1. 1 structural selection Liaoning Huaqiang industrial professional bus duct sales company, welcome to click on the website.
There are two types of bus duct structures: air type and dense type. The conductors between phases of air type bus duct are separated by insulating blocks. The interphase conductors of the dense bus duct are wrapped with insulating materials and pressed together. Because there is no air in the middle of the dense bus, the heat energy is directly transferred and dissipated quickly, which is suitable for high current power supply. Air-type bus duct has slow heat dissipation and is suitable for small current power supply. Taking 600A current as the boundary, it is the most economical to choose air type and intensive type. > 600 A, it is better to choose dense bus, and < 600 A, it is better to choose air type, which is more cost-effective in this current range.
1.2 site selection
According to the use of different places and the level of engineering, different bus duct types and technical parameters should be selected.
1.2. 1 performance
1.2.2 The bus duct includes fireproof bus duct, fireproof bus duct, fireproof smoke bus duct and common bus duct.
Fire-resistant bus duct is specially used for power supply of fire-fighting equipment and cannot be used for other purposes. Therefore, the bus has good heat resistance and heat insulation, and the heat energy of the bus duct cannot be dissipated, so it cannot be used at full load for a long time. Except for the fire-resistant bus duct, other buses can run at full load for a long time.
1.2.3 Difference between fire-resistant bus duct and fire-resistant bus duct:
1.2.3. 1 refractory materials with high temperature resistance ≥ 1 100℃ and insulating materials with high temperature resistance ≥300℃ shall be used for the shell and insulation layer of the refractory bus duct. The fire resistance time of this product is 60 minutes and 90 minutes, 120 minutes and 65438.
1.2.3.2 Fire-proof bus duct: The common bus duct or the bus duct shell where fire smoke spreads is provided with a fire-proof interlayer, and some shells are coated with fire-proof paint, so that the fire heat energy can be introduced into the interior within the specified time, and the bus duct can operate normally, with the fire burning temperature reaching about 800 degrees, and the fire-proof time is 30 minutes, 40 minutes and 60 minutes respectively.
1.2.4 Fire-proof loose smoke bus is generally flame retardant. In the event of a fire, the bus in this section will not spread beyond 2 meters in other sections.
1.2.5 Ordinary bus duct is not flame retardant. In case of short circuit, it will burn other connecting buses, which is easy to cause fire accidents.
Second, the choice of technical parameters
2. 1 protection level Liaoning Huaqiang industrial professional bus duct sales company, welcome to click on the website.
2. 1 1 The protection level of bus duct is an important index to prevent people or animals from directly contacting live equipment, and to prevent foreign bodies and water from entering the bus duct and affecting the safety of the equipment.
According to the practical experience of many projects, it is suggested that the protection level of bus duct should be selected according to the following conditions according to different places:
2. 12 substation bus adopts IP40 or IP54；;
2. 13 IP54； Vertical bus selection of shaft and production workshop;
2. 14 IP65； Selected as the horizontal safety bus in the basement;
2. 15 IP66； Should be chosen in the place near the seawater intrusion pool or wharf and outdoors;
2. 16 IP68 is selected for underground, cable trench or underwater places.
2.2 Temperature appreciation
Temperature rise is the most critical technical parameter of bus duct. The maximum temperature in the bus duct minus the ambient temperature is equal to the temperature rise, which is expressed by k ... This is the maximum temperature increment of the bus duct under the full load and stable state. It involves current carrying capacity, service life, power loss, voltage drop, personal injury degree, environmental temperature change and so on. Therefore, temperature appreciation is the most important index in the technical parameters of bus duct. At present, there are 55K, 77K, 90K, 100k bus duct temperature appreciation in the market. Many products above 100K have been put on the market. 100K plus the ambient temperature, the internal temperature exceeds 130 degrees, which has serious safety hazards. Now most projects have no control over the temperature appreciation, which is worthy of attention! Because IEC60439.2 and GB725 1.2 are heat-resistant and heat-dissipating.
