How to skillfully use aluminum alloy cable in photovoltaic system?

The cost of control system is very important in the era of photovoltaic affordable Internet access. Over the past decade, the price of modules and inverters has decreased by 90%, which has made a great contribution to the overall cost reduction of photovoltaic system, but the cost of cables has not decreased. In large projects, the proportion of cables in the system reaches 10%, which is higher than that of inverters. In fact, as long as the design and installation are proper, on the premise of ensuring the normal operation and safety of the system, some AC cables adopt aluminum alloy cables, which can reduce some costs.
The cables of photovoltaic power station are divided into DC cables and AC cables. The DC cables between components and between components and inverter are generally required to use photovoltaic special DC cables, while the cables from inverter to AC distribution cabinet and from distribution cabinet to transformer are not required to use any ACSR Cables.

What is aluminum alloy cable: aluminum alloy cable is a new material power cable with aa8030 series aluminum alloy material as conductor. The resistivity of aluminum alloy is between aluminum and copper, higher than copper and slightly lower than aluminum. Under the premise of the same current carrying capacity, the weight of aluminum alloy conductor with the same length is only half of that of copper.
When the cross-sectional area of aluminum alloy conductor is 1.5 times that of copper, aluminum alloy ACSR Cable and copper cable achieve the same current carrying capacity, resistance and line loss.
Service life: different metal oxides are formed after the metal surface reacts with oxygen. Aluminum oxide can form a dense surface protective film with a certain hardness. Copper oxide, commonly known as copper green, is a toxic substance between the above two.
Economically, this is the most important aspect. The cost of aluminum alloy cable is about 25% ~ 50% of that of copper core cable. The cost advantage of aluminum alloy cable is relatively large. We can make a comparison. In a 400KW village level poverty alleviation power station, the distance from the AC distribution cabinet to the step-up transformer is 1500 meters, and the maximum output current of the 400KW power station is 580A. If copper cables are used, two 150 square meters are required for each phase and six for three phases, with a total length of 9000 meters and a price of 864000; If you use two 240 square meters of aluminum alloy, the total length is 9000 meters, and the price is 450000 yuan, 414000 yuan can be saved, and the loss of 240 square meters of aluminum wire is lower than that of 150 square meters of copper wire.

There is also a rare earth aluminum alloy cable, which is made of high elongation aluminum alloy material. By adding rare earth trace element materials such as boron to pure aluminum and treated by rolling technology and special annealing process, the cable has good flexibility. When its surface is in contact with air, it can form a thin and firm oxide layer, which can withstand all kinds of corrosion. Even when overloaded or overheated for a long time, it can ensure the stability of the connection, and the cost is about 10% higher than that of ordinary aluminum alloy cable.
Application scope of aluminum cable: aluminum cable can be considered for long-distance overhead line, underground cable trench with large space and places with reliable fixed bridge.
Precautions for use of aluminum cable:
The melting point of copper is 1080 ℃, while that of aluminum and aluminum alloy is 660 ℃, so copper conductor is a better choice for fire-resistant cable. At present, some aluminum alloy AAC Cable manufacturers claim that they can produce fire-resistant aluminum alloy cables and have passed the relevant national standard tests, but there is no difference between aluminum alloy cables and aluminum cables. If they are in the fire center, that is, when the temperature is higher than the melting point of aluminum alloy and aluminum cables, no matter what heat insulation measures are taken, the cables will melt in a very short time and lose their conductive function, Therefore, aluminum alloy should not be used as fire-resistant cable conductor, nor in densely populated urban distribution network, buildings, factories and mines.

Compared with aluminum core cable, the copper core is flexible, the allowable bending radius is small, and it is not easy to break after repeated bending. Therefore, aluminum cable should not be used when there are many bends, many pipes or complex lines.
As the terminals of electrical switchgear are made of copper, copper and aluminum are directly connected, and the chemical reaction of primary battery will occur after power on: aluminum with higher activity will accelerate oxidation, resulting in higher resistance and lower current carrying capacity at the joint. Therefore, some measures need to be taken when copper and aluminum are connected, such as using copper aluminum transition terminal or copper aluminum transition terminal block, Eliminate electrochemical reaction.

Why are mineral insulated cables so hot?

