Power Transmission

The power transmission is the conduit for which power makes it way from the street to your equipment. Uninterruptable Power Supplies (UPS), transformers, Static Transfer Switches (STS), PDUs, breaker panels, Remote Power Panels (RPP), Cabinet Distribution Unit (CDU aka power strip), and Transient Voltage Surge Suppressor (TVSS) are all means for which power is conducted to the cabinets.

Just about every avenue for this power transmission charges a toll called “power factor”. The key is to reduce the avenues that cost the most. Current UPS are pretty efficient with power factors of 90%. This means that it costs 10% of the power that the UPS is delivering to the racks. Old UPS have power factors in the 80% range or worse. Many times this power factor is relative to the load that is placed on the UPS. The closer to the maximum rated load, the more efficient the UPS operates. This creates a bit of a conundrum for best practices. Typically redundant UPS does not carry a load more than 45% of its maximum rated capacity. This practice leaves overhead for fail over in the event of a UPS failure.

To remedy this issue, consider a UPS with internal N+1 redundancy. Size the UPS so that it has enough capacity for growth but not so much that it compromises efficiency. Be sure to review manufacturers’ specifications. Also find a UPS that is capable of being scaled up with the installation of modules and a software update.

Voltage reduction has a large tax associated with it. Most large buildings have 480 Volts 3phase servicing it. From there it passes through a transformer which breaks the power down to 240V, 220V, 208V, or 110V. A transformer can have a de-rated value of up to 75% of its rated capacity. The key here is to deploy an efficient transformer or run a higher voltage to the rack so that a transformer is not required at all.

These step-down de-rated losses can be eliminated by converting the UPS output power to 415V. The 415V three-phase output provides 240V single-phase input to the server. The higher voltage not only eliminates step down losses but also allows an increase in server power supply efficiency. Servers and other IT equipment are capable 240V input without any problems. The key downside is the inability to deliver 110V to legacy devices.