Root causes of insulation failures and development of insulation system for variable speed driven motors: Performance of a corona resistant magnet wire

Insulation failure is the most common reason for total damaging of an electric motor. Motor with damaged winding can be repaired only by rewinding it, and in most cases costs will be more than the price of a new motor. Currently used magnet wire was planned to be replaced with an improved corona resistant magnet wire in variable speed driven applications, where partial discharge is general reason of winding failure. The purpose for using a new kind of wire is to reduce insulation failures, especially between adjacent turns. In this thesis stator winding insulation systems, insulation failures and properties of winding wires are presented. At first, a stator winding insulation system, its components and their properties are introduced. After this, various types of winding insulation fail-ures, root causes of failures and effect of variable speed drive for insulation system are presented. Then magnet wire constructions and properties are presented. Next test me-thods for winding wires are presented. Investigations in this thesis are separated into three sections: laboratory tests for the corona resistant magnet wire and the reference wire, statistical investigations of damaged motors and generators and costs comparison between the corona resistant magnet wire and the reference wire. The objectives of this thesis were to resolve if the properties of a new wire are sufficient compared to the reference wire, to find out if there are some connections between varia-ble speed drives and insulation failures, and what would the effects of the new wire be concerning manufacturing costs. A literature survey of examined subjects was per-formed. Laboratory tests confirmed that the properties of a new wire fulfilled the re-quirements. Statistical investigations brought out the high share of insulation failures of all warranty costs and high share of faults between adjacent turns from all insulation failures. Finally, the costs comparison presented quite low financial risk concerning the use of the new wire. Some developing targets in investigation methods and statistics were discovered. The next step with the new wire will be manufacturing the prototype and testing it with various tests.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format