In recent years, the city has developed rapidly
Subway, station, hospital, school, high-rise housing
Expansion of public facilities construction
The number of high-rise buildings has soared
The demand for urban electricity is rising
Such a densely populated focus area
Serious consequences of fire
In recent years, the fire spread trend of such sites presents similar pattern

Analysis of experts in building and safety fire protection
There are still many AAC Cables for public facilities
No fire protection
It is difficult to play an appropriate role in the fire
The law expressly stipulates that the fire protection system needs mineral insulated cable in the code of fire protection design of building engineering to pass the fire inspection and acceptance.
Because mineral insulated ABC Cable can not only ensure the fire power supply within the fire duration (more than 180 minutes), but also will not delay the fire, no smoke and secondary disasters, thus winning valuable time for fire rescue.
It can be said that mineral insulated cable is a special cable used in the fire protection of important national facilities, large public areas, high-rise buildings and other places. Its fire resistance, durability, safety, reliability and economy are irreplaceable by traditional power cables.
1、 Structure form of mineral insulated cable
Chengtiantai mineral insulation cable is a kind of cable which is wrapped with copper sheath and separated from the conductor and sheath with magnesium oxide powder as inorganic insulation material (optional for outer sheath), and forms a close whole with metal core and sheath.
Magnesium oxide is also a kind of non combustible material, and it will not produce toxic smoke or other harmful substances when encountering high temperature. Therefore, the cable with magnesium oxide as the insulator of copper core and copper sheath has better performance and many advantages.
2、 The properties and advantages of mineral insulated cables
Chengtiantai mineral insulation cable mainly includes bbtrz (flexible mineral insulated fire-proof cable) and yttw (flexible inorganic mineral insulation cable), which has good fire resistance, high temperature resistance, high carrying capacity, waterproof, corrosion resistance, mechanical damage, radiation resistance, electromagnetic compatibility, beautiful and generous appearance. At the same time, the cable will not emit any smoke under fire conditions Halogen and toxic and harmful gases.
1. Fire protection performance
Because mineral cables are all made of inorganic materials, they will not cause fire, combustion or combustion supporting, and toxic gas will not be produced. Even if there is fire outside, the cable can still work normally. Mineral insulated cable is made of magnesium oxide as insulator, and the melting point of magnesium oxide is as high as 2800 ℃, which is difficult to burn easily, so the fire resistance of mineral insulated cable is excellent.
The test shows that the mineral insulated cable can be operated normally for 2 hours in a flame with temperature of 800 ℃ -900 ℃; The cable is still intact and continues to operate normally after 30 minutes of combustion under the flame of 1000 ℃.
2. High temperature resistant operation, high load flow
The normal operating temperature of mineral insulated cable can reach 250 ℃, and in special cases, the cable can be maintained in a short time at the temperature close to the melting point of copper sheath. It is very suitable for laying in high temperature places, such as metallurgy, boiler, glass furnace, blast furnace and other environments.
The cut-off flow of MgO powder is far higher than that of other cables. Because magnesia powder has better conductivity coefficient than plastic, the same working temperature and flow rate are larger. For lines with more than 16mm, one section can be reduced, and two sections can be reduced for places where people are not allowed to contact.

3. Waterproof, explosion-proof, high mechanical strength
The insulation layer of mineral insulated cable is processed by high density compaction process, and then protected by seamless copper sheath. In the product standard, it must be subject to three requirements of fire resistance, spray resistance and mechanical impact resistance, which can withstand severe impact and mechanical damage. Therefore, it not only prevents the water, moisture, oil and some chemical substances from being infringed, but also suitable for connecting the explosion-proof equipment and equipment in places with explosion risk.
4. Overload protection
When the line is overloaded, the plastic cable will cause insulation heating or breakdown due to over-current or overvoltage. For mineral insulated cables, as long as the heating temperature of copper is not reached, the cable will not be damaged. Even if the breakdown occurs in a short time, the high temperature of magnesium oxide at the breakdown point will not form carbides. After overload removal, the cable performance will not change and can still be used normally.
5. Long service life, more safe and reliable
Because the structure of mineral insulated cable is composed of copper core and insulating sheath, it is a closed whole, so it is difficult for the material to aging due to the oxygen action in the outside air. This makes the overall service life of the cable longer (2-3 times the life of the ordinary cable), and the copper sheath’s own characteristics make the cable better grounded, Therefore, the lightning protection and grounding measures are effectively implemented, so as to ensure the safety and reliability of the electrical line operation.
Due to the many excellent characteristics of mineral insulated cables, many electrical design codes or standards have been adopted in recent years, and also used in many engineering projects in different industries. It can be expected that the use of mineral insulated cables in China will increase greatly in the next ten years.

