I. Relevant standards and specifications related to cable type selection
1,dl/t5044-2004 People's Republic of China Power industry standards
When the multi core cable is selected, the allowable load flow can be calculated numerically with the same section single core cable.
The copper conductor cable should be selected for the control line and signal line drawn from the DC cabinet. The pressure drop should not be greater than 5% of the nominal voltage of the DC system.
The selection and laying of DC cables shall conform to the relevant provisions in GB50217.
Code for design of cable for 2,gb50217 Power engineering
Two-core cable should be used in DC power supply circuit, and single core cable can be used when needed.
PVC insulated cable is not suitable for high temperature (above 100 ℃) or low temperature (20 ℃ below).
When laying the cable directly, the steel tape armored cable is applied when the cable is under greater pressure or the mechanical damage is dangerous.
The maximum operating current under the action of the cable core temperature shall not exceed the allowable value determined by the cable service life.
Determine the ambient temperature at which the cable is continuously allowed to load, and if the cable is laid in the air or in a cable trench, the average temperature of the hottest monthly day shall be taken.
3, the choice of cable path should comply with the following provisions
(1) To prevent the cable from mechanical forces, overheating, corrosion and other hazards.
(2) to meet the safety requirements to make the cable shorter.
(3) Easy to lay and maintain.
(4) Avoid the place where the excavation will be
(5) Cable in any laying way and all the path conditions of the upper and lower parts of the change, should meet the cable allowable bending radius requirements.
Second, the PV power system cable type, characteristics and laying way the main types of PV power system cable are:
PV Special cable Power cable control cable communication cable RF cable
PV Special Cable: pv1-f1*4mm2
Series of cable to the bus box for general use: Photovoltaic dedicated cable pv1-f1*4mm2.
Features: Photovoltaic cable, simple structure, the use of polyolefin insulating materials with excellent heat-resistant, cold, oil, UV-resistant, can be used in harsh environmental conditions, with a certain degree of mechanical strength.
Laying: can be protected through pipe, using assembly bracket as cable laying channel and fixed, reduce the impact of environmental factors.
Power Cable: Zrc-yjv22
Steel Tape Armored Flame-Retardant Xlpe cable zrc-yjv22 is widely used in: Bus to DC Cabinet, DC cabinet to inverter, inverter to transformer, transformer to power distribution device connection cable, power distribution device to power grid connection cable.
The most common zrc-yjv22 cable nominal sections in PV systems are: 2.5mm2, 4mm2, 6mm2, 10mm2, 16mm2, 25mm2, 35mm2, 50mm2, 70mm2, 95mm2, 120mm2, 150mm2, 185mm2, 240MM2, 300mm2.
Characteristics：
(1) hard texture, temperature-resistant grade of 90 ℃, easy to use, with a small dielectric loss, chemical corrosion resistance and the laying of the characteristics of the gap is not restricted.
(2) High mechanical strength, good resistance to ambient stress, good thermal aging and electrical properties.
Laying: Can be directly buried, suitable for fixed laying, adapt to different laying environment (underground, water, ditch pipe and tunnel) needs.
Power Cable: NH-VV
NH-VV copper Conductor PVC Insulated PVC sheathed Fire-resistant power cable. Suitable for rated voltage 0.6/1kv.
Use characteristics: long-term allowable operating temperature of 80 ℃. Allowable bending radius when laying: Single core cable is not less than 20 times times cable diameter, multi-core cable is not less than 12 times times cable diameter. When the cable is laid, the ambient temperature is not less than 0 degrees Celsius, without prior heating. Voltage laying is not limited by the drop.
Laying: Suitable for occasions with refractory requirements, can be laid in indoor, tunnel and ditch pipes. Attention can not withstand the role of mechanical forces, can be directly buried laying.
Control Cable: ZRC-KVVP
ZRC-KVVP copper Conductor PVC insulated PVC sheathed Braided shielded control cable. Suitable for AC rated voltage 450/750v and below control, monitoring circuit and protection line.
Features: Long-term allowable temperature of 70 ℃. The minimum radius of bending radius is not less than 6 times times the outer diameter.
Laying: General laying in indoor, cable trench, pipe and other requirements of shielding, flame-retardant fixed places.
Communication Cable: Djyvrp2-22
Djyvrp2-22 polyethylene insulated PVC sheathed copper wire Woven Shield armored Computer special soft cable, applicable to the rated voltage of 500V and below for interference-resistant computer and automatic connection cable.
Features: Djyvrp2-22 cable with antioxidant, high insulation resistance, good voltage, dielectric coefficient of small characteristics, in ensuring the service life, but also to reduce the circuit between the crosstalk and external interference, high quality signal transmission. The minimum bending radius is not less than 12 times times the diameter of the cable.
Laying: The cable is allowed to be fixed for installation under the condition of ambient temperature -40℃~50℃. Laying in indoor, cable trench, pipe and other requirements of electrostatic shielding sites.
Communication Cable: RVVP
Copper conductor PVC Insulated PVC sheathed Insulated shielded soft cable RVVP, also known as electrical connection Anti-interference Soft cable, is applicable to alarm, security and other interference, safe and efficient data transmission communication cable.
Features: Rated working voltage 3.6/6KV, the long-term operating temperature of cable conductor is 90 ℃, the minimum allowable bending radius is 6 times times of cable od. Mainly used for communication cable, play an anti-interference role. Laying: RVVP cable can no longer sun exposure, the core must be good grounding. If you need to restrain the electrical interference intensity of the weak circuit communication cable, laid in steel pipe, box. When parallel with power cable laying, it is advisable to distance from each other in the possible range.
RF Cable: SYV
Solid core polyethylene Insulated PVC sheathed RF coaxial cable syv.
Features: Monitoring of the commonly used video line is mainly syv75-3 and syv75-5 two kinds. If you want to transmit video signal in 200 meters can use syv75-3, if within 350 meters range can use syv75-5.
Laying: Can be worn pipe laying.
Third, the selection of photovoltaic cable calculation
The selection of cable section should meet the requirements of allowable temperature rise, voltage loss, mechanical strength and so on, the DC system cable according to the cable long-term allowable load flow selection, and according to the cable allowable pressure drop check, the formula is as follows:
Long-term allowable load flow by cable: ipc>=ical
allowable voltage drop by loop: scac=p˙2lica/up
Type: Ipc----cable allowed to load, A;
ICA----compute Current, A;
Ical----loop for long-term work calculation current, A;
SCAC----Cable calculation section, mm2;
P----resistance coefficient, copper conductor p=0.0184ω˙mm2/m, aluminum conductor p=0.0315ω˙mm2/m;
L----Cable length, m; up----circuit allows voltage drop, v.
Note: The load flow of the cable is affected by the way of laying and surrounding environment, cable voltage drop is affected by cable length, so the load flow can be considered to be the long-term operation of the cable will never exceed the value of the best cable load flow 70%~80% to select the cable to effectively ensure that the line temperature rise and voltage drop.