Study On Application Of Multirate Filter Banks Theory To The EHV Transmission Line Transient Protection

The reliability of HV/EHV transmission line protection is important to the safety and efficiency of power system. Exploring the new theory and approach of transmission line protection is the key problem in the field of protection. Much valuable fault information is contained in the transient signal when HV/EHV transmission line encounters fault, the relay protection based on transient signals attracts extensive attention.Fault information is the ultimate gist of the relay action. To get the fault information, we must make use of digital signal processing and mathematic tools. At present, transient fault signal of HV/EHV transmission line is analyzed by wavelet transform. However, this method has disadvantages, that is, in the high frequency field, the resolution is low, in the low frequency field, the resolution is high. But plenty of information is contained in the high frequency field of the fault signal. Moreover, the implement of the wavelet transform is similar as the tree-like architecture of the multi-rate filter bank, which brings some disadvantages like large computation, high implement complexity, low processing speed and poor real-time capability. However, there are many advantages in processing high frequency signals when multi-rate filter banks theory is applied to HV/EHV transmission line transient protection, such as high resolution, high processing speed and so on. Therefore, the application of multi-rate filter banks theory on the transient protection of EHV is researched in this paper. The main productions of this paper are as follows:First, based on the theory of multi-rate cosine-modulated filter banks, the transient protection criterion is put forward. That is, taking the energy ratio between the 7th, 8th, 9th channels and the 2nd channel of the transient current that passing the filter bank to distinguish the local and remote fault. If the fault occurs in the local region, all ratios are larger than 1, otherwise, less than 1. Lots of simulation results indicate that this criterion can accurately distinguish the faults within the protection region or not. And this criterion cannot be affected by faults position,faults resistance, faults type and faults occurring time.Second, when series-wound compensatory capacitance is installed on the EHV transmission lines, the results of academic analysis and simulation indicate that so far as adjusting the fade factor, the high frequency transient signal generated by the series-wound compensatory capacitance and its protection circuit will not affect the criterion correctness.