This standard specifies the method for determining the power frequency electric strength of unimpregnated power cable paper and similar fibrous insulating paper, used to evaluate its dielectric properties. The core test method involves applying a continuous and uniform power frequency voltage to the paper sample under specified conditions using testing equipment until breakdown occurs, and recording the breakdown voltage at that moment. Conducting this test requires specialized voltage breakdown testers or dielectric strength testers. Such instruments typically include a high-voltage test transformer, a voltage regulation system, measuring electrodes, and a protection device capable of rapidly cutting off the power supply at the moment of sample breakdown. This method provides a standardized technical basis for evaluating the reliability of cable paper as a critical insulating material.