A new differential protection algorithm for transmission lines connected to large-scale wind farms

Abstract

The fluctuated output power of the large-scale wind farms (WF) and their fault transient characteristics have an adverse effect on the current differential protection systems of the transmission lines. With increased transmission line length and in the case of weak output power from the WF, the differential current between both line ends increases in normal conditions since the capacitive current is comparable to the load current. This paper proposes a new differential protection algorithm for transmission lines connected to large-scale wind farms. The proposed current differential protection algorithm is developed based on the signs of the phase current samples at both line ends, instead of utilizing directly the current magnitudes. The similarity between the signs of the phase current samples at both line ends is evaluated utilizing the signed correlation criterion, and the fault detection index is calculated to discriminate the internal faults from other events. In addition, a new online technique is introduced to adjust the protection settings considering the different output power levels of the WF. The conducted PSCAD/EMTDC simulation studies confirm the acceptable performance of the proposed protection algorithm for numerous normal and fault scenarios, including different fault resistances and inception angles as well as all fault types. The effect of line length, type of wind turbine generator, and different values of WF output power are also considered.