Interview with Dr. Shen Dazhong, MR: Application of on-load tap-changer in HVDC field

The application of HVDC transmission in the field of long-distance transmission has become a trend. Recently, the Polaris Power Network reporter interviewed Dr. Shen Dazhong, Senior Manager of China Business Development at MR Corporation, and conducted in-depth exchanges on the application of on-load tap-changers in the field of HVDC transmission:

Polaris Power Network: Can you introduce MR companies first?

Shen Dazhong: MR Company is an old company with a history of more than 100 years and has more than 80 years of experience in the field of on-load tap-changer R&D, production and sales. MR is the world's No. 1 in terms of both output and sales volume. At the same time, MR is a recognized leader in the market and technology. In the early years, MR was the only professional manufacturer in the world to independently manufacture on-load tap-changers. In the course of many years of development, we have always maintained our professionalism, which is to define our business scope as a segmented product with on-demand decomposition switches, because only focusing on one product can be done deep and specialized. This is also one of our strategies.

Polaris Power Grid: This company was originally engaged in wood processing machinery. Is there any special story?

Shen Dazhong: The MR company's name was registered in 1901, and as early as 1886, the predecessor of MR was a wood processing machine. The reason for establishing a company in Regensburg is that Regensburg is where the Danube and Reagan meet. The Reagan River flows through Regensburg from the Bavarian forest. The timber from the Bavarian forest is transported by river to Regensburg for recovery. The wood is used here for drying and cutting. It requires a lot of machinery, so the machinery factory It is built on the edge of the logging plant and close to the user, providing logging machinery as well as service and maintenance. A turnaround took place in 1926. At the time, Regensburg built the first 110 kV transmission line. At that time, however, the transformer had no regulation function and could not meet the requirements of power quality. The fluctuation of the power grid was very severe. Dr. Yang Sen, general manager and chief engineer of Regensburg Electric Power Co., Ltd. made an invention in his spare time. In 1926, his invention was successfully registered at the German Imperial Patent Office. Afterwards, Janssen did not sell the patent to others. He knew that the patent was ahead of schedule and no one would be interested, so he managed to make a prototype to realize the patent. During the production process, he encountered difficulties in machining, and asked the MR factory to produce the entire prototype. Since then, Dr. Yang Sen has proposed to change the logging plant to an on-load tap-changer factory. As a result, the two parties have been partners since 1926 and until now they have focused on on-load tap-changers. MR is still a family-owned company and is jointly owned by the descendants of the logging machinery factory and Dr. Yang Sen.

It can be seen from this story that after one generation's efforts, MR had processing capability from 1901 to 1926, and the second generation switched to Dr. Janssen's invention and specialized in on-load tap-changers, around 1970. The third generation of talents did this business and completed a mechanical revolution. The previous switch was not only expensive to produce but also complicated. The introduction of on-load tap-changers in 1973 established MR's leading position in technology worldwide. Since 1973, a new product has been introduced almost every 10 years, and continuous innovation has kept MR's technological leadership in this field.

Polaris Power Grid: In recent years, there are many concerns about HVDC transmission and UHV in China. Countries around the world are conducting HVDC projects, which may be due to the inevitable need of long-distance transmission. It is understood that MR's on-load tap-changers are also used in HVDC transmission. Can you tell us about MR application cases in this field?

Shen Dazhong: HVDC technology was born in the 1960s. Instead of a thyristor, the mercury vapor valve was used. Since that time, MR has provided on-load tap-changers for converters. In 1978, MR provided on-load tap-changers for the world's first high voltage direct current (HVDC) transmission project using thyristors in the United States. We have been the leading supplier of on-load tap-changers in HVDC transmission.

All commutation of HVDC transmission is regulated by on-load tap-changers. Therefore, high-voltage direct current has also played a role in promoting the on-load tap-changer technology. This high-end application requires very high voltages, frequent operation times, and high requirements on safety and reliability.

China’s current technology in this field is world-leading. First, because our national resources are mainly distributed in the northwest, and the power load is concentrated in the south and east, the transmission lines are very long. The voltage of HVDC transmission is proportional to the distance, and the longer the distance, the higher the voltage. The Three Gorges transmission voltage is ±500 kV, which is basically the same as the line voltage of most of the DC transmission lines in the world. This is because the transmission distance is only about 1,000 kilometers. If the Jinsha River or Yunnan, Guizhou as the starting point, to Guangzhou, Shanghai transmission, the need to span more than 1500 km. The relative need to increase the voltage, this is the world's first use of ± 800 kV voltage, for all (equipment) manufacturers, including on-load tap-changer manufacturers, posing a technical challenge .

MR is the world's first ±800 kV Yunguang project, providing all 56 vacuum switches. MR also provided 28 vacuum switches for the Xiangjiaba-Shanghai ±800 kV project. In addition, we have also provided 28 vacuum switches for the current ±800 kV transmission project in Nuozhadu. The Zhazadu project is basically the same line as the Yunguang transmission project, but the capacity is high. China's DC transmission voltage will also increase, and China will develop coal bases from Xinjiang to transport coal and electricity to various regions. For example, transported from Hami and Zhudong to Chengdu, Chongqing and other load areas.

Polaris Power Network: In addition to the application of on-load tap-changers in the field of HVDC transmission, does MR have other products and services?

Shen Dazhong: MR currently has five business divisions. On-load tap-changers belong to the Transformer Control Division and are still our main products, accounting for about 85% of sales. In addition, we also produce high-voltage testing equipment that is used in transformer testing and on-site testing of cables. There are also composite insulators. This is an extension of our own production of MR insulation cylinder technology for more than 30 years. The MR on-load tap-changer is made of glass fiber, and the insulator is made of silicone sleeve on this basis, so this division has expanded on the basis of independent production of insulation barrels for more than 30 years.

Power quality management is also one of our businesses. The main application focuses on the low pressure and medium voltage fields. The grid has higher requirements for harmonic pollution generated by industrial users. MR provides customers with engineering consulting, testing, program development and implementation services.

The plasma technology division is newly established. The plasma technology sounds unrelated to MR's on-load tap-changer, and in fact the on-load tap-changer is a very complex mechanical product. Since the products are used in the high pressure field, strict requirements are placed on the treatment of all mechanical parts surfaces. MR has always paid great attention to the surface treatment process, and plasma technology is the future of surface treatment technology. Although the current technology is still in development, it has not yet been applied to machining. This technology has been used in the automotive industry. The car shell uses a lot of industrial plastics. To make the steel plate and the plastic plate look the same after the paint, it needs to be processed by the plasma technology.

MR has five divisions including transformer control, power quality, composite insulators, high-voltage test technology, and plasma technology. MR has set up 23 subsidiaries in 15 countries in the world, covering the world's five major regions. The Americas and Europe are all divided by region, and China is the only one set up in a single country. German SMEs are more specialized in a certain industry. Companies that focus on establishing a global sales system, pay close attention to customers, and even consider customers close to customers as a success factor that is more important than technology. After years of hard work, MR established its first subsidiary in Brazil in 1980 and has now established 23 subsidiaries, covering all regions of the world, and completed the establishment of a global sales network. This is an overview of our company.

Polaris Power Grid: MR vacuum switches can currently replace other similar switches on the market or are they based on the environment?

Shen Dazhong: Until now, we have developed two series of oil-immersed switches and vacuum switches. Each series is perfect, with various voltage levels and various current levels. For any application, it is now possible to select the corresponding product in both series, but from this year onwards, the output of our vacuum on-load tap-changers exceeds that of traditional oil-immersed ones. The vacuum on-load tap-changer will exceed the oil-immersed type.

This year, we also introduced the VM-type vacuum switch. After many years of promotion, the vacuum switch has gained market recognition and has a long experience in market operation. Since 1989, some models have started using vacuum technology. After years of development, this vacuum series has gradually improved. Abundant application experience makes the vacuum technology switch output surpass the traditional oil immersion technology for the first time, and MR VM model introduced at the right time is interchangeable with the widely used M type oil immersion switch. Many customers now use vacuum technology in their new transformers. On the other hand, they also replace oil-immersed switches in existing transformers to reduce maintenance. Transformers have experienced double-digit rapid growth in recent years, but the maintenance personnel of transformers have not increased as fast, so when it comes to a certain maintenance period will bring a lot of maintenance work, one way is to need additional recruits, Train them. Another method is to replace the switch with a relatively small maintenance amount. This replacement amount will be large, so MR will launch the VM type switch that is interchangeable with the M type in due course.

Polaris Power Network: Performance increased by an order of magnitude. So cost-effective?

Shen Dazhong: Yes. The first thing to look at is the performance of the product. In the case of the same application, if the vacuum switch is used, the oil filter is not needed. Because the vacuum does not require maintenance for many years, maintenance does not require oil change, and the oil to be replaced does not need to be recycled or disposed of. If these costs are added, it is actually less than the traditional switch.

Polaris Power Grid: The maintenance period of the vacuum switch is very long?

Shen Dazhong: It is maintenance-free for power transformers. The power transformer is for civil transmission in the power supply bureau, and its maintenance interval is 300,000 operations. What is the concept of these 300,000 times? Our country's power transformers generally have a total of less than 10 operations a day. If we count 10 times a day, we have more than 3,000 times a year, and only 30,000 times in 10 years and 100 years. More than 300,000 times, so it can be said to be maintenance-free.

Polaris Power Network: Is there a requirement for the original transformer model?

Shen Dazhong: No. In the past, if an M-type switch was used, it is only necessary to take the switch-off part, that is, the independent oil-type core, and put the new vacuum switch core into it.

Polaris Power Network: Maintenance-free is indeed a great advantage.

Shen Dazhong: Maintenance-free is of positive significance to environmental protection and saving manpower and material resources. Another important advantage is the increased product reliability. Maintenance is actually the cause of many accidents, because the maintenance depends on the quality, experience, and many unpredictable factors. People are also able to try not to operate as far as possible without surgery, and there will be nothing in the room after surgery. This switch is best not to open without opening.

Polaris Power Grid: In the future, the application of oil-immersed switches in the market will be less and less, and the vacuum may be more and more?

Shen Dazhong: This depends on the development of the market. Since the beginning of this year, the production of oil-immersed production has been lower than that of vacuum-type production. That is to say, there has been such a trend. One is rising and the other is decreasing.

Polaris Power Grid: The vacuum-type switch was introduced on the market very early. Has it been for a long time?

Shen Dazhong: It was also a model that was introduced one by one. It was gradually introduced to the market in 1989, 1995, 2000, 2004, and 2006.

Polaris Power Network: Can a vacuum switch be used for non-gold alloy transformers?

Shen Dazhong: Non-gold alloys are also used for relatively small distribution transformers. Currently, on-load tap-changers have not been used. Generally, no-load switches are used. However, with the application of renewable energy and photovoltaic energy, many distribution network voltage fluctuations are also very severe. The flow of electricity is not in the same direction as before, that is, it flows from the electric field to users. Therefore, the future development trend is not It is clear, but its fluctuation will certainly be great. We need to use on-load tap-changers and we are also concerned about.

Polaris Power Grid: What about the wind energy sector?

Shen Dazhong: Wind energy is an area that we are very concerned about. Especially in Europe, such as Germany, wind energy was developed earlier and now Germany is ready to close all nuclear power plants by 2021. At present, the power generation of nuclear power plants accounts for 1/3 of the total power generation in Germany, and the energy that replaces this 1/3 of the power generation will rely mainly on wind power and natural gas.

Polaris Power Grid: Because the wind power is uncontrollable, can the on-load tap-changer work here to balance the voltage?

Shen Dazhong: The generator of wind power can also adjust the voltage through the adjustment of the excitation adjustment, and the excitation adjustment may be more flexible. Since the voltage from the fan is relatively low, the transformer must use the on-load tap-changer when the voltage rises to 110 kV and 220 kV. The weather conditions on offshore platforms or offshore are very bad. The winds are large, the salt content is high, and the corrosion is very strong. Therefore, the transformers used for offshore wind power generally require full sealing, so the switches must also be fully sealed. The oil-immersed switch extinguishes the arc in the oil. During the process of extinguishing the arc, some gases will be generated. Therefore, it is impossible to achieve full sealing. An oil pillow must be provided to output the gas through the respirator.

Vacuum switches offer the possibility of manufacturing sealed transformers. The possibility of regulating pressure for the transfer of renewable energy to land is also our contribution to clean renewable energy. Only the vacuum switch can be used at sea because it is closed and maintenance-free. The maintenance of offshore platforms requires the deployment of helicopters. This maintenance cost is high and the operation is also cumbersome and dangerous. Therefore, the application of vacuum switches does play a significant role in wind power projects.

Polaris Power Grid: (Vacuum tap changers have a large market in the field of wind power).

Shen Dazhong: Yes. Traditional offshore wind power exchanges are back and forth. A transformer is placed directly at sea to regulate the pressure, and then it is sent back through the cable. In offshore wind farms, because of the long distance from the shore and the large wind, the weather conditions and maintenance conditions are all more difficult. Vacuum switch is the only feasible switch in the field of wind power.

Polaris Power Network: Is there an application case at present?

Shen Dazhong: Yes, MR has many applications for offshore wind power applications, such as the Danish coast, the German North Sea, and the British coast. Even the world's largest wind power center, the Alta Wind Energy Center, and six or seven offshore wind power plants in the sea between Germany and Denmark also use vacuum on-load tap-changers. The offshore wind power projects that we have participated in in China mainly include the Donghai Bridge offshore wind farm.

Another possibility for the transmission of wind power is the use of HVDC transmission. If the wind power plant is built a little further, for example when the distance from the shore reaches 30 to 40 kilometers, it will be difficult to use AC transmission. Too long cable distance will make the loss too much and must use direct current transmission. DC is an on-load tap changer that is used inside a commutation transformer like HVDC power transmission. Although there is a converter station on the road, generally, it uses vacuum tap-changers on both sides.

Polaris Power Network: At present, in the field of high-voltage and special-pressure DC transmission, MR has other products besides vacuum on-load tap-changers. What is the development and layout of future products?

Shen Dazhong: The first is the planning of HVDC. We participate in the planning of HVDC and provide our switch solutions. This is a good cooperation between our customers and us. During project planning, customers communicated with us regarding switch capacity and voltage levels. On the one hand, we must ensure that the program is implemented, and the other is to increase the intelligence of the switch. In view of the importance of HVDC transmission, the monitoring requirements for the on-line state of the switch have also been improved. In order to improve the performance of the switch, our Messko subsidiary and some of MR's electronic product businesses are conducting research in this area. We keep track of development trends at any time. Once users have plans for higher voltage and higher capacity, we will make timely development and program development. We are not only a product supplier, but also provide program development and consulting services. We develop a series of on-load tap-changer solutions for follow-up maintenance and operation, and provide a complete set of services.

Polaris Power Network: What is the development trend of on-load tap-changers?

Shen Dazhong: The development trend of on-load tap-changers is first to vacuum-type development. This year's vacuum-type production is higher than traditional oil-immersed production, which proves that this is the trend of future development.

Second, with the increase in the amount of renewable energy, new demands have been placed on the entire power grid. The previous grid was not designed for the layout of this kind of power supply. Now that so many new renewable energy sources have been added, the grid has undergone great changes. No matter how it is changed, one thing is certain: (grid) fluctuations will increase, and the requirements for on-load tap-changers will increase. The quality of the switch plays a more important role in ensuring the operating reliability of the power grid under frequent fluctuations.

In the future, customers will pay more attention to the reliability and quality of switches. For a long time, some domestic switches have been used at a low frequency, because in the 1970s and 1980s, some on-load tap-changers were technically out of order, and some accidents occurred. The user was a little scared about the switch and moved it as little as possible. However, in order to improve the power quality of the power grid, it is still necessary to use switches. As the amount of renewable energy increases, the number of operations will certainly increase.

