Hengli Motor Classroom | Motor Air Cooling System
The motor structure using air cooling is simple and cost-effective; Its disadvantage is that the cooling effect of air is poor, causing significant friction losses in high-speed motors. There are many types of ventilation systems that use air cooling, and their basic characteristics will be explained from the following aspects:
● Open circuit cooling (or free circulation) or closed circuit cooling (or closed circulation)
The constant force motor with open circuit cooling draws cooling air from around the motor, passes through the constant force motor, and then returns to the surrounding environment. The motor with closed-loop cooling has its primary cooling medium circulating along a closed circuit through the motor; The heat in the primary cooling medium is transferred to the second cooling medium through structural components or coolers.
Radial, axial, and hybrid ventilation systems
According to the direction of cooling air flow inside the motor, the air cooling system can be divided into three types: radial, axial, and mixed (radial, axial). Due to the ease of utilizing the blowing effect of components on the rotor that can generate wind pressure, such as duct blades and magnetic poles, radial ventilation systems have been widely used. Axial ventilation system facilitates the installation of larger diameter fans to increase airflow. The main disadvantage is uneven cooling along the axial direction, and it is not convenient to utilize the blowing effect of the components on the rotor. Axial ventilation systems are generally only used in small and medium-sized DC motors in China. In fact, the so-called radial or axial ventilation system is only the main aspect of the cooling effect of the cooling medium inside the motor, and pure radial or axial ventilation systems are relatively rare.
A hybrid ventilation system has both axial and radial channels, but often focuses on one. Large DC motors are hybrid systems that are mainly axial, and some steam turbine generators are widely used in hybrid systems that are mainly radial.
● Inhalation and compression type
According to whether the cooling air first passes through the heating part of the motor and then through the fan, or vice versa, air cooling systems can be divided into two types: suction type and pressure type. Due to the fact that the inhaled cold air first comes into contact with the heating part of the motor and can use a larger diameter fan, while the compressed cooling air first passes through the fan and is heated by the fan's losses before coming into contact with the heating part of the motor (in high-speed motors, the air temperature rise caused by fan losses can reach about 5 ℃), the inhaled cooling capacity is higher.
In DC motors, fans are often installed at the non commutator end. If a press in cooling system is used, it can prevent carbon powder caused by brush wear from entering the motor. However, at this time, most of the air is blown through the space between the stator poles, and the amount of air blowing through the rotor is relatively small, making it difficult for the rotor with more losses to dissipate heat. In this case, appropriate measures should be taken, such as fully relying on the air duct blades of the armature core and the blowing effect at the end of the winding to dissipate heat.
● External cooling and internal cooling
Air cooling systems generally use external cooling or so-called surface cooling methods, but in order to improve cooling capacity, there are also systems that use internal cooling, such as the excitation winding of a hydroelectric generator, which can use air internal cooling. Air internal cooling has also been used on the rotor windings of small capacity steam turbine generators abroad. However, the internal cooling system has a complex structure and requires very clean cooling gas, so it is currently rarely used in motors that use air as the cooling medium.