Teach you to choose high quality wire through insulating layer!

The relationship between the rated voltage of cable and the number of cable cores

1、 Selection conditions of 1-5-core cable for 1kV and below
(1) Single core cable
When the line is long and the working current is large, or when it is laid under water, in order to avoid or reduce the intermediate joints, or when the single core AAC Cable has better comprehensive technical economy than the multi-core cable, the single core cable can be selected.
Low voltage DC power supply circuit, when necessary, single core cable can be used.

(2) Core cable
When the neutral point of 1kV and below power supply is directly grounded, the number of cable cores of single-phase circuit, when the protection line and neutral line share the same conductor, the 2-core cable shall be used.
2-core cable should be used for DC power supply circuit.
(3) Core cable
When the neutral point of 1kV and below power supply is directly grounded, the number of cable cores of single-phase circuit is: when the protection line and neutral line are independent, 3-core cable should be used.
(4) Core cable
For 4-core cable (3 + 1 cable) of 1kV and below, the fourth core not only serves as protective grounding, but also transmits unbalanced current and short-circuit current of power system. Its size is determined by unbalanced current and short circuit current, but generally not less than 1 / 2 of phase line.
When the protective line and neutral line share the same conductor, 4-core cable should be used in the three-phase four wire low-voltage distribution system of 1kV and below, instead of 3-core cable combined with single core cable to form a loop, or even directly using the metal sheath or armor layer of 3-core cable as neutral line. Otherwise, when the three-phase current is unbalanced, it is equivalent to the operation state of single core cable, which is easy to cause power frequency interference.
(5) Core cable
For the three-phase four wire low-voltage distribution system of 1kV and below, some distribution lines of electrical devices with high safety requirements, and some communication centers and automation equipment that not only ensure electrical safety, but also have anti-interference grounding, the TN-C low-voltage distribution system with 5 cores should be adopted, so that the protection line (PE line) and neutral line (PN line) are independent, The cross-sectional area of cable core is generally 3 large, 2 small or 4 large, 1 small or 5 large.

2. Selection of medium and high voltage cable cores
For 3 ~ 35kV three-phase power supply circuit cable core number selection. When the loop or cable with large working current is laid underwater, 3 single core cables can be selected for each loop; In addition to the above conditions, 3-core cable should be selected. The 3-core cable can be of common package type or 3 single core cable stranding structure type.
For 110kV three-phase power supply circuit, except for laying in Lake, sea water and other places and when the cable section is small, three single core cables can be selected for each circuit.
For three-phase power supply circuits above 110KV, three single core cables shall be selected for each circuit.
For high voltage AC single-phase power supply circuits such as electrified railway, two core cables or two single core cables shall be selected for each circuit.
Single core cable should be selected for HVDC transmission system; Coaxial 2-core cable can also be used for underwater laying in Lake and sea.

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Japan plans to build its largest submarine cable

According to foreign media reports, in order to improve the environment for transmitting a large amount of electricity generated by renewable energy to the capital circle and Kansai consumer areas, Japan’s Ministry of economy, industry and other countries are exploring ways to enhance the transmission network by laying the largest submarine cable in China. The route connecting Hokkaido and Kanto and the route from Kyushu to China and Shikoku are very likely. The government has proposed to achieve the goal of net zero emission of greenhouse gases by 2050, and strive to achieve it through the leap forward expansion of renewable energy.

The Ministry of economy and industry began to discuss the adjustment of the national power supply wide area operation promotion organization (wide area organization) in March this year summarized the discussion plan. The government has positioned offshore wind power generation as the core of renewable energy in the future. The coastal areas of Hokkaido and Kyushu have many suitable places for stable wind, and efforts will be made to deliver power to urban areas.

