Introduction and Selection of Photovoltaic Cable
2017-04-25
1. standards and codes related to cable selection
1,DL/T5044-2004 the People's Republic of China power industry standard
When multi-core cable is selected, the allowable ampacity can be calculated based on the numerical value of single-core cable with the same section.
The control line and signal line drawn from the DC cabinet shall be copper core cable. The voltage drop shall not be greater than 5% of the nominal voltage of the DC system.
The selection and laying of DC cables shall comply with the relevant provisions of the GB50217.
2,GB50217 power engineering cable design specifications
Two-core cable should be used for DC power supply circuit, and single-core cable can be used when necessary.
High temperature (above 100 ℃) or low temperature (below -20 ℃) places should not use PVC insulated cable.
When directly buried cables are laid, steel tape armored cables shall be used when the cables bear large pressure or are in danger of mechanical damage.
The temperature of the cable core under the action of the maximum working current shall not exceed the allowable value determined according to the service life of the cable.
Determine the ambient temperature for the continuous allowable ampacity of the cable. If the cable is laid in the air or in the cable trench, the average of the maximum daily temperature on the hottest month shall be taken.
3, the choice of cable path should meet the following requirements
(1) Avoid the cable from mechanical external force, overheating, corrosion and other hazards.
(2) Make the cable shorter under the condition of meeting the safety requirements.
(3) Easy to lay and maintain.
(4) Avoid the place to be excavated
(5) The cable shall meet the requirements of the allowable bending radius of the cable in any laying method and the up, down, left and right changing parts of all path conditions.
2. photovoltaic power generation system cable types, characteristics and laying mode photovoltaic power generation system cable types are mainly:
Photovoltaic special cable power cable control cable communication cable RF cable
Photovoltaic cable: PV1-F1 * 4mm2
The cable from the group to the combiner box is generally used: photovoltaic special cable PV1-F1 * 4mm2.
Features: Photovoltaic cable, simple structure, the use of polyolefin insulation material has excellent heat resistance, cold resistance, oil resistance, UV resistance, can be used in harsh environmental conditions, with a certain mechanical strength.
Laying: can wear pipe to be protected, the use of component support as a cable laying channel and fixed, reduce the impact of environmental factors.
Power cable: ZRC-YJV22
Steel tape armored flame retardant cross-linked cable ZRC-YJV22 are widely used in: junction box to DC cabinet, DC cabinet to inverter, inverter to transformer, transformer to power distribution device connection cable, power distribution device to the grid connection cable.
The nominal sections of ZRC-YJV22 cables commonly used in photovoltaic power generation systems are: 2.5 mm2, 4mm2, 6mm2, 10mm2, 16mm2, 25mm2, 35mm2, 50mm2, 70mm2, 95mm2, 120 mm2, 150 mm2, 185 mm2, 240 mm2, 300 mm2.
Features:
(1) The texture is hard, the temperature resistance grade is 90 ℃, the use is convenient, the dielectric loss is small, the chemical corrosion resistance and the laying is not limited by the gap.
(2) It has high mechanical strength, good environmental stress resistance, good thermal aging performance and electrical performance.
Laying: can be directly buried, suitable for fixed laying, to adapt to different laying environment (underground, water, trench and tunnel) needs.
Power cable: NH-VV
NH-VV copper core PVC insulated PVC sheathed fire resistant power cable. Suitable for rated voltage 0.6/1KV.
Use characteristics: long-term allowable working temperature is 80 ℃. Allowable bending radius during laying: single-core cable shall not be less than 20 times of cable outer diameter, and multi-core cable shall not be less than 12 times of cable outer diameter. When the cable is laid, the ambient temperature is not less than 0 degrees Celsius, without pre-heating. Voltage laying is not limited by drop.
Laying: suitable for fire-resistant requirements of the occasion, can be laid in the indoor, tunnel and trench pipe. Note that can not withstand the role of mechanical external forces, can be directly buried.
control cables: ZRC-KVVP
ZRC-KVVP copper core PVC insulated PVC sheathed braided shield control cable. It is suitable for control, monitoring circuit and protection circuit of AC rated voltage 450/750V and below.
Features: long-term allowable use temperature is 70 ℃. The minimum bending radius is not less than 6 times the outer diameter.
Laying: generally laid in indoor, cable trench, pipeline and other fixed places requiring shielding and flame retardant.
Communication cable: DJYVRP2-22
DJYVRP2-22 polyethylene insulated PVC sheathed copper wire braided shield armored computer special flexible cable, suitable for rated voltage 500V and below for anti-interference requirements of electronic computers and automation connection cable.
Features: DJYVRP2-22 cable has the characteristics of oxidation resistance, high insulation resistance, good voltage resistance, and low dielectric coefficient. While ensuring the service life, it can also reduce the mutual crosstalk and external interference between the circuits, and the signal transmission quality is high. The minimum bending radius shall not be less than 12 times the outer diameter of the cable.
Laying: the cable is allowed to be fixed and laid at the ambient temperature of -40 ℃ ~ 50 ℃. Laying in indoor, cable trench, pipeline and other places requiring electrostatic shielding.
Communication cable: RVVP
Copper core PVC insulated PVC sheathed insulated shielded flexible cable RVVP, also known as electrical connection anti-interference flexible cable, is suitable for alarm, security and other communication cables that require anti-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 ℃, and the minimum allowable bending radius is 6 times the outer diameter of the cable. Mainly used to do communication cable, play the role of anti-interference. Laying: RVVP cable can no longer be exposed to sunlight, and the bottom core must be well grounded. If it is necessary to suppress the electrical interference intensity of weak current circuit communication cable, laying in the steel pipe, box. When laying in parallel with the power cable, the distance between each other should be far away from the possible range.
RF cable: SYV
Solid core polyethylene insulated PVC sheathed RF coaxial cable SYV.
Features: The video lines 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, if you can use SYV75-5 within 350 meters.
Laying: can be laid through pipes.
Selection and Calculation of 3. Photovoltaic Cable
The selection of cable section shall meet the requirements of allowable temperature rise, voltage loss, mechanical strength, etc. The DC system cable shall be selected according to the long-term allowable current carrying capacity of the cable and verified according to the allowable voltage drop of the cable. The calculation formula is as follows:
Long-term allowable ampacity by cable: Ipc>= Ical
According to the allowable voltage drop of the circuit: Scac = P˙ 2LIca/△Up
In the formula: Ipc ---- allowable ampacity of cable, A;
Ica ---- calculated current, A;
Ical ---- calculated current for long-term operation of the loop, A;
Scac-calculated section of cable, mm2;
P ---- resistance coefficient, copper conductor P = 0.0184Ω · mm2/m, aluminum conductor P = 0.0315Ω · mm2/m;
L ---- cable length, m;△ Up ---- allowable voltage drop of circuit, v.
Note: The current carrying capacity of the cable is greatly affected by the laying method and the surrounding environment, and the voltage drop of the cable is greatly affected by the length of the cable, so the current carrying capacity can be considered as the value that the cable can never exceed in long-term operation. It is best to select the cable according to 70% ~ 80% of the current carrying capacity of the cable to effectively ensure the temperature rise and voltage drop of the line.
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