Ms. Can visited a motor factory, where the production line displayed a dazzling array of motors with various structural designs. Her companion, Xiao Q, was full of questions, asking Ms. Can many questions related to structural selection, such as: Why do some motors have windows but no fans? What is the purpose of the caps on top of some motors? Today, we'll discuss the structure and operating conditions of motors.
The choice of motor structure is closely related to the motor's operating conditions, directly affecting the motor's output power per unit volume, operational reliability, and economy.
Evolution of motor structure
The structure of electric motors has evolved into the diverse and functionally refined structures we see today, undergoing a series of processes including application, expanded application, and specialized application to adapt to actual working conditions.
Initially, motors lacked any structural components to prevent foreign objects from entering. However, as applications shifted from protected indoor to outdoor settings, these shortcomings became apparent, leading to the adoption of fully enclosed motors. With the rapid expansion of motor applications and the increase in motor capacity and speed, protective motors emerged. In applications where there is no dust but only a risk of water droplets, enclosed motors were no longer necessary, and shielded protective motors were used instead. Due to the role of ventilation in motor manufacturing and its impact on the effective consumption of various motor components, simple open-type and protected self-ventilated motors appeared. The specific nature of applications and operating conditions necessitates the use of explosion-proof motors, submersible motors, and submersible oil motors.
Motor operating conditions
Across the entire technology spectrum, electric motors are used in metal processing, wood processing, agriculture, ferrous or non-ferrous metal smelting, hydropower or thermal power generation, pumping equipment, mining, and sea, land, and air transportation. Possible operating locations include:
● It is sheltered, and the air in the location does not contain any corrosive or explosive gases, such as a machine shop.
● There is cover, and water droplets or small objects (fragments, small parts, etc.) may fall on the machine, such as in a factory metal processing workshop.
● It is well-concealed, and fibrous dust can easily enter the motor, such as in the textile section of a textile factory.
● It is shielded and contains acidic, alkaline, or chemically reactive gases.
● A concealed mixture or gas of explosive gases.
● In mines containing gas, there is a risk of explosion. Motors sometimes operate in locations that are frequently moved and difficult to access.
●Open-air venues, especially by the sea.
●The ship has concealed internal buildings.
●Open to the elements, in bad weather, and on ship decks where seawater splashes.
●Deep water.
●Airplane.
Mechanical protection of motors
Different operating locations or conditions require various protection methods for motors. The mechanical protection structures of motors can be categorized as follows:
● Open-type motors do not have special protection devices for the live parts and rotating parts, but the part with the fan must be fitted with a protective net.
●Drip-proof motors have a protective cover installed on top of the live parts, usually over openings where something might fall into the motor.
● Protective motors have special protective devices to prevent objects from entering the motor. These motors are not protected against dust, moisture, and gases. Most protective motors are equipped with fans for added protection and to prevent dripping.
The enclosed motor is enclosed on all sides (but not sealed) to prevent outside air from entering.
● A drip-proof and splash-proof motor is equipped with a device to prevent water droplets and water flow from any direction from entering the motor.
● Explosion-proof motors prevent the internal gas from exploding and being transmitted to the outside gas, and are designed for isolation explosion protection or explosion isolation; those that adopt special and stricter electrical and mechanical safety explosion protection measures are classified as increased safety explosion-proof motors.
● For enclosed slip ring type motors, the rotor slip rings are housed in a specially sealed box. In this case, unless otherwise specified in the ordering technical conditions, the slip ring protection should not be lower than the protection of the motor itself; typically, the slip ring protection has a higher level.
●The sealed motor body is tightly sealed, so moisture will not penetrate even if the motor is immersed in water for 4 hours.
Mechanical protection extension
Many protective motors with openings for heat exchange with the outside air can have their opening shielding easily converted into the following protection methods:
●Drip-proof type;
●Prevents water spray from tilting at 30° to the horizontal plane;
● Enclosed motor designed to protect against water spray from any direction and ventilation via ducts beneath the base. For motors with relatively low total production volume, although the manufacturing of individual components is more complex, the actual production efficiency is higher and the performance is more perfectly suited to different applications.
The impact of mechanical protection on motors
Various types of protective structures are closely related to the ventilation and heat dissipation of motors, especially for large-size, high-capacity motors. The larger the capacity, the more serious the heat dissipation and cooling problem becomes, and the ventilation system and mechanical protection structure must be carefully selected.
