The Government of Spain funds a non-profit research organization CIC BiomaGUNE, specializing in molecular-level and biological nanostructure applications. Vitatech was contacted to perform a 50 Hz AC ELF (extremely low frequency) magnetic flux density level assessment within an existing TEM laboratory with elevated and high magnetic fields levels located in San Sebastian. Imaging and resolution quality degraded over the years due to an increase in magnetic field levels in both microscopy suites emanating from the adjacent electrical rooms and overhead cable trays. During the EMI site survey Vitatech detected elevated and high ground/net currents on the cable tray supplying the adjacent electrical room and recommended a Ground/Net Current Remediation Program to correct the problem.
Vitatech returned several months later and identified the source of elevated and high ground/net currents on the adjacent cable tray: electromagnetic induction between multiple phases, neutrals and grounding conductors responsible for circulating current throughout the building. Not only was this a serious EMI issue, this was also a life-safety issue for the grounding system. Vitatech performed a two week comprehensive ground/net current testing remediation program of all distribution panels, electrical subpanels and branch circuits with elevated ground/net current. Preliminary investigations recorded peak magnetic flux density levels of 9.48 mG to 12 mG at the tool columns and a peak level of 83 mG along the cable tray corridor. The dominant vertical Bz peak magnetic field levels confirmed the second source of concern radiated from overhead cable tray feeders and exceeding 24 amps of circulating ground currents. Vitatech recommended separately bundling the three-phases, neutrals and grounding conductors in to four (4) separate cable groups traveling on the cable tray, thereby self-canceling the electromagnetic induction effect on the grounding cables and significantly reducing the circulating ground currents on the grounding conductors, cable tray and throughout the building. The magnetic field levels from the cable tray and distribution room after ground/net current remediation still exceeded 2 mGp-p at the TEM column, and AC ELF magnetic shielding was recommended for the TEM room and future SEM room to ensure long-term optimal imaging performance and compliance.
Vitatech returned with our installation crew supplemented by local labor and suppliers within the Basque Region to install AC ELF shielding system. After the AC ELF magnetic shield was installed in the TEM and SEM rooms, the TEM room column levels were 0.1 mGp-p and less in the Bx, By and Bz axes measured from 0.25m to 3m above the floor. The levels in the SEM room were less than 0.3 mGp-p even with a cable tray located directly above the shielded SEM room..Posted in: Scientific
Bioscience Cooperative Research Centre
EMI/RFI Site Testing, Utility & LV Electrical Distribution Simulations & Impact Analysis, EMI/RFI Shielding Designs, Fabrications & Installation & Final Commissioning
San Sebastian, Spain