As shown in Figure 1, if a low-cost voltage sensor has two flats, then, for the standard overhead transmission lines, with the increase of (Mousavi, Bozorg, & Cherkaoui, 2013), the value is only a few millimeters to centimeters. Compared with the change in , the change in will be more obvious and if using low-pass RC filter in the end to measure the voltage of , then, the displacement current value can be obtained by the following equation: