How much you know about the Combiner box for solar system?

(Last Updated On: 2020年11月27日)

Introduction of Photovoltaic Power Plants Overview.

A photovoltaic power plant is a photovoltaic power generation system that uses the sun’s light energy and electronic components such as crystalline silicon panels and inverters to generate electricity that is connected to the power grid and delivers power to the grid.

The PV power generation system consists of solar arrays, battery packs, charge/discharge controllers, inverters, AC power distribution cabinets, solar tracking control systems, and other equipment. The PV power generation system usually consists of PV modules, inverters, PV distribution boxes, meters, and power grids, and the distribution boxes, although the distribution box is not accounting for a high percentage of the total system cost, but play an important role in the PV power generation system.

Photovoltaic Applications

Solar energy is an inexhaustible source of renewable energy, which is sufficiently clean, absolutely safe, relatively widespread, really long-lived and maintenance-free, resource-sufficient and potentially economical, etc., and plays an important role in long-term energy strategies. Photovoltaic power plants are currently among the most strongly encouraged green power development energy projects. The use of limited resources to achieve the maximum amount of energy for human use.

Power Distribution Boxes in Photovoltaic Power Plants

Photovoltaic power generation is developing rapidly in China, and the application of photovoltaic in all aspects of life has been reflected. Household photovoltaic power stations, large photovoltaic ground power stations, photovoltaic buildings, photovoltaic street lights, photovoltaic traffic lights, photovoltaic caravans, photovoltaic electric vehicles, photovoltaic carports, and more and more electricity-using environments have a photovoltaic figure, in which the photovoltaic box plays a vital role in the entire photovoltaic system, the main functions of which are as follows:

1. Power isolation function

Switchboards require a physical isolation device that allows the circuit to have a sharp break-point for the safety of personnel in service and maintenance situations. This device is called an isolation switch, which could ensure safety while the electricity has a short circuit, and the current increases and cause the cut off of the isolation switch.

2、Short circuit protection function

Once a short-circuit occurs in a circuit, it will cause a sudden increase in current, which will burn out the appliance and generate a lot of heat, making it susceptible to fires, with serious consequences. Therefore, when a short circuit occurs, a device is needed to cut off the power. The air switch is the device, which occupies an important role in the PV box. When you choose the air switch, please try to use reliable products and choose reliable manufacturers to ensure the safety.

3、Energy measurement

Generally, PV energy meters are installed together with the distribution box. There are also some places where the meter is separate from the distribution box. You can choose according to the local power supply department.

4、Over-voltage protection

The majority of distributed PV power generation is connected to the rural power grid. One of the characteristics of rural grids is that they are unstable, it is common that the power outages usually, and the voltage fluctuates greatly. In this case, the PV distribution box has a device indispensable, that is, an under-voltage protector. In the case of over-or under-voltage, it acts as a circuit breaker to protect other components. Under-voltage protection in the entire photovoltaic box, is more prone to failure of accessories, even if maintenance and replacement are required.

5、Lightning protection

Lightning is also a common natural phenomenon in life, especially in the summer, the thunderstorms are frequent happened and many accidents happened to people, Lightning is a scary thing in life, and there are lightning protectors in many places. There is also an important lightning protection device in the distribution box – the surge protector. A surge protector, also called a lightning protector, is an electronic device that provides safety protection for different electronic equipment, instruments, and communication lines. When the electrical circuit or communication lines because of external interference in the sudden generation of current or voltage, the surge protector can be turned on in a very short period of time to shunt, thereby reducing the circuit damage to other equipment, is an indispensable component.

6、About the cabinet

Generally speaking, the design service life of photovoltaic power generation is 25 years, so the distribution box should be used for 25 years, requiring a waterproof and dust-proof function. With the development of society and the progress of the times, the original distribution box made of cheap tin was not up to the requirements. Now the power supply bureau generally requires to use the of galvanized plate spray plastic, iron plate spray plastic, stainless steel, plastic steel, and other materials of the distribution box. Otherwise, you will forbid to the parallel network, in order for your safety, choose the appropriate box is very important.

