# Adaptive Leakage Protection for Low-Voltage Distribution Systems Based on SSA-BP Neural Network
## 5 Experimental Verification
### Adaptive Protection Test  
If the fluctuation range of the normal leakage current is large and the interval is small, the gears will be switched frequently; if the fluctuation range of the normal leakage current is small and the interval is large, the effect of adaptive adjustment will not be obvious. Therefore, the normal leakage current division interval should comprehensively consider the fluctuation range of the normal leakage current and the complexity of gear adjustment. Taking the maximum normal leakage current range of 200 mA as an example, it is appropriate to divide it into five intervals: [0, 40], [30, 80], [70, 120], [110, 160], and [150, 200]. The action thresholds of the corresponding leakage intervals are set to 60 mA, 120 mA, 180 mA, 240 mA, and 300 mA, respectively. Figure 7 depicts the adjustment curve of the protection action threshold. The brown, purple, orange, and green dashed lines represent 1, 2, 3, and 4 intervals of gear adjustment, respectively. In general, the normal leakage current changes relatively slowly. Although the integration of the SSA-BP neural network has a higher computational complexity than that of a single BP neural network, the efficiency of this model will not be affected, due to the lower real-time requirement of leakage current prediction. In most cases, the method of gear adjustment is to switch between two adjacent gears. If the leakage current changes greatly, it can also be switched across intervals. Figure 8 shows the comparison between the predicted leakage current and the actual leakage current in a certain period of time, and the gear switching process. The specific process of gear switching will be described below, in conjunction with Figure 7.  
1. The leakage action threshold automatically selects the highest level at the beginning of the algorithm running, that is, the 300 mA gear. However, the leakage current at this time is 83 mA, which is less than the lower limit of the highest gear (150 mA), and there is no situation exceeding [70, 120] within the next 1 min, so the leakage action threshold is lowered to the 180 mA gear after 1 min. Figure 8: Leakage protection action threshold adjustment curve. Figure 7: Predicted and actual normal leakage curve and gear adjustment. 2. During the period of 1-23 min, the predicted leakage current does not exceed the leakage interval of [70; 120], and the protection action threshold remains unchanged. 3. At 23 min, the leakage current was 121 mA, which was greater than the upper limit of the original leakage interval (120 mA), and did not return to the original interval within 1 min. In this case, the gear upward adjustment condition is met, and the action gear is adjusted to the fourth gear, which corresponds to a change in the action threshold to 240 mA. 4. In the period of 24-32 min, the predicted leakage current does not exceed the interval of [110; 160], and the protection action threshold remains unchanged. 5. At 32 min, the leakage current value was 109 mA, which was less than the lower limit of the original interval of 110 mA, and did not return to the original interval within 1 min. In this instance, the action gear was adjusted to the third gear. That is, the action threshold is 180 mA. Afterwards, gear shifting continues to be performed according to the rules of Equation (19). A variety of leakage current changes were simulated in the test, and the floating of the leakage action threshold was consistent with the design. Effective leakage protection can be performed no matter which gear the normal leakage current is in. The operation availability and accuracy of the leakage detector with an adaptive action threshold have been enhanced in comparison to the leakage protector with a fixed action threshold. The ratio of protector activation and leakage fault identification accuracy of the leakage protection device has been increased from less than 50% to over 90%.