Protections for Data Centers Powered by Direct Current (Technical Paper)

Overview

The paper compares floating, high-resistance and solid grounding, each at +/-400 V and 800 V. On the device side it simulates fuses, mechanical breakers, solid-state and hybrid breakers. Interruption speeds are laid out together: solid-state breakers act in under 0.5 ms, hybrids in 1-3 ms, while a fuse reached its melting I2t in about 1 ms and needed about 20 ms to recover. In the 1 MW floating 800 VDC case study, a solid-state circuit breaker (SSCB) held peak fault current below 800 A and healthy loads saw only about 1 V of variation.

Because the fault current is limited, neighbouring racks keep running unaffected. The result shows concretely why AC-style selectivity logic has to be rebuilt for DC. Personnel protection and arcing expose gaps in the standards. UL 943C Class E ground-fault interruption is about 850 us at 400 VDC and about 300 us at 800 VDC, while UL 2367 covers e-fuses only up to 60 VDC. Arc mitigation shorted an initiated arc in about 3 ms.

For ride-through, holding voltage within 10% for 10 ms at 1 MW needs about 80 mF of capacitance. The work is simulation-based, covers one block size and selected topologies, and is neither field measurement nor a full standard proposal. It is still a core reference for anyone planning 800 VDC because it shows that DC arc-flash cannot reuse the IEEE 1584 results used for AC and that protection choice is tied to the grounding decision.

Key points

1. Solid-state breakers interrupt in under 0.5 ms; hybrid 1-3 ms; fuse reached melting I2t in about 1 ms with about 20 ms recovery.
2. With SSCB, peak fault current under 800 A and about 1 V variation on healthy loads (1 MW floating 800 VDC simulation).
3. Keeping voltage within 10% for 10 ms at 1 MW needs about 80 mF.
4. UL 943C Class E ground-fault interruption: about 850 us at 400 VDC, about 300 us at 800 VDC.
5. UL 2367 covers e-fuses only up to 60 VDC.
6. Arc mitigation shorted an initiated arc in about 3 ms.
7. Grounding schemes compared: floating, high-resistance, solid; +/-400 V and 800 V.

Using it in design

• If 800 VDC is selected, require SSCB/hybrid breakers in the protection catalog.
• Require an explicit grounding-scheme decision (floating, high-resistance, solid).
• Add a DC arc-flash study as a mandatory task; do not reuse AC IEEE 1584 results for DC.
• Size load-side ride-through capacitance against the 10 ms / 10% criterion (about 80 mF at 1 MW).
• Record the UL gaps (the UL 2367 60 VDC limit) in the personnel-protection risk register.

Who should read it

Electrical engineers designing 800 VDC distribution and protection for megawatt-class AI racks.

Related standards

• UL 943C
• UL 2367
• IEC 60364-4-41
• NFPA 70E (DC arc flash)
• IEC 60947-2

Publication details

Authors

Guang Yang; Mike Tu

Publisher

Siemens / NVIDIA

Year

2025

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