Third, increasing energy is one aspect. Reducing losses is also a very effective environmental protection method. Domestically, the steps taken by advanced countries have not yet been implemented in terms of line loss. One of the steps is the adjustment of the on-load tap-changer to the voltage. If the adjustment is made from the point of view of the entire line loss, the loss will be greatly reduced, and at the same time, higher requirements are imposed on the number of operations of the switch.

The future trend is that vacuum switches will be maintenance-free in power transformers and will contribute greatly to improving the reliability of transformers. The second is that the number of operations of the switch will inevitably increase due to the increase in the amount of renewable energy. The third is that the reduction of the line loss also needs to adjust the on-load tap-changer in the transformer to control and adjust from the goal of minimizing the line loss.

Polaris Power Grid: What is the concept of intelligence just mentioned?

Shen Dazhong: First, intelligence is not for on-load tap-changers, but for the entire transformer. What we call intelligence is the intelligentization of a series of transformers such as automation control and status monitoring of substations. Condition monitoring includes both the transformer and the status monitoring of the on-load tap-changer. We want to provide more services in the condition monitoring of the switch and transformer, and learn more about its status to make the transformer stronger. Control and automation capabilities.

I very much agree with China's understanding of the smart grid. First of all (intelligent grid) is a powerful grid, it can control its automation on the basis of a strong grid, and it will naturally have higher operation on on-load tap-changer in the process of transformer being intelligent. Claim. The intelligence of the transformer is to carry out various forms of control over it, not just voltage adjustment, (for example) when it is overloaded, where the limit is, but also to increase the emergency response capability of the transformer. The more you understand the state of the transformer, the higher its intelligence. With a smart transformer, we must fully use it. If not, what is the use of intelligence?

Polaris Power Grid: Does harmonics have any effect on this operation?

Shen Dazhong: No, because our operation is through electric energy agencies. If an electric energy organization is automated in an unattended substation, it is signaled by transferring it. Someone who is on guard gives a signal. This signal is no longer weak, and it is the DC signal of the station itself. We also provide a lot of protection, MR switches are equipped with protection relays, is specifically formulated for the MR switch, the sensitivity is matched with the switch.

Polaris Power Network: MR's power quality is mainly to do reactive power compensation?

Shen Dazhong: More than reactive compensation. The Power Quality Division provides a complete set of services for industrial users, including detecting customer contamination of the power grid, and then providing corresponding solutions, such as selecting filters, reactive power compensation, or isolation, and finally implementing them. For example, the Shanghai maglev project is powered by civilian electricity in Shanghai. When it is turned on, it needs a huge amount of power. Since the principle of synchronous motors has some harmonics, we provide filtering solutions after testing. Avoid the impact on the Shanghai power grid.

Polaris Power Network: MR vacuum on-load tap-changer is currently provided to the transformer factory or directly to the power company?

Shen Dazhong: We mainly provide transformer factory.

Polaris Power Network: Do you have any suggestions for users to choose and use on-load tap-changers?

Shen Dazhong: Since 2008, we have launched a 360-degree sales and customer support system to subdivide after-sales services. Our products are called customer support during this period of the transformer plant. Once shipped to the final customer with the transformer, we call for after-sales service, maintenance and repair.

Our services include three phases. Order purchase period, transformer factory installation period, terminal customer use period.

During installation, we also provide a full range of services to provide on-site installation guidance, training and technical seminars for the transformer plant. We also provide consulting services at the time of the previous purchase. We now have an order form that clearly shows the standard preparations. If the customer does not choose, we will provide them with the standard. If they need special configuration, we provide further consulting services. After consultation, if the customer really needs a special configuration, we will process the order and take into account their requirements. We have all-round and close contact with our customers. Our personnel responsible for orders and sales have kept in touch with certain specific customers and are familiar with some of their habits and traditional practices. Therefore, basically there is no problem in this part of the selection switch through mutual communication.

Through seminars, we allow our customers to fully understand our products. The more customers use it, the more smoothly they can use it. On the other hand, we carry out concrete support in various aspects in all aspects. It's not that the order will be over. We don't care. We provide installation instructions during installation. We also conduct on-site guidance when we go to the user. When such a complete set of service goes down, the customer's problem is solved and feedbacks in time. Then the next step will not be. problem appear. This is good for us too, let us fully understand the whole process of the customer.

