*4.3. AC State Estimation*

For the AC power flow network, an AC SE is used for the detection of attacks. We also used AC SE for the detection of simple and stealth attacks, and the results are given in Figures 4 and 5. The conventions used in a DC state estimation for displaying the results are also used in these figures. In Figure 4, a safe zone, simple-attacked measurements, and stealth-attacked measurements are plotted. Safe measurements and stealth attacks are present in the safe zone, and simple-attacked measurements are outside the zone. It shows that stealth attacks were not detected by the AC state estimation. Similarly, in Figure 5, these results are shown in the form of a bar graph. The value of the difference in the residue from the threshold was positive for safe measurements and stealth-attacked measurements. However, the difference was negative for simple-attacked measurements. This indicated that the AC SE could detect a simple attack but it could not detect the stealth attack. Therefore, it is displayed in the results that simple attacks were detected by the DC state estimation, as well as the AC state estimation techniques, but stealth attacks bypassed these techniques.
