The invention of heat pipe cooling technology can be traced back to the American patent filed by 1942 and published in 1944. In fact, the earliest successful application was American space science and technology in 1964. Subsequently, with the efforts of scientific circles in various countries, the heat pipe technology has made great progress in theoretical design, manufacturing technology and application fields. At present, as a mature cooling technology, heat pipe has been widely used in many industrial fields. In China, the Institute of Mechanics of the Chinese Academy of Sciences and other units began to carry out the research work of this technology in the 1950s, and successively developed various heat pipes. After 1980s, more domestic units participated in the application research of heat pipe technology, which was successfully applied in the fields of electronic industry, space technology and energy engineering.

The application of heat pipe in motor cooling technology has been put forward for a long time, and some achievements have been made, and some motor prototypes with relatively small capacity have been developed, but most of the work is still in the experimental research stage, which is far from the actual production and application. Researchers only put forward the feasibility study paper of high-voltage motor heat pipe cooler [1>; , or just a comprehensive prospect of heat pipe technology in motor cooling [2]:, but as a document [2]; The author said in the conclusion of the article more than ten years ago that "the application of heat pipe in motor cooling is still in the experimental exploration stage, and the experimental motor capacity is relatively small." To realize the industrial application of heat pipe in motor cooling (especially in large and medium-sized motors), a lot of theoretical research and experimental analysis are needed. "There is no precedent that can be imitated during the research and development of this project. Relying on the basis of motor design and manufacturing, the successful application experience of heat pipe technology in other industries, and the strong motor production capacity of Liangxiang Electric Power Repair Factory, we have embarked on a new road of cooling technology for large and medium-sized motors.

Therefore, we have carried out exploratory experiments and applications on the application of heat pipe cooling technology in large and medium-sized high-voltage motors.

2 Feasibility of applying heat pipe technology to large and medium-sized high-voltage motors in thermal power plants

2. 1 Problems of traditional tube cooler

At present, large and medium-sized high-voltage motor coolers mostly adopt tubular water-air or air-air structure. When the water-air cooler is running, the cooling water is introduced into the cooling pipe, and the hot air inside the motor flows through the outer surface of the cooling pipe under the action of wind pressure to exchange heat with the cooling water inside the pipe, thus cooling the motor. The heat exchange principle of air-air cooler is the same as that of water-air cooler, except that the cooling water in the cooling pipe becomes cooling air.

If air-to-air heat exchange is adopted, that is, the hot air in the motor is cooled by the external cold air, and the hot air exits the pipe and the cold air enters the pipe. The main problems are small heat exchange area, large flow resistance and heavy cooler.

If water-air heat exchange is adopted, the hot air in the motor will flow out of the pipe and the cooling water will enter the pipe. Its initial main problems are:

◆ The copper tube used in the cooler has high requirements, otherwise it will cause dezincification corrosion of the copper tube, leading to water leakage, and the water leaked into the motor will cause serious damage to the motor;

◆ High requirements for cooling water. If the water is not clean or sediment is easy to block the pipeline, and the maintenance of the cooler is large, the cooler pipeline should be cleaned and brushed regularly. Once water leaks into the motor due to wear, the motor will be seriously damaged.

◆ Due to the low water temperature, it is easy to see that the local pipe wall temperature is lower than the dew point temperature of the air in the motor, and condensed water is entrained in the air, which will damage the insulation of the motor.

2.2 Advantages of using heat pipe air cooler

The heat pipe cooler is completely different from the above two traditional coolers in heat exchange principle, which uses the thermal effect principle when the state of the cooling medium changes, that is, when the cooling medium changes from liquid to gas, it needs to absorb heat and when it changes from gas to liquid, it needs to release heat. This is a brand-new cooling method and opens up a new way for motor cooling.

Heat pipe cooler has the following advantages instead of traditional pipe cooler.

A) For air-to-air heat transfer:

● Using the high heat transfer performance of the heat pipe, the heat transfer in the cold air pipe is converted into the heat transfer outside the pipe, so it is easy to expand.

Heat exchange area, thereby reducing the volume and weight of the cooler;

The flow resistance outside the tube is low.

B) For water-air heat transfer:

● Water does not flow in each pipe, but flows out from the heat pipe to the end pipe. As long as the partition is sealed, water can be prevented from leaking into the motor;

● Each heat pipe is an independent heat transfer element. Even if it is damaged by water erosion, water will not leak to the empty side, which can ensure the safe operation of the motor. Moreover, the failure of a few heat pipes will not affect the performance of the whole equipment. Unlike the tube cooler, once it leaks, it must be stopped for treatment;

● This design is convenient to adjust the surface temperature of the heat pipe to keep it above the dew point temperature of the circulating air, so as to avoid condensed water droplets in the air and ensure the insulation requirements for the motor.