7、Cable Wire selection

Photovoltaic distribution boxes can calculate the size of the rated current, depending on the installation capacity, and multiply it by a factor to calculate the larger current. The thickness of the cable determines the larger current it can carry. Cables generally use copper wire, and the thicker the wire diameter, the more current it could carry.

Composition of PV distribution box composition

Photovoltaic distribution boxes generally consist of circuit breakers, self-duplicating overvoltage protectors, surge protectors, surge protector backup circuit breakers, and knife switches.

1. circuit breaker

A circuit breaker is a switching device capable of closing, carrying and disconnecting the current under normal circuit conditions and closing, carrying and disconnecting the current under abnormal circuit conditions within a specified period of time.

In terms of the selection of circuit breakers (1.2-1.5 times the maximum output current of the inverter), the common specifications are 16A, 25A, 32A, 40A, 50A and 63A for your choice, For example, an 8kW single-phase inverter can be used as a single-phase inverter.

For example, if the maximum output current of an 8kW single-phase inverter is 38.6A, a 2P circuit breaker with a rated current of 63A is selected.

2. leakage circuit breakers

Leakage circuit breakers are switches that operate automatically when the leakage current in the circuit exceeds a predetermined value (1.2-1.5 times the maximum output current of the inverter).

3. Self-compounding over-voltage protector

Self-replicating over-voltage protector can automatically disconnect when the over-voltage and under-voltage in the line exceeds the specified value, and can automatically detect the line voltage and close automatically when the voltage in the line returns to normal.

It is also divided into single-phase self-replicating overvoltage protectors and three-phase four-wire self-replicating overvoltage protectors, with common specifications of 25A, 32A, 40A, 50A, etc. When the overvoltage protector is broken, it can be used to protect the line voltage. When the overvoltage protector is bad or the circuit breaker is tripped, the inverter will report a loss of grid fault.

4. disconnect switches and knife switches

When the PV system fails or needs to be overhauled, a disconnect switch or knife switch should be installed on the grid side of the grid-connected box to ensure reliable isolation of the inverter from the grid.

5. surge protector (SPD)

Surge protector, also known as lightning protection, is a variety of electronic equipment, instrumentation, communication lines to provide security for electronic devices.

When encountering strong thunderstorms, external interference generated by spikes in current or voltage, the surge protector can be conducted in a very short period of time shunt, thereby avoiding surge damage to other equipment in the circuit.

6. enclosure materials

The two common types of cabinets are stainless steel cabinets and galvanized steel cabinets.

Stainless steel box : antirust and anti-corrosion, waterproof and dustproof, durable and easy to install; and galvanized steel box : antirust and anti-corrosion, beautiful and durable, cheaper than stainless steel.

This is the complete PV distribution box with all the components that mentioned above.

Inspection of Distribution Box

What do we need to pay attention to in post-operation and maintenance?

1 The switch box should have the name, purpose, markings for splitting and system wiring diagram.

2 The door of the switch box should be equipped with a lock and someone should be in charge of it.

3. The N and PE rows in the distribution box must be grounded separately.

4. always use matching copper bushings for cables to prevent the wires from loosening.

5. Always remind owners to check surge protectors to prevent failure during thunderstorms.

5. The material can be stainless steel or galvanized steel, remember not to choose poor quality, it is easy to rust later.

6. Pre-wiring must be standardized to avoid the later operation and maintenance maintenance personnel can not identify the existence of certain security risks.

Conclusion

The distribution box, as the link between the household photovoltaic power station and the power grid, is related to the safe operation and maintenance of the photovoltaic system, and although it does not account for a large proportion of the cost in the photovoltaic system, it is also an important part of the photovoltaic system; the types of photovoltaic distribution boxes on the domestic market are also relatively numerous, so we must buy the right distribution box according to the different requirements of local grid-connectedness and customer demand.