The capacity of the line from Hokkaido to Kanto is 8-12 million KW, which is about 10 times of the 900000 kW transmission line connecting Hokkaido and Honshu. This paper discusses the submarine ACSR Cable as the largest capacity of transmission line in China. For the route, several options are considered, such as connecting to the Kanto region through the Pacific Ocean or the sea of Japan, and connecting to the northeast region.

According to the analysis, the distance of the line will reach nearly 1000 km. There are only two submarine cables connecting dozens of kilometers in Japan, which will be the longest one. Compared with the common AC power transmission line, the submarine cable transmits power by the DC mode with less loss.

As for the route from Kyushu To Kansai, new submarine cables (with capacity of 1.4-2.8 million KW) connecting Kyushu to China and submarine cables (with capacity of 700000-2.8 million KW) connecting Kyushu to Shikoku will be considered. In addition, the transmission equipment connecting the East Japan border with the West Japan border will be strengthened.

So far, the power giant has focused on connecting the company’s nuclear power plants, large thermal power plants and consumer areas within its jurisdiction to build a transmission network. It was pointed out that, together with the small capacity of transmission equipment in interconnected areas, it constituted an obstacle to the realization of renewable energy projects far away from consumption areas. The submarine cables under discussion are connected to or across the jurisdiction. If completed, it will achieve the change of transmission network appearance.

Huge construction costs are needed to strengthen the transmission network. Wide area agencies intend to curb costs as much as possible, and it is said that submarine cables cost 100 million to 180 million yen per kilometer (about 6.01 million to 10.81 million yuan). If the connection between Hokkaido and Kanto requires at least hundreds of billions of yen in construction costs, it may lead to a rise in electricity charges.

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The load that the indoor common wire can bear

Wire load is a concern before we buy wires. At present, the wire specifications commonly used in our life include 1 square wire, 1.5 square wire, 2.5 square wire, 4 square wire, 6 square wire, etc., so how many watts can these wires load? Let’s look at the number of watts the 1, 1.5, 2.5, 4, 6 square wires can load.

1、 How many watts can a square wire load

An “empirical formula” commonly used by electricians: as long as it is copper core wire, the cross-section area of each square millimeter can pass through the rated current of 4-5a safely; In the single-phase circuit of 220V, the current is about 4.5a for every 1kW power; In 380V three-phase balance circuit, the current is about 2a for every 1kW power. The above values are very close to the results calculated by physical calculation formulas. Therefore, in order to remember the “cumbersome” calculation formulas, electricians can remember these in the work. Then according to this algorithm, we know that: if the copper core wire is used in 220V single-phase circuit, it can safely carry the current passing through 1kW load; If used in three-phase balanced load (such as motor) circuit, the current passing through 2.5kW load can be safely carried.

2、 1.5 how many watts can the square wire load

If the power supply line is copper core wire, the first is that the maximum allowable working current for open wire installation is 20a, namely 4400 watts; The second is the concealed steel pipe, with current of 16a and power of 3520 watts; Third, PVC pipe is concealed, current is 14a, then the power is 3000 watts.

3、 2.5 how many watts can the square wire load

The power supply of 2.5 square wires is about 5500 watts, and the aluminum core wires are 2.5 square millimeter, 13a-20a, 4400 watts of 220VAC voltage, which is no more than 15A for a long time, and the maximum standard of 10A is not more than 15A.

4、 How many watts can the 4 square wires load

The 1kW of single-phase power supply is about 4.5a and 8kw is about 36a. The current carrying capacity of 4 square wires (single plastic copper wire) is about 30A. Smaller ones, change 6 square wires (single running power supply). Your watch and gate must be changed. Don’t use such a high power, minimum 4kw, also can. How much kilowatt power is the power supply of 4 square wires depends on whether you use 220V in your home or 380V in the factory. If the 4 square wires of 220 can load 6 to 8 kilowatts.

5、 How many watts can 6 square wires load

The power line diameter of the 6 square wire can load is not directly related to the power delivered. Generally speaking, 6 square wires are more than enough for air conditioning wires. The maintenance power supply on the construction site is generally 10X6 + 1×4 cable. As for the current intensity, according to my experience in construction, this kind of cable is generally controlled by 63A air switch. 6 square aluminum wire can load 6 kW, 6 square copper wire can load 10 kW.

