infrastructure//data center//power chain

A power chain is the sequence of equipment that carries electricity from the utility grid to the processors of a data center, converting voltage and form at each stage and keeping the supply continuous when any stage fails. Its job is not only to deliver power but to deliver it without a gap: a server's own supply holds its output for roughly ten to twenty milliseconds after its input disappears, so any interruption longer than that reboots the machine.

A power chain is the sequence of equipment that carries electricity from the utility grid to the processors of a data center, converting voltage and form at each stage and keeping the supply continuous when any stage fails. Its job is not only to deliver power but to deliver it without a gap: a server's own supply holds its output for roughly ten to twenty milliseconds after its input disappears, so any interruption longer than that reboots the machine.

The stages run from high voltage to the chip:

1Utility feedtens to hundreds of kV2Substation transformersdown to medium, then low voltage3Switchgear and transfer switchesutility or generator4UPSbatteries bridge the gap5Busway and PDUsalong the rows, into each rack6Server power supply and VRMAC to DC, then core voltage

Each conversion loses a little energy as heat (Joule heating, switching losses), which is why designers remove stages where they can (higher-voltage distribution, DC busbars inside the rack) and why the power chain's efficiency appears in the electricity bill twice: once in the losses, once in the cooling that removes them.

The chain is as available as its weakest series link.

Every stage is a series element, so a fault anywhere drops the load unless that stage is duplicated or bypassed. Data centers therefore duplicate the chain itself, two complete paths feeding servers with two power supplies, and describe how much spare they carry with a redundancy level.

The time scales differ by six orders of magnitude, and each stage covers one. Milliseconds belong to the UPS and the server's own capacitors, seconds to the generator starting and accepting load, minutes to the battery's reserve, hours and days to the fuel stored on site. Seeing them on one axis is the quickest way to understand why each stage exists.

The chain carries risks of its own. Batteries age and must be tested, generators must be run under load periodically, and a transfer switch that has never been exercised is a single point of failure nobody has seen fail.