2.3 Problems to be solved when using heat pipe technology in motor air cooler

Because large-scale motor equipment requires safe and stable operation, the design and manufacture of heat pipes must meet strict reliability requirements.

The main technical difficulty in the application of heat pipe cooler in high-voltage motor is the calculation and selection of design parameters such as heat pipe type, material, technology and size. In actual construction and reconstruction, it is required to transform the space of the original motor pipe cooler, and the cooling effect is better than the original cooler in principle. At the same time, we should consider controlling production costs and other factors to save money as much as possible.

Judging from the current development of heat pipe technology, whether it is air-to-air heat transfer or water-to-air heat transfer, the design should be said to be relatively mature and the engineering design parameters are relatively complete. Judging from our mastery of heat pipe technology, the types of heat pipes that can be selected include pipes and working fluids, which can meet our design requirements.

In order to ensure the long-term reliable operation of the motor, the selection of heat pipe materials and working fluids and the inspection of manufacturing process quality need to be strictly controlled, leaving no quality hidden dangers.

In the capacity design of the cooler, there is still room for further expansion on the premise that the cooling effect is not lower than that of the original cooler. If necessary, the cooling effect can be easily increased by adding heat pipe elements. Therefore, the design of heat pipe capacity and structural size should have a relatively accurate and specific calculation scheme for a specific type of motor.

3 heat pipe cooler

With the development of heat pipe technology, the available materials, processes and design parameters are relatively complete. Detailed design and calculation can be found in the research report of this topic, which is not detailed here.

The heat pipe cooler adopts aluminum rolled fin tubes, and its structure is separated heat pipe structure, which makes it easier to arrange heat exchange surfaces.

The separated heat pipe structure is convenient to arrange the flow channels of motor circulating airflow (hot airflow) and cooling air (cold airflow), and also reduces the number of pipes passing through the partition plate, which is beneficial to sealing.

In addition, the heat pipe cooler is designed for the complete countercurrent heat exchange of cold and hot air, which can reduce the number of heat pipes.

In the aspect of quality assurance of heat pipe, the choice of heat pipe working medium should ensure long life and safety. When ammonia is selected as a proven working medium, ammonia and aluminum can be compatible for a long time, the working temperature range is also suitable for air coolers, and its thermal performance is also very good.

4 Selection and installation test of test motor

According to the normal production progress of Liangxiang Electric Power Repair Plant, three different types of high-voltage motors are selected for the design and calculation of heat pipe coolers, namely YMKQ600-6 650kW6kV high-voltage motor, YMK600-6/KLOC-0 630 KW10kV high-voltage motor and YMKQ500-6 450kW6kV high-voltage motor, which belong to three different companies.

After detailed demonstration and calculation, we installed heat pipe coolers on three motors to replace the original tube coolers.

Due to some objective reasons, the first of the three motors did not carry out the type test, but the subsequent users reported that the motor was running well and there was no abnormality. The latter two kinds of motors are specially made of the same model, and only the cooler is a traditional tube cooler, and the type test including performance assessment is carried out in Beijing Heavy Machinery Factory. The comparative test results of four motors show that the temperature rise of the motors has decreased, but it is not obvious. This is because in order to control the test cost when designing the heat pipe, the capacity of the heat pipe is close to that of the original cooler, and there is a certain expansion margin in the actual installation space. If necessary, the capacity of the heat pipe can be increased to make the temperature drop more.

The actual operation and performance test results show that the technical transformation scheme of installing heat pipe cooler on high voltage motor is successful.

Application prospect of 5 heat pipe cooler in motor cooling technology

Compared with the traditional tubular air-air cooler or water-air cooler, the heat pipe cooler has obvious advantages because of its different heat exchange principle. First, the heat exchange efficiency is high; second, the corresponding cooler is light in weight and low in cost. At the same time, there is no pipeline blockage problem, which reduces the maintenance workload. Because water is not used, there is no motor failure caused by water leakage, which is also very beneficial to saving water resources. The first successful application of heat pipe cooler in high voltage motor shows that the application prospect is very considerable.

1) replacing the traditional tubular air-to-air cooler on large and medium-sized high-voltage motors can improve the cooling effect, prolong the service life of the motors, reduce the faults of the cooling system, and thus improve the operation reliability of the motors.

2) Replacing the traditional water-air cooler on large and medium-sized high-voltage motors can save a lot of water resources, which has important economic value and social benefits in the water-deficient areas in northern China.

3) If the traditional water-air gas (hydrogen or air) cooler is replaced on the large generator, it can not only reduce the temperature rise of the generator, improve the output, but also save a lot of water resources.

