From a structural point of view
The rotor part of the motor includes the rotor core, rotor winding, and shaft. The rotor core is part of the motor magnetic circuit. It is generally made of 0.5mm thick mutually insulated silicon steel sheets punched and laminated. The outer circle of the punched sheets is punched with evenly distributed slots to accommodate the rotor winding; the rotor winding is used to generate induced electromotive force and current, and generate electromagnetic torque under the action of the rotating magnetic field to make the rotor rotate; the shaft supports the rotor core and winding, and transmits the mechanical torque output by the motor, while ensuring a certain uniform air gap between the stator and the rotor.
When it comes to rotors, the most common ones on the market are cast aluminum rotors and cast copper rotors, which are widely used in small and medium-sized motors. The process of casting aluminum or copper is carried out in the rotor winding part. The rotor winding can be divided into cage type and winding type according to its structure. The cast aluminum rotor and cast copper rotor we are talking about belong to cage rotors. If the iron core is removed, the winding is actually equivalent to a cage, that is, the coil of the rotor. Since it is a coil, the line resistance needs to be reduced. In addition, the winding requires higher conductivity, so it is naturally necessary to use copper or aluminum to make it.
Cast aluminum rotor
The cast aluminum rotor is made of aluminum casting, which casts the guide bars in the slot and the end rings of the two sections of the core, the balance column and the fan blades, making the rotor a solid whole. The slot shape of the cast aluminum rotor is not limited by the cross-section of copper or aluminum, and the optimal shape can be flexibly designed; the rotor fan blades, cage bars, end rings and balance columns are cast at the same time, which can improve the heat dissipation efficiency; the cast aluminum rotor structure is symmetrical and compact, and it is easy to achieve mechanical balance. Due to its short production cycle, low cost and suitability for mass production, cast aluminum rotors have been widely used. The cast aluminum of the rotor directly affects the size of the rotor resistance, which has a great impact on the starting performance and rated speed of the motor. However, since the cage bars are in very close contact with the core, the cast aluminum rotor may cause large stray losses. In addition, if the aluminum liquid does not flow smoothly during casting, the aluminum bars in the cast aluminum rotor slot will be disconnected or thinned, which will increase the noise of the motor and deteriorate the performance.
Cast copper rotor
Cast copper rotor technology is recognized in the industry as the most economical and simple solution among technical solutions for high efficiency of electric motors. Copper rotor motors have four major advantages:
1. Improve efficiency. Cast copper rotors instead of aluminum rotors can significantly improve the efficiency of small and medium-sized motors, resulting in huge energy-saving benefits. Taking the Y132M-4 7.5KW motor as an example, after replacing the cast copper rotor, the motor efficiency increased from 87% to 90.4%. Calculated based on ten years of use of the motor, the electricity bill can be saved by 16,080 yuan, which is 16 times the replacement cost. The benefits are very obvious. At present, Nanyang Explosion-Proof Group has developed a copper rotor induction motor with IE5 efficiency level. The measured efficiency of the 15HP-4P motor can reach 93.6%.
2. Reduce temperature rise. Taking a 25HP 18.7KW motor as an example, the temperature rise of a copper rotor motor is reduced by 41% compared to an aluminum rotor motor, only 47.2℃. And the service life of the motor can be doubled for every 10 degrees Celsius reduction in the operating temperature. Therefore, the copper rotor motor can effectively extend the life of the motor. At the same time, it also increases electrical safety, especially suitable for special explosive environments.
3. Reduce volume, reduce weight, and reduce costs. Under the same efficiency, the volume of the cast copper rotor motor is about 15% smaller than that of the aluminum rotor motor, which is suitable for the application of motors with reduced base numbers, such as motors for reducers, compressor motors, and pump motors. Through optimized design, the weight of the cast copper rotor motor can be reduced by about 20%. For example, the total weight of a 15 HP TEFC motor is reduced by 8KG after being converted to a cast copper rotor. In terms of cost, the cast copper rotor motor of the same efficiency can be reduced by about 10%. When the price of copper decreases or the price difference between copper and aluminum becomes smaller, the cost reduction will be more obvious.
4. Corrosion resistance. Copper has excellent corrosion resistance, making copper rotors very suitable for application scenarios such as brine pumps and hot water circulation pumps.
The cast aluminum rotor has a low melting point and low price; the cast copper rotor has strong magnetic induction and a high melting point. The biggest difference between the two is durability and power. Although the manufacturing cost of copper rotors is high, on the whole, copper, as an essential basic material for the development of renewable energy, will use its high efficiency and environmental protection characteristics to help global energy transformation. The use of copper rotors can significantly improve motor efficiency. This results in reduced electricity consumption and further reduces overall costs. Among all technologies and methods to improve the electrical efficiency of small and medium-sized squirrel-cage motors, using copper rotors instead of aluminum rotor die-casting technology is considered to be one of the best ways.
Wolong Nanyang Explosion Protection, aluminum rotor motor, high voltage motor