Polaris Power Network: How many large-scale transformer companies in China have a cooperative relationship with MR?

Shen Dazhong: Almost all the transformer factories have worked with us, but the size of the company is different. There are indeed many transformer factories in China. More than 300 companies are currently in contact with us. In fact, there are actually more than 1,000 transformer factories in China, especially the production and distribution companies.

Polaris Power Network: Does MR have a factory in Suzhou for production? How about the equipment in Suzhou factory?

Shen Dazhong: Suzhou is a very important milestone in the localization of MR's entire company. In 2006, we established Jiangsu Kaide Electric Equipment Manufacturing Co., Ltd. in Suzhou. This place produces M-type switches and produces electric drives. The switches produced here are identical to those produced in Germany. The workshop in the Suzhou factory is much more beautiful than the factory in Germany. This is a new factory. Germany is a hundred-year-old factory. It is a step-by-step expansion. The Suzhou factory was built entirely on the basis of logistics planning, embodying our many years of experience in production and logistics. Many of them are professional monitoring equipment shipped from Germany.

Polaris Power Network: Is it a production plant or an assembly plant?

Shen Dazhong: It is mainly assembled. One of the characteristics of our products is the relatively small number. If we divide raw materials into several places, the cost of quality control will increase, and the supply cost will increase. Therefore, according to this purchase volume, we must purchase in the whole world.

Polaris Power Network: MR's sales area is also mainly for China?

Shen Dazhong: Yes, mainly for China, of course, part of it is exported. The export of our country's transformers uses our Suzhou switch or German switch. The global AVT products are produced by the Suzhou plant, if only from other places Chinese exports.

Polaris Power Grid: Let's have a vacuum on-load tap-changer. Is there any other competing company?

Shen Dazhong: In terms of vacuum technology strength and experience, there are relatively few companies that are comparable to MR. We introduced vacuum technology to on-load tap-changers since 1989, while other manufacturers now also produce vacuum on-load tap-changers, but they have a relatively short history of using vacuum technology on on-load tap-changers, and we have Nearly twenty years of experience.

Polaris Power Network: There is no good application case or solution to introduce.

Shen Dazhong: The use of vacuum switches in HVDC transmission is a very good case. Because of the large amount of high-voltage direct current, there are 56 transformers on one line, 56 lines of transformers are very long, and the sending end is in the mountains. Traffic is very difficult. To transport such a giant must meet certain conditions, weight and volume. Can not exceed a certain limit. Under these restrictions, if the transformer can save space is a great advantage.

It was said that the current of the HVDC transmission is not pure rotation. It is after DC conversion. There are some influences on the AC. Strictly speaking, harmonics are superimposed on it. Vacuum has this kind of performance, it cuts off the electric current with the harmonic current and the positive vortex electric current to have the difference is not big, but this oil immersive type is in the oil, once has the harmonic wave, the arc extinguishing ability must reduce a lot. In the HVDC transmission, the transformer is generally a one-way transformer and two oil-immersed switches are needed because the quenching performance in the oil will be reduced due to harmonics. The vacuum type will not, a vacuum type can play two oil-immersed functions, thus saving the space of a switch, which is very critical for the transformer.

The space saved can be used for ±800 kV or ±1100 kV insulation. Vacuum on-load tap-changers have technical advantages in HVDC applications. Practice has also proved that it works very well and can indeed replace two oil-immersed switches. Substations have huge commutation variables. If more than 50 units are to be overhauled, they will have to power outages. This time, they will lose a lot of transmission time. The vacuum switch reduces maintenance time. This is very advantageous for a set of lines.

The second is the application of offshore wind power. Offshore wind power requires a switch to be fully enclosed with the transformer, oil pillows, and respirator can not be used, and the vacuum switch to achieve a closed power transformer. This can also be used in such harsh environments as underground substations, mines, and drilling platforms.

