Nanotechnology Research Facility

In 2005/2006, during the design build phase, VitaTech Engineering was commissioned by an architectual team to perform an EMI assessment of a proposed nanotechnology facility on a university campus in Georgia. VitaTech assessed the EMI impact from the main electrical distribution room equipment (switchgears, transformers, ATS’s, distribution panels, etc.), main primary transformers (located outside building), passenger and freight elevators, and any other potential EMI source located within the building’s EMI sensitive areas. VitaTech simulated the main electrical switchgear units, distribution panels and other EMI sources under various loads and predicted transformer decay rates to illustrate the typical magnetic flux density levels anticipated at specific distances from the electrical distribution equipment. The predicted simulated emissions for the main switchgear on the basement level will be examined.

4000 Amp Main Switchboards
Limited information was provided for the two 4000 amp main switchgears (dual ended parallel switchgear), which are located in the main electrical switchgear room on the Basement Level. VitaTech has measured the magnetic emissions from standard single/dual bus 4000 amp switchgears around the country and was able to correlate that levels for the metal switchgear housing near the bus would range from 1500 mG to as high as 3000 mG depending on the load and circulating net/ground currents with the emissions decaying at 1/r2 rate from the bus (although there is attenuation from the steel housing - approximately -3 dB) and 1/r linear rate from the net/ground currents . Normally, the levels above the switchgear are elevated 10 - 99 mG and high 100 - 200 mG up to 3-4 meters away because the bus is usually in the middle or offset higher within the switchgear. As shown in Figures #1 - 3, the dual 4000 amp switchgears were modeled at 75%, 50%, and 20% loads with a 5% unbalance returning on the neutral bus. Under 75% load the combined maximum switchgear 1mG isoline extends more than 80+ feet in the north-to-south direction while the 50% and 20% isolines are 75 ft. and 70 ft., respectively. Therefore, AC ELF magnetic shielding was required in the main electrical switchgear room to achieve EMI threshold levels to 0.5 mG and less inside the characterization labs and 1.0 mG inside the adjacent office areas under all normal (average and summer/winter peak) building loads.

 

FIG. #1: Generic Main Electrical Switchgear Room Magnetic Flux Density Output Simulation, 4000 Amp Dual-Ended Switchgear Simulated at 75% Load with 5% Unbalanced Loads Return on Neutral.
Main Electrical Switchgear Room Magnetic Flux Density Output Simulation, 4000 Amp Dual-Ended Switchgear Simulated at 75% Load with 5% Unbalanced Loads Return on Neutral

FIG #2: Generic Main Electrical Switchgear Room Magnetic Flux Density Output Simulation, 4000 Amp Dual-Ended Switchgear Simulated at 50% Load with 5% Unbalanced Load Returning on Neutral
Main Electrical Switchgear Room Magnetic Flux Density Output Simulation, 4000 Amp Dual-Ended Switchgear Simulated at 50% Load with 5% Unbalanced Loads Return on Neutral

FIG. #3: Generic Main Electrical Switchgear Room Magnetic Flux Density Output Simulation, 4000 Amp Dual-Ended Switchgear Simulated at 20% Load with 5% Unbalanced Loads Return on Neutral
Main Electrical Switchgear Room Magnetic Flux Density Output Simulation, 4000 Amp Dual-Ended Switchgear Simulated at 20% Load with 5% Unbalanced Loads Return on Neutral

 

 

 

 

 

 

 

 

 

 

 

 

DC EMI Sensitivity

Placement of scientific tools in the Laboratory area depends on the actual DC EMI susceptibility under defined thresholds, which are often not easy to ascertain from the manufacturer’s performance criteria. Magnetic flux density susceptibility can be specified in one of three terms: Brms, Bpeak-topeak(p-p) and Bpeak (p) according to the following conversion formula below.
DC EMI Sensitivity
Electron microscopes are sensitive at 1 mG Brms from DC disturbances while SEM’s and TEM’s, such as the TEM JOEL 2010 have 0.4 mG horizontal and 0.2 mG vertical performance requirements while next generation EM tools are less than 0.1 mG Brms.

Sources of DC Emissions

  • Moving Vehicles
  • Moving Elevators
  • Metal Ferrous Doors
When an unloaded 18 wheel truck passes, the DC levels at 1-meter distance varies between 30 – 50 mG while a truck loaded with steel plates will peak at 200 mG. The magnetic field decay at 6 meters ranges from 5 mG to 20 mG, at 12 meters 0.5 mG to 2 mG, 18 meters 0.05 mG to 0.2 mG and at 24 m less than 0.02 mG. VitaTech always uses the worst-case decay levels to define EMI zones (without DC magnetic shielding).
Large and small ferromagnetic masses in motion such as elevators, cars, trucks, and metal doors produce geomagnetic field perturbations in the sub-extremely low frequency (SELF) 0 - 3 Hz band that radiate (similar to throwing a pebble in a pond) from the source generating DC electromagnetic interference (EMI) in sensitive scientific tools and instruments.  The magnitude of the geomagnetic field perturbation and radiated distance from the source depends on the size, mass and speed of the moving ferromagnetic object.  Other problematic DC EMI sources include electromagnetic pulse (EMP) devices, which are usually high-voltage discharge instruments, subways, trolleys, NMRs, and MRIs.  Electron microscopes (SEMs, TEMs, STEMs), Focus Ion Beam (FIB) writers and E-Beam Writers are also very susceptible to DC EMI emissions and require environments of 1 mG and less.