(1) The insulation performance test will place the multimeter at "R × Measure the resistance values between the primary winding and each secondary winding, iron core, and electrostatic shielding layer at 10k "gear, and ensure that the resistance values are infinite. If the resistance value is too small, it indicates that there is leakage, which leads to poor insulation performance of the transformer. (2) The pins of the primary and secondary windings of a power frequency transformer are generally led out from both sides of the transformer, and the primary winding is often marked with the words "220V". The secondary winding is marked with the rated output voltage value, such as 6V, 9V, 12V, 15V, 24V, etc. By using these markings, the function of the winding can be identified. However, if some transformers are not marked or have unclear markings, it is necessary to use a multimeter to detect the primary and secondary windings of the transformer. Due to the fact that most power frequency transformers are step-down transformers, their primary winding has a high input voltage and low current, as well as a large number of turns and fine wire diameters of enameled wires, resulting in a high DC resistance. Although the output voltage of the secondary winding is low, the current is high, so the diameter of the enameled wire in the secondary winding is thicker and the number of turns is smaller, resulting in a smaller resistance value. In this way, different windings can be identified by measuring the resistance values of each winding