Inverters have become installed in many types of electrical equipments, as efficient variable-speed control units. Inverters are switched at a frequency of several kHz to several ten kHz, to cause a surge voltage at every pulse thereof. Inverter surge is a phenomenon in which reflection occurs at a breakpoint of impedance, for example, at a starting end, a termination end, or the like of a connected wire in the propagation system, and consequently, to apply a voltage twice as high as the inverter output voltage at the maximum. In particular, an output pulse occurred due to a high-speed switching device, such as an IGBT, is high in steep voltage rise. Accordingly, even if a connection cable is short, the surge voltage is high, and voltage decay due to the connection cable is also low. As a result, a voltage almost twice as high as the inverter output voltage occurs.
As coils for electrical equipments, such as inverter-related equipments, for example, high-speed switching devices, inverter-driven rotary electric machines, and transformers, use is made of insulated wires, which are mainly enameled wires, as magnet wires in the coils. Further, as described above, since a voltage almost twice as high as the inverter output voltage is applied in inverter-related equipments, it has become required to minimize the inverter surge deterioration of the enameled wire, which is one of the materials constituting the coils of those electrical equipments.

In general, partial discharge deterioration is a phenomenon in which an electrical-insulation material undergoes, in a complicated manner, for example, molecular chain breakage deterioration caused by collision with charged particles that have been generated by partial discharge of the insulating material, sputtering deterioration, thermal fusion or thermal decomposition deterioration caused by local temperature rise, and chemical deterioration caused by ozone generated due to discharge. For this reason, reduction in thickness, for example, is observed in the actual electrical-insulation materials, which have been deteriorated as a result of partial discharge.

It is believed that inverter surge deterioration of an insulated wire also proceeds by the same mechanism as in the case of general partial discharge deterioration. That is, inverter surge deterioration of an enameled wire is a phenomenon in which partial discharge occurs in the insulated wire due to the surge voltage with a high peak value, which is occurred at the inverter, and the coating of the insulated wire causes partial discharge deterioration as a result of the partial discharge; in other words, the inverter surge deterioration of an enameled wire is high-frequency partial discharge deterioration.

This article is from US8586869B2 United States
 

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