Views: 2 Author: Site Editor Publish Time: 2021-10-12 Origin: Site
2. Failure analysis of resistance Rcr
The crimping resistance Rcr is mainly related to the crimping quality and the crimping process. We can judge the quality of crimping by the compression ratio and crimping profile. Good crimping requires a tight profile without gaps, and a regular appearance (refer to Figure 9). For the commonly used 4mm2 cable crimping, the contact resistance at the crimping point is also required to be less than 0.2mΩ in the standard IEC2742/05, while IEC60352-2 stipulates that the pull-out force of the crimping end should be greater than 310N.
Figure 9: Good crimping (left) VS poor crimping (right)
When it comes to the crimping process, we need to pay attention to the stripping process. The standard has strict regulations on the number of copper wires to be cut in the stripping process. If more copper wires are cut off, it will affect the quality of crimping and flow, resulting in a higher temperature rise. In the failed samples, we found that many copper wires in the cable had been cut before crimping (see Figure 10).
Figure 10: Broken copper wire at the crimping end
In order to ensure good crimping quality, we recommend using the regular wire stripping tools and crimping tools provided by the manufacturer. At the same time, it is recommended that the professional and technical personnel of the connector manufacturer do detailed system training during installation.
2. Failure analysis caused by sealing performance
Since the connector is outdoors, it has strict requirements for sealing performance.
For example, some photovoltaic connectors have reached the protection level of IP65 and IP68. Since the photovoltaic connector is matched with the cable, the choice of the cable becomes very important when it comes to airtightness. Generally speaking, different connector models correspond to different cable outer diameters, the purpose of which is to ensure the sealing performance. For example, the MC4 connector can match photovoltaic cables with an outer diameter of 3-9mm (conductor cross-sectional area 1.5-10mm2), but there are as many as 6 corresponding models. In order to verify the matching of the cable, after the connector is assembled, it must be subjected to related tests, such as IP test, wet insulation test, and withstand voltage test, etc.
Two of the failed samples used different cables, and the outer diameters were very different. The picture on the left in Figure 11 uses a photovoltaic cable (black) with an outer diameter of 6mm on one side of the photovoltaic connector, and an ordinary cable (blue) with an outer diameter of only 4mm on the other side. After unscrewing the screw cap of the blue cable end, it was found that the red plastic sheet was used to fill it due to insufficient sealing. In this case, it is difficult to guarantee the sealing performance of the photovoltaic connector. Therefore, water and dust may enter during outdoor application, which will damage the insulation performance and cause a fire.
One end of the connector on the right in Figure 11 is a black photovoltaic cable with an outer diameter of 6.1mm, while the other end uses a red ordinary cable with an outer diameter of only 3.9mm.
Three, this can be entered in the title of the failure analysis caused by the insulating material
The choice of insulating material directly determines the quality of the connector. A good connector needs to choose a suitable insulating material, and the suitability is mainly determined by the requirements of the use of the connector, such as the weather resistance, heat resistance, flame retardancy, mechanical properties, and insulation properties of the material. Photovoltaic connector insulation The choice of material is the result of comprehensive consideration of these properties. Choosing the right material can reduce the probability of product misfire under higher temperature rise.
In addition, it is not possible to use recycled materials for photovoltaic connectors. The reason for saying this is that the use of recycled materials has extremely strict regulations and product inspection measures. Only in this way can the performance of its products not drop a lot. And photovoltaic connectors are required to be used for more than 25 years in many clients, which means that very high requirements are placed on materials.
Although the use of recycled materials can reduce the cost of the product, it increases the failure probability of the product at the end of the use, so the connector manufacturer should stop it.
Four, failure summary
Photovoltaic connectors account for a relatively low proportion of the cost of photovoltaic power plants, but they are key components. In the early stage of the construction of the power station, the risk of failure caused by the connector is often ignored, but it will become a pain point in the operation and maintenance of the power station in the later stage. The operation and maintenance costs caused by connector failure include the loss of power generation revenue, the cost of spare parts, labor costs, and safety risks. These operation and maintenance costs will ultimately affect the return on investment of the power station. The reliable quality and the photovoltaic connector provided by the supplier with rich experience in production and assembly is one of the foundations to ensure the normal and stable operation of the photovoltaic power station, and the normal operation of the power station is one of the prerequisites to ensure the owner's maximum profit.