The Influence of Electro Magnetic Field on Data Center
By Tarek Fawaz, Lead Consultant - Data Center Engineering Services
Why EMF
World population growth and its trend to computerize everything in the globe, which can be easily noticed from the quantity and type of internet-dependent appliances i.e. smart phones, tablets, many type of laptops and personal computers are invading our normal life, where most of known manufacturers are racing to provide the globe markets with the highest technology, and all of these devices are power-dependent which found their way to the end users with high demand. To provide a worthy reliable facilities to manage such growth demand, it was noticeable lately that the world trends to have high reliable facilities started with computer rooms, server rooms, data centers and later called clouding and colocation, including the IT virtualization, all of such demands and need for high power density requirement per square meters and might exceed 15 kW per rack (around 42 KW per square meter), this means that such building or even the square meter will require high current flow, and by consequence high EMF as we will explain later on. One of the most factors affecting the performance of a data center is the Electro Magnetic field EMF or EMC (Electro Magnetic Compatibility) as defined by IEC (International Electrical Code) The EMF is created by voltage or/and current, electrical field created by voltage and measured in V/m and magnetic field by current and measured by Tesla or Gauss; the small power in low voltage facilities, when creating electrical field is constant and will not affect the facility’s equipment as we will see in the following paragraphs, therefore, the magnetic field is the only factor will affect electronicbased equipment i.e. Blade Servers, Servers, Switches, Routers, PCs, etc.
Sources of EMF.
The EMF will be caused either naturally or by human-made Naturally where the earth magnitude field is measured to be around 0.5 mG. Besides to the natural sources the electromagnetic field also includes fields generated by human-made sources: such as X-rays, The electricity that comes out of every power outlet with low frequency, various kinds of higher frequency like radio-waves, whether via TV antennas, radio stations, GSM sites, Microwave links, HV/MV overhead and underground power line transmission and finally LV high current flow of carrying current conductors inside the facility.
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In our article we will present the effect of EMF caused by high current flow inside a data centers or mission critical facilities, having in mind that the mission critical facility location took into consideration the outside EMF during the site selection and was avoided to be near HV/LV power transmission lines, Electrical Generating and substation, GSM or radio station, etc. Note that the Electric filed can be easily shielded by conducting objects such as trees and buildings while the magnetic field is not easily shielded by most materials.
International Standards and Norms
All international standards had specified the effect of EMF on Human and equipment I.e. EN/BS 61 000-4-8, EN55022, EN 55011, WHO (World Health Organization), NIEHS (National Institute of Standards and Technology), ICNIRP (International Commission on Non-Ionizing Radiation Protection), etc. IEC 61000-4-8 had defined that the equipment must be immune to magnetic field up 37.5 mG while NCRP/HPA defined that human-body exposures to EMF should not be less than 10 mG, and less than 4 mG in other countries by WHO. General Information: Germany was the first nation to adopt a national rule on EMF exposure on January 1997
EMF measurement and its influence on IT equipment
Following Biot–Savart law we will have the magnetic basic formula B = f(i) = (µ_0 I)/2πR (µ_(0: )permeability 4π〖10〗^(-7) NA^(-2),I: Current in A,R ditance between Source of EMF in m,and point of measurement )
From the above formula the magnetic field is proportional to the current and inversely proportional to the distance. We conclude that the Magnetic Field will strengthen when the current will be increased and its strength d e c r e a s e s rapidly with increasing distance from the source. As described earlier that with this high demands on IT based equipment with the obvious trend to have Colocation facilities or cloud facilities with high density up to 15 KW per rack (and might be above), then we can deduce that the branch of the carrying current conductor (Single Phase) feeding such high density racks will require 85.2 A at 380/220 V (most of Data Racks require Single Phase power supply) with Magnetic Field strength almost equal to 170 mG.
To have a tangible understanding of such values, we will refer to the following table which illustrates the magnetic field in mG at approximately 1m from the source of EMF of the carrying current of three different methods, calculated based on Biot–Savart law
100
Single case cable 200
Three Phase cable 70
500
1000
350
40
1000
2,000
700
80
2500
5,000
1,700
200
5000
10,000
4,500
400
Rating A
Busway 8
The above table indicates that a 100 A (17.6 KW rack) single phase conductor will produce at 1m a 200 mG which is not in accordance with the standards and definitely will affect the performance of the IT equipment exposed to such current. By having an average Rack with around 4 Kw or 23 A, will create 46 mG at 1m from the conductor and still is not in accordance with the international norms and strictly requires a certain measurement to be taken to cancel such effects. Just imagine a bad design or construction allow to pass a 5000 Amp main cable (Three Phase) under, above or just near enough to the data center to create such high EMF.
Conclusion:
The EMF is a critical parameter which will affect the performance of such critical facilities, and will definitely require specialists to provide solutions to cancel such EMFs.
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