Before Deploying 100 kW+ Racks: Reassess Your Power Quality Configuration

As AI data centers move toward higher rack power densities, power supply and cooling systems are changing at the same time. In this situation, whether the existing power quality configuration is still sufficient cannot be judged simply by how much capacity has been added.

A more reliable review should focus on three things: where the new loads are connected, how the actual harmonic current has changed, and how much usable capacity remains in the existing APF and SVG.

1. Check where the load has changed

New loads are not limited to servers.

UPS or high-voltage DC systems, PDUs and rack-level power supplies belong to the IT power chain, while CDUs, circulation pumps, chillers and fans belong to cooling and auxiliary systems. These loads may have different operating patterns and connection points.

If new loads bypass existing monitoring points, historical data may no longer represent the expanded system.

2. A lower THDi does not always mean lower harmonic current

THDi is a ratio, so it should not be viewed alone.

For example, if the fundamental current increases from 1,000 A to 1,800 A, while THDi decreases from 18% to 12%, the actual harmonic current still rises from about 180 A to 216 A.

That means the review should include fundamental current, individual harmonic currents and total harmonic current under representative operating conditions.

3. Reassess the available capacity of APF and SVG

The nameplate capacity of an APF is not the same as its remaining usable capacity.

Actual output, current-limiting records, dominant harmonic orders, reactive power compensation, three-phase imbalance, ambient temperature and redundancy requirements can all affect the capacity still available.

Where both harmonic and reactive power demands are increasing, the allocation between APF and SVG should be based on measured operating data rather than expansion ratio alone. If sufficient headroom remains, adjusting control priorities may be enough without adding new equipment.

4. What should be reviewed?

Before making a decision, it is useful to bring the following information together:

• Single-line diagrams, transformer capacity and load rate
• IT and cooling load capacity, operating modes and connection points
• Fundamental current, harmonic current, power factor and APF/SVG operating records
• Connection points and operating curves of PV, energy storage or direct green power systems

For AI data center expansion, the key is not to estimate power quality requirements simply from added capacity, but to reassess the system based on actual load changes and operating data.