What is power cables overload?

During the operation of the wire and cable, heat will be generated due to the existence of resistance. The resistance of the wire is generally very small, and its heating power can be expressed by the formula q=I^2R. q=I^2R indicates: for a piece of Power Cable in actual use (R is basically constant), the larger the current through the wire, the greater the heating power; if the amount of current is constant, the heating power of the wire is also constant . The heat released during operation will be absorbed by the wire itself and cause the temperature of the wire to rise. Although the wire is constantly absorbing the heat released by current work, its temperature will not rise indefinitely. Because the wire is absorbing heat, it is also constantly releasing heat to the outside world. The facts show that the temperature of the wire gradually rises after the wire is energized, and finally the temperature is constant at a certain point. At this constant point, the wire has the same heat absorption and heat dissipation power, and the wire is in a thermal equilibrium state. The ability of the wire to withstand higher temperature operation is limited, and operation exceeding a certain maximum temperature will be dangerous. This maximum temperature naturally corresponds to a certain maximum current, and running a wire that exceeds this maximum current is an overload. The overload of the wire directly causes the temperature of the wire itself and nearby objects to rise. The increase in temperature is the most direct cause of this type of fire.

Overload damages the insulation layer between the twin Overhead Cable and causes a short circuit, which burns down the equipment and causes a fire. The double-stranded wires are separated by the insulating layer between them, and overload causes the insulating layer to be softened and destroyed, which leads to direct contact between the two wires to cause a short circuit and burn the equipment. At the same time, the high temperature generated by the large current at the moment of short-circuit causes the line to catch fire and fuse, and the resulting molten beads fall to combustibles and cause fire. Overload temperature rise can also directly ignite nearby combustibles. The heat transfer of the overload wire increases the temperature of nearby combustibles. For nearby combustibles with low ignition point, it is possible to ignite them and cause a fire. This danger is particularly prominent in warehouses that store flammable materials and buildings that are easy to use and combustible decorations.

There are so many types of cables, how can I remember them?

Each industry has skills and shortcuts for each industry, so in the wire and cable industry, how to remember the problem of cable models is a skill of the industry. Only those who are knowledgeable can remember, and those who don’t understand can learn and understand.
There are many specifications and models of power cables, and they are also very complicated. To be honest, you brought an unusual model, and I don’t know it. Therefore, this article mainly introduces: the composition law of cable specifications. Once you have mastered this law, even if you see something you don’t know, you can know what kind of cable it is and what materials it consists of as long as you find the meaning of the corresponding letter or number.

We often put the specifications and models together. In fact, these two are different categories. You can see from your company’s certificate that the specifications, models, and rated voltages are written separately.
Specification is the main material composition of the cable. Different materials are suitable for use in different places, and different specifications have different uses. Our common cable specifications are VV, YJV, NH-YJV, YJLV, etc. Each letter and number in it has a different meaning.
Common insulating materials are: V (polyvinyl chloride), YJ (cross-linked polyethylene)
Conductor: T (copper, generally omitted and not written), L (aluminum), HL (aluminum alloy)
Common outer sheath materials are: V (polyvinyl chloride), Y (polyethylene)
The armor layer is represented by numbers: 22 (double steel belt wrapping), 32 (thin round steel wire)
Some cables need special properties: NH (fire-resistant), ZR (flame-retardant)
The above is the composition rule of the specification, namely: (special performance)-insulation-conductor-outer sheath-armor layer. For example, NH-YJV is a fire-resistant XLPE insulated PVC sheathed copper core cable; ZR-YJLV is a flame-retardant XLPE insulated PVC sheathed aluminum core cable; WDZ-YJV22 is a low-smoke, halogen-free Type XLPE insulated PVC sheathed copper core cable.

Another category is the intuitive cable model. The cable model indicates the number and size of the neutral wires of the main line. There are 3 grades, 4 grades, 5 grades, 3+1, 3+2, 4+1, etc. 3×4 means three 4mm2 cables; 3×120+1×70 means three 120mm2 main wires and a 70mm2 four-core cable.
There is nothing to elaborate on the model, you just need to remember one point: According to the GB/T standard, the main line of the cable is generally not less than twice the zero line (except for aluminum alloy cables), and only two are special, namely: 35mm2 The main line adds a 16mm2 zero line, and the 150mm2 main line adds a 70mm2 zero line.

