Calculating EMI
Calculating EMI
(OP)
Does anyone have an idea on how to calculate the EMI in an electrical room given the nameplate ratings of the gear: switchboards, branch panels, transformers, feeder sizes etc....
any help would be appreciated,
-Steve
any help would be appreciated,
-Steve






RE: Calculating EMI
TTFN
RE: Calculating EMI
RE: Calculating EMI
You will find that, even within a particular model of a particular mfr's equipment, there is significant variation in radiated EMI, due to tiny variations in construction (there's always some sort of tolerance), coupled with a very unpredictbale loading pattern in the equipment.
The only reliable way to get an EMI for a particular setup is to to empirical measurements. Even these will be suspect as emitted EMI is dependent on the specific loading conditions at the time of the testing.
RE: Calculating EMI
Fe = (Fx2 + Fy2 + Fz2 )1/2
Where,
Fe= Resultant (root-mean-square) sum of three internal orthogonal magnetic fluxes
Fx, Fy, Fz = are the magnetic flux densities obtained by the Gauss meter for the three directions coils on the x-, y- and z-axis,.
See a sample of a Gauss meter in the enclose site: http://
The enclose images are from VitaTech Eng.:
RE: Calculating EMI
RE: Calculating EMI
I am under the impression that what did not work in the case described is the shielding of the room not the EMI measurement of the existing installation.
Shielding effectively a room is not an easy task and very expensive proposition. However, the level of EMF is possible to be determining with a reasonable degree of accuracy in existing facility.
RE: Calculating EMI
Have a pleasant day all.
RE: Calculating EMI
Could one not just put up IRON sheeting?
RE: Calculating EMI
Radio Frequency Interference (RFI) is a form of EMI and is what normally is objectionable.
EMF, as described by cuky2000, is Electromagnetic Fields, in particular, magnetic fields or flux.
EMI is radiated energy and EMF is non-radiant. See Power Lines and Cancer FAQs at http://www
RE: Calculating EMI
Then I come along and plug in my heavy duty industrial arc welder into one of the branch feeds. What do you suppose the effect of that might be on the theoretical values throughout the whole system ?
It is difficult enough to test and measure radiation from a single closed "black box" entity. Something open, like a power distribution system it is just not possible to model because you do not know how clean the power coming in will be, or the nature of all the loads that may possibly be connected.
The power coming in is never clean, there are always switching transients, arcing insulators, remote lightning strikes, induced Rf voltages, all sorts of horrors not possible to predict for computer modeling.
All you can do is try to measure it after installation is complete, and hope.
RE: Calculating EMI
EMI stands for electromotive interference.
There are 4 basic types defined
1) conductive "on a wire"
2) conductive susceptable "subject to on a wire"
3) radiated? "energy in the air"
4) radiated sus "subject to energy in the air."
Each indepent item has its specs and the summation of these
must meet the total requirments.
The only items that should apply are 1 and 2.
and are controled by specs.
For someone doing power systems you have no control
over the line (which is what you are implying).
The only choice you have is to do resonant filter
or some such thing.
Boy did I get these out of order.
In short I think you are coping with only
P F (harmonic content), as the R F specs
address individule units.
For going to the power grid most energy fc above 10k
can be delt with a .1uf cap delta +line to nut configuration.
Fcc 15-49 defines the present requirements for com use.
Hope this helped.
RE: Calculating EMI
RE: Calculating EMI
Sorry in strict terms you are correct.
The military lumps all types together.
Than seperates them as conducted and radation.
Fcc is the same?
The point is for power (AC IN) by the time you
get to the input mains, it "should" be just conduction,
which makes it a form of voltage, (current) either by
conduction or fields (as described by cuky2000).
Good example cuky2000
THink of this, (for testing) the mil started with one type "LISN" then to a 10u cap than to a different "LISN".
And each time the measurement concept changed.
This is only the major changes, it seems "when you understand and generate programs (computer) they
change the rules".
The last battle I lost on EMI was to a client who had speced the wrong LISN "line stabalization network".