1. Source of moisture

In a humid environment, it is easier for moisture to enter the inside of the motor than in a normal environment. To sum up, the main sources of moisture are as follows:

(1) Motors running outdoors are directly exposed to rain, and a small amount of water enters the inside of the motor through the gap on the explosion-proof surface;

(2) When the motor stops working in a humid environment, moisture enters the inside of the motor and condensation occurs;

(3) Motors stored for a long time are susceptible to moisture and condensation due to moisture intrusion;

(4) Motors working in harsh environments may suffer from flooding, immersion, and other accidents, causing moisture to enter;

(5) During the motor production process, moisture remains in the insulation capillary pores caused by failure to perform pre-baking according to process requirements or incomplete drying after varnish dipping.

2. Hazards caused by moisture inside the motor

For motors, good insulation is a prerequisite for the safe operation of the motor. In the winding stator, whether it is slot insulation, interlayer insulation, interphase insulation, binding tape, or the outer layer of the power lead wire, there are a large number of capillary pores, which are very easy to absorb moisture in the air, reduce its own insulation performance and make the thermal conductivity of the insulation worse, causing insulation breakdown and damage to the motor, causing personal and equipment safety accidents. High relative humidity tends to cause a water film to condense on the surface. When the humidity is higher than 95%, water droplets often condense inside the motor, making metal parts easy to rust, lubricating grease to deteriorate due to moisture, and some insulation materials swell due to moisture, and some become soft and sticky. The mechanical and electrical properties deteriorate, and insulation breakdown and surface flashover are prone to occur. In addition, mold is easy to grow in high-humidity environments, and the secretions of mold can corrode metal and insulating materials, causing the insulation to rapidly deteriorate and causing short-circuit accidents.

3. Waterproof measures for the shell of explosion-proof motors

The main waterproof protection object of the motor is the motor casing. The waterproof performance of the motor depends on the protection provided on the casing. To reduce the presence of moisture inside the motor, the waterproofing process of the casing is generally solved in two aspects. The first is to take measures to prevent the entry of moisture; the second is to discharge the moisture in a timely and effective manner after it enters. Focusing on these two aspects, we can provide the following effective protection on the shell:

(1) Add a water retaining ring or rainproof cap to the motor shaft extension.

(2) Use shaft surface oil seals with better dustproof and waterproof effects to replace ordinary V-rings.

(3) Motors with special installation methods, such as V1 motors, must be equipped with a top cover on the wind hood.

(4) Add a sealing ring to the flameproof surface of the stop.

(5) Apply sealant to the important joint surfaces of the motor and the fastening screw holes on the stator.

(6) Add an explosion-proof breathing and drain valve to the stator.

4. Drying method after the motor gets damp

In a humid environment, the main cause of motor burnout is the reduction in insulation performance caused by the dampness of the coil. Therefore, for motors that have been stored for a long time, suffered accidents such as immersion or flooding, or have a measured insulation resistance value lower than 0.5 MQ, they must not be repaired or dried before being processed. , cannot be used directly. The motor should be dried under the guidance of professionals, and the motor can be turned on only after the insulation resistance returns to normal value. The following methods are usually used to dry damp motors: circulating hot air drying method, bulb baking drying method, AC drying method, low voltage DC drying method, and iron loss drying method.

(1) Circulating hot air drying method. A drying chamber is made of heat-insulating materials, with an air outlet on the top and an air inlet on the side. The air inlet is connected to the heating chamber. Set up a 220V heater of about 3 kW in the heating room, and use a hair dryer to blow the hot air in the heating room into the drying room to dry the damp motor. The hot air temperature in the drying room should be controlled at around 100°C, it should not be too high.

(2) Bulb baking and drying method. In a drying room made of thermal insulation material with air outlets and thermometer sockets, install several incandescent bulbs or infrared bulbs with a power configuration of about 4 to 5 kW per cubic meter of box volume to bake the damp motor. You can bake it around, or you can pull out the motor rotor and put the incandescent bulb into the stator cavity for baking, but you should be careful not to get the bulb too close to the coil to prevent the coil from burning out. The motor casing can be covered with canvas or other materials to keep it warm.

(3) AC drying method. Pull out the motor rotor and pass the three-phase low-voltage alternating current into the three-phase winding. The voltage value should be 7% to 15% of the rated voltage of the winding, and the current should not exceed 50% to 70% of the rated current of the winding. In order to avoid excessive current, an ammeter should be connected in series in the three-phase line. If the current is too large, adjust it in time. Dry at low voltage. It is recommended to use an induction transformer for a voltage-regulating transformer.