2.3 Short-circuit withstand strength
Short-circuit withstand strength: this index is the maximum short-circuit current that can be tolerated when a bus short-circuit accident occurs. At present, the breaking ability of switches in many places has also been improved. If the short-circuit tolerance of bus duct is low, it is meaningless to configure a switch with high breaking ability.
It is suggested that the short-circuit withstand strength should be selected according to different bus duct currents:
More than 2500A ≥80KA
1600A~2000A ≥65KA
1000~ 1250A ≥50KA
800A~630A ≥30KA
500A~ 160A ≥ 15KA
Three. Bus duct protection system
3. 1 The continuity of protection circuit is related to PE line.
3. 1. 1 The protective conductor of the two-unit bus and the jumper PE conductor bus shall reach 50% of the phase line, with equivalent cross-sectional area.
3. 1.2 The continuity resistance between the shell and the PE line protection circuit is ≤0.005 ohm, and the unit transmission conductor with jumper is not less than the equivalent cross-sectional area of the protection conductor PE line.
3. 1.3 The PE line of the bus duct is used for the safety protection of the bus duct, except that the accident current of the power supply equipment in this line is all dispersed by the PE conductor of the bus. Therefore, different PE conductor specifications are set according to different current specifications to ensure the dispersion of accident current. The switch that provides signals to the bus can quickly cut off the power supply and quickly evacuate the emergency current. Ensure personal safety under low accident voltage. Therefore, when designing and selecting bus duct, the requirements of 3. 1. 1 and 3. 1.2 should be met to ensure the safety and stability of power supply system.
3.2 temperature control protection
3.2. 1 The most critical technical index of bus duct is temperature rise. How do you control the bus duct to run at low temperature? How to ensure that the products supplied by bus duct manufacturers can run at full load and reach the temperature rise you require? This is the most critical question.
Detection and protection
Each bus duct of each loop is equipped with a protector at each current level, which is installed at the joint of the first trunk unit (the bus protector has two functions of over-temperature alarm and over-temperature cut-off of the bus master switch). Overtemperature alarm refers to the ambient temperature plus the temperature rise you set. For example, if the product you ordered is 70K and the ambient temperature is 20℃ today, the over-temperature alarm temperature is set to 9 1℃. When the bus duct temperature reaches 9 1℃, the bus duct protector starts to give an alarm to prompt maintenance. If the temperature continues to rise to the limit temperature (the limit temperature is the insulation selected for the bus. If the insulation material you choose is Grade B, the limit temperature is set to 130℃. When the temperature reaches 1℃, pay attention to the bus master switch to cut off the power supply and ensure the bus safety).
32.3 the source of high temperature
3.2.3. 1 The resistivity of copper is quite different.
3.2.3.2 conductor's specifications are very small.
3.2.3.3's insulation material and shell have poor heat dissipation.
3.2.3.4 is overloaded.
The connection of 3.2.3.5 connector is unstable, and the resistivity of the connector is high.
3.2.3.6 skin effect, impedance and inductance are all related to the temperature rise of bus duct. At the same time, some bus ducts use varactors, which are unprotected. Therefore, in order to ensure the stability of the bus duct power supply system, it is essential to set a bus protector for each loop and each current level.
Fourthly, conductor selection.
4. The conductor materials of1bus duct are copper, aluminum, aluminized copper and copper-clad aluminum. At present, most projects in China use more copper. In recent years, more and more aluminum conductors have been used in Europe, America, South Korea and Japan. There are several reasons why China and developed countries choose differently:
4. 1. 1 Before 2003, the price difference between copper and aluminum was only several thousand yuan per ton. At that time, the cost difference between copper and aluminum was very small, and the price difference was also very small because the aluminum conductor was nearly 1 times larger than the shell and insulation material. There is little point in using copper and aluminum. At that time, copper conductor was the right choice for most projects. With the soaring price of copper, which is three times that of aluminum, the weight of copper has also decreased. Choosing aluminum as conductor can save cost. The finished product price of aluminum conductor bus duct is almost half of that of copper conductor. China is a country poor in copper and rich in aluminum, and importing a large amount of copper is a problem worthy of consideration in China's construction industry.
