Monthly Archives: November 2017

Mechanical Insulation

Induction machines rely on a relatively simple yet robust construction, considering that their durability can vary according to the durability of the insulation of the winding, and can be varied by factors such as possible vibrations, humidity and corrosive environments. Among these factors, the most significant is the temperature supported by the insulating materials used. Experience has shown that insulation has an almost unlimited duration if its temperature is kept below the limit of its thermal class. Above this limit, the insulation durability becomes shorter as the working temperature gets higher.

The increase of about ten degrees above the thermal class limit of the insulation temperature, allows the winding durability to decrease by half. For longer durability, the use of thermal sensors is recommended for retention of the winding. The decrease in engine durability does not refer to high temperatures, when the insulation burns out and the winding is destroyed. The durability of the insulation refers to the gradual aging of the insulation, which over time becomes dry, losing its insulating action until it can no longer withstand the applied voltage and results in a short circuit.

Class and Thermal Effects

The thermal class is determined on the nameplate. These are aramid and polyester based and obtain films and laminates which are used at the following points, between the coil and the groove, which is the groove bottom film, to insulate the steel sheet package from the coil of enameled yarn; between the phases, to electrically isolate the phase from one another; closure of the stator slot to electrically isolate the coil found at the top of the stator slot and also to operate mechanically so as to keep the wires within the groove.

Currently, the enamel used in the wires ensures the mechanical property ensured by the outer layer of the enamel which resists abrasion forces during the insertion thereof into the stator grooves. The inner enamel layer ensures high dielectric strength to the assembly and attaches 200 degree grade to the wire. This wire is used on all class B, F and H engines. On smoke extraction engines, the wire is specific for very high temperatures. Insulating films and laminates have the function of thermal and electrically insulated parts of the motor coil.