Since the development of photovoltaic industry, the transformation of skills has emerged one after another. For the photovoltaic adapter, it has only experienced two generations of changes, and perhaps "stability" is the way to carry out it. "Stability" means reliability and safety, which is closely related to the electrical connection skill level and experience of connector manufacturers. As a conductive medium, the strap contact refers to a specially formed elastic connecting element, which can significantly improve the quality of electrical connection and energy transmission, so that the connector has a continuously low touch resistance.
1. Brief history of photovoltaic adapter
Before the photovoltaic connector is presented, the connection of photovoltaic power station is mainly completed by the method of "splice" (screw terminal or joint connector). With the development of the profession, the demand for fast, safe and easy-to-use connection plans in the industry is becoming more and more intense.
In 1996, a new type of plug-in connector came into being, which is stobil MC3 photovoltaic connector. Junction box supplier MC3 is a photovoltaic connection product in the real sense. It is two completely different connection methods from "splice". Its meaning is to define the connection of photovoltaic modules from scratch. In 2002, stobil MC4 was launched and once again defined the photovoltaic connector from the beginning, which truly completed the "plug and play". With the increasing requirements of photovoltaic power station system, whether from the normative level or the safety level, it is inevitable for MC4 to present and replace MC3. MC4 has been successfully applied for nearly 17 years since it was developed and put into the market in 2002, and has gradually become a professional standard. At present, there are many kinds of adapter products on the market, but most of them choose the style of MC4 in terms of structure or appearance, so we can call it "similar to MC4".
2. Application of strap touch skill in photovoltaic adapter
Compared with various types of strap finger applications in power transmission and distribution and other occupations, the strap finger used by photovoltaic adapter is relatively single. The "stability" of the photovoltaic adaptor mentioned above refers to that the structure and shape of the photovoltaic adaptor have not changed much in the past 20 years, on the other hand, it is the stability that the photovoltaic adaptor should reflect in long-term application, which is closely related to the touch of the watch band.
According to different application environments, the strap touch finger has strict rules in data, coating, type, scale, positive pressure, device slot planning and so on. This paper focuses on the analysis from the perspectives of scale cooperation and the whole process of strap touch.
3. Cooperation scale
For market considerations, many manufacturers talk about the concept of "MC4 compatibility" when promoting it. In fact, this is misleading. Both stauber and third-party certification organizations have clearly stated that mutual insertion is prohibited, and some countries have made rules on the connectors used in photovoltaic power plants from the perspective of laws and regulations.
The interposing of connectors cannot guarantee the long-term useful touch of the core component - the strap touch finger. For this kind of connection, the dimensional tolerance of the device groove and the cooperative dimensional tolerance of the strap contact finger and metal parts are summarized through repeated tests and calculations by stauber. Although other adapter manufacturers claim that they can plug into MC4, the uncertainty of metal parts, mulilam and device slot will constitute the addition of resistance in this part. In addition, it is also necessary to emphasize the long-term usefulness of photovoltaic adaptors in operation. Although the initial resistance of some adaptors is not significantly added after intercalation with MC4, this does not mean the stability of resistance after a few months or even years. In order to verify the above theory, stauber conducted tc200 + DH1000 and short-time high current test for the mutual insertion of different connectors.
4. Tc200 (on rated current) + DH1000 long term test
The useful results are shown in Figure 4, except for the failure of the adapter caused by inter insertion. Junction box specifications: after the adapter of other manufacturers is inserted into MC4, the touch resistance will be added rapidly. Under the same current, the temperature rise caused by large touch resistance will accelerate the aging speed of non-metallic parts of the adapter, and in some pole cases, the adapter will be melted.