Travelling wave based directional comparison protection scheme and its application in 750 kV transmission lines

Travelling wave based line protection has the advantage in fast response speed, however, its performance in practice is still unsatisfactory due to the high frequency limitation characteristic of coupling capacitor voltage transformer (CCVT). This paper presents a directional comparison protection principle based on travelling wave, which utilizes the polarities of high frequency current and low frequency voltage, thus it is not influenced by the characteristics of CCVTs. Dyadic wavelet transform is used to extract the polarities of voltage and current increments for fault direction identification. A protection device prototype based on this principle is further developed, which has been successfully applied in 750 kV transmission system in Northwest China. An external fault record is captured by the prototype, and validates the correctness and reliability of the protection principle.