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According to statistics, as of the end of 2013, 22 major provinces and cities across the country have cumulatively connected 741 large-scale photovoltaic power generation projects and are mainly distributed in the northwest region of China. The top five provinces with cumulative installed capacity are Gansu, Qinghai, Xinjiang, Ningxia, and Inner Mongolia. The sum of these five provinces accounts for about 80% of the total number of photovoltaic power stations in the country. And these five provinces are precisely the areas with heavy sand and dust. In other words, the application environment of most photovoltaic power plants is still very poor.
Recently visited a number of power stations in the northwest of Golmud and found that one of the headaches commonly reported by the operation and maintenance personnel was dust accumulation and dust cleaning of the inverter equipment and the inverter room. Obviously, this problem has not been clearly taken into account, but it has brought a lot of work to O&M. In particular, large-scale ground power stations in areas with severe wind and sand in the northwest, such as Gansu, Ningxia, and Qinghai, have spent a lot of manpower and costs. Deal with wind and dust. Then where does the dust come from, how serious is the accumulation, what impact does the station have, and can the conventional sweep solve this problem? This paper will briefly analyze this, and initiate discussions with industry experts.
one. Dust hazard
Where does the dust come from?
Many people are surprised when they open the inverter door and feel unscrupulous dust inside! Just after the sweep, why is it still a long time later? In fact, there are two main reasons: First, the conventional civil or container-type engine room claims IP54 protection level. However, due to the general direct-ventilation heat-dissipation scheme in the engine room, it can only reach IP44 or lower, and it can not block dust and corrosive gases. Enter the inverter. The cooling fan at its air inlet will continuously suck in gas from the outside and form a cycle to reduce heat. In this way dust, dust, particles, hair and other things in the air were all sucked in together. The whole room naturally became gray and dirty.
Most of the ground-based photovoltaic power plants in China are concentrated in the northwest region. The natural environment in the area is harsh and sandstorms often occur. The actual situation is even more serious. The second is static electricity. The inverter itself also has a cooling fan. It also sucks the dust inside the room into the chassis. Dust is absorbed by the static electricity generated by the electronics inside the chassis. Therefore, it can be seen that a large amount of dust is adsorbed around the inverter room and the electronic equipment, electrical components, and fans in the room.
2. Hazard
So what is the danger of dust accumulation on our equipment? After investigating the situation of several domestic centralized high-power inverter power plants, we discovered that after many inverters are used for a period of time, they are prone to shutdown, control failures, internal abnormal ignition failures, and serious fire and combustion. Major property damage. Analyze the cause of the problem and most of it is related to dust. Recently, the main reason for the container inverter room fire in the Northwest Power Station was caused by poor heat dissipation caused by dust accumulation.
Dust is ubiquitous in air and can cause printed board assembly failures or poor internal contactor contact. Due to the small size of dust particles, it is not possible to use the conventional technology to completely filter the air filter in the equipment room or equipment at this stage. These fine particles deposited on all vertical surfaces, typically 0.5 μm in diameter, constitute the main contaminants inside the device.
Let's analyze the specific hazards of the dust to the inverter.
1) Leakage failure
In dry air conditions, the impedance is generally high and failure does not manifest. In the case of rain and fog, when the weather is humid, the dust turns into wet dust after absorbing moisture, and the wet dust exhibits strong conductive activity. Leakage effect is formed between PCBs or components, causing abnormal signals or arcing at high voltages. It may also cause a short circuit in the power grid to the PE. Although some PCBs are protected by three anti-paints, after the three anti-paints are coated, pinholes are still formed on the pins and edges of the components. Wet dust can still affect the electrical properties, causing inverter failure, abnormal shutdown or frying. destroy.
2) Corrosion failure
In wet weather such as heavy fog and rainy days, the wet dust formed inside the inverter has another danger, that is, it will corrode the electronic components inside the equipment. Single board or PCB components increase in humidity, wet dust reaches a certain condition, acid and metal ions in the wet dust become abnormally active, become acidic or alkaline, easy to PCB copper, solder, the formation of the end of the device Corrosion effect. Caused abnormal equipment operation.
3) poor heat dissipation failure
Accumulation of dust leads to blockage of the air filter, radiator heat dissipation performance deteriorates, the temperature of high-power devices rises sharply, causing temperature alarms, fan speed increases, noise increases, more serious internal IGBT devices will be damaged, the device restarts, and even Burned out.
two. Large amount of operation and maintenance, considerable cost
The author carried out in-depth exchanges with the operation and maintenance personnel of several power plants in the northwest on sand and dust issues. O&M personnel complained about the problem of dust and sand, complained and complained.
Take the actual situation of a power station in Golmud as an example. At present, each large inverter requires dust to be cleaned once a month. For a large ground power station, it can be cleaned once every three months because their teams can only clean every night. It will take at least three months to clean up the 300-megawatt power station at around 10 stations. What's more serious is that it has just been cleaned up, and it will remain the same for several weeks. Therefore, it is necessary to continuously perform the cleaning of dust and dust in 365 days a year.