4) We only developed the air-to-air heat pipe cooler this time. If the water-air heat pipe cooler is developed in the future, only the cold end of the heat pipe needs to be cooled. The hot end of the heat pipe cooler is placed on the top of the motor to exchange heat with the hot air inside the motor, while the cold end of the heat pipe is placed on the top or side of the motor to prevent the motor from failing due to water leakage. Further research is needed in the future.

5) The basic working principle of generator cooler is the same as that of motor cooler, whether it is air cooler (such as most hydro-generators and pumped storage generator-motors, all air-cooled turbogenerators) or hydrogen cooler (such as most large turbogenerators are cooled by hydrogen). Although the cooler has many internal structures, it still belongs to the traditional tube cooler for heat exchange. Our successful experience in motor has laid a good foundation for the next step to transform the generator cooler. The transformation of generator cooler is expected to achieve similar effects as motor, such as reducing the internal temperature rise of motor, reducing the failure probability of cooler, reducing the maintenance workload and improving the reliability of equipment. Its economic benefits will be considerable.

6 Application and benefit analysis

The application units of high-voltage motor heat pipe cooler are mainly motor maintenance departments and motor manufacturers of industrial production enterprises such as power plants. Because of the large number of this kind of motor, it is the key power equipment in various industrial production departments, so the project has a wide range of applications, broad application prospects and huge economic and social benefits.

Compared with the traditional tube cooler, the heat pipe cooler has higher heat exchange efficiency, lighter weight and lower cost. At the same time, there is no pipe plugging problem, which reduces the maintenance workload. Because water is not used, there is no motor failure caused by water leakage, which is also very beneficial to saving water resources. Therefore, the economic benefit of the application of heat pipe cooler in high voltage motor is very considerable.

1) replacing the traditional tube cooler in large and medium-sized high-voltage motors in power plants can improve the operation and reliability of the units and bring good economic benefits for the continuous and safe power generation in power plants. Usually, the abnormal shutdown accidents of power generation equipment are reduced, and the direct economic losses avoided are calculated in millions of yuan, and the indirect economic losses are even greater.

2) Replacing the traditional water-air cooler on large and medium-sized high-voltage motors can save a lot of water resources, which has important economic value and social benefits in the water-deficient areas in northern China. The data show that a single motor can save water up to 380,000 tons/year [1>; .

3) If the heat pipe cooler is applied to a large generator, it can not only reduce the temperature rise of the generator and improve the reliability of the generator, but also save a lot of water resources, and its economic benefits will be considerable.

There are thousands of high-voltage motors with old coolers in power plants in China (regardless of other industrial sectors for the time being), and the application prospect of the transformation of old motors is very broad. At the same time, hundreds of high-voltage motors are put into production every year in the power field. According to conservative calculation, the total amount of renovation or new production is not less than 500 units per year. The output value of each cooler is calculated at1.5,000 yuan to 20,000 yuan, and the profit is calculated at 20%, so it is aggregated for the whole year.

Because of the large number of high-voltage motors, which are the key power equipment in various production departments, the cooler reconstruction project can bring benefits such as improving the operating conditions of equipment, prolonging the service life of equipment, improving the reliability index of equipment operation and saving industrial water. Although the economic benefits of each motor transformation are relatively limited, the economic and social benefits created by it are extremely considerable from the perspective of the whole department, the whole region and even the whole country. In addition, if the application technology of generator cooler is further developed successfully, the economic benefits generated by a single generator will be more considerable.

7 conclusion

The application of heat pipe cooler instead of traditional tube cooler in high voltage motor can bring obvious benefits to motor operation performance and maintenance.

First of all, designing a suitable heat pipe cooler can reduce the temperature rise of the motor, improve the running state and improve the running performance. Secondly, the maintenance workload of the cooler is reduced, and the possibility of water leaking into the motor is basically avoided, thus obviously improving the operation reliability of the motor, which undoubtedly has important practical significance and broad industrial application prospects, and has obvious social and economic benefits.

The main technical difficulty in the application of heat pipe cooler in high-voltage motor is the calculation and selection of design parameters such as heat pipe type, material, technology and size. In the actual construction transformation, it is required to transform the space of the original motor tube cooler. In principle, the cooling effect is better than the original cooler, and the production cost should be controlled. There is a certain margin in the design of heat pipe capacity for preliminary exploration.

The design and installation of air-to-air heat pipe coolers for three high-voltage motors with different capacities are successful. If you need to improve the cooling effect of the cooler, you can add more heat pipes to solve it.

According to the successful experience of research and development of air-air heat pipe cooler, we are sure that we can further develop water-air heat pipe cooler for motor and water-air heat pipe cooler for turbo-generator and expand the application range of heat pipe cooler in power plant motor equipment.