Electrical Distribution Equipment in Data Center Environments

Overview

The power path runs from the utility service through MV switchgear, MV/LV transformers, LV switchgear, UPS switchboards, PDUs/RPPs, busway, panelboards and rack PDUs. The paper explains what each assembly does and where it normally sits: MV switchgear typically marks the service entrance for data centres above 1 MW IT load, LV switchgear or switchboards below 1 MW. Three-phase 3-wire and 4-wire systems, regional nominal voltages and standard ampere series are covered too.

The voltage and current tables are practical references: North America 480Y/277 and 208Y/120 (415/240 V for new data centres), Europe 400Y/230 at 50 Hz, China 380Y/220, Japan 200 V 3-wire, with measured voltage varying about +/-10%. The IEC 60059 R10 series runs 1, 1.25, 1.6, 2, 2.5, 3.15, 4, 5, 6.3, 8 x 10^n, while ANSI/IEEE lists ratings from 15 A to 6000 A. The difference between breaking capacity and short-circuit withstand rating is explained separately.

A comparison table gives typical ranges: UPS about 20-1,600 kW with roughly 15 minutes of battery ride-through, PDU 50-500 kW, panelboard 1.5-75 kVA with 42 poles. Data centres under 2 MW without redundancy have about 4 to 7 LV switchgear breakers per MW of IT capacity, which can easily double with redundancy and concurrent maintenance. The electrical system including UPS and generator is 40-50% of capex excluding the building, split about 50-60% equipment, 25-35% installation and 15-20% design. An appendix separates US switchgear, switchboards and panelboards by their ANSI/UL standards.

Key points

1. MV switchgear marks the service entrance above 1 MW IT load; LV switchgear/switchboard marks it below 1 MW.
2. Nominal LV systems: 480Y/277 and 208Y/120 (North America, 415/240 V for new builds), 400Y/230 50 Hz (Europe), 380Y/220 (China), 200 V 3-wire (Japan); measured voltage may vary about +/-10%.
3. IEC 60059 R10 ampere series is 1, 1.25, 1.6, 2, 2.5, 3.15, 4, 5, 6.3, 8 x 10^n; ANSI/IEEE standard ratings run from 15 A to 6000 A.
4. Example ratings: ANSI MV switchgear 15 kV, 95 kV BIL, 1200 A, 40 kA SCCR; IEC LV switchboard 690 V, 12 kV impulse withstand, 5000 A, 85 kA withstand; dry transformer 2500 kVA, 10 kV/400 V, 5% Z.
5. UPS batteries typically give about 15 minutes at full load; UPS 20-1,600 kW, PDU 50-500 kW, panelboard 1.5-75 kVA with 42 poles.
6. An STS gives fast (1/4 cycle) open-transition switching between two UPS feeds; an RPP has about a 2'x2' tile footprint and up to four panelboards.
7. Below 2 MW without redundancy there are about 4-7 LV breakers per MW of IT; redundancy and concurrent maintenance can double it, and above 20 MW MV breakers tend to outnumber LV.
8. Electrical is 40-50% of capex excluding building: equipment 50-60%, installation 25-35%, design 15-20%; 1N cost per kW: MV switchgear $8-92, transformers $35-90, LV switchboard $80-200, panelboard $20-40, PDU/RPP $100-400.

Using it in design

• In the single-line editor define node types for MV switchgear, MV/LV transformer, LV switchboard/ATS, UPS input/output/distribution boards, STS, PDU, RPP, busway, panelboard and rack PDU, each with rated voltage, rated current, breaking capacity (kAIC/Icu) and withstand rating (SCCR/Icw).
• Check that each device's breaking or withstand rating is at least the available fault current at its bus, and suggest an MV service entrance when IT load exceeds 1 MW.
• Choose breaker frame sizes from the IEC R10 or ANSI series according to the selected standard region, and use the Table 1 regional voltage presets with a default 5% transformer Z.
• In the cost estimator use the Table 2 per-kW ranges as rough 1N defaults.

Who should read it

Electrical designers building single-line diagrams and choosing equipment classes, and engineers new to data-centre power.

Related standards

• IEC 60059
• IEC 61439
• IEC 62271
• IEEE/ANSI C37.20.1
• UL 891
• UL 67
• UL 1558
• NFPA 70

Publication details

Authors

Pearl Hu

Publisher

Schneider Electric

Year

2015

Document number

WP 61

Document language

English

Source type

Manufacturer

Access

Free to read

Licence

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

Citation