As an extension of my previous inquiry into air-core ch […]
As an extension of my previous inquiry into air-core chokes, I'm trying to determine the voltage insulation rating of enamelled wire, without much luck. Few of the audio air-core choke manufacturers list that data, and none of the enamelled wire manufacturers I've checked give it either.
How can I be sure that the insulation on enamelled wire will not break down under a given voltage? Am I not looking in the right place for this rating? Am I looking at the wrong kind of enamelled wire for high-voltage applications? Are we required to build chokes such that consecutive windings of enamelled wire are close enough in voltage that the insulation rating of the wire doesn't matter?
Breakdown voltage depends on the thickness of the covering, which can be of 3 types: Grade 1, Grade 2 and Grade 3. Higher grades have thicker insulation and thus higher breakdown voltages.
The temperature class indicates the temperature of the wire where it has a 20,000 hour service life. At lower temperatures the service life of the wire is longer (about a factor 2 for every 10 °C lower temperature). Common temperature classes are 105° C, 130° C, 155° C, 180° C and 220° C."
The breakdown voltage depends mainly on the thickness of the insulation (see formula below), but also on the bare wire diameter, the application temperature of the coil and the type of enamel.
Xinyu enamelled wire has been developed which gives at least an order of magnitude longer life than a conventional enamel. System tests, using this enamel in a form wound coil, have shown that the turn-to-turn capability of this enamelled wire is superior to the capability of a reliable service-proven ground wall insulation.