[Guide] Modern motors use higher electromagnetic loads to improve the utilization of materials, and the single capacity of the motor is also increasing. Therefore, the cooling system of the motor must be improved to increase its heat dissipation capacity. Except for individual small or special motors, most motors use fans to force air flow to cool the motor.
Modern motors use higher electromagnetic loads to improve the utilization rate of materials, and the single capacity of the motor is also increasing. Therefore, the cooling system of the motor must be improved to increase its heat dissipation capacity. Except for individual small or special motors, most motors use fans to force air flow to cool the motor.
Overview of Motor Cooling System Development
As early as 1928, synchronous cameras used to improve the power factor of power grids used hydrogen as a cooling medium. The test proves that due to the reduction of the mechanical friction loss of the gas and the improvement of the heat dissipation capacity, the motor of the same size can increase the capacity by 20-25% or more after hydrogen cooling, and the efficiency is also improved. Over the next 20 years, the use of hydrogen cooling technology for turbo-generators was rapidly promoted. After the 1950s, internal cooling systems were used in large-capacity motors, especially turbo-generators. The so-called internal cooling means that the heat generated in the conductor is directly transferred to the cooling medium without passing through the insulation. Initially, hydrogen was generally used as a cooling medium in internal cooling systems. Later, in order to further improve the cooling capacity, liquid (water or oil) was used as a cooling medium.
In 1955, the British Maowei Motor Company first completed a steam turbine generator with a capacity of 30,000 kilowatts, stator water cooling, and generally hydrogen-cooled rotor. The electrical load is 4 to 5 times higher than that of air cooling and the winding temperature The liter has not exceeded the allowable value. For the research and manufacture of dual-water internally cooled turbogenerators whose stator rotor windings are internally water cooled, the majority of motor workers in China have made remarkable achievements. In addition to further in-depth research on existing cooling methods, countries around the world are also researching and developing various new cooling methods including the use of low-temperature superconducting technology.
It is more convenient to divide the cooling system of the motor according to the different cooling media. At present, the most widely used in motor manufacturing is an air cooling system that uses air as a cooling medium. Today I mainly talk to you about the air cooling system.
Motor air cooling system
The air-cooled motor has a simple structure and low cost; its disadvantage is that the cooling effect of air is poor, and the friction loss caused by the high-speed motor is large. There are many types of air-cooled ventilation systems, and their basic characteristics are now explained from the following aspects:
● Open circuit cooling (or free circulation) or closed circuit cooling (or closed circulation)
For an open-circuit cooled motor, the cooling air is drawn around the motor, and after passing through the motor, it returns to the surrounding environment. In a closed-circuit cooled motor, the primary cooling medium passes through the motor and circulates along a closed line; the heat in the primary cooling medium is transferred to the second cooling medium through the structural member or cooler.
● Radial, axial and hybrid ventilation systems
According to the direction of cooling air flow in the motor, the air cooling system can be divided into three types: radial, axial and mixed (radial, axial). The radial ventilation system is widely used because it facilitates the use of the blowing action of components (such as air duct pieces, magnetic poles, etc.) that can generate wind pressure on the rotor. The axial ventilation system facilitates the installation of fans with larger diameters to increase the amount of ventilation. The main disadvantage is that the cooling is uneven in the axial direction, and it is not convenient to use the blowing effect of the upper parts of the rotor. The axial ventilation system is 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 in the motor. Pure radial or axial ventilation systems are relatively rare.
Hybrid ventilation systems have both axial and radial channels, but they are often biased toward one type. Large DC motors are axial-based hybrid systems, and some turbine generators are widely used in radial systems. Mainly a hybrid system.
● Suction type and press-in type
Depending on whether the cooling air first passes through the heat-generating part of the motor and then through the fan, or vice versa, systems that use air cooling can be divided into suction and press-in systems. Because the suction type cold air first contacts the heating part of the motor, and a fan with a larger diameter can be used, the pressurized cooling air passes through the fan first, is heated by the loss of the fan, and then contacts the heating part of the motor ( In high-speed motors, the temperature rise of the air caused by the loss of the fan can reach about 5 ° C), so the cooling capacity of the suction type is high.
In the DC motor, the fan is mostly installed at the non-commutator end. If the press-in cooling system is used to avoid the carbon powder of the brush from entering the motor, most of the air volume is blown through the space between the stator poles and the rotor The low air volume makes it difficult for the rotor with more losses to dissipate heat. At this time, appropriate measures must be taken, such as fully relying on the air duct piece of the armature core and the blowing effect at the end of the winding to dissipate heat.
● Outer cooling and inner cooling
Air cooling systems generally use external cooling or so-called surface cooling, but in order to improve the cooling capacity, there are also internal cooling methods, such as the excitation winding of the hydroelectric generator, which can use air internal cooling. Foreign countries have also used air internal cooling on the rotor windings of small-capacity turbogenerators. However, the internal cooling system has a complicated structure and requires very clean cooling gas, so it is rarely used in motors that use air as a cooling medium.
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