Abstract: Busway limit temperature rise is directly related to the conductor current carrying capacity and safety problems, for which the limit mark busbar temperature rise is necessary, it is the most critical health busway safety technology parameters.
Key words: limit temperature rise
With the modernization of China's economy and the rapid development of the electricity load is growing. Replace the cable with the developed countries in recent years Busway is a common phenomenon, and China also has formed a directional trend. However, some designers, users, and quality supervision and personnel safety and health Busway most critical technical parameters - limit temperature rise, awareness and understanding is not deep, resulting in engineering there are security risks and wasteful investment, not an interview about the limit on Busway temperature rise of a number of issues.
In our fire accident, caused by an electrical fire accidents accounted for more than 60%, while the fire caused by the electrical perpetrators include: cable, wire, high and low voltage equipment, transformers, busbar, electrical components, etc. Long-term temperature rise is largely due to heat, causing a short circuit insulation aging caused by fire, heat detection standard terminology that is temperature rise.
Low voltage electricity transmission lines are wires, cables, branch cables, busbar, bare conductive row, puncture cables. Due to a variety of different cooling products, per square millimeter current carrying capacity is somewhat different: the same product, the same conductor size, when through the same current, the temperature different; same conductor cross-sectional area, due to the design structure different temperature are different. Of course, the temperature rise, the resistance value increases, the voltage drop is also increased along with the increased power loss. For example: 35mm2 80A current through the wire temperature is low, through 100A current standard, if the current or 150A through 120A current, temperature rise will exceed the standard, followed by rapid aging of insulating materials , eventually leading to a short circuit. If the 35mm2 wires through 100A Current, per square millimeter equivalent to the passing 2.85A current, 6mm2 wires through 38A current 6.3A per square millimeter is equivalent to the current through If the 6mm2 wire the same per square millimeter through 2.85A current, then 6mm2 At this point the current through the wire is 18A, its voltage drop and power loss ratio 35mm2 is much smaller, because the conductor temperature dropped, along with the decline in energy consumption. Busway is the same, so that the conductivity of the conductor busbar in accordance with flow capacity per square millimeter (current density) to calculate the error, but with the design of the structure and the cooling of the skin effect, impedance, reactance and other factors are closely related. So GB GB7251-2006 (equivalent to IEC standards IEC60499.2-2000) requirements to limit temperature rise through the busbar rated current to determine the current carrying capacity.
International Electrotechnical Standards IEC60439.2-2000 with the national standard GB7251.2--2006 standard is the same: busbar temperature rise is based on thermal insulating materials to determine the level of allowed temperature rise. If the busbar insulation material class F, the heat resistance ≥ 155 ℃, at ambient conditions allowed, it is permissible temperature 115K (155 ℃ ambient temperature minus 40 ℃) is allowed temperature rise. So Busway is full load tests to determine the busbar current carrying capacity, limiting the temperature rise is the most critical one busbar technical parameters. According to the national compulsory 3C certification test standards, busbar temperature rise ≤ 70K limit is reasonably safe.
Busway as wire and cable, it is also used as power transmission lines equipment. Similarly a 35mm2 wires can be used to carry the rated current of 80A can carry 125A rated current, the difference is the rated current 80A and 125A of the temperature rise is completely different. Busway is the same, when the limit temperature rise 70K and 90K, respectively, the same busbar, its carrying capacity difference of 15% or more. Busbar temperature rise on the market today there are 55K, 70K, 90K or even more. High temperature rise the following issues, recommends that users use the Busway best ≤ 70K or limit the temperature rise ≤ 55K.
3.1 Temperature rise, directly reflected in increased energy consumption.
3.2 Higher the temperature, the faster aging of insulation materials, abrupt shortening the life of the busway.
3.3 Higher the temperature, resulting in the surrounding insulating material accelerated aging equipment, such as those in the adjacent busbar ride (rpm) connected wires and cables; or electrically insulating supports, etc., can cause fire accidents.
