Data Center as a Good Grid Citizen

Overview

The paper covers fast frequency response, UPS-assisted generator load steps and ramping (instead of a dedicated BESS), performing under-frequency load shedding inside the UPS rather than tripping MV feeders, fault ride-through and post-fault power recovery requirements now imposed on data centres, simulation-model and short-circuit-ratio requirements for grid connection, and the impact of GPU load pulsation on UPS rectifiers, batteries and the grid. Typical BESS Li-ion energy cells are limited to about 1C discharge, which increases BESS size and cost for transient support.

If a gas turbine ramps to full load linearly in 20 minutes or less, the UPS battery energy needed to bridge the ramp is about 20% of load (kWh per kW); below about 1 h of runtime, enlarging UPS batteries is cheaper than a dedicated BESS. A pilot with a 200 kW UPS on a 250 kVA generator improved the frequency dip by more than 8 Hz during a 160 kW load step, and a 2.5 MW gas genset with a 1.7 MW UPS was simulated for 0-1.5 and 1.5-2.5 MW steps.

European under-frequency load shedding typically triggers its first stage at 49.0-48.8 Hz and sheds 5-10% of demand, up to 30-60% after the last stage; UPS-based shedding responds within 150 ms with up to eight programmable steps. UPS rectifier undervoltage trip is usually 50-80% of nominal, and the proposed changes are power sharing down to 50%, a 150 ms timer to distinguish ride-through events and a fast post-fault ramp (RTE France asks 50% per second). Per the ITI (CBEMA) curve, IT equipment tolerates roughly one line-cycle outage, far below proposed data-centre LVRT requirements.

GPU bursts seen upstream last 50-200 ms and idle is about 30%; the worst-case UPS load step for pure GPU load is assumed at 20-100%. The 9395XP was tested at 20-100% steps and the 9395XC at 10-90% steps at 6 Hz without battery engagement. Supercapacitor UPS back-up time is seconds to about half a minute, suitable for filtering pulsations but not for normal autonomy.

Key points

1. If a gas turbine ramps in 20 minutes or less, UPS battery energy to bridge is about 20% of load (kWh/kW); below about 1 h runtime, bigger UPS batteries beat a dedicated BESS.
2. A 200 kW UPS on a 250 kVA generator improved the frequency dip by over 8 Hz in a 160 kW step.
3. Typical BESS Li-ion cells are limited to about 1C discharge.
4. European UFLS first stage at 49.0-48.8 Hz sheds 5-10% of demand; UPS-based UFLS responds in 150 ms with up to eight steps.
5. UPS rectifier undervoltage trip is usually 50-80% of nominal; proposals: power sharing down to 50%, 150 ms timer, fast ramp (RTE 50% per second).
6. Per the ITI (CBEMA) curve IT equipment tolerates about one line-cycle outage.
7. GPU bursts last 50-200 ms, idle is about 30%; worst-case step 20-100%.
8. Supercapacitor UPS back-up is seconds to about half a minute: for filtering pulsations, not autonomy.

Using it in design

• Add grid-code parameters to the utility connection object: UFLS stages, LVRT curve, post-fault power recovery ramp (%/s) and short-circuit ratio at the PCC.
• In the UPS catalog record grid-interactive features (FFR, UFLS steps, generator support), minimum input voltage for power sharing and tested AI load-step range.
• When on-site gas engines or turbines are the source, check their maximum load step and ramp time against IT load steps and size UPS batteries for the ramp (first estimate about 20% of kW as kWh).
• Warn when an AI hall has no defined load-step profile, and flag weak-grid (low SCR) connections for harmonic and flicker study.

Who should read it

Electrical engineers designing grid connection and UPS interaction with on-site generation for large or AI-heavy data centres.

Related standards

• EU 2016/1388 (Demand Connection Code)
• EU 2017/2196 (Emergency and Restoration Code)
• ITI (CBEMA) curve
• IEC 62040-3

Publication details

Authors

Janne Paananen

Publisher

Eaton

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