A Novel Differential Protection Scheme for Distribution Lines Under Weak Synchronization Conditions Considering DG Characteristics.

A large number of DGs(distributed generators) in the ADN (active distribution network) bring great uncertainty to the power systems, making it difficult to quantify fault characteristics. Undoubtedly, the setting of traditional protection becomes more complex and difficult. Therefore, the differential protection is an effective solution to cope with it. However, the differential protection requires high time synchronization, which is difficult to be satisfied based on the current communication conditions of ADNs. What’s more, accurate extraction of fundamental frequency components is also very difficult considering the distortion, the frequency offset, and the instability of fault currents. In view of this, a new differential protection scheme that makes full use of fault information is proposed in this paper. First, the pre-fault current waveforms are taken as reference. Then the similarity characteristics of the current waveform sequences at both terminals of the line are calculated separately. Finally, a new differential protection scheme considering weak synchronization conditions are constructed using Hausdorff distance, which is based on wide frequency components. The proposed scheme only transmits calculation results instead of sampling values, which effectively avoids the impact caused by data synchronization errors. Simulation shows that the proposed scheme can reliably identify internal faults in various points of the protected line and external faults. Compared with the conventional differential protections, it also shows great resistance to the transition resistance up to $30\Omega $ , which is common in the ADN. Moreover, it has strong resistance to time synchronization errors, which can withstand time synchronization errors of up to 20ms. The proposed protection scheme has excellent engineering application value, especially suitable for distribution networks with weak communication conditions.