The third is that with the needs of environmental protection and safety, alternative insulating oils will surely be promoted. Our country uses less, and there are already many other countries in the United States. No mineral oil transformer can be used in all groundwater protection areas. Even if it is sealed, it may leak. Once it has contaminated groundwater, it cannot be removed for decades. Moreover, in many areas, groundwater is used for drinking. Therefore, mineral oil cannot be used in such areas, instead, instead of insulating oil transformers. The ignition point of the alternative insulating oil is very high and can be decomposed in nature, but the insulating properties of the alternative insulating oil are not as good as those of mineral oil.

Traditional oil-immersed switches are required to extinguish arcs in oil, and replacing insulating oils may not work. Oil-immersed tap changers must use mineral oil. The inner arc of the vacuum switch is in a closed vacuum bubble, which provides the possibility of many alternative oil applications.

In general, vacuum switches are a breakthrough in the HVDC field. The replacement of two oil-immersed switches with an on-load tap-changer eliminates transportation restrictions, saves insulation space for further voltage supply, and offers the possibility of sealing transformers such as offshore wind farms. The other is to provide alternatives for the application of insulating oils. Because the surrounding oil is the same as the transformer, insulation, cooling oil.

Polaris Power Network: What new products are available in these areas?

Shen Dazhong: We now have two series of oil-immersed and vacuum-type. We are familiar with the oil-immersed type is the M-type, R-type, and V-type, is from 35 kV to 500 kV transformer oil immersed Currents range from 200 amps to 3000 amps. The 1000 kV is basically not used yet. Vacuum MR provides VM type, VV type and VR type, also from 35 kV to 500 kV, current from 200A to 2600A, basically two series like this.

Instead of forcing customers to implement a certain series of products, we let users decide for themselves that many customers will choose vacuum-type. We also have no influence on the customer’s decision on price. The initial investment in vacuum is slightly higher, but there is still an advantage over the entire life cycle. Because there is no need to use an oil filter, nor to change the oil every four years, maintenance is also avoided, and these costs are saved.

Polaris Power Grid: Is there a series of products or a total solution?

Shen Dazhong: Because we are a group, on-load tap-changers provided by MR, we have TapGuard, an electronic device that monitors the status of the switches, which can detect the status of the switch, the number of operations, and all the operations that can be performed during the life cycle. The situation is recorded and its overall status is evaluated. Messko provides thermometers, levelers, and maintenance-free ventilators for transformer monitoring, as well as recorders for collisions during transformer transportation.

We provide all the transformer's peripheral components and meters. Our slogan is that there are transformers and MR products. We have developed a lot of peripheral products for transformers, and our product range is relatively complete. We are still further perfecting, for example, Messko has now launched transformer gas relays, gas relays, and will continue to introduce new products in the future.

In addition to the on-load switch, we also provide a no-load switch. No load switch We have DU type, mainly used for 500 kV, 330 kV transformers, 220 kV is also used in part. We also have on-load tap-changers for dry-type transformers in the Chinese market. The VT model is for 35 kV and there is also the AVT model developed specifically for China's 10 kV dry-type transformers. In the United States also introduced a reactive vacuum on-load tap-changer. These are the family of MR on-load tap-changers. Nowadays, domestic transformer companies have entered the international market and their export volume has steadily increased. Many transformer factories may export to the United States. This involves MR's reactive products in the United States. They have to learn how to use this product. This is the earliest The vacuum on-load tap-changer was introduced in the US market in 1989 and it is used very well.

Polaris Power Network: What is MR's commitment to users?

Shen Dazhong: MR has such a long experience with vacuum on-load tap-changers. By 2007, 20,000 units had been produced, and many operational cases have been accumulated. In addition, the maintenance and service life of the MR switch depends only on the number of uses of the switch. No matter how many years have elapsed, its oil will not age. This is MR's commitment to customers.

No oil change is needed, as long as the oil's insulation performance is monitored on a regular basis. The oil-immersed switch is usually replaced in four or five years. Oil change also has a certain amount of work and needs to clean up the carbon ions in the oil. Carbon ions can cause oil aging and increase mechanical wear. Some components must also be disassembled and evaluated before they can be tested to determine the length of time for safe operation. If necessary, they must be replaced. The vacuum switch promises normal operation as long as the number of operations does not reach 300,000 times.