The Stanford National Accelerator Center (SLAC) is home to a two-mile long linear accelerator – the longest linear accelerator in the world.   This multipurpose laboratory for astrophysics, photon science, accelerator and particle physics research is operatedby Stanford University, but used by scientists from many countries.  In fact, a few scientists have been awarded the Nobel Prize for work carried out at SLAC.  With that kind of pedigree, it is understandable why data storage needs are taken very seriously on this Menlo Park, CA campus. 

A few years ago the facility was experiencing some problems with harmonics affecting servers’ power supplies.  Then two disc arrays crashed, and Boris Ilinets, P.E., electrical engineer assigned to the Data Center, knew it was time for action.  Since installing StacoSine® active harmonic filters from Staco Energy Products Company, Ilinets has seen no problems from harmonic distortion.

“We were having problems with harmonics from the computer load in our data center” says Ilinets.  “Our 100% non-linear load is actually inside the building, but outside the building we have another non-linear load - for example medium voltage rectifiers.  Sometimes we have voltage harmonics originated at remotely located loads that could affect some server rows.  But current harmonics from computing loads also create voltage harmonics.  That’s why we decided to stay on the safe side, especially considering we had some unpleasant incidents with high level of harmonics – we actually lost some very sensitive disc arrays” concludes Ilinets.

While Ilinets looked at both passive and active harmonic filters, he opted for active filtering in this instance because installation was simpler and more cost-efficient for the existing facility – and most importantly, they automatically corrected the multiple harmonic orders which were present.

“In a new facility you can design passive filters on the front end – in an existing building with all equipment in place, however, it is not as easy” explains Ilinets. 

His first step, however, was to perform some analysis to determine what exactly he was dealing with.  “In my case I have prevalent 11th, 13th 23rd, 25th harmonics” reports Ilinets, “in other instances you might have more 5th and 7th order harmonics – it depends upon what type of load and power supply you have.”

The wide range of harmonics present from the servers, disc arrays and switches in the SLAC facility – led Ilinets to choose active harmonic filtering. 

How it works

Harmonics are currents and voltages that have multiplied within an electrical system.  Commonplace linear loads become more non-linear due to the electronic and digital devices.  This causes the traditional sine wave to change shape, reflecting these many current and voltage distortions.  Harmonic currents due to non-linear loads generally flow from the load to the utility source. 

The presence of harmonics may impede equipment from functioning properly.  In the SLAC instance this was manifest in crashing a pair of disc arrays. 

To mitigate the problems associated with harmonics, it is necessary to filter out at the source the problem harmonic orders, and thus clean up the sine wave.  If the specific harmonic order is known (which can be determined through on-site analysis), passive filters can mitigate the problem. Tuning to a specific harmonic frequency (for example the 5th order) allows the other currents to flow into and out of the filter, while essentially eliminating problems from the 5th harmonic order.  Other (orders) harmonics (for example the 7th and 11th) can be reduced as well.  The key to successful implementation of passive technology is determining which orders are present, and installing filters specifically designed to those harmonic orders.  If, however, equipment is installed in the future with a harmonic order that differs from the ones corrected (the 23rdorder, for example) the solution will be ineffective for the new harmonic orders present.

Recall that SLAC was experiencing problems from numerous orders – so passive harmonic filtering technology would not be sufficient.  Active harmonic filtering, however, was suitable for the challenge.  Ilinets installed ten50-amp and one 100amp StacoSine® active harmonic filters, which “have been working well ever since.” 

All of the filters are installed between the distribution transformers and the panel main breaker.  Four of the 50-amp filters are installed on the first floor of a computer room, while the remaining six 50-amp filters and the 100-amp filter are located on the second floor of a different computer room.  Two of the 50-amp filters on the second floor installation are connected in parallel to the same panel because this was easier than using a single 100-amp filter.

Installation was not difficult says Ilinets, though the 100-amp filter was more challenging given the larger size, heavier weight and the fact that the floor was raised.   Overall, said Ilinets “the most difficult part of the installation was getting approved power outages to connect the filters to the panels.” 

StacoSine® active harmonic filters use power electronic technology to monitor the non-linear loads and dynamically correct every harmonic order from the 3rd through the 51st.  Through an injection and cancellation process, the sine wave is restored and distortion is reduced to less than 5% THD (total harmonic distortion) meeting the stringent IEEE 519 Standard.  By injecting a compensating current into the load, the waveform is restored, dramatically reducing distortion to below 5% THD.  Power is moved from the AC source to the DC electronic platform, then back to the AC.  This occurs at a very rapid rate, allowing for cancellation of the high frequency output current, then followed by determining the precise value of the injected load current.  The power electronics platform continuously adapt to rapid load conditions, yet maintains a small physical footprint.  The 50-amp filters installed at SLAC are wall mounted to further minimize floor space requirements.

Although Ilinets performed the analysis to determine which harmonic orders were posing problems, with the StacoSine® active filtering product he could have skipped this step since the technology is effective in eliminating distortion from all necessary harmonic orders.  Because they correct this wide range of harmonic orders automatically, users experience immediate gains in electrical efficiency upon installation.  Additionally, the StacoSine® provides a graphics display/analyzer, which will provide detailed information on the line/load/filter, allowing greater monitoring and control by SLAC. 

In addition to the elimination of harmonics, installation of the StacoSine® filters also allows SLAC to “use smaller than K-13 rated transformers since there is much less heat impact on the equipment and the cables” said Ilinets.

While the SLAC researchers and other scientists who utilize the SLAC facilities for their varied research projects probably have no idea that the StacoSine® filters are on site, they can rest assured that their data is safe and secure – and that their results will not be distorted by harmonic problems.

Staco Energy Products Company manufactures voltage control, VAR compensation, uninterruptible power supplies and engineered power quality solutions.   For more than 70 years, customers worldwide have relied on Staco as their dependable source for standard and tailored solutions to a wide range of electrical power problems.  Headquartered in Dayton, Ohio, Staco Energy Products is a wholly owned subsidiary of Component Corporation of America, located in Dallas, Texas.  For more information, visit www.stacoenergy.com, call 866-266-1191, write to Staco Energy Products Co, 301 Gaddis Blvd, Dayton, OH  45403, or e-mail to sales@stacoenergy.com.