Compared to small motors, the production and manufacturing of large and medium-sized high and low voltage motors are more difficult, especially in terms of maintenance during customer use. For motors used in many occasions, there may be irregular shutdowns.
During the shutdown of the motor, on the one hand, moisture from the surrounding environment will invade the motor cavity, and condensation will continue to accumulate on the surface of the winding; On the other hand, after the motor is stopped, the air inside the motor cavity changes from hot to cold, and the moisture in the air will also condense on the surface of the winding. At the same time, due to the thermal expansion (during operation) and contraction (during shutdown) of the air, the external cold air is drawn into the motor cavity. When the winding gradually cools (during the process of stabilizing the cold state after shutdown), the moisture in the cold air continues to condense on the winding. Therefore, after a long period of shutdown, the winding and insulation will become damp, and direct power on operation may cause electrical breakdown faults. In view of the above reasons, large and medium-sized motors are equipped with winding moisture-proof heating devices during production and manufacturing. Before starting the motor, the winding and internal air of the motor are heated and dehumidified.
How to correctly select, install, and use moisture-proof heating devices? The heating power of the moisture-proof heating device is determined based on the volume of the motor cavity space and the volume of the motor. The voltage and phase number of the power supply are specified by the customer or in the technical agreement attached to the purchase contract.
The location for installing the moisture-proof heating device can be at the end of the winding (moisture-proof heating strip), on the inner cavity side of the end cover (moisture-proof heating tube), in a certain inner cavity space of the machine base (such as a suitable position below the stator core of a box type high-voltage motor and the machine base, heating plate), or in other appropriate spaces inside the machine casing (with a threaded heating rod that extends into the inner cavity through the screw hole on the machine base, so it is also called a space heater).
The principle for selecting installation is: heating will not cause any damage to the winding, quickly remove condensation on the winding and moisture in the internal cavity space, and make the insulation resistance of the winding reach the factory test state. When using, the moisture-proof heating device should be powered on before the winding is energized. After about 15 minutes, the moisture-proof heating device will be powered off and the motor will be powered on, and the motor will start running normally.