Choose 4. 1.2 aluminum conductor bus duct. Because the switch conductor of switch cabinet and plug box is copper, when aluminum conductor bus duct is used, the incoming connector and plug box of switch and bus must be treated by copper-aluminum over-plating process. To prevent the chemical oxidation and electromagnetic oxidation of different alloy safety materials caused by direct lap joint, which will lead to the increase of resistance at the lap joint and heat up, resulting in short circuit accidents.
4. 1.3 copper-clad aluminum conductor
In fact, the copper-clad aluminum bus duct is that most products are plated with aluminum and copper, which has been tested by experiments. Aluminum can't be plated with copper directly, and it can only be plated with zinc or other common metal processes. The resistivity after electroplating is higher than that before electroplating, indicating that the conductor of aluminized copper bus is not less than pure aluminum. Regarding the lap joint with the distribution cabinet, it can be directly lapped with copper, and the copper-aluminum over-plating process should also be done at the box insertion place. Because the coating is very thin, it is easy to damage the surface with the pins of the box, so it can not be inserted directly.
4. 1.4 copper-clad aluminum conductor
Copper-clad aluminum is an aluminum cladding, and the copper cladding is only 0.3 mm ~ 0.5 mm Most of the current flows to the inside of the surface layer, and a small amount of aluminum passes through it. Copper-clad aluminum conductor has been applied in some projects in recent two years, but we should pay attention to whether the bonding process of copper-clad aluminum is reliable. If the combination is not good, it will cause oxidation between copper and aluminum after a period of time and increase the resistance. The current carrying capacity naturally decreases, because the aluminum body inside the copper-clad aluminum shares part of the current as a conductor, and the copper plating transition process of the aluminum conductor is different: 1. He only designed the copper-aluminum transition and did not share part of the current carrying capacity. 2, the area is small, and it is well treated by electroplating process.
4.2 conductor specifications
Because users don't know much about the conductor selection specification, the losses are serious, and some projects don't know what happened after the electrical fire accident. Knowing the current carrying capacity of bus duct conductor specifications is an indispensable engineering and technical index for supervisors, users, quality inspection stations and technicians of power acceptance units.
4.2. 1 Wrong choice: At present, some technicians think that it is wrong to calculate the current of copper conductor of bus duct according to 2A/MM2. For dense bus structures 2500A~630A, the conductor with 6MM layer thickness is about 2A/MM2, but different currents have different structures and different conductor thicknesses. His current carrying capacity is different because of skin effect and heat dissipation.
4.2.2 Misleading
Many projects in the market have been misled by suppliers of production and sales. He refers to the current carrying capacity of the conductor in the power rating manual or design manual, and refers to the current carrying capacity of the manual with the ambient temperature of 35℃ or 30℃, which has serious safety hazards and increases the loss of electric energy.
If 6× 125 conductor is selected centrally, 2000A bus duct standard shall be adopted. Many projects are in use and fire accidents happen from time to time. The manufacturer explained to the user that your ambient temperature is only 30℃, but according to the instructions, the conductor 6× 100 is XXA, and the current 6× 125× 1.25=XXA is misleading to meet the requirements of 2000a. In fact, the instructions show that the conductor is in the air with an ambient temperature of 30℃. It reaches 2000 A current, so the download flow is different at different ambient temperatures. The reason is that the temperature of the conductor is 70℃, and the temperature rise is different, so the current carrying capacity of the same conductor is different. But no matter what you are in, the bus duct is not the same as the ambient temperature. The standard setting is the temperature rise, not the maximum temperature of the conductor. So no matter how many degrees the environment is, the current carrying capacity of the same conductor with the same structure is the same. Because the conductor of the bus duct is covered with insulating material, and the temperature around the conductor enclosed in the metal shell will increase. According to the test of temperature rise of 70K at 3℃, the current carrying capacity at 40℃ in the design manual or electrician's manual is discounted by about 8 ~ 8.5%. There is a certain gap between structural heat dissipation and current, and the bus duct with large current and poor heat dissipation is even more discounted.
