Solar energy technology will become one of the green energy technologies in the future. The use of solar energy or photovoltaic (PV) applications will become increasingly widespread. Photovoltaic power plants will develop rapidly. The construction of a cost-effective, profitable photovoltaic power plant represents the most important goals and core competencies of all solar manufacturers. In fact, profitability depends not only on the efficiency or performance of the solar module itself, but also on the components of the system. The high-quality components ensure the efficient, stable, long-term operation of the solar PV system.
In the solar photovoltaic power generation system, the amount and cost of the cable are the basis of supporting electrical equipment. The usage of the cable is larger than that of the general power generation system, and it is also one of the larger factors affecting the efficiency of the entire system.
The cost of cable engineering in photovoltaic power generation projects is generally relatively large. Reasonable selection of cables and selection of laying methods have a direct impact on construction costs. Therefore, rational planning and correct selection of cable types and laying methods are the most important aspects of cable design work. In the photovoltaic power generation system, the cable selection that is being taken is an important part of reducing the cost of power generation.
1 Basic principles of cable selection
Photovoltaic power cable selection follows the general requirements for cable selection, ie selection according to voltage class, current permissible for continuous operation, short-circuit thermal stability, allowable voltage drop, economic current density, and laying environmental conditions.
At the same time, photovoltaic power generation has its own characteristics. Solar energy systems are often used under harsh environmental conditions, such as high temperatures, severe cold, and ultraviolet radiation.
Therefore, the following factors must be taken into consideration in the selection of cables in the photovoltaic system:
(1) The insulation performance of the cable;
(2) Heat and flame resistance of the cable;
(3) moisture-proof, light-proof (anti-radiation) cable;
(4) laying of cables;
(5) Cable conductor material (copper core, aluminum alloy core);
(6) Specifications of the cable cross-section.
2 cable selection
2.1 Photovoltaic Cable Types
Photovoltaic power generation system cables, according to the photovoltaic power generation system can be divided into DC cables and AC cables, among which the series cables between components, and the DC cables connected in parallel between the strings occupy more than half of the amount of cables, after the use of the inverter AC cable.
According to different application environments, the cables of photovoltaic power generation systems can be divided into:
1. DC cable
(1) A series cable between the component and the component. This part should use a dedicated cable with a PV certification.
(2) Rare-earth aluminum alloy conductor cables may be used for the parallel cables between strings and their strings to DC distribution boxes (confluence boxes).
(3) The cable between the DC distribution box and the inverter, this part can also choose to use rare earth aluminum alloy conductor cable.
The above cables are all DC cables. They are laid outdoors in large quantities and need to be protected from moisture, sunlight, cold, heat, and UV rays. In some special circumstances, they must also be protected against acids and alkalis. The connection cable between the component and the component is usually supplied in complete sets with the component.
2. AC cable
(1) Connecting cable from inverter to step-up transformer.
(2) Connecting cable from step-up transformer to power distribution unit.
(3) The connection cable from the power distribution unit to the grid or user.
The focus here is on the selection and laying of DC cables in photovoltaic grid-connected power generation. The principles are also applicable to some other types of photovoltaic power generation projects.
2.2 Photovoltaic Special Cable
Photovoltaic power generation systems require a large number of DC cables to be laid outdoors, and the environmental conditions are harsh. The cable materials should be based on UV resistance, ozone, severe temperature changes, and chemical erosion. The long-term use of cables with common materials in this type of environment will result in fragile cable jackets and even breakdown of cable insulation. These conditions can directly damage the cable system, and at the same time increase the risk of short-circuiting the cable. In the medium and long term, the possibility of fire or personal injury is also higher, which greatly affects the service life of the system.
For the above reasons, it is very necessary to use photovoltaic dedicated cables and components in solar energy systems. With the continuous development of the photovoltaic industry, the photovoltaic component market has gradually taken shape. In terms of cables, a variety of photovoltaic professional cable products have been developed.
Such as the recent development of electronic cross-link cable, rated temperature of 120 °C, can withstand harsh weather conditions and subjected to mechanical impact, is a solar cable choice. For example, RADOX cable is a kind of special solar energy cable developed according to the international standard IEC216. In the outdoor environment, the service life is 8 times that of rubber cable and 32 times that of PVC cable. Solar PV special cables and components not only have the best weather resistance, UV and ozone resistance, but also can withstand a wide range of temperature changes (eg: from -40 °C -125 °C). In Europe, technicians have tested that the temperature measured on the roof can reach 100-110°C.
During the installation, operation and maintenance of photovoltaic power generation systems, the cables may be in the soil below the ground, in the weeds, or on the sharp edges of the roof structure, and may also be exposed in the air. The cables must withstand pressure and bends. Fold, tension, cross tensile load, and strong impact. If the strength of the cable jacket is not sufficient, the cable insulation will be damaged, which will affect the service life of the entire cable or cause short circuit, fire and danger of personal injury.
