Research On Current Differential Protection For Lines In Digital Substation

Differential protection based on Kirchhoff s law, which is very simple and reliable, is widely used as the main protection in transmission line. In the traditional substations, differential protection uses the electromagnetic current transformers (CT) to gain the both ends current flow of the transmission line, CT saturation caused by external short-circuit faults can bring about large unbalanced current. So when designing the traditional differential protection, some technology problems like CT saturation and compensation of the capacitance current have to be took into account. However, as a result of the bottleneck of traditional substation, they've existed for a long time, but not solved successfully yet. The appearance and fast development of the digital substation hopefully can solve these problems.In this text, firstly, by deep analysis the differential protection theory and the relevance part in digital substation, demonstrated the differential protection technology Oriented digital substation has two big advantages comparing to the one Oriented traditional substation. one is ECT in the digital substation can completely solve CT saturation. The other is data sampling and communication network systems can easily meet demand of the capacitance current compensation methods. on that basis proposed the improvement of the differential protection to adapt with the digital substation technology.Then, constructed a simulation system in PSCAD and MATLAB. Demonstrated the great positive effect in reliability, sensitivity, and a little bit in quick section.At last, generally introduced the chief synchronization method at present, analysis the reason of digital substation not using the existing method, introduced two interpolation methods which can be appropriate for IEC61850-9-1 or IEC61850-9-2. And then make the error analysis of interpolation method. Demonstrated the two interpolation methods using linear Lagrange's interpolation can easily meet the existing base on fundamental component Differential protection criterion's demand of error...