*6.4. Effect of Noise*

There is a possibility of interference from external factors on the power system distribution and transmission lines while passing through the terrain, which may superimpose noise on the faulty transients travelling from the faulty point to the location of PS. Noise may affect the performance of the protection schemes resulting in false tripping. To investigate the effect of noise on the performance of algorithm, a noise level of 10 dB signal to noise ratio (SNR) is introduced on both the voltage and current signals. The algorithm was tested for all types of faults whereas the results of PG fault simulated on phase A at 0.1 s on node 646 are illustrated in Figure 12, where superimposed noise can be seen easily. Current and voltage signals captured at node 650 for a period of 0.2 s (12 cycles) are detailed in Figure 12a,b, respectively. Current signals are processed using WDF and WD-index is computed, which is described in Figure 12c. It is observed that the WD-index corresponding to phase A has a higher magnitude after the incidence of PG fault. However, this index corresponding to the phases B and C has values comparable to the pre-fault values. Performance of the WD-index is not affected by noise. The ALN-index is computed from the voltage signals and described in Figure 12d. It is concluded that the ALN-index corresponding to all the phases has a high magnitude throughout time range, indicating that performance of ALN-index will be affected by the noise.

Figure 12 details the FI corresponding to all the phases during the event of PG fault with superimposed noise on both voltage and current signals. It can be inferred that FI corresponding to the faulty phase (phase A) has a higher magnitude compared to TM after the incidence of PG fault. However, FI corresponding to healthy phases B and C has a lower magnitude as compared to TM. Hence, it is established that algorithm is effective for the identification of PG fault and discrimination of the healthy and faulty phases even when there is high level noise (10 dB SNR) superimposed on the current and voltage signals in the hybrid grid in the presence of RE generation. High resolution plot of FI is illustrated in Figure 12f, where it can be seen that FI corresponding to phase A crosses the TM and FI for phases B & C is below the TM.
