Busbar Fabrication

You have not provided enough information for us to give you good advice. All busbar design is based on five factors; the cost, the voltage, the amount of current the busbars are required to handle, the amount of temperature that the system can dissipate, and the forces that would be generated in the event of a fault.

The voltage is the least significant. It determines the amount of creepage distance between the separate phases (the length of the path between two phases that the current would have to take if it followed the shortest route along the insulation) and is one factor in determining the short circuit forces.

The current capacity for low current systems is determined by the size of the copper/aluminum used. Usually flat bars l or multiple sets of flat bars lll are used. For higher current applications the surface effect (current only flows along the skin layer of the conductor) becomes important. If there is no current flowing along the center of the copper why have a center. So hollow tubes and sections like <> and [] are used.

Heat dissipation is a whole subject in itself and there are many factors that will influence it. These include (not a complete list): ambient temperature; the bar material (copper can stand more heating than aluminum); the configuration of the bars ( l, lll, O, <>, [] ); the orientation of the bars (phases laid in the horizontal plain dissipate more heat than phases in the vertical plain and vertical runs of bars are different again, but flat bars of any one phase should always be vertical if possible); the type of enclosure and how constricted the airflow around the bars is (forced ventilation can be used but I don't recommend this as if it fails the heat build up can cause serious damage); the length of the run (needed to determine total resistance, voltage drop and is a major consideration in calculating short circuit forces); non-segregated, segregated phase or isolated phase; the standard that the panel is constructed to (Varies in different parts of the world, you should always build to local standards unless the contract specifies otherwise).

Short circuit forces. Like conductors repel each other. In the case of a short circuit all the conductors are carrying current in the same phase for a short time until the breakers isolate the circuit. Choice of breaker determines how long that will take and so the overall power. How far apart the conductors are (inverse square law), the square of the current, the length of the run, any intervening material (segregated or isolated phase barriers) determines the size of the force. The force acts in the form of a massive short term impulse. If the insulator mountings are not strong enough to resist this impulse the system destroys itself.

Cost. You will always be asked to keep costs to a minimum but cutting corners is not cost effective in this instance. Non segregated is cheaper than segregated which is cheaper than isolated. Some hints. Use modular busbar/insulator packages for smaller systems, the current capacity and force calculations are already done and proven in prior applications. Use the minimum IP rating compatible with safety as this will give a greater air flow. Mount phases horizontally rather than vertically where possible. As you can see from above the task you are undertaking is formidable. Buying in from an established supplier may be slightly more expensive but it reduces risk considerably. Building it yourself, if you don't get it right first time the costs will spiral out of control. If you a re not fully confident this needs to be pointed out to management before as decision is made to proceed.