Digital Distance Protection For Cable Transmission Line

As increasing the under ground cable length, the harmonic content ratio of low harmonic orders, such as 2nd 3rd harmonic , in the transient current and voltage on the fault occurrence , have been remarkable . the phenomena causes a big problem for the line protection system especially for distance protection of the existing type. To cope with above, new distance protectionrelay using digital micro-processor technique has been developed. The reactance and resistance from relay to fault point are directly calculated by using high sampling ratio of 15 electrical degrees and high performance digital filter which eliminates the 3rd, and higher harmonic components. To confirm the actual operation of the developed relay with heavely distorted waves, the relay has been extensively tested by using current and voltage converted from EMTP (Electro-Magnetic Transient Program) simulation output data of large capacitive system.