2021-03-16
Photovoltaic modules have a design service life of more than 25 years. Correspondingly, corresponding requirements are set for the working life of its supporting electrical components. Each electrical component has its mechanical life. The electrical life is related to the ultimate benefit of the power station. Therefore, the life and quality of components need to be paid attention to.
Many photovoltaic power plants are used in plateau areas, and some of them are distributed in the form of distributed power generation. The distribution is relatively scattered. This situation is relatively difficult to maintain. In order to reduce maintenance costs, the effective way is to improve the reliability of the system, and the reliability of the system depends on the reliability of the components used in the system.
The components we pay attention to here are not the main parts that you usually notice, but relatively small parts such as connectors, low-voltage electrical appliances, cables, etc. The more details, the more likely to cause problems. Today we will analyze the connectors.
In the daily maintenance of photovoltaic power plants, main equipment such as components, DC power distribution cabinets, and inverters are the main objects of concern. This part is that we must maintain normal and stable, because they have a high probability of failure and have a great impact after failure.
But in some links, there are some faults that people don’t know or ignore. In fact, they have already lost power generation unknowingly. In other words, this is where we can increase power generation. So which equipment affects power generation?
There are many places in the power station where interfaces are needed. Components, junction boxes, inverters, combiner boxes, etc. all need a device——connector. Each junction box uses a pair of connectors. The number of each combiner box is related to the design. Generally, 8 pairs to 16 pairs are used, while inverters use 2 pairs to 4 pairs or more. At the same time, a certain number of connectors must be used in the final construction of the power station.
The connector is small, many links need to be used, and the cost is small. And there are many companies that produce the connector. For this reason, few people pay attention to the use of the connector, what will happen if it is used well, and if it is not used well what are the consequences. However, after in-depth visits and understanding, it is found that it is precisely because of these reasons that the products and competition in this link are very chaotic.
First of all, we start to investigate from the terminal application. Since many links in the power station need to use connectors, we can see the product applications of various connectors at the site, such as junction boxes, combiner boxes, components, cables, etc., connectors The shape is similar. These devices are the main components of the power station. Sometimes there are accidents, people originally thought it was a problem with the junction box or the component itself. After investigation, it was found that it was related to the connector.
For example, if the connector catches fire, many owners will complain about the component, because one end of the connector is the component’s own, but sometimes it is actually caused by the connector.
According to statistics, the related problems caused by the connector include: increased contact resistance, heat generation of the connector, shortened lifespan, fire on the connector, burnout of the connector, power failure of the string components, failure of the junction box, and component leakage, etc., which can cause system failures, product recalls, circuit board damage, rework and repairs will then cause the loss of main components and affect the power generation efficiency of the power station, and the most serious one is fire disaster.
For example, the contact resistance becomes larger, and the contact resistance of the connector directly affects the power generation efficiency of the power station. Therefore, “low contact resistance” is a necessary requirement for photovoltaic connectors. In addition, too high contact resistance may also cause the connector to heat up and cause fire after overheating. This is also the cause of safety problems in many photovoltaic power plants.
Tracing back to the source of these problems, the first is the installation of the power station in the final phase. The investigation found that many power stations had problems with the operation of some connectors during the process of rushing to the construction period, which directly laid hidden dangers for the subsequent operation of the power station.
The construction teams or EPC companies of some large-scale ground-based power stations in the west have insufficient understanding of connectors, and there are many installation problems. For example, a nut-type connector requires professional tools for auxiliary operation. Under correct operation, the nut on the connector cannot be screwed to the end. There should be a gap of about 2mm during the operation (the gap depends on the outer diameter of the cable). Tightening the nut to the end will damage the sealing performance of the connector.
At the same time, there are problems in crimping, the most important is that the crimping tools are not professional. Some workers on site directly use poor quality or even general tools for crimping, which will cause poor crimping, such as bending of copper wire at the joint, failure of crimping some copper wires, wrong pressing to cable insulation, etc., and the consequence of poor crimping is directly related to the safety of power station.
Another performance is due to the blind pursuit of installation efficiency, resulting in a decrease in the quality of crimping. If the construction site cannot guarantee the quality of each crimping in order to rush work, coupled with the use of unprofessional tools will cause more problems.
