Let’s start with the structure of the capacitor. The simplest capacitors are constructed with plates at both ends and an insulating dielectric (including air) in between. After being energized, the plates are charged to form a voltage (potential difference), but because of the insulating material in the middle, the entire capacitor is non-conductive. However, such a situation is under the premise that the critical voltage (breakdown voltage) of the capacitor is not exceeded. We know that any substance is relatively insulating. When the voltage across the substance increases to a certain extent, the substance can conduct electricity. We call this voltage the breakdown voltage.