Selecting Wire & Cable For Solar PV systems

1. Specifications for cables for solar power generation projects

The DC cable power supply circuit generally uses two-core solar cables, and single-core solar pv cables can be used when necessary. High temperature (above 100℃) or low temperature (below -20℃) places should not use PVC insulated cables. When laying cables directly, when the solar pv cables are under greater pressure or there is a danger of mechanical damage, 0.6/1kv low-voltage steel tape armored power cables should be used. The temperature of the cable core under the action of the maximum working current shall not exceed the allowable value determined by the service life of the cable. Determine the ambient temperature of the continuous allowable current carrying capacity of the solar pv cables. If the solar pv cables is laid in the air or in a cable trench, the average value of the highest temperature in the hottest month and day should be taken.

2. Requirements for the use of solar pv cables

(1) Avoid the solar pv cable from being exposed to mechanical external force, overheating, corrosion and other hazards.

(2) Make the pv cables shorter when the safety requirements are met.

(3) Easy to lay and maintain.The grounding system for a solar pv system includes lightning rods, lightning protection strips, and low-voltage lightning arresters. The system is designed to redirect lightning strikes into the ground.

(4) Avoid the place where the construction will be excavated

(5) The upper, lower, left, and right transition parts of the solar cable in any laying method and all path conditions shall meet the requirements of the allowable bending radius of the cable.

3. Types of pv cables for solar power generation systems

The main types of pv cables for solar power generation systems are: solar pv cables, power cables, control cables, communication cables and coaxial cables

Solar PV Cable: PV1-F/H1Z2Z2-K

Solar pv cable generally refers to the cable from the string to the combiner box. Common types of solar pv cables are 2.5mm2, 4mm2, 6mm2 and 10mm

Features: solar pv cables have a simple structure. The polyolefin insulating material used has excellent heat resistance, cold resistance, oil resistance and ultraviolet resistance. It can be used in harsh environmental conditions and has a certain mechanical strength.

Laying: It can be protected by passing through the pipe, and the component bracket is used as the channel and fixing for solar pv cables laying to reduce the influence of environmental factors.

Power cable

Power cables refer to the connecting cables from the combiner box to the DC cabinet, from the DC cabinet to the inverter, from the inverter to the transformer, from the transformer to the power distribution device, and from the power distribution device to the power grid. Mainly include low voltage (0.6/1kv) and medium voltage (12/20(24)KV) cables with AWA or SWA (single-core and multi-core) underground power cable.

The more common nominal power cables in solar power generation systems are: 2.5mm2, 4mm2, 6mm2, 10mm2, 16mm2, 25mm2, 35mm, 50mm2, 70mm2, 95mm2, 120mm2, 150mm2, 185mm2, 240mm2, 300mm2

Features: (1) The texture is hard, the temperature resistance level is 90 °C, it is easy to use, has the characteristics of small dielectric loss, chemical corrosion resistance, and the laying is not limited by the drop. (2) It has high mechanical strength, good resistance to environmental stress, good thermal aging properties and electrical properties. Laying: It can be directly buried, suitable for fixed laying, and adapt to the needs of different laying environments (underground, water, trenches and tunnels).

Control Cable

Copper core PVC insulated braided shielded control cable. It is suitable for control, monitoring and protection circuits of AC rated voltage 450/750V and below.

Features: The long-term allowable use temperature is 70 ℃. The minimum bending radius radius is not less than 6 times the outer diameter.

Laying: control cables are generally laid in fixed places that require shielding and flame retardant such as indoors, cable trenches, pipes, etc.

Communication Cable

RS485 Twisted pair pvc insulated braided shielded copper communication cables are suitable for electronic computer and automation connection cables with a rated voltage of 1kv and below and high requirements for anti-interference.

Features: It has the characteristics of anti-oxidation, high insulation resistance, good withstand voltage and small dielectric coefficient. While ensuring the service life, it can also reduce the mutual crosstalk and external interference between circuits, and the signal transmission quality is high. The minimum bending radius is not less than 12 times the outer diameter of the cable. The cable is allowed to be fixedly laid and used under the condition of ambient temperature -40°C~50°C. Lay it indoors, in cable trenches, pipelines and other places that require electrostatic shielding.

RVVP copper wire PVC insulated PVC sheathed insulated shielded flexible cable, also known as electrical connection anti-interference flexible cable, is a communication cable suitable for alarm, security and other needs to prevent interference, safe and efficient data transmission.

Features: The rated working voltage is 3.6/6KV, the long-term working temperature of the cable conductor is 90 °C, and the minimum allowable bending radius is 6 times the outer diameter of the cable. Mainly used for communication cable, play the role of anti-interference.

Laying: RVVP cables cannot be exposed to sunlight, and the bottom core must be well grounded. If it is necessary to suppress the weak current circuit communication cable of the electrical interference intensity, lay it in a steel pipe or box. When laying parallel to the power cable, the distance from each other should be kept as far away as possible.

Coaxial cable

Solid core polyethylene insulated PVC sheathed RF coaxial cable SYV. The video cables commonly used in monitoring are mainly SYV75-3 and SYV75-5. If you want to transmit video signals within 200 meters, you can use SYV75-3, and if you want to transmit video signals within 350 meters, you can use SYV75-5. Can be laid through pipes.

Battery cable

SGT & SGX rubber or PVC battery cables are used for the connection between the solar panel and the junction box and the jumper from the inverter to the battery. The allowable working range of the cable is -40°C ~ 105°C. The nominal cross-sectional area of the battery cable is 1.5-100mm2.

Ground wire&Earth Cable

The lightning protection grounding of the solar pv system includes lightning rods, lightning protection strips and low-voltage lightning arresters, the porcelain bottle iron feet on the external outlet poles, and the metal sheath of the cables connecting the overhead lines to be grounded, so as to introduce the flowing lightning into the earth. Ground the inverter, the neutral point of the battery, the secondary coil of the voltage transformer and the current transformer. Protective grounding of photovoltaic cell module racks, controllers, inverters, power distribution cabinet shells, battery brackets, cable sheaths, and the sheaths of wire-threaded metal pipes are grounded. Repeated grounding On low-voltage overhead lines, ground every 1km. The yellow-green ground wire usually uses the H05V-K/H07V-K earth cable, and the earth cables operating temperature is 90°C. Generally used for direct burial.

4. Selection and calculation of solar pv cables

The selection of the cross section of the solar pv cable should meet the requirements of allowable temperature rise, voltage loss, mechanical strength, etc. The DC solar cable is selected according to the long-term allowable current carrying capacity of the solar pv cable, and is checked according to the allowable voltage drop of the cable. The calculation formula is as follows:

According to the long-term allowable current carrying capacity of the cable: Ipc>=Ical

According to the allowable voltage drop of the loop: Scac=P˙2LIca/△Up

Ipc—the allowable current carrying capacity of the cable, A;

Ica—calculated current, A;

Ical—the long-term working calculation current of the loop, A;

Scac—the calculated cross-section of the cable, mm²;

P—resistivity coefficient, copper conductor P=0.0184Ω˙mm²/m, aluminum conductor P=0.0315Ω˙mm²/m;

L—cable length, m;

△Up—The allowable voltage drop of the loop, V.

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