Detection of power oscillation and simultaneous faults using Clark transform

Distance relays are widely used to protect transmission lines. Sometimes, in these lines due to the occurrence of the swing of the power, the impedance calculated in the distance relay enters into its functional zones and leads to the cutting off of the lines. This issue can cause global power outages. Accordingly, in this paper, a Clark-based method for detecting the swing of power and distinguishing it from simultaneous faults is presented. The proposed method operates based on the calculation of the average current signal in the Clark transform output. This method is independent of network parameters and it is capable of detecting various types of swings, including stable and unstable power fluctuations and all types of simultaneous faults. To evaluate the proposed method, different modes of power swing and simultaneous errors are simulated in DIgSILENT software and then using the matrix data obtained from the current signal, the proposed algorithm is implemented in the Matlab software using the Clark transform. In addition to software evaluation, the proposed method has been tested using a tester and relay made by the Vebko Amirkabir knowledge-based company. The results of the software and practical tests show the success of the proposed method in identifying the types of power swings. The results also show that the proposed method has a high speed in detecting simultaneous faults with power swings.