Motor Insulation Systems (2)

2. A Typical Motor Insulation System

Motor insulation systems vary considerably among the various motor manufacturers, but the following paragraphs provide a general description of the various components that comprise a typical insulation system.

Magnet wire is insulated with a thin coating of a varnish that is specifically designed as an electrical insulation material. The magnet wire insulating varnish provides the turn-to-turn insulation and a portion of the other elements of the motor insulation. In most motors, a large part of the winding-to-ground insulation is provided by a paper insulation lining in the stator slots. Paper insulation is also used to separate the windings of different phases. These components of the insulation system are called Slot Papers and Phase Papers. A rigid piece of insulation called a Top Stick Slot Wedge may be inserted in the opening of the slot to hold the windings securely in position. A diagram of a stator slot, showing the slot paper, a phase paper and the top stick are shown in Figure 2, below.


Figure 2 Stator Slot Insulation — Slot Paper, Phase Paper and Top Stick

At each end of the stack of laminations, portions of the coils of wire, called the end-turns, pass from one slot to another. The end-turns are often separated from one another by paper insulation. Once the coils are wound into the stator laminations, the stator is dipped into a tank of insulating material, and baked, to coat the windings with another layer of insulation. This additional coating compensates for nicks and irregularities in the original coating, created during the manufacturing process and adds insulation to the magnet wire. After the additional coating cures, the stator may be dipped a second time for added protection from contaminants and moisture. This second, and subsequent dips and bakes, are typically an option offered by motor manufacturers.

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