2.3 Selection of Conductor Materials for Photovoltaic Power Cables
Most of the DC cables used in photovoltaic power generation are long-term outdoor work. Due to the restrictions of construction conditions, there are two types of cable connections, one is the use of connectors; the other is the use of bolts. Cable conductor materials can be divided into copper cores and rare earth aluminum alloy cores. Traditionally, copper core cables have been used more and more. With the use of rare earth aluminum alloy cables in recent years, we have found that rare earth aluminum alloy cables have better anti-oxidation capabilities than copper cables, high creep resistance, long service life, and better stability. Good, low pressure drop and small power loss characteristics; due to the flexible construction of rare earth aluminum alloy cable, the allowable radius of curvature is small, and the weight is light, so the turning is convenient, and the pipe is easy to wear; and the rare earth aluminum alloy cable is resistant to fatigue and repeated folding. The bending is not easy to break, no memory effect, so the wiring is convenient; at the same time, the rare earth aluminum alloy cable has high mechanical strength, can withstand greater mechanical tension, and brings great convenience to construction and laying, and also creates conditions for mechanized construction.
On the contrary, the copper core cable, due to the chemical properties of the copper material, will cause oxidation (chemical reaction) for a long time after the connector is installed, which will easily lead to failure. In addition, according to IEC287 calculations, at the same ampacity, although the aluminum section is second gear, in the production process, special compaction technology is adopted. The outer diameter of the cable is only 15% larger than that of the copper core cable, and there is no problem in laying the laid pipe of the copper core cable design.
Rare earth aluminum alloy cable chain armored jacket, but also can be laid directly buried. This has outstanding advantages in the field of cable power supply. It has the characteristics of reducing accident rate, improving reliability of power supply, convenient construction and maintenance.
There are currently many photovoltaic power plant construction projects using rare earth aluminum alloy cables. Such as: Tibet 10MW Photovoltaic Power Plant Power Generation Project, Longyuan Mingguang Wind Power Project, Xuzhou 6MW Photovoltaic Power Generation Project, Yangbajing 10MW Photovoltaic Power Generation Project, Jiangsu Sanqi Cable Plant Rooftop 1MW Photovoltaic Power Station Project, etc.
2.4 Cable Insulation Material
In operation, the DC loop is often affected by various unfavorable factors and causes grounding, making the system unable to operate normally. Such as extrusion, poor cable manufacturing, insulative material failure, low insulation performance, insulation aging of the DC system, or the presence of certain loss defects can cause grounding or become a grounding hazard.
In addition outdoor environment, small animals invade or bite can also cause DC ground fault.
Therefore, under the premise of conditions, armored and cable with functional sheath for rodent protection can be selected.
2.5 Cable Cross Section Selection
The cable cross-section should be selected to allow for temperature rise, voltage loss, mechanical strength, etc. The DC system cable should be selected according to the long-term allowable ampacity of the cable, and verified by the allowable voltage drop of the cable.
2.6 voltage loss
Normally, line loss = current * circuit bus length * cable voltage factor. According to the requirements, the pressure drop of the transmission line from the PV array to the PV generator controller must not exceed 5%, and the output branch pressure drop should not exceed 2%. Each part of the connection cable size specification design, also need to follow the following principles:
(1) AC load connection: the rated current of the selected cable is 1.25 times the maximum continuous current in the calculated cable;
(2) Inverter connection: The rated current of the selected cable is 1.25 times the maximum continuous current in the calculated cable;
(3) Connection between square matrix and square matrix: the rated current of the selected cable is 1.56 times the maximum continuous current in the calculated cable;
(4) Consider the effect of temperature on the performance of the cable;
(5) Consider that the voltage drop should not exceed 2%.
3 Cable laying
3.1 Cable laying classification
The cable laying method shall be selected according to the conditions of the project, the characteristics of the environment, the type and quantity of the cable, etc., and shall be selected in accordance with the requirements of reliable operation and easy maintenance, and the principle of technical and economical reasonableness. Photovoltaic power generation projects lay DC cables such as direct burial, pipe laying, slot laying, cable trench laying, tunnel laying, etc. The laying of AC cables is similar to the general power system.
The DC cables between the PV modules, between the strings and the DC combiner box, and between the combiner box and the inverter have small cross-section specifications and a large number of them. Mostly, the PV arrays are laid along the assembly brackets or laid through pipes and buried directly. When laying the conductors, it is generally considered when laying:
(1) Connect the cable between the components and the connection cable between the string and the combiner box, use the component bracket as the channel support and fixing of the cable laying as much as possible, and in a certain sense can reduce the impact of environmental factors;
(2) The tightness of cable laying should be appropriate. Generally, the temperature difference between day and night in photovoltaic sites is large, and the cable breakage caused by thermal expansion and contraction should be avoided;
(3) The photovoltaic material cable lead on the building surface should consider the overall aesthetics of the building. The laying position should avoid laying cables on the sharp edges of the wall and the bracket so as to avoid short circuit caused by cutting and grinding damage to the insulation layer, or cutting off the wire and cause a disconnection. At the same time, we must consider the issue of lightning transmission along the cable.
3.2 Cable Connection
The DC cables in photovoltaic power generation systems are mostly laid outdoors. The connection between components and components is mainly based on joints. The other cable connections are similar to those of the general power system.
Undermount Stainless Steel Kitchen Sink
Kitchen Sink,Undermount Sink,Stainless Steel Sink,Undermount Stainless Steel Kitchen Sink
SUNRISE HOME GOODS(M)SDN.BHD. , https://www.sunrisesink.com