The insulation performance of electrical equipment is usually judged by measuring its insulation resistance. In order to ensure the personal safety and the operation safety of electrical equipment, a minimum requirement is imposed on the insulation resistance between conductors of different phases or between the conductor and the equipment casing. In power engineering, the insulation resistance is measured quantitatively through an insulation tester, also called megohmmeter or megger, so as to determine whether there are insulation problems or hidden safety hazards.