New Line-selection Methods For Single Phase Grounding Fault In Distribution Networks With Two Phase's Current Transformers

In China, there are only two-phase current transformers(CTs) installed in most of distribution systems whose grade are no more than 66kV with neutral non-effective grounding(NNR). It has been a very difficult problem for protective relay engineers for a long time to identify faulted line when single phase to ground fault(SGF) occurs.The line-selecting method adopted most widespread nowadays is based on the zero-sequence current, so the zero-sequence must be acquired. There are two different methods to do so: One is to use zero-sequence TA, and the other is to connect the 3-phase TAs to the zero-sequence filter style. In China, the expense will be increased if we add B-phase TA or zero-sequence TA just for the line-selection. And it will also bring more difficulty to the implementing work. Until now, there is not any practical instrument which can select the faulty line with 2-phase currents home or abroad and all of the related methods are in the process of theory research.After analyzing the mutational current of A-phase and C-phase when B-phase grounding fault occurs with wavelet package reconstruction algorithm, the fault line detection algorithm actualized by using the transient characters of the sum of A-phase mutational current and C-phase mutational current is proposed. With the former research production of our group that when A-phase to ground fault or C-phase to ground fault occurs, the produced zero-sequence current can be used to select the faulted line, a new integrated algorithm used to identify single phase to ground fault line in two TAs distribution networks is represented. The algorithm is independent of the mode of neutral grounding and the unbalanced current under normal operation condition. It can satisfy the requirement of fault line selection in field operation. The ATP simulations and experiments verify the validity and reliability of the proposed algorithm. The theme's accomplishment is very useful to the improvement of the Two TAs distribution network's security and reliability in our country.