3.4 Busway internal temperature rises, the voltage drop increase.
3.5 Temperature rise, busbar mechanical strength has declined. Metallic conductors began to relax after heat stress which reduces the mechanical strength;
3.6 Reduces the safety factor, the shell temperature is easy to burn people.
3.7 Temperature rise, so that the surrounding temperature significantly affected.
4.1 Copper copper content is low, resistivity larger.
People often mention the copper content and copper resistivity, etc., they do with busbar current carrying capacity. Copper content of 99.95%, or ≧ 99.93%, resistivity ρ ≤ 0.01777 (Ohm · mm / m) of copper in copper bus bar is relatively high quality copper. If copper copper content is low, the resistivity is large, can only increase the conductor size, in order to ensure that the current carrying capacity and temperature rise. Otherwise, the temperature will be too high.
4.2 Shell structure thermal insulation and poor.
Process structure is better, better heat insulation material busbar conductors according to the design of its manuals manuals or electrician can meet after discount carrier requirements. However, some products insulating material is a resin casting, or the use of other less heat insulating material, the air cooling structure and less intensive busbar busbar to fall off more. Some of the product structure and poor thermal insulation materials, electrical conductor according to the manual 30 ℃ ambient temperature selection, misled the user, it is understood that some of these products can only reach 60% to 70% of the interception capability to China's power supply caused serious security risks and the loss of power, to deserve the attention of people.
Some projects, along with the device increases, the load increases, or the original design of the bus can not meet site requirements, some project construction section when ordering using varactor varactor, did not take effective protection measures, overload operation temperature rise, so there are security risks.
4.4 Connector connection instability, joint resistivity increased.
Connector connection instability, bad joints, resistance will increase, the temperature rise can cause elevated busway.
4.5 Temperature rise and skin effect are not unrelated.
Inside the conductor, easy to distribute the heat generated resistance, high temperature, price and the electronic operation of the high speed, the line is not very flat, thus leading to a relatively narrow electron pathway, the resistance is high. Surface of the conductor, fast heat dissipation, low temperature, valence and electronic operation rate is low, flat line, thus leading to a relatively large electron pathway, so the conductor surface resistance, electronic run faster, and this is the main reason for the current set of skin . For example: copper busbar conductor 6 × 100 and 10 × 60, the same copper cross-sectional area are 600mm2, but the former than the latter 19% of the carrying capacity, which is the current the effect of the skin effect caused by the same current, former than the latter runs low temperature, less power loss and voltage drop also smaller than the latter, that is at the same temperature, the latter is small 19% of the current carrying capacity. Thus unilaterally conclusion conductor cross-sectional area and the current carrying capacity of the power loss is completely wrong.
4.6 Conductor calculated to mislead
Some technical personnel matter what structure Busway, which uses a conductor specifications are in accordance with the "electrician Handbook" (or "Electrical Design Manual") list to calculate, and per square millimeter busbar current carrying capacity to infer useful life , this is wrong. Conductor is copper or aluminum busbar length of life critical look at its operating temperature. The higher the operating temperature, the faster its aging (including copper, aluminum row and insulation materials for electrical copper conductor, electrical aluminum, creep strength, tensile strength, and the oxidation rate of a close relationship with the temperature ). Because the design of the bus structure is different, different cooling, the internal temperature will be different. Conductor forms according to the design manual selection at 35 ℃ ambient temperature, the heat better Compact Busway further decreased by 5% to 15% of the current-carrying capacity, in order to meet the temperature rise ≤ 70K, heat is not good to be down 20-intensive bus %, and air type busbar current carrying capacity decreased to bigger.
Summary: busbar conductor current carrying capacity, regardless of product structure, not counting the skin effect, in accordance with conductor cross-sectional area and current carrying capacity per square millimeter to determine the selected conductor size is wrong.
5.1 Design Institute of Design and temperature
Currently most of the institute there is no rise in the design conventions, only the rated current, and phase four-wire or three-phase five line, which is more general design. If the amount of current 1000A temperature rise ≤ 55K with F class insulation material busway project used in 115K, you can paste the above identified as 1600A rated current of the signs, so the design conventions busbar temperature rise is very important . Busway recommended limit temperature rise ≤ 70K or ≤ 55K, if all the control of electrical equipment operation temperature rise ≤ 55K less (1000V), not only electricity line losses declined significantly; while also reducing electrical fire caused an accident, both energy conservation , but also benefit the people's lives and property and security.
5.2 Project management, quality inspection stations and power requirements for acceptance of units of the temperature rise.
