By Jeff Norton
Technical Services Committee Member
Brandon & Clark, Inc.
Fort Worth, Texas

When securing random wound stators, one of the things to watch for is that you don’t pull the end turn phase insulation out past the separator between the coils when the string is tightened between the slots. Doing so increases the chances for failure due to potential between coils and phases. The risk of this happening increases with concentric windings and higher RPM windings. To help prevent this from happening, wrap and secure one or two wraps of the tie string on the back side of the end turns at the edge of the slot liner and tie it securely (Figure 1). When tying the end turns, insert the string between the iron and the ties placed on the back side of the winding each time the string is wrapped around the end turns (Figure 2). The string securing the end turns will be held near the edge of the slot liner by the string wrapped around the back side of the coils and will not allow it to pull the phase insulation out of place (Figure 3). 

Figure 1: Tie string wrapped on back side of end turns

Figure 2: Tie inserted under string wrapped around end turns

Figure 3: Ties held near edge of slot liner