Medium voltage increases savings to power multistory data centers

Overview

This 2023 article by Bruce Young was published in Consulting-Specifying Engineer. It argues that 13.2 kV distribution should be used inside multistory data centres instead of long 480 V runs. The argument rests on a case study with a centralized system and dual-ended main-tie-tie-main substations in physically separated rooms.

The author quantifies the savings through conduit and copper: at 13,200 V one 4 in. conduit can carry up to about 4,000 kW, while the same load at 480 V can need up to twelve 4 in. conduits or busway. In multistory buildings such runs along the floors raise conduit and copper cost markedly, so medium-voltage distribution becomes more economical over long distances.

The article lists the control and protection features needed for reliable MV operation. Parallel redundant PLCs in separate enclosures and redundant I/O remove control single points of failure. Multiple control-power sources are provided, switched by an 83 relay, with one fed directly from the on-site generator, and a black-start relay is included. Neutral grounding resistors and snubbers also appear in the list.

Safety practices centre on de-energizable paths and remote operation outside the arc-flash zone. Close-coupled transformers are protected by snubbers against switching transients produced by vacuum breakers with VPI transformers. The article is an expert opinion piece based on a single case scenario; its conclusions cannot be applied directly to every facility, but it gives a concrete checklist for evaluating MV distribution.

Key points

1. At 13,200 V one 4 in. conduit can carry up to about 4,000 kW; the same load at 480 V can need up to twelve 4 in. conduits or busway.
2. Substations use dual-ended main-tie-tie-main arrangements with each side in a physically separated room.
3. Parallel redundant PLCs in separate enclosures and redundant I/O remove control single points of failure.
4. Multiple control-power sources are switched by an 83 relay, one fed directly from the on-site generator, plus a black-start relay.
5. Snubbers protect close-coupled transformers from switching transients produced by vacuum breakers with VPI transformers.
6. Safety practices rely on de-energizable paths and remote operation outside the arc-flash zone.
7. Neutral grounding resistors are also named among MV control and protection features.
8. The article is an expert opinion based on a single case scenario.

Using it in design

• Offer an MV distribution template (13.2 kV, main-tie-tie-main, separated rooms) for multistory halls and compute conduit and cable quantities against 480 V.
• Suggest snubbers when vacuum breakers feed close-coupled dry-type transformers.
• Require redundant control power and black-start provisions for MV gear in concurrently maintainable designs.
• Add remote operation and de-energizable paths to the design checklist.

Who should read it

Electrical design engineers and consultants planning power distribution for multistory data centres.

Publication details

Authors

Bruce Young

Publisher

Consulting-Specifying Engineer

Year

2023

Document language

English

Source type

Expert / community

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation