# Fault Analysis and Protection Principle for the Distribution Networks Integrated with PV and BESS
## 4 Simulation Analysis
### Simulation Tests for Symmetrical Faults  
#### 4.2.1 Operating Performance of the Voltage Blocking Criterion Under Symmetrical Faults  
As can be seen from Figure 9, after the voltage criterion is activated, when high resistance and low resistance faults occur at the ends of the forward area and the reverse area of PR4, the negative sequence voltage criterion can accurately determine that the fault type is a three-phase short-circuit fault. As shown in Figure 10, when a high resistance fault occurs at a remote location, the proposed direction criterion will be blocked.  
Figure 8: Fault at line CD under different operating conditions. (**a**) Positive sequence voltage at PR4. (**b**) Reactive current measured by PR4. (**c**) Negative sequence impedance angle measured by PR4.  
2.2 Operating Performance of the Reactive Current Direction and Active Current Amplitude Direction Criteria  
Three-phase short-circuit faults are respectively set at the exit of the reverse area of PR4 on line CD, at the midpoint of line CD in the reverse area, and at the midpoint of line AC in the forward area. The simulation results are shown in Figures 11-13.  
Figure 11 shows that when a fault occurs in the proximal area of bus C on line CD, the voltage drops significantly, and the reactive current detected by PR4 is greater than 0. In this case, if only relying on the flow direction of the reactive current, it will be mistakenly judged as a forward fault. At this time, it is detected that the amplitude of the reactive current exceeds the set value and the sign is greater than 0, and the active current amplitude criterion is entered. At this moment, the active current flowing through PR4 is provided by the synchronous power source, and its amplitude is greater than the setting value, so it can be correctly judged as a reverse fault.  
When a three-phase short-circuit fault occurs in the non-proximal area of the reverse line, such as at the midpoint of line CD, the simulation results are shown in Figure 12. In this case, the amplitude of the reactive current is greater than the set value, and the sign is negative. The reactive current criterion can correctly determine that a reverse fault has occurred, and there is no need to activate the active current amplitude criterion.  
Figure 10: Positive sequence voltage criterion action performance under symmetrical faults in diverse fault conditions.  
Figure 9: Negative sequence voltage criterion action performance under symmetrical faults in diverse fault conditions.  
Figure 11: Reverse proximal fault: Fault on line CD near bus C (**a**) Positive sequence voltage at PR4. (**b**) Reactive current measured by PR4. (**c**) Amplitude of active current measured by PR4.  
Figure 12: Reverse fault: Fault at the midpoint of line CD (**a**) Positive sequence voltage at PR4. (**b**) Reactive current measured by PR4.  
When a three-phase fault occurs at the midpoint of line AC in the forward area of PR4, the voltage criterion detects that the PCC voltage drops below 0.9 p.u., activating the reactive current direction criterion. At this time, the detected amplitude of the reactive current at PR4 is larger than the set value and the sign is positive. Since a positive sign cannot distinguish whether the fault is in the forward area or the reverse proximal area, the active current amplitude criterion is activated. Ultimately, the amplitude of the active current flowing through PR4 being less than the set value allows the fault to be correctly determined as a forward area fault.