discussed. The equations of currents measured by relay in S domain are deduced applying the Peterson principle. The energy ratio of a high frequency component to a low frequency component is mainly influenced by the fault position. Protection based on the ratio will be more adaptive if a higher frequency component is selected to be the low frequency component. Such protection also has satisfactory performance when used on series compensated lines. Discrete meyer wavelet packet decomposition technique is used to determine the energy ratio. Simulations have verified all conclusions demonstrated in this paper