3C test report misleading:
Since 2003, China has implemented the national compulsory 3C certification. The first batch of 19 products include 132 low-voltage switchgear, and the national standard GB725 1 bus duct is one of these products. Due to the various specifications of bus duct at present, the testing cost of 3C compulsory certification is tens of thousands of yuan per product. Therefore, the division of authentication center units is not based on current, but on short circuit tolerance. There are two problems in several current specifications covered by each short-circuit withstand strength: ① the conductor of the covered current specifications is not strictly examined by laboratories and certification centers; ② The unified statement of 3C report is that the test results are only valid for the tested samples, but there is a problem that the current carrying capacity of the covered conductors is not strictly examined. For example, 6× 125 conductor 2000A bus, he used 2500A prototype test. The test sample is 6×200 to 2500A current with a current carrying capacity of 2.083A per square millimeter. According to this sample, the current of 2000A should be 6× 160, but written as 6× 125. According to this prototype, the maximum current can only reach 1600A to 125. My product has passed the certification of conductor specifications misleading users and acceptance units. It is worth noting that it has set up potential safety hazards for the construction projects in China, and increased the loss of electric energy.
5. How to control the quality of passenger cars?
Bus duct is the main power line of the project, and it will have a great impact once there is a problem. It involves the loss of electric energy, the influence of voltage drop on equipment and the existence of potential safety hazards. Therefore, the quality control of bus duct is very important. I briefly introduce the quality control of bus duct in the project.
5. 1 design: at present, most projects in engineering design only have three-phase four-wire or tn-s current, and some projects have increased IP protection level. When designing and modeling, some important safety technologies should be written on the drawings as much as possible to prevent the difficulties caused by technical parameters in project settlement and reduce potential safety hazards. .
5.2 User's Choice of Production Enterprises
The national compulsory certification of bus duct has increased with the replacement of the card in recent years. After the new standard was issued in 2006, 3C certification was standardized. The 3C certificate, website and 3C test report of National Certification Committee and China Quality Certification Center have some technical parameter announcements to review the production qualification of the enterprise. Auditing enterprise production can ensure the quality of the following aspects:
5.2. 1 The 3C certificate and test report of the certified bus duct can show that the enterprise has passed the technology and current specifications of the certified products to determine whether it meets the project requirements. Technical contents of the audit: ① Current specification ② Protection grade IP ③ Short-circuit tolerance ICW= KA④ Ordinary bus or fire-proof smoke exhaust bus or fire-resistant bus ⑥ Temperature appreciation ⑥ Conductor interrupting ability ⑥ Protection circuit continuity, etc.
If the above seven technical data meet the technical requirements, the certified products can basically be used with confidence.
5.2.2 Audit of production quality control
Inspection: For conductor inspection, whether there are instruments for measuring conductor resistivity, bus withstand voltage test equipment, bus duct sectional capacity temperature rise test equipment and circuit continuity protection test equipment for the conductor of bus duct is directly related to the qualified rate of products of production enterprises. If you have these testing equipment, you can ensure the quality assurance of the factory products of this enterprise and provide an effective basis.
5.2.3 Examination and testing of conductors
The conductor specification of the bus duct is discounted by 15 ~ 20% compared with the current carrying capacity of the electrician manual at 40℃ ambient temperature, and the bus duct with poor heat dissipation is even more discounted. If there is a gap in the calculation of bus duct carrying capacity, it is suggested to do a temperature rise limit verification test.