Tripping of wind turbines during a system fault

In a power system with significant wind power penetration, the tripping of wind turbines for a system fault condition can be a major concern to the system operator. With wind turbines employing different under-voltage protection settings available in the system, a fault on a transmission line can lead to tripping of a large number of wind farms depending on the voltages at the wind farm buses during the fault and the protection settings of the wind farms. As a result, an N-l contingency may evolve into an N-(K+1) contingency, where K is the number of wind farms tripped due to low voltage conditions during a fault. The severity of such a condition depends on the output of the wind farms during a fault, and if it coincides with the high wind and off peak loading condition, it might lead to system instabilities. Therefore, it is important for the system operator to be aware of such limiting events during system operation and be prepared to take proper control actions. This can be achieved by incorporating the wind farm tripping status during N-1 static security assessment procedure. In this paper a methodology based on Z-bus algorithm is proposed to determine the tripping status of wind farms for a worst case fault, so that it can be used in contingency evaluation procedure. The proposed algorithm is implemented in MATLAB and tested with a 23 bus test system.