Cable selection for photovoltaic power station

In the whole photovoltaic system, although the cost of the cable does not account for a high proportion, but as a photovoltaic system "blood vessels", played an important role in connecting the components, inverters, distribution boxes and power grids, on the operation of the entire system security, whether stable and efficient, and even the overall profitability of the power station have an important impact. Therefore, in the photovoltaic system design process of cable selection also seems very critical.

First, the type of photovoltaic cable:

From the point of view of the different functions undertaken, the cables in the photovoltaic system can be divided into two main types of DC cables and AC cables.

1, DC cable

(1), components and components between the series cable.

(2), parallel cable between strings and between strings to DC distribution box (convergence box).

(3), DC distribution box to the inverter between the cable.

The above cables are DC cables, outdoor laying more, need to moisture-proof, sun exposure, cold, heat, ultraviolet resistance, some special circumstances also need to prevent acid and alkali and other chemical substances.

2、AC cable

(1), the inverter to the step-up transformer connection cable.

(2) The connection cable from the step-up transformer to the power distribution device.

(3) The connection cable from the distribution unit to the power grid or the user.

This part of the cable for the AC load cable, indoor environment laying more, according to the general power cable selection requirements.

Second, why choose photovoltaic cable

Photovoltaic power station in a large number of DC cables need to be laid outdoors, harsh environmental conditions, the cable material should be based on resistance to ultraviolet radiation, ozone, drastic temperature changes and chemical erosion. Ordinary material cables used for a long time in that environment will lead to broken cable sheaths and even decompose the cable insulation layer. These conditions will directly damage the cable system, as well as increase the risk of short-circuiting the cables, and in the medium to long term, the likelihood of fires or injuries to personnel is also higher, greatly affecting the service life of the system. Therefore, the use of PV-specific cables and components in PV power plants is very necessary. PV-specific cables and components not only have the best weather resistance, UV and ozone erosion resistance, but also can withstand a greater range of temperature changes.

Third, the principles of cable design and selection

(1), the voltage withstand value of the cable should be greater than the maximum voltage of the system. Such as 380V output AC cable, to choose 450/750V cable.

(2), the connection within and between the photovoltaic square arrays, the selected cable rated current is 1.56 times the maximum continuous current in the calculated cable.

(3), the connection of AC loads, the selected cable rated current is 1.25 times the maximum continuous current in the calculated cable.

(4), the connection of the inverter, the selected cable rated current is 1.25 times the maximum continuous current in the calculated cable.

(5), Consider the effect of temperature on the performance of the cable. The higher the temperature, the lower the current-carrying capacity of the cable, the cable should be installed as far as possible in a ventilated place to dissipate heat.

(6), consider the voltage drop should not exceed 2%.

DC circuit in operation is often affected by a variety of unfavorable factors and cause grounding, making the system can not operate normally. Such as extrusion, cable manufacturing poor, unqualified insulation materials, low insulation performance, DC system insulation aging, or the existence of certain damage defects, can cause grounding faults or become a grounding hazard. In addition, the outdoor environment, small animal invasion or bite will also cause DC ground fault. Therefore, in this case, the general use of armored cable with rodent-proof sheath.