The phase issue when using busbar trunking as a low-voltage incoming line: Currently, low-voltage distribution cabinets use busbar trunking as the incoming line connection, usually for the incoming line of the cabinet. According to relevant specifications, the arrangement of three-phase busbars can be roughly divided into two types based on the model of the low-voltage distribution cabinet and the manufacturer: horizontal arrangement and arrangement of down conductors, arranged in this order. From the front of the cabinet, the horizontal arrangement from front to back is N, L3, L2, L1. The arrangement of down conductors from left to right is LI, L2, L3, N. On the other hand, as is well known, the arrangement order of the low-voltage bushing of the transformer is N, L1, L2, L3. The transformer is installed indoors according to the design requirements, generally with the high-voltage side facing inward and the low-voltage side facing outward.
When the incoming busbar of the low-voltage distribution cabinet is arranged horizontally, there is no need to phase change between the busbar duct and the transformer, only a transition piece needs to be added. However, when the incoming busbar of the low-voltage distribution cabinet is arranged in a down type, due to the different phases, the busbar duct cannot be directly used as a low-voltage incoming line to connect the transformer and the low-voltage distribution cabinet. Therefore, the busbar duct can only be connected through phase change.
The method is: it can be connected by changing the phase of the bus duct, or by using an incoming auxiliary box (which can be installed on the top of the cabinet, and the zero bus can be swapped inside the box) to achieve correct connection of the equipment at both ends of the bus duct in the same phase.
The fixing method of transformer room busbar trunking: The busbar trunking provided on the manufacturer's sample is generally lifted with round steel. This method is not suitable for fixing the transformer room busbar trunking because it is a "flexible" fixing that can only lift the busbar trunking and prevent it from moving up and down. When the busbar trunking is improperly installed and subjected to torsional stress or short-circuit electric force, it may shake left, right or up, which will cause damage to the transformer low-voltage bushing connected to the busbar trunking or oil leakage at the rubber sealing ring at the root of the bushing. Even if the expansion joint is used as a transitional connection between the bus duct and the transformer, the use of the bus duct as the main busbar for low-voltage incoming lines generally results in high current, some of which have reached 2500A. The corresponding expansion joint has a larger cross-section and smaller elasticity, which may still cause stress on the low-voltage sleeve of the transformer.
Use a channel steel bracket to support the bus duct, and use round steel as a hoop to fix the bus duct on the channel steel bracket. The two ends of the channel steel bracket are connected to the embedded parts on both sides of the transformer room wall with bolts. In this way, the "rigidity" fixation of the channel steel bracket and the "flexibility" connection of the expansion joint are fully matched, and the "combination of steel and flexibility" ensures that the low bushing of the transformer will not be damaged under stress
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