The development of photovoltaic power generation can be said to be changing with each passing day, accelerating towards the goal of carbon neutrality. From photovoltaic modules to photovoltaic combiner boxes, from photovoltaic combiner boxes to inverters, and from inverters to grids, the entire photovoltaic system needs to bring together the power of a large number of components. All links rely on cables and connectors, and photovoltaic connectors must not only be durable enough to withstand harsh environments, but also meet the ever-increasing demands of electrical performance.
In all connector categories, we will first focus on reliability, especially in photovoltaic connectors, photovoltaic connectors should have the same life cycle as the entire photovoltaic system. Photovoltaic systems are exposed to wind, rain, scorching sun and extreme temperature changes for a long time. Connectors must not only be waterproof, high temperature resistant, but also UV resistant.
DC link: Improve reliability, reduce power loss
The international standard MC4 (class MC4) connector is widely used in the DC terminal connection of the entire photovoltaic system. In addition to international standards, each country or region also has locally recognized industry standards. The standard has made clear requirements for the insulation strength, electrical clearance, IP protection level and safety performance of the connectors in the photovoltaic system, and the connectors only need to meet these standards.
TUV/UL/JET three certifications represent the highest reliability of photovoltaic DC connectors. At present, only Stäubli’s original MC4-Evo 2 series can achieve DC 1500V TUV/UL/JET three certifications. The well-known Kuike QC4.10-cds series of domestic manufacturers is 1500V TUV/UL dual certification, TE’s SOLARLOK SLK 2.0 series is also TUV/UL dual certification, and some domestic and foreign manufacturers’ TUV single certification can also reflect the device enough reliability.
Reliability is also reflected in the termination link. There are many doorways in the crimping technology of photovoltaic DC connectors. DC terminals should be crimped with professional tools, and the reliability of crimping depends to a large extent on the tool and operation. Most photovoltaic connectors are crimped in the factory by automated equipment, so the quality is relatively more guaranteed.
After solving the risks of safety and reliability, reducing contact resistance and improving energy transmission efficiency have always been the technical development trend of photovoltaic DC connectors. The lower contact resistance (<0.35mΩ) can ensure the efficient transmission capacity of the equipment, greatly reduce the power loss, which also contributes to long-term reliable operation. Continued increases in contact resistance, such as material property defects, can significantly reduce device efficiency.
Bus-bus connection: Eliminate combiner boxes for safe electrical connections
In the DC combiner box of the photovoltaic system, dense lines and electrical appliances are arranged. In the sealed metal box environment, the heat of the connection point in the box will be relatively high, and the long-term operation is prone to problems such as electrical heating, and the hidden danger is not small.
Bus bus This solution uses IPC insulation piercing connectors to connect photovoltaic modules in series and parallel to the bus bus, directly replacing the DC combiner box. The connection scheme aimed at eliminating the combiner box greatly reduces the number of PV module jumpers, and the overall cost is also more advantageous.
Insulation Piercing Technology, IPC, provides protection, insulation and high-quality sealing for electrical connections by eliminating the need for the connector to strip the wire insulation before making a connection. Combined with a photovoltaic fuse cable with a fuse function, the bus connection can provide near-end protection for the photovoltaic module string.
In addition, the metal blade of the insulation piercing connector is wrapped with a sealing compound, ensuring that the photovoltaic cable can withstand electrical connections up to 1.5 kV DC.
AC Boost Connections: Safety Considerations for Intermediate Connectors in Medium and High Voltage Cables
In AC booster stations, 35kV medium-voltage electrical systems and 110kV/220kV high-voltage booster systems are common. The voltage levels of medium and high voltage products are relatively high, and cable accessories are prone to partial discharge and breakdown problems. Safety is the most important aspect of an AC boost connection.
Usually, in order to ensure the safety functions such as waterproofing of cables, cables in photovoltaic systems use as few intermediate joints as possible, mainly to avoid potential safety hazards caused by improper handling of cable joints. If you want to use an intermediate connector, you must use a junction box, and ensure that the connection is normal.
The heat shrinkable cable joint uses heat to shrink the insulating sleeve and tightly wrap the cable, so as to realize the sealing protection of the cable. The cold shrinkable cable joint is to use the elastomer material to compress the cable to achieve sealing protection. When used in AC boost connections, the main consideration is the withstand voltage. According to the CENELEC HD 629.1 standard, the voltage range of these connectors should be as high as 42kV. According to the IEEE 404 standard, the withstand voltage should be able to reach 35kV.
The junction box should preferably provide a contact capacitance test point to determine whether the circuit is energized. This ability to monitor and detect voltage will improve the reliability and safety of the entire photovoltaic connection system.
summary
The safe operation of the photovoltaic system is the focus of everyone’s attention. To ensure its safe and stable long-term operation, every link of the entire connection system must be foolproof. After meeting the safety and reliability requirements of the photovoltaic system, the connector selection should consider the indicators related to efficient transmission, so as to prevent problems before they occur.