Question 1

How Should AC LV Cables Be Selected for Solar Power Projects?

Accepted Answer

When a solar power station is close to the load center or is itself a distributed generation, you only need to use low-voltage cables to directly connect to a three-phase 400V or single-phase 230V low-voltage distribution network. To connect to a medium or high-voltage grid, low-voltage cables must first be used to connect to a transformer.

The AC voltage output by the inverter usually comes in various standards. For example, the output voltage of a central inverter can be 315V, 360V, 400V, and so on, while the output voltage of a string inverter can be 480V, 500V, 540V, 800V, and so on.

Therefore, in PV systems, it is generally possible to use low-voltage cables with a rated voltage of 450/750V, 0.6/1 kV, or 1.8/3 kV. Depending on whether the cable is buried or not, an armored layer may be added.

Question 2

How Should AC MV Cables Be Selected for Solar Power Projects?

Accepted Answer

If a photovoltaic power generation system needs to connect to a medium or high-voltage grid, low-voltage cables must first be used to connect to a transformer, which will then step up the voltage to the appropriate level. Medium-voltage cables are then used to deliver power to the substation. The number of medium-voltage cables required depends on the connection method.

Traditional Star Structure

In the traditional star structure, each transformer has a single medium-voltage output line connecting to the substation. This structure is the simplest and most straightforward, and it is commonly used in the design of photovoltaic power stations. Each cable only carries the power of a single transformer, so the cable specifications are smaller, reducing costs. However, since each transformer has only one line connecting to the substation, the reliability is not very high.

Single-Output Ring Structure

The single-output ring structure connects several transformers in a ring using cables, and the closest transformer to the substation is connected to the substation using medium-voltage cables. Compared to the double-output ring structure, the single-output ring structure uses fewer medium-voltage AC solar cables. However, because the entire ring has only one line connecting to the substation, the reliability is lower.

Double-Output Ring Structure

The double-output ring structure has an additional line connecting the ring to the substation compared to the single-output ring structure. If one output line fails, the other line can continue to allow the inverters in the ring to output power to the grid. Similar to the single-output ring structure, considering the flow direction during a fault, all cables must be selected to withstand the power of all transformers, resulting in relatively higher costs.

Bridge Structure

Before the ring structure was proposed, the bridge structure was often used. In this structure, based on the star structure, each pair of adjacent transformers is connected using medium-voltage cables. This way, each transformer has two lines connecting to the substation, greatly improving system reliability. However, the cost is relatively high due to the additional cables between each pair of transformers.

For photovoltaic power stations of different sizes, the cable selection analysis varies under different requirements. When selecting medium-voltage cables, it is essential to comprehensively consider mandatory requirements, costs, and benefits to determine the most advantageous solution and decision.

Question 3

What Are the Principles for Selecting AC Cables for Solar Power Systems?

Accepted Answer

The selection of AC cables for solar projects follows the general requirements for cable selection, which include considering voltage levels, continuous operating current, short-circuit thermal stability, allowable voltage drop, economic current density, and installation environment conditions. Additionally, photovoltaic power generation has its own characteristics, requiring consideration for cables that may be used in harsh environmental conditions such as high temperatures, severe cold, and ultraviolet radiation. Therefore, the following factors should be taken into account:

Insulation performance of the cable
Heat resistance and flame retardancy of the cable
Moisture resistance and UV protection of the cable
Installation methods of the cable
Type of cable conductor
Cable specification

ZMS can provide you with a comprehensive solar cable solution for your photovoltaic power generation project, greatly facilitating your power cabling needs.

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