Eliminating Harmonics in a Server Rack with 3DFS

Data centers electrical networks are filled with thousands of loads all demanding power at the same time. In this video, we isolate a server rack loaded with various storage arrays and GPU accelerated blade servers and individually review a few of the beneficial effects of subcycle correction. The server rack shows a clear operational difference when subcycle correction is turned on.

The demonstration video that accompanied this post is no longer available.

The first section demonstrates the Current and Voltage waveforms being rebuilt in real time.
In the second section, we demonstrate the effect of subcycle correction dynamically maintaining power factor near unity and sustaining harmonic distortion at near ideal levels.

Power Factor (PF) Average:

Total Harmonic Distortion (THD) Average:

In the third section, we demonstrate the effect of automatic load balancing across the phases. Automatic phase balancing is a claim unique to our patent and only available with 3DFS technology.

Current Average:

Below are a number of resources by various industry leaders describing the additional costs associated with high harmonics and non-unity power factor in data centers as well as some of the piece meal competitive products that make up existing “solutions.”

To learn more about our electrical network analysis, click here

Resources:

Data Center Power System Harmonics: An Overview of Effects on Data Center Efficiency and Reliability, The Green Grid

Power Protection for Data Centers, a leading maker

Harmonics in Your Electrical System, a leading maker

Mitigating PQ Problems in Legacy Data Centers, SLAC

Experts speak on UPS output Watt, VA, and Power Factor ratings, a leading maker

Impact of Leading Power Factor on Data Center Generator Systems, a leading maker

Why a server rack distorts its own supply

Each server draws its power through a switching power supply. The supply is a nonlinear load, so its current is not proportional to the voltage. The Data Centers and Compute page follows that current from the rack to the transformer, the UPS and the cooling plant.

A pulsed current is the fundamental plus a stack of harmonics. Each harmonic heats the wire, loads the transformer and pulls the voltage out of shape, but does no work. Triplen harmonic currents add in the neutral instead of canceling. So the neutral can carry more than a phase, as the Harmonics article shows.

Single-phase supplies also load the three phases unevenly, and the neutral carries the difference. The Phase Balance article treats neutral current as a safety issue before it is a loss.

What correction changes, and what it leaves

The controller reads the waveform on the three phases at the panel. It separates the load current into the working current and the reactive, harmonic and unbalanced share. It supplies that share at the panel, so the source carries working current for the corrected loads. Removing or powering down the controller leaves the panel as installed.

Some things stay as they were. The power distribution unit keeps its K-rating, because removing the controller returns the harmonics. Our own instrumented assessment of two server racks found no drop in active power at the connection. The case for correction rests on rating headroom, neutral current and the record, not on cooling load.

Where this stands today

The Press and Case Studies page summarizes a server rack power analysis at a data center. A VectorQ2a, connected in parallel, corrected one entire server rack in each of two assessments. Each installation went in without disrupting power to the racks. The VectorQ2 page shows the controller part by part.

Related reading

• Power Factor: penalties, and correction to unity
• Electric Optimization: wasted current fills the transformer
• Request a site analysis: an engineer replies with what we would measure first