Data centre and power applications: busbars, busway and thermal parts

The duty cycle is the difference

A data centre power part does not see a varied duty cycle. It sees a high load for most of the day, in a room that is kept cool for the servers and not for the metal. That changes the design priorities. A busbar sized for a short peak in a factory may run hotter in a rack that never drops below half load. A joint that is checked once at commissioning may never be touched again until the hall is rebuilt.

The second difference is service access. Part of the value of a data centre is that it can be maintained without switching everything off. Isolators, tap-off boxes and joints need to be reachable, labelled and replaceable. A design that is efficient in copper but impossible to service is not a good design for this market.

The chain from incoming supply to the rack

The power path is usually described in layers, and each layer has its own parts and its own specification. Reading the chain in order makes it easier to see where a tolerance, a joint or a thermal limit actually sits.

1. 01

   Incoming distribution

   Transformers, switchgear and main busbars take the supply and split it across the facility.

2. 02

   Distribution busway

   A run of enclosed busbar carries current across the hall, with tap-off points along the route.

3. 03

   Rack distribution

   Busway tap-offs or cables feed rack PDUs, which distribute power to the servers.

4. 04

   Conversion and backup

   Uninterruptible supplies and rectifiers sit in the path and add their own losses and heat.

5. 05

   Thermal removal

   Air or liquid cooling carries the heat from the rack to the plant.

6. 06

   Monitoring

   Current, temperature and power meters provide the data that operations rely on.

Busbars and busway are not the same product

A busbar is a conductor. A busway is an assembly of conductors, insulation, an enclosure and tap-off points, tested as a system. The distinction matters at the buying stage, because a supplier who bends and plates copper may not be able to test a busway to the standard the project requires. Ask for the tested rating of the assembly, not the calculated rating of the bar inside it.

Joints, plating and temperature rise

Every bolted joint in a power path has a contact resistance, and that resistance rises if the surface oxidises or the bolt relaxes. Silver plating is common on copper joints because it holds a low contact resistance, but the plating thickness, the underplate and the coverage on the mating face all matter. A thin silver layer that wears through at the bolt head is worse than a thicker tin layer that is designed for the pressure.

Temperature rise is the number that ties the design together. It should be quoted at a stated current, with a stated ambient and a stated mounting condition. A test on a free standing bar in a laboratory is not the same as a bar in a closed enclosure with other conductors nearby. Ask for the test condition, and check whether the installation matches it.

Thermal parts and mounting

Heat sinks and cold plates are mounting parts. The thermal path runs from the device, through an interface, into the metal and out to the air or the coolant. A heat sink with tall thin fins and a poor base flatness can be beaten by a shorter sink that makes better contact. For a cold plate, the channel design sets the pressure drop, and the pressure drop sets the pump and the pipe size.

Liquid cooling adds a new set of checks. The coolant must be compatible with the metals and the seals, the loop must be leak tested, and the materials must resist corrosion over years. Aluminium cold plates need a corrosion inhibitor and a coolant specification. Copper and aluminium in the same loop need a careful check for galvanic effects.

Inspection and documentation

The inspection plan should follow the current path and the thermal path. On the current path, measure the conductor dimensions, the plating thickness on the mating faces and the joint torque. On the thermal path, measure flatness over the contact area and record the leak test on any liquid part.

The documentation matters as much as the measurement. A data centre project usually needs a declaration of conformity, test certificates, material certificates and a drawing package that matches what was installed. Label the parts so a maintenance team can trace them years later.

• Conductor dimensions and bend geometry
• Plating thickness and adhesion on joint faces
• Joint torque and contact resistance record
• Temperature rise test at the rated current
• Flatness over the device contact area
• Leak and pressure drop test for liquid parts
• Label, drawing and declaration package

Sourcing notes for Indian suppliers

Indian suppliers already make busbars, heat sinks, enclosures and rack hardware for export programmes. The capability is real, but it is uneven. A supplier that is strong in busbar bending may have little experience of a tested busway assembly. A heat sink extruder may not have a machining line for a flat base. Map the process step by step rather than buying a category.

Ask for the test equipment and the last test report for a comparable product. Check the plating line, because plating is often subcontracted and the subcontractor may change without notice. Confirm the packing too, because a busbar that arrives twisted has lost the tolerance it was built to.

• Process list with in-house and subcontracted steps
• Plating subcontractor and change notification
• Temperature rise test report with conditions
• Machining and flatness capability for thermal parts
• Leak test method and acceptance limit
• Packing method for long or thin parts