Digital relaying scheme for EHV transmission system incorporating Regulated Power Index (RPI) concept using synchronized measurement

In this research work,a new per phase protection scheme of uncompensated and series compensated transmission line is proposed using both end synchronized measurement regulated power index (rpi). rpi per phase is defined as the ratio of the sum of sending end apparent power and receiving end apparent power to the power at receiving end for that phase. this scheme is developed for the detection of fault,identification of faulty phase and tripping the faulty phase as a relaying scheme which is of supreme priority in protection of series compensated lines. this scheme has immunity to series compensation current,line charging current and other end in-feed current effect and detects the faults within half cycle. proposed scheme uses only one cycle moving window,sample by sample checking information and has low computational burden,fast decision with high rate of accuracy even in presence of high fault resistances. the simulation results are tabulated for abundant test cases considering severe fault conditions with very low resistance,load encroaching high fault resistance conditions,internal and external faults with fixed series capacitors (fsc) at various prime locations. novelty of this scheme is that there is no requirement to change the proposed relay threshold settings even with different fsc installation locations,% compensation levels,fsc bypass mode operation which has to be changed in conventional and modern digital relay settings. matlab/simulink model generated data using an actual installed 400 kv-400 km real transmission system parameters have been used to investigate the accuracy level of the scheme. the performance results demonstrated here validate the superiority of rpi based scheme over conventional protection schemes. extensive simulation experiments deliver accurate results,which demonstrate high accuracy,simplicity and robustness of the proposed scheme.