1. Dust net cleaning
Dust nets can effectively improve the dust accumulation of the equipment, but they cannot completely block the entry of dust. The dustproof nets of containers and inverters generally use G4 or 50PPI filters; when the inverters work during the daytime, the high-power fans have high rotation speeds and bring external dust into the interior of the equipment room. Some of these particles accumulate on the floor of the equipment room, and some are blocked. In the air filter, some fine dust particles still enter the cabinet. In the northwestern sand area, filters need to be replaced or cleaned within 2 to 3 months. Once the maintenance and cleaning are not completed, the air filter will cause the air intake of the equipment room to be less and the heat radiation will deteriorate rapidly. The temperature of the equipment room will increase. Because of poor heat dissipation, the inverter causes the output power to decrease, and even shuts down. If the derating and the protection mechanism are not perfect, it may cause burn-out or even fire accidents.
When the dustproof environment of the equipment room is poor, the frequency of dust removal should be increased. At the same time, dust removal also requires professional personnel to prevent internal board or electrical damage. The maintenance time of the air filter of each container or equipment room is more than 0.5 hours. The maintenance of the air filter once every two months means that the power station needs to deploy special personnel to maintain the air filter for a long time.
2. Room cleaning
The frequency of internal cleaning and maintenance of large machines is maintained according to the actual situation; it is once a month on average. At the same time, according to the weather conditions in the northwest sandstorm, it may be necessary to maintain every dust storm.
When cleaning, the front and rear doors of the inverter need to be disassembled; the protective cover needs to be disassembled, the structural design of each manufacturer is not the same, and it is very difficult to disassemble the door panel and the protective cover. Staffs with professional skills are required, and they cannot be simply outsourced to cleaning. the company. As an example of a manufacturer's inverter, there are more than 30 light-screw screws and a large workload. Demolition also requires special tools. At the same time, frequent disassembly has increased the potential for faults.
In addition, electricity is generated during the day; cleaning and dismantling can only be performed at night. There are many mosquitoes in the summer and it is too cold in winter. Everyone knows that winters like Ningxia, Xinjiang and other regions are quite normal. The staff’s hands and feet are not very flexible. Cleaning takes a lot of time and manpower. As mentioned above, taking the 300M PV power plant as an example, 10 people dismantled and cleaned the reverse 10 units on an average night; 300 MW required a total of 3 months. Some equipment may not be able to use a broom in a local area. It is necessary to blow dust with professional tools such as an air pump. The three-month cycle is too long and requires more manpower to carry out cleaning and maintenance to ensure the work of the engine room and equipment. In addition, the photovoltaic power station construction area is far away from the urban and rural areas, and the field operation and maintenance cleaning work is inconvenient.
In the Northwest power station, a common phenomenon in summer is that the door is opened to cool down. When the inverter door opens, the heat wave surges, the temperature reaches as high as 50 degrees, and the outdoor temperature is only 30 degrees. The fastest cooling measure is to open the door to dissipate heat, which is the whole day. However, with it, a large amount of wind and sand will blow into the inverter room, which will further affect the equipment. The dust dust will be cleaned more frequently.
3. Cost
According to the 100MW power plant project, 10 people can only clean 10 machines a day. 100MW has a total of 200 machines. According to the actual conditions of the Northwest Power Plant, it should be cleaned at least once a month. 100MW power station cleaning again, it takes 20 working days (1 month). According to this frequency, one person needs 300 yuan for one day, 10 people for one day, and 3,000 yuan. According to one month and 20 working days, one year's light labor cost will be at least 3000*20*12=72 thousand. In the power plant's life cycle of 25 years, a total of 25 * 72 = 18 million yuan, equivalent to this piece of light manpower cleaning costs up to 0.18 yuan / W. This cost is quite alarming. If we further consider the increase in labor costs and inflation in 25 years, the actual cost paid will be much higher than this figure.
In addition, the air filter needs to be replaced every 1-2 months. There are also professional procurement and depreciation of cleaning tools, all of which bring practical costs and difficulties to the operation and maintenance of the power station.
three. to sum up
In summary, the problem of dust and dust in centralized inverter houses is a major test of nature for centralized inverters, which increases the potential for equipment failures and also brings a lot of costs and difficulties to power station operation and maintenance. . In the 25-year life cycle of the power station, the manpower, material resources, and intangible power generation losses paid for this are all considerable, and may even exceed the value of the equipment itself. Although some inverter rooms are designed with sand-proof shutters or higher-level dust-proof designs, improvements have been made to prevent dust and sand in a certain degree and time. However, in the northwestern sandstorm areas, the situation is still quite serious. A lot of dust cleaning work is done to prevent the entry of dust.
When investing in photovoltaic power plants, the owner needs to consider the initial construction cost, but it should pay more attention to the long-term product life, safety, and the total cost of operation and maintenance. The sand dust problem of centralized inverter houses has increasingly affected the long-term reliability of power plants. run. Therefore, it is particularly critical to first choose the right brand inverter solution. Or can we take the initiative to find a solution to protect dust from outside the inverter instead of passively sweeping the dust? These issues deserve our deep thinking! (Author: Lee Teng-hui in Photovoltaic Technology Co., Ltd. Lu Xiaoyi)
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