Development history of bus ducts

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This post was last edited by jennifer12580 on 2016-11-25 at 11:06. The development history of bus ducts: Starting from the mid-1950s, companies such as Beijing Baizifang Airport Electrical Apparatus Factory began to use insulating pads to support the conductive strips inside enclosures, relying on air as an insulating medium. The spacing between them is 50 mm. The intensive approach began in the mid-1980s; represented by Zunyi Changzheng Electrical Control Equipment Factory, it involved covering the conductive bars with insulating material and then securing them together on both sides. Insulating materials: PTFE tape, with a working temperature of 200 degrees; its drawback is that it releases deadly toxic gases (perfluoroisobutylene and phosgene) when decomposed at high temperatures. PVC heat-shrink tubes vary greatly in quality – some manufacturers use cheap products, and in actual tests the insulation performance does not meet Class B standards. Irradiated cross-linked flame-retardant tape (PER) performs well: it can operate at a temperature of 150 degrees, has good water resistance, is elastic, and provides a tight fit when wrapped around objects. A special type of busbar that emerged in the evolution of second-generation busbars, namely the dense-type busbar air plug. Due to changes in the manufacturing process, it has essentially become a compact bus with dense connectors, that is, an integrated compact bus duct. In composite-insulated bus ducts, in addition to the insulating layer on the conductive bars themselves, there is also a certain amount of air dielectric insulation between the various phase wires. Vulcanized insulation technology is used in various elbows. MT-7-3 rubber sleeves are used for straight sections. Sulfurized insulation technology: The material used is CZ260 fast-setting insulation powder, with quaternary cross-linking for curing; there is no gap between the insulation layer and the conductive bars. It boasts excellent heat dissipation, moisture resistance, and reliable insulation performance. However, it has not been widely adopted due to higher costs compared to the second-generation busbars. Other relevant information: 1. According to the results of supervision and random inspections in 1995 and 2000, the pass rate for domestically produced busbars increased from 57.14% to 71.4%. 2. For busbar welding: Busbars in L-shaped (flat bend) and T-shaped configurations are all welded together; however, there are no relevant standards set by national regulations. It is said that weld inspection using GB3323’s Class III standards is being considered. 3. Nowadays, busbars with a high protection rating of IP66 or higher are available, which solves the problem of water resistance. Shanghai Waigaoqiao uses domestic IP68 outdoor bus ducts. 4. The advantages and disadvantages compared to cables are, in simple terms, the differences between trunk-type power supply and radial power supply. Classification of bus ducts: Based on the insulation method, bus ducts can be divided into three types: air-insulated plug-in bus ducts, densely insulated plug-in bus ducts, and high-strength plug-in bus ducts. 1: High-strength enclosed bus duct (CFW). Its manufacturing process is not restricted by the type of sheet material used; the enclosure is designed in a gabled shape, which increases the mechanical strength of the busbars. The horizontal sections of the busbars can be manufactured up to 13 meters in length. As the enclosure is designed in a gabled shape, the grooves are used to separate and fix the busbars intentionally; there is a spacing of 18 mm between the busbars, which ensures good ventilation between them. This significantly improves the moisture resistance and heat dissipation capabilities of the busbar tray, making it well-suited for the climate in the south. The presence of gaps between the wires reduces their temperature rise, thereby enhancing their overload capacity and reducing magnetic oscillation noise. However, the stray current and inductive reactance it generates are much greater than those of dense bus ducts; therefore, when comparing products of the same specification, its conductor cross-section must be larger than that of densely insulated plug-in bus ducts. 　II: Air-type plug-in bus ducts (BMC). Since the joints between the busbars are connected by copper sheets, in the humid climate of the south oxidation tends to occur at these joints, resulting in poor contact between the joints and the busbars. This leads to overheating of the contacts, which is why such connections are rarely used in the south. Furthermore, the volume between the joints is too large, the dimensions of the horizontal bus sections are inconsistent, and the overall appearance is not attractive. 　III: Dense-insulated plug-in bus ducts (CMC). Its moisture resistance and heat dissipation performance are poor. In terms of moisture resistance, busbars are prone to getting damp and flooded during construction, which leads to a decrease in the inter-phase insulation resistance. The heat dissipation of the busbar relies mainly on the enclosure; due to the compact arrangement of the wires, the heat from phases L2 and L3 dissipates slowly, resulting in a higher temperature rise in the busbar tray. Due to the limitations imposed by the enclosure panels, densely insulated plug-in bus ducts can only be manufactured in horizontal sections of no more than 3 meters in length. Due to the small inter-phase gap of the busbars, when large currents flow through them, a strong electromotive force is generated, causing the magnetic oscillation frequencies to overlap and resulting in excessive noise. Plug-in bus ducts belong to the trunk system type, and they offer advantages such as small size, compact structure, reliable operation, high current-carrying capacity, ease of tapping for power distribution, convenient maintenance, low energy consumption, and good dynamic and thermal stability; as a result, they are widely used in high-rise buildings. The busway starting box is the terminal end of the bus system. Simply put, it consists of a metal enclosure that is typically installed at the top of the distribution cabinet; it works in conjunction with the busbars. The busbars pass through this starting box, and the incoming wires from the distribution cabinet are connected via connection strips. There is usually a locked door on the front side of the starting box, which facilitates opening it for inspection during maintenance. The busway starting box is essential in a busbar system