Currently, most of the projects on the busbar current carrying capacity can not be directly verified. Because according to national standards and international standards GB7251.2 IEC60439.2, environmental permitting, busbar insulation limit temperature is allowed to determine the temperature of heat-resistant grade appreciation. Institute of design drawings and Party are not clearly temperature rise, it is not on the current carrying capacity of busbar confirm. Moreover, there is no established about users and businesses to limit temperature rise, so it can not determine how much K is the temperature rise busway project on the use of qualified products. Recommended engineering supervision and inspection stations and electricity inspection personnel, the query 3C 3C certificate and check the test report of various current conductor specifications are consistent with the product. Ensure busbar current carrying capacity and low temperature operation.
5.3 National compulsory 3C certification limits of temperature rise on the busway verification.
China implemented a mandatory 3C certification verification for busbar temperature rise limits, except for the special fire busbar products, other Busway unified by the temperature rise ≤ 70K test standards to carry out, but the busbar current specification range, 3C certification Each product test fee and certification fee required several million, so the authentication center to reduce the burden on enterprises, divided by short-time withstand current of each unit, each unit can cover several rated current specifications. Uniform provisions in each unit are the largest current specifications do take the test, other specifications projected by the enterprises themselves, were audited by the test. The current range of the cover, conductor size per square millimeter of the sample according to the number A standard carriers to project. If the conductor size is less than the temperature rise test samples must be done commissioned test, or other units within the specifications of the conductors. But now there are individual trials reviewed by the enterprises themselves are not filled by current carrying capacity of the specimen current and its scaled-down cover current certificates and test reports. For example, in CCC type test report, 2500A unit covers the 2000A, 1600A, 1250A, 2500A production business is to take a bus to make the unit test, the specimen 2500A conductor size is 6 × 205, the limit temperature rise ≤ 70K, press The sample projections conductor size, should be on every square millimeter carrier 2.0325A, 2000A busbar conductors recommendation should be 6 × 165, but he was producing businesses within product description written in 6 × 125, apparently only increase temperature to reach 2000A current carrying capacity, so difficult to control covering current certification center conductor specifications. Some certificates and test reports covering current carrying capacity per square millimeter of difference between the larger the sample, it is worth deep consideration.
China Quality Certification Center and Test Unit 3C certification test recommended strictly better off, accurate data on the safety and reliability of the announcement on the Internet, such as the limits of the certified products and the current conductor temperature specifications and conductor materials, user queries, ensure the safety of life and property and the interests of users, mobilize the good quality for the project.
6.1 Designs. Busway in the design, the drawing you want to mark the limit temperature rise, while in the drawings or design within the technical requirements for each current rating marked on the map to set a busbar protection device (or temperature controller) for operating temperature monitoring is recommended to set at each a current at the head of the first connection.
Note: The protection device has two signal output, over-temperature alarm and temperature limit cut off the current, so you can ensure Busway during operation of the internal temperature rise.
6.2 Party and supervision can be viewed in the 3C test report specifications and conductor temperature rise, or visit the website of the China Quality Certification Center related technical parameters. 3C certificate and the website has some technical parameters bulletin, such as IP protection class, Icw (short-time withstand current), rated current specifications, so as to ensure that the purchase agreement Busway and certification.
6.3 Limit temperature rise test.
6.3.1 To ensure the quality of the purchased Busway fully able to achieve full load operation of low-temperature low-loss safety best way is to do extreme temperature testing.
6.3.2 Limiting temperature detection position is also critical. Busway line detection section, conductors, plug-in connection conductors, connectors, shell temperature, after running through the full load current, the maximum temperature stabilized, the temperature rise obtained by subtracting the ambient temperature, the unit in K. Other specifications according to the current conductor passing through the test sample per square millimeter carrying capacity calculations, the projected current best current smaller than the sample.
Guangle busway GLMC-T / □-F copper conductor Compact Busway, 3200A less per square millimeter through 2.5A current, 3200A 2A current through the above, the limit temperature rise were ≤ 55K, saving the series busbar about 25% of the copper resources, reducing line loss of about 20%, to achieve energy saving, by many users. Busway Busway temperature rise is directly related to the current carrying capacity, voltage drop, power losses and security risks and other issues, so when the temperature rise agreed necessary, hope you pay attention Busway limit temperature rise, it is the control bus slot key to the quality parameters for the modernization of our country energy conservation and people's lives and property safety checks and work!