Factors affecting service life of cable

Wire and cable as the domestic manufacturing industry second only to automobile manufacturing, it can be said that Aluminum Cable is closely related to our lives, has long been unable to separate, we all know that Chinese electric power penetration is very high, even better than many developed countries. Nowadays, all walks of life can not live without power, and the cable responsible for transmitting power is becoming more and more important.

Many people are concerned about the service life and safety of the Service Drop Cable. The service life of the cable is determined by the oxidation induction period of the sheath material, the average cable design is 20 years old, but many factors can accelerate cable aging, so keep these factors in mind for better cable maintenance.

1. External Force damage this is one of the most common causes of cable aging, such as: Cable installation is not standard construction, easy to cause mechanical damage.Sometimes if the damage is not serious, it will take months or even years to cause complete breakdown of the damaged parts to form a fault, sometimes serious damage may occur short-circuit fault, directly affect the safety of electricity and production.

2. Moisture in the insulation is also common, such as cable joints, such as poor cable quality, such as wet environment, may accelerate cable aging.

3. chemical corrosion severe cable aging due to long term overload operation, due to Joule’s laws load current flowing through the cable will inevitably lead to conductor heating, at the same time, the additional heat will be produced by the skin effect of electric charge, the eddy current loss of steel plate and the dielectric loss of insulation, which will increase the temperature of cable. Long-term overload operation, too high temperature will accelerate the aging of insulation, insulation is breakdown. Especially in the hot summer, the cable temperature often leads to the first breakdown of the weak insulation, so in the summer, the cable fault is particularly.

Ingenious use of aluminum alloy cables for photovoltaic systems(2)

In the era of low-cost Internet access, the cost of the control system is critical. In the past ten years, the prices of modules and inverters have fallen by 90%, which has contributed greatly to the overall cost reduction of photovoltaic systems, but the cost of cables has not been reduced. In large-scale projects, cables account for 10% of the system, which is even higher than that of inverters. In fact, as long as the design and installation are proper, under the premise of ensuring the normal operation and safety of the system, some AC cables are made of aluminum alloy cables, which can reduce part of the cost.
Rare earth aluminum alloy cable uses high elongation aluminum alloy material. By adding boron and other rare earth trace element materials to pure aluminum, and processed by rolling technology and special annealing process, the cable has good flexibility. When the surface is in contact with air, a thin and strong oxide layer can be formed, which can withstand various corrosions. Even when overloaded or overheated for a long time, the stability of the connection can be guaranteed, and the cost is slightly higher than that of ordinary aluminum alloy cables by about 10%.
The application range of aluminum cables: long-distance overhead lines, underground cable trenches with a relatively large space, and places with reliable fixed bridges, aluminum cables may be considered.

Precautions for the use of aluminum cables:
The melting point of copper is 1080°C, while the melting point of aluminum and aluminum alloy is 660°C, so copper conductors are a better choice for fire-resistant cables. Now some aluminum alloy cable manufacturers claim that they can produce fire-resistant aluminum alloy cables and have passed the relevant national standard tests, but there is no difference between aluminum alloy cables and aluminum cables in this respect. No matter what kind of heat insulation measures the cable adopts, the cable will melt in a short time and lose its conductive function. Therefore, aluminum alloy is not suitable for fire-resistant cable conductors, nor is it suitable for use in densely populated urban distribution networks, buildings, factories and mines.

Compared with the aluminum core cable, the copper core is flexible, the allowable bend radius is small, and it is not easy to break after repeated bending. Therefore, the aluminum cable is not suitable for the occasions with many turns, more pipes, or complicated lines.
Since the terminals of the electrical switch equipment are all made of copper, the copper and aluminum are directly connected, and the chemical reaction of the galvanic battery will occur after power on: the more active aluminum will accelerate the oxidation, resulting in higher resistance at the joints and current carrying capacity. Therefore, some measures need to be taken when the copper and aluminum are connected, such as the use of copper-aluminum transition terminals or copper-aluminum transition terminals to eliminate electrochemical reactions.