Study On Sufficient Criterion-Based Differential Protection Using Current Amplitude Comparison For Distribution Network With DGs

Currently, protection methods for distribution system with DGs are still inapplicable and unsatisfactory. DG is still isolated if any network fault was detected, which has been hindered further development of renewable energy technology. With the impact of information missing and communication network limitation in existing distribution system with DGs, it has dropped into a serious dilemma of lacking practicality. Therefore, this paper proposes a novel sufficient principle which can make a better balance between the strategies and cost of protection in existing distribution network with DGs.Firstly the principle of sufficient protection is studied. It doesn’t require protection to be satisfied of all theoretical fault conditions with absolute selectivity, but to seize the fault characteristics which will appear in most fault conditions with priority and is also easy to capture and resolve. It gets low-cost, high-efficiency and absolute selectivity for common fault characteristics by sacrificing some sensitivity and speed of few uncommon fault characteristics. Other important elements of sufficient protection system have been introduced then such as the preferred combinations of sufficient criterion, action sequence in time, inverse discrete action mechanism and automatic isolation technology of DG.Secondly a novel sufficient differential criterion with current amplitude comparison is studied for weak synchronization and communication of distribution system with DGs. It verifies the criterion’s general applicability by analyzing fault recognition of current amplitude information. It not only makes up the maladjustment of traditional current protection by solving issues such as multi-source, large capacity and varied access location of DG. It also has a characteristic of quasi-asynchronous without strict synchronization for sampling data, which can greatly reduce the cost for communication.Finally, in order to further enhance the criterion’s fault recognition, add in amplitude information of sequence current and current variation with a sufficient preferred mechanism. It can adaptively remove the fault with the highest sensitivity under various fault conditions which achieve the complementary of sensitivity with different amplitude information and it also has a certain resistive coverage by using amplitude of negative current and current variation. With the cooperation of DG isolation and other sufficient criterions using phase information it can make up the drawback of theoretically blind action for differential criterion with current amplitude comparison. Through the design of actuating element, communication configuration and workflow of protection, a complete sufficient criterion-based differential protection scheme using current amplitude comparison with the adaptive preferred characteristic for distribution network with DGs is proposed. All the practicability, rationality and credibility were tested in the final simulation.