The skills of the installers themselves have an impact on the level of connector installation. For this reason, professional companies in the industry suggest that if professional tools and correct operation procedures are used, the quality of the project will be improved.
The second problem is that various connector products are used in confusion. Connectors of different brands are plugged into each other. Junction boxes, combiner boxes, and inverters all use connectors of different brands, and the matching of connectors is not considered at all.
The reporter interviewed several power station owners and EPC companies, and asked if they knew about connectors, and when the connectors had matching problems, their answers were all at a loss. The operation and maintenance personnel of individual large ground power stations said: “The connector supplier declares that it can be plugged into each other, and it can be plugged into MC4.”
It is understood that the feedback from the owners and operation and maintenance personnel is indeed true. At present, basically all photovoltaic connector suppliers will declare to their customers that they can plug in with the MC4. Why is the MC4?
It is reported that MC4 is a connector product model. The manufacturer is Swiss Stäubli Multi-Contact (usually referred to as MC in the industry), with a market share of more than 50% from 2010 to 2013. MC4 is a model in the company’s product series, which is well-known for its wide application.
So, other brand connector products on the market can really plug in with MC4?
In an interview, Hong Weigang, manager of the photovoltaic department of Stäubli Multi-Contact, gave a definite answer: “A large part of the problem of connectors is from mutual insertion. We never recommend that connectors of different brands are mutually inserted and matched. It is also not allowed. Connectors of different brands cannot be mutually matched, and the contact resistance will increase if operated in that way. The certification body also stated that mutual mating is not allowed, and only products of the same series from the same manufacturer are allowed to be mutually mated. MC products can be mutually matched and plugged and compatible.”
On this matter, we consulted two certification companies, TüV Rheinland and TüV South Germany, and the answer was that connector products of different brands cannot be mutually matched. If you must use it, it is best to do a matching test in advance. Xu Hailiang, Manager of TüV SÜD Photovoltaic Department, said: “Some of the imitation connectors have the same design, but the electrical performance is different, and the products are essentially different. Many problems have appeared in the current matching test. Through testing, power station owners can learn more about the problems in advance, for example, after long-term use, there will be mismatches in harsh environments in the future. “He suggested that component and power station owners should pay attention to the product materials and certificate descriptions, and then consider how to choose connectors.
”The best situation is to use the same set of products from the same company in the same array, but most power stations have several connector suppliers. Whether these connectors can be matched is a hidden danger. For example, a power station has the connectors of MC, RenHe, and Quick Contact, even if the three companies guarantee product quality, they still need to consider the issue of inter-matching. In order to reduce the risk as much as possible, many companies and some power station investors are actively requesting matching tests. According to Zhu Qifeng, sales manager of TüV SÜD photovoltaic product department, Zhang Jialin, sales manager of TüV Rheinland photovoltaic department, also agrees. He said that Rheinland has done a lot of tests, and since problems are found, mutual mating is not recommended.
”If the resistance is too large, the connector will catch fire, and high contact resistance will cause the connector to burn out, and the components of the string will be cut off. In addition, many domestic companies rely on hard connections when installing, which causes the interface to heat up, and the cable is prone to problems. , The temperature error reaches 12-20 degrees.” Shen Qianping, a product expert in the photovoltaic department of Stäubli Multi-Contact, pointed out the seriousness of the problem.
It is reported that MC has never disclosed the tolerances of its products. In other words, most of the photovoltaic connectors on the market are based on the analysis of MC4 samples to formulate their own product tolerances. Regardless of the influence of production control factors, the tolerances of various products are different. There are great hidden dangers when connectors of different brands are plugged into each other, especially in large power stations that use more connectors.
At present, there is a big controversy in the connector and junction box companies in the industry regarding the issue of mutual insertion. A considerable number of domestic connector and junction box companies stated that products of different brands have passed the test of the inspection company and have no effects.
Because there is no unified standard, the standards of certification and testing companies in the industry are not the same. Intertek has some differences with t ü V Rhine, Nande and UL in the problem of connector mutual matching. According to Cheng Wanmao, manager of photovoltaic group of Intertek, a large number of problems have not been found in some current matching tests. However, as far as the technical level is concerned, in addition to the resistance problem, there is the problem of arcing. So there are hidden dangers in the inter-plugging and mating of connectors.
The third problem is that connector manufacturing companies are mixed, and many small companies and even workshops are involved. I found a funny phenomenon in the survey. Many domestic connector manufacturers call their own connector products are MC4. They think this is the general term for connectors in the industry. There are also individual companies that even leave out counterfeit and directly print the logo of MC company.
”When these counterfeit connectors marked with the MC company logo were brought back for testing, we felt very complicated. On the one hand, we were pleased with our product share and popularity. On the other hand, we had to deal with various counterfeit problems, and it’s also low price.” According to MC Hong Weigang, according to MC’s current global production capacity of 30-35GW, the scale has been reduced to the extreme, and cost control has been done very well. “But why are they still lower than us? We start from Material selection, core technology input, manufacturing process, manufacturing equipment, quality control and other aspects are analyzed. The realization of lower prices often sacrifices many aspects. The use of secondary return materials is currently a common error in cost reduction behavior. Low-price competition tends to This is a simple truth in connection with cutting corners and materials. As far as the photovoltaic industry is concerned, cost reduction is a continuous and arduous task. All aspects of the industry are working hard, such as improving conversion efficiency, increasing system voltage, and disruptive component design. Increasing the degree of automation, etc. But at the same time reducing costs and never lowering product quality is a principle that must be adhered to.”
Shen Qianping of MC Company added: “Copycats also need technology. MC has Multiam Technology watchband technology (patented technology), which can not only ensure that the contact resistance of the connector is very low, but also has a continuous low contact resistance. It can also be calculated and controlled. How much current flows and contact resistance can be calculated. The resistance of the two contact points can be analyzed to find out how much space to dissipate heat, and choose the appropriate connector product according to the customer’s needs. The strap technology requires some complicated process technology, which is very imitated. Imitated ones are easy to deform. This is the technology accumulation of the Swiss company, and the investment and value of the product design itself cannot be compared.”
It is understood that it is a basic requirement for connectors to maintain low contact resistance, and many companies in the industry have begun to do so, but long-term stability and low contact resistance require more stable technology accumulation and R&D support, continuous long-term stability and low contact Resistance not only effectively guarantees the normal operation of the small links of the power station, but also generates unexpected benefits for the power station.
How much does the contact resistance of PV connector affect the efficiency of PV power generation system? Hong Weigang calculated this. Taking a 100MW PV project as an example, he compared the contact resistance of MC PV connector (average 0.35m Ω) with the maximum contact resistance of 5m Ω specified in the international standard en50521. Compared with the high contact resistance, the lower contact resistance makes the PV system more efficient About 160000 kwh more electricity is generated every year, and about 4 million kwh more electricity is generated in 25 years. It can be seen that the economic benefit brought by the continuous low contact resistance is very considerable. Considering that higher contact resistance is more prone to failure, more parts replacement and more maintenance time are needed, which means higher maintenance cost.
”In the future, the industry will be more professional, and there will be more and more obvious differences between junction box manufacturing and connector manufacturing. Connector standards and junction box standards will be further improved in their respective fields, and the concentration of materials in all links of the industrial chain will be enhanced,” said Hong WeingGang. Of course, in the end, companies that really want to be long-term will pay attention to the material itself, the process, the manufacturing level and the brand. In terms of the material itself, both foreign copper materials and domestic copper materials are copper materials with the same name, but the element ratios in them are different, which leads to differences in the performance of the components. Therefore, we need to learn and accumulate for a long time.”
Because the connector is “small”, the current power station designer and EPC company rarely consider the matching of the connector when designing and building the power station; the component supplier also pays very little attention to the connector when choosing the junction box; Power station owners and operators have no way of understanding the impact of connectors. Therefore, there are many hidden dangers before the problem is exposed in a large area.
Photovoltaic backplanes, PID solar cells, are also the industry’s attention after the problem is exposed. It is hoped that the connector can attract attention before the problem is exposed in a large area, and prevent the problem before it occurs.
Dongguan Slocable Photovoltaic Technology Co.,LTD.
Add：Guangda Manufacturing Hongmei Science and Technology Park, No. 9-2, Hongmei Section, Wangsha Road, Hongmei Town, Dongguan, Guangdong, China
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