Problems needing attention in the installation of

2022-10-03
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Problems that should be paid attention to in the installation of dense insulated bus duct

1 introduction

dense insulated bus duct has the advantages of small volume, compact structure, large transmission current, safety, convenient maintenance and so on. It has been widely used in low-voltage power distribution devices in enterprises. However, in the process of construction management, it was found that due to monotonous product specifications of the manufacturer, too simple installation and operation instructions and poor design considerations, it was difficult to install on site at the melting point of 268 degrees. Here are some problems that should be paid attention to in the installation of the dense insulated bus duct from the transformer to the low-voltage distribution cabinet for reference during construction

2 phase problem when bus duct is used as low-voltage incoming line

at present, low-voltage distribution cabinet adopts bus duct as incoming line connection, which is generally the incoming line on the cabinet. According to the requirements of relevant specifications, the arrangement of three-phase busbar can be roughly divided into two types according to the model of low-voltage distribution cabinet and the manufacturer: horizontal arrangement and arrangement of downlead, according to this arrangement order. From the front of the cabinet, the horizontal arrangement is n, L3, L2, L1 from front to back. The arrangement of down conductors is Li, L2, L3 and N from left to right. On the other hand, it is well known that the low-voltage bushing of the transformer is arranged in the order of N, L1, L2 and L3. The transformer is installed in the transformer room according to the design requirements. Generally, the high-voltage side is inward and the low-voltage side is outward. When the incoming bus of the low-voltage distribution cabinet is arranged horizontally, there is no need to change the phase between the bus duct and the transformer, just add transition pieces. However, when the incoming bus of the low-voltage distribution cabinet is arranged in a down lead manner, due to different phases, the bus duct cannot be directly used as the low-voltage incoming line to connect the transformer and the low-voltage distribution cabinet, so the bus duct can be connected through phase change. The method is that the viscosity of the oil is too high: it can be connected through the bus duct commutation section, or the incoming auxiliary box (which can be installed on the top of the cabinet) can be used. Through the bus transposition in the box (generally transposing the zero bus), the equipment at both ends of the bus duct can be correctly connected in phase

3 connection of bus duct

connection of plug-in bus duct. For the connection of busbar, the high-strength insulating board with high insulation, arc resistance and flame retardancy shall be used as the connection accessories, and the bolts with insulating sleeve shall be used for fastening. According to the requirements of the specification, in order to meet the overlapping area of the bus, the gap between the bolt hole and the bolt is small, and the gap is narrower due to the increase of insulating sleeve in the bus duct bolt. Therefore, when connecting the main busbar of the two busbar trunking sections, the axes of the two busbar sections should be strictly maintained on the same central line, and the bolt holes of the busbar of the two busbar trunking sections and the insulating plate should be completely aligned. When threading bolts, each bolt should be applied with uniform force in turn. The purpose is to prevent the insulating sleeve on the bolt from being damaged by shear force during installation. The periodic boundary condition of its crystal will be destroyed. In the process of project construction management, the author found several cases of bus duct insulation reduction due to the stress damage of bolt insulated bushing. The use of bus shell for grounding can meet the grounding requirements, but when the bus shell is completely sprayed, the two sections of bus duct must be connected with grounding bolts with wires. The insulation of bus duct shall be checked before and after installation, and it shall be compared to check whether the insulation of bus duct is reduced due to installation quality problems

4 fixing method of the bus duct in the transformer room

the bus duct provided on the sample of the manufacturer is generally hoisted by round steel. This method is not suitable for the fixing of the bus duct in the transformer room, because this kind of hoisting and fixing is a "flexible" fixing, which can only hoist the bus duct so that it cannot move up and down. When the bus duct is improperly installed and affected by the torsional stress or the short-circuit electric force of the bus, The bus duct may shake left and right or up, which will cause damage to the low-voltage bushing of the transformer connected to the bus duct or oil leakage at the rubber seal ring at the root of the bushing

even if the bus duct and the transformer are transiently connected by expansion joints, the current of the main bus using the bus duct as the low-voltage incoming line is generally large, and some have reached 2500A. The corresponding expansion joint has a large section and small elasticity, which may still force the low-voltage bushing of the transformer. Therefore, it is recommended that the bus duct in the transformer room be fixed as shown in Figure 3. Install the bus duct under the bus duct with channel steel support, and fix the bus duct on the channel steel support with round steel as hoop. Both ends of the channel steel support are connected with the embedded parts on the walls on both sides of the transformer room with bolts. In this way, the "rigid" fixation of the channel steel support is fully matched with the "flexible" connection of the expansion joint, and the "combination of steel and flexibility" ensures that the low bushing of the transformer will not be damaged by stress

5 waterproof of bus duct

bus duct is generally designed to be used indoors. The humidity in the air will not affect the operation of bus duct, but the water inflow of bus duct in use is bound to cause insulation reduction, and long-term operation will cause short circuit and burn bus duct. Therefore, necessary protective measures should be taken for the installation mode that may cause water ingress into the bus duct. For example, when the bus duct passes through the raking layer, due to various reasons such as resistance strain gauge production or roof leakage inside the health sensor, the floor water will leak down along the bus duct passing through the floor, causing water to enter the bus duct and reducing the insulation of the bus duct. After the bus duct in the polymerization workshop of acrylic fiber plant was put into use, a short-circuit fault caused by water entering into the bus duct when it passed through the floor occurred, causing the shutdown accident of the whole production plant. The solution is to add a waterproof cofferdam when the bus duct crosses the floor. (end)

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