Photovoltaic system cable design, selection and construction

In the construction process of photovoltaic power plants, in addition to the main equipment, such as photovoltaic modules, inverters, step-up transformers, supporting connection of photovoltaic cable materials to the overall profitability of photovoltaic power plants, operation safety, whether efficient, also play a vital role, the following photovoltaic power plant common cables and materials in the use of the use of the environment in detail
.

Cables can be divided into DC cables and AC cables according to the system of photovoltaic power plants, which are classified according to different uses and use environments as follows:

First, DC cable

(1) Series cable
between components.

(2) Parallel cables
between strings and between their strings to DC distribution boxes (combiner boxes).

(3) Cable
between DC distribution box and inverter.

The above cables are DC cables, outdoor laying more, need moisture, sun exposure, cold, heat, ultraviolet resistance, some special environments also need to prevent acid and alkali and other chemicals
.

Second, AC cable

(1) Connection cable
from inverter to step-up transformer.

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

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

This part of the cable is an AC load cable, and the indoor environment is laid more, which can be selected
according to the general power cable selection requirements.

3.
Photovoltaic special cable

A large number of DC cables in photovoltaic power plants need to be laid outdoors, the environmental conditions are harsh, and the cable materials should be determined according to the resistance to ultraviolet rays, ozone, severe temperature changes and chemical erosion
.
Long-term use of ordinary materials in this environment will cause the cable sheath to be brittle and even decompose the cable insulation layer
.
These conditions will directly damage the cable system, but also increase the risk of cable short circuit, and in the medium and long term, the possibility of fire or personal injury is also higher, greatly affecting the service life
of the system.
Therefore, it is very necessary to use photovoltaic special cables and components in photovoltaic power plants
.
PV-specific cables and components not only offer optimum weather, UV and ozone resistance, but also withstand a wider range of temperature changes
.

Fourth, the principle of cable design selection:

(1) The withstand voltage value of the cable is greater than the maximum voltage
of the system.
For example, 380V output AC cable, to elect 450/750V cable
.

(2) For the connection between the photovoltaic square matrix and the square matrix, the rated current of the selected cable is 1.
56 times
the maximum continuous current in the calculated cable.

(3) For the connection of AC load, the rated current of the selected cable is 1.
25 times
the maximum continuous current in the calculated cable.

(4) For the connection of the inverter, the rated current of the selected cable is 1.
25 times
the maximum continuous current in the calculated cable.

(5) Consider the influence of
temperature on the performance of the cable.
The higher the temperature, the less ampacity of the cable, and the cable should be installed in a ventilated and dissipated place
as much as possible.

(6) Consider that the voltage drop should not exceed 2%.

DC circuits are often affected by a variety of unfavorable factors during operation and cause grounding, making the system unable to operate normally
.
Such as extrusion, poor cable manufacturing, unqualified insulation materials, low insulation performance, aging insulation of DC system, or some damage defects can cause grounding or become a grounding hazard
.
In addition, the invasion or bite of small animals in outdoor environments can also cause DC ground faults
.
Therefore, in this case, an armored cable
with a rodent-repellent sheath is generally used.

Distributed photovoltaic common inverter cable selection:

Note: The cable in the table is determined according to the
standard of national standard copper wire.

If the cable length is greater than 50 meters, refer to the cable
size 1.

5.
Cable construction of photovoltaic power generation system

The construction cost of cable engineering in photovoltaic power generation projects is generally relatively large, and the choice of laying method directly affects the construction cost, so reasonable planning and correct selection of cable laying method is an important part of
cable design work.

1.
The laying method of the cable is comprehensively considered according to the engineering situation, environmental conditions, cable specifications, models, quantities and other factors, and is selected according to the principle of meeting the requirements of reliable operation, easy maintenance and technical and economic
reasonableness.
The laying of DC cables of photovoltaic power generation projects mainly includes direct burial sand laying pads, pipe laying, trough laying, cable trench laying, tunnel laying, etc
.

The laying of AC cables is not much
different from the laying method of general power systems.
DC cable is mostly used between photovoltaic modules, between strings to DC combiner boxes, between combiner boxes and inverters, its cross-sectional area is small, the number is large, usually the cable is tied along the component bracket or buried directly through the pipe for laying, DC cable in the laying generally need to consider:

(1) The connecting cable between components and the connecting cable between the string and the combiner box, as far as possible, the use of the component bracket as the channel support and fixation of the cable laying, can reduce the influence of
environmental factors to a certain extent.

(2) The force of cable laying should be uniform and appropriate, not too tight, photovoltaic places generally have a large temperature difference between day and night, and should avoid cable breakage caused by thermal expansion and contraction
.

(3) The photovoltaic material cable leads on the surface of the building should consider the overall beauty of the building, and the laying position should avoid laying cables at the sharp edge of the wall and bracket, so as not to cut and grind the insulation layer and cause short circuit, or cut off the wire by shear force and cause a broken circuit
.
At the same time, it is necessary to consider problems such as
direct lightning strikes on cable lines.

(4) Reasonably plan the cable laying path, reduce crossing, and combine the laying as much as possible to reduce the amount of earthwork excavation and cable consumption in the construction process of the project
.

2.
The DC cable in the cable connection photovoltaic power generation system is mostly laid outdoors, and the connection method is mainly plugged in the joint, which can be protected through the pipe, and the component bracket is used as the channel and fixed for cable laying to reduce the influence of
environmental factors.
Other cable connections are connected in much the same way
as in general power systems.