No abstract

The structure of DC transmission system is complexity, and the characteristics differ from components to components. It is difficult to adopt a single reliability assessment method for HVDC transmission protection system to be comprehensive, rapid and accurate. A reliability assessment method based on hierarchical modeling is proposed. At first the structure of DC transmission protection system is analyzed. It is divided into system layer, module layer and component layer. Then according to the characteristics of each layer, appropriate assessment methods are selected to assess each layer of the protection system. And corresponding reliability index is set the to realize the connection between each layer. Taking a DC transmission project as an example, the comprehensive reliability assessment of the protection system is carried out. Thereby the correctness and effectiveness of the proposed method is validated.

With the increasing capacity of grid-connected renewable energy power plants (REPPs), the fault current characteristics are remarkably altered. The limited amplitude and controlled initial phase angle of REPPs’ short-circuit current become highlighted. As a result, the differential current is no longer greater than restraint current on both sides of the protected devices when a fault occurs. It may lead to mal-operation of the current differential protection, which is used widely. It is necessary to demonstrate the cause-and-effect relationship between REPPs’ rated capacity and the protection adaptability. To solve this problem, the relationship between the rated capacity of inverter-interfaced REPP (IIREPP) and fault current amplitude, as well as its initial phase angle, is deduced first based on the IIREPPs’ fault behaviors. Further, by analyzing the influence of different rated capacity of REPPs on the ratio of operate to restraint current, the analytical expression of the IIREPP’s maximum rated capacity is deduced, which is suitable for analyzing the adaptability of differential protection. Finally, the simulation tests were carried out based on PSCAD/EMTDC. The test results show that the aforementioned expression is effective for evaluating the adaptability of current differential protection.