In a photovoltaic power station, to bring together the power of a large number of components and enter the inverter, you must rely on cables and connectors. The photovoltaic connector is one of the components, combiner boxes, controllers, and inverters in the photovoltaic power generation system. key parts connected to each other.
       As of the end of September 2018, my country's cumulative installed photovoltaic capacity was about 133GW, ranking first in the world.Based on 4,000 sets of 1MW consumption, there are currently about 530 million sets of connectors in domestic photovoltaic power plants.From the perspective of risk, it means that there are at least 530 million risk points, which need the attention of power station owners. Nevertheless, photovoltaic connectors are often ignored in the stage of power station design, construction and operation and maintenance. The reason is that People don't pay enough attention to connectors.
       For photovoltaic connectors, 1996 and 2002 are two very important years.Before 1996, there were no special photovoltaic connectors. The photovoltaic cables were connected by general screw terminals or splice connections, and the outside was covered with insulating tape. This method was time-consuming, labor-intensive, and unreliable. increase, everyone wants a fast, safe and easy-to-operate connection solution.
       In 1996, based on these application environments and market demands, a new type of plug-in connector came into being, which is the real photovoltaic connector - MC3.Its inventor is the Swiss company Multi-Contact (in 2002, incorporated into the Stäubli Group), MC is the brand abbreviation, and 3 is the size of the diameter of the metal core.The main body of the MC3 is made of TPE material (thermoplastic elastomer) and is physically connected by friction fit.More importantly, the MC3's connection system uses MULTILAM technology to ensure the lasting stability of the connection.
       In 2002, the birth of MC4 redefines the photovoltaic connector again, it truly realizes "plug and play".The insulation uses rigid plastic (PC/PA) and is designed to be easier to assemble and install in the field.After MC4 came into the market, it was quickly recognized by the market and gradually became the standard of photovoltaic connectors.
       MC4 connectors are divided into line ends and board ends. Generally speaking, MC4 refers to line ends.MC4 is composed of two parts: metal parts and insulating parts.MC is the abbreviation of Multi-Contact, and 4 is the size of the diameter of the metal core.
       Connectors from different manufacturers are inconsistent in terms of specifications, dimensions and tolerances, so they cannot be 100% matched.If they are forcibly inserted into each other, it will lead to problems such as temperature increase, contact resistance change and IP level cannot be guaranteed, which will seriously affect the power generation efficiency and safety of the resistance.
       Since Multi-Contact is the first professional photovoltaic connector in the world, many standards are set by it, which has a huge impact. Many people mistakenly think that the foreign name of photovoltaic connector is MC4, but it is not. Another one is photovoltaic connector. Amphenol/Amphenol, shipments are similar to it, model HeliosH4.
       Photovoltaic systems are exposed to wind, rain, hot sun, and extreme temperature changes for a long time, and connectors must be able to adapt to these harsh environments.They must not only be waterproof, high temperature and UV resistant, but also touch protected, high current-carrying capacity and efficient.At the same time, low contact resistance is also an important consideration.All of this must also run through the entire PV system life cycle, at least 25 years.
       The application environment of photovoltaic connectors is generally very harsh, ranging from seaside saline-alkali land to plateau deserts and other terrains, from hot equatorial to cold high latitudes, as well as perennial erosion such as solar radiation, rain and snow, and wind and sand, and the weather resistance of shell insulation materials. Performance, heat resistance, flame retardant properties, mechanical properties, insulation properties and other aspects of performance are very good, can only be used for 25 years, to ensure the inner copper core and outer insulation.
       The inside of the photovoltaic connector is the copper core of the plug-in and the copper core of the cable. It has no anti-corrosion function. The connector needs to keep the copper core isolated from the outside world. The on-board connector is also together with the inverter (or controller). To ensure the sealing function of the inverter, the sealing function of the connector should also be very reliable.In addition, when installing, the sealing screw should be tightened.
       According to the latest international standard IEC 62852 for photovoltaic connectors, after the test, the contact resistance after the male and female is inserted should not increase more than 5 mΩ or the final resistance value should be less than 150% of the initial value.Using high-quality photovoltaic connectors, the power consumed by the connector is less than 1/10,000 of the total system power, and the power consumed by inferior connectors is more than 30 times that of high-quality connectors.The root cause of the failure of the connector and the fire: In the case of current flow, the contact resistance of the connector increases, which leads to an increase in temperature rise, which exceeds the temperature range that the plastic shell and metal parts can withstand.The contact resistance is mainly related to the material and size of the copper core. Connectors of different brands have different specifications. It is recommended not to mix them.When installing, the male and female connectors should be inserted in place, and the connectors of the regular brand will make a sound when they are inserted in place.
       Types and characteristics of the metal core: The metal core is the main body of the connector and the most important path for the current to pass through.At present, there are two types of photovoltaic connectors on the market. One is "U"-shaped metal core, which is stamped and formed from copper sheets, also known as stamped metal core, which is suitable for automated wire harness production.Another part of the photovoltaic connector uses an "O"-shaped metal core, which is formed by drilling holes at both ends of a thin copper rod, also known as a machined metal core.The "O" type metal core is connected reliably and requires low crimping tools.Suitable for production with hand crimping tools.
       There is also a very rare metal core that is free of crimping, which is connected by spring sheets and cables.Since no crimping tool is required, installation is relatively simple and convenient.However, leaf spring connections result in high contact resistance and cannot guarantee long-term reliability.Some certification bodies also do not recognize this metal core.
       Crimp is one of the most basic and common joining techniques.The reliability of crimping depends to a large extent on the tool and operation, both of which determine whether the final crimping effect meets the requirements of the standard.Taking the "U"-shaped metal core as an example, it is basically made of tinned copper and needs to be connected to the photovoltaic cable by crimping. The crimping process is as follows:
       It is not difficult to see that the "U"-shaped metal core crimping is a process in which the copper wire wrapped by the copper sheet is gradually compressed as the crimping height gradually decreases (while the crimping force gradually increases).In this process, the control of the crimp height directly determines the quality of the crimp.
       B. Pull-off force, that is, the force required to pull out or break the copper wire from the crimping place, such as 4mm2 cable, IEC60352-2 requires at least 310N;
       D. Cross-sectional analysis, non-destructive cutting of the crimping area, analysis of width, height, compression ratio, symmetry, cracking and burrs, etc.;
       The vast majority of photovoltaic connectors are installed in the factory through automated equipment, and the crimping quality is high.However, for connectors that have to be installed on site, crimping can only be done with crimping pliers.The crimping must use the original professional crimping pliers. Ordinary vise or needle-nose pliers cannot be used for crimping. On the one hand, the quality of the crimping is low, and this is also a method that is not recognized by connector manufacturers and certification agencies.
       When the power of the components is small and the number is relatively large, two or more components are required to be combined together. Common confluence kits include two-way one, three-way one, four-way one, five-way one and so on.According to the method, it can be made into an injection-molded one-piece type or a wire harness type.