# A New Passive Islanding Detection Solution Based on Accumulated Phase Angle Drift
## 6 Tests Based on Field Waveforms  
This proposed composite PAD solution has been implemented in one commercial relay. The disturbance recorders from the conventional VVS relays installed in the several different sites are used to play back to that relay to evaluate its performance in a real power system. Most of these recorders are triggered by the mal-operations of VVS relay. The default settings are applied during the playback tests.  
Figure 11: (**a**) Maximum and instantaneous ROCOF values; (**b**) accumulated phase angle drift under frequency fluctuation after large load switching off.  
Figure 10: Frequency measurement under the frequency fluctuation after large load switching off.  
For the unbalanced system faults, the proposed PAD solution can intrinsically keep stable due to the \"balanced VVS criteria\". For the waveform recorders of single phase fault and phase to phase fault, three voltage phase changes are not in the same direction. Figure 12a is the waveform recorder from one phase to phase fault and the conventional VVS relay mal-operates at the instant fault clearance. During the playback test with the waveform in Figure 12a, the phase to phase voltage angle changes are recorded by the relay with PAD solution. Figure 12b shows \(V_{AB}\) and \(V_{BC}\) angle changes are always in the different direction during the AC phases fault. So, the calculation of phase angle drift is never initiated and the PAD solution can keep stable.  
For the three-phase fault, the voltage angle changes are in the same direction and the calculation of phase angle drift would be initiated. So, the setting \(\sum Ang\_set=18^{\circ}\) is expected to ensure the stability during the three-phase fault for at least 100 ms. Figure 13 is the waveform recorder from one three-phase fault and the conventional VVS relay mal-operates at the instant fault clearance. The fault duration is about 135 ms and the fault voltage is about 60% Vn. During the playback test with the waveform in Figure 13, the phase angle drift shown in Figure 14a, the instantaneous ROCOF value and maximum ROCOF value shown in Figure 14b, are recorded by the relay with PAD solution. The maximum angle drift is about 5.0\({}^{\circ}\) during the fault and the angle drift is reset about 400 ms after the fault clearance, where the maximum ROCOF value is less than the setting \((df/dt)\_set=0.5\) Hz/s. Generally, the composite PAD solution can remain stable under the three-phase fault with the default phase angle drift setting \(\sum Ang\_set=18^{\circ}\).  
Figure 12: (**a**) Waveform recorder from AC phase to phase fault; (**b**) phase to phase voltage angle change during fault.  
Figure 13: Waveform recorder from three-phase fault.  
For other waveform recorders, this composite PAD solution can also work correctly. It can detect the islanding condition and remain stable under system fault. It is a pity there is no waveform recorder from the system frequency fluctuation condition. Hence, to fully estimate the performance and to get the setting configuration guide for this composite PAD solution, more field tests are necessary.