EMC Filters Guide - EMCIA - EMC Industry Association ... Filters Guide.pdf · EMC Filters Guide REO(UK) LTD Units 8 -10 Long Lane Industrial Estate, Craven Arms, Shropshire SY7 8DU

EMC Filters Guide

REO (UK) LTD Units 8 -10 Long Lane Industrial Estate,Craven Arms, Shropshire SY7 8DU UKTel: 01588 673411 Fax: 01588 672718Email: [email protected] Website: www.reo.co.uk

REO UK LTD

REO INDUCTIVE COMPONENTS AGBruehler Strasse 100, D-42657 Solingen, GermanyTel: 0049-(0) 2 12-88 04-0Fax: 0049-(0) 2 12-88 04-188

REO USA8432 East 33rd Street, IndianapolisIN46226-6550, USATel: 001 317 8991395 Fax: 001 317 8991396

Electromagnetic field theory

What makes up the electromagnetic spectrum?

Electromagnetic compatibility (EMC) and the law

Where does electromagnetic interference come from?

EMC filters

Testing

Points to consider when selecting a filter

Standards

Installation

Standard filters

Hans Christian Oersted was aprofessor of science at CopenhagenUniversity. In 1820 he arranged ascience demonstration to friends andstudents in his home. He planned todemonstrate the heating of a wire byan electric current, and also to carryout demonstrations of magnetism, forwhich he provided a compass needlemounted on a wooden stand. Whileperforming his electric demonstration,Oersted noted to his surprise thatevery time the electric current wasswitched on, the compass needlemoved. He kept quiet and finished thedemonstrations, but in the months thatfollowed worked hard trying to makesense out of the new phenomenon. Buthe couldn’t! The needle was neitherattracted to the wire nor repelled fromit. Instead, it tended to stand at rightangles (see drawing below). In the endhe published his findings (in Latin!)without any explanation.

N S

+-

Electromagnetic field theory

REO (UK) LTDUnits 8-10 Long Lane Industrial Estate, Craven Arms, Shropshire SY7 8DU UKTel: 01588 673411 Fax: 01588 672718Email: [email protected] Website: www.reo.co.uk

2

5

7

8

9

12

13

14

15

16

Finally, a Scottish mathematician,James Clerk Maxwell, picked up onFaraday’s ideas and was successful indeveloping a theory of electromag-netism which enabled testable predic-tions to be made. Inspired by Faraday’slines of force, he developed a modelthat unified magnetic and electricalforces. Maxwell unified the study ofelectricity and magnetism in four tidyequations. In essence he discoveredthat electric and magnetic fields wereintrinsically related to one another, withor without the presence of a conductivepath for electrons to flow. Stated simplyMaxwell’s discovery was this:-

A changing electric field produces aperpendicular magnetic field

and A changing magnetic fieldproduces a perpendicular electric field

Michael Faraday

Electric Field

Magnetic Field

Direction of Wave

Quite interestingly Maxwell predictedthat electromagnetism would be propa-gated through space at a finite rate andwas struck by the similarity betweenthe predicted speed of electromagnet-ism and the speed of light. From thisconnection sprang the idea that lightwas an electric phenomenon and thesubsequent discovery of radio waves.

It was the scientist Michael Faradaywho first studied in detail thephenomena involving the interactionbetween electricity and magnetism.Amongst his many achievements, he iscredited with the construction of thefirst electric motor and the discovery ofboth the principle and the methodwhereby a rotating magnet can beused to create an electric current in acoil of wire (still the basis of modernelectricity generating plants).

He also observed the way in which ironfilings arrange around a magnet. Theyappear to follow lines of magnetismleading out from one magnetic poleand back to the other pole. Hesuggested that the effect of a magneton a wire carrying a current is theresult of lines of force . Faraday spentthe latter part of his life working todevise an experiment that wouldconfirm his theory of electromagneticfields but without success.

The electromagnetic spectrum is afamily of waves that travel throughspace by way of the production ofelectric and magnetic fields. Changingelectric fields are set up by the oscilla-tion of charged particles and thesechanging electric fields inducechanging magnetic fields in thesurrounding space. Changing magneticfields then set up more changingelectric fields and so on. The net resultis that the wave energy travels acrossspace.

All electromagnetic waves travel at thesame speed through the same mediumor substance but they have a variety offrequencies which provide a correspon-ding variety of wavelengths. If theoriginal charged particle vