Characteristics of enameled wire under application of voltage when immersed in water or under humid conditions

Electric machines intermittently used in an atmosphere of high humidity have relatively many faults. When we investigated these machines with coils using polyester enameled wire the following was proved: 1. Few faults occur in the machines when operated continuously. Most faults occur when the machines are started either on Monday, the day after a holiday, or on a humid or rainy day. 2. Many faults occur in the machines where a voltage is normally applied at the coil, even when the machines are not used. 3. The break-down points concentrated at the coils, located on the humid side of the machines, and to which a high voltage is applied. Then, the break-down is often accompanied with decrease of insulation resistance or the gathering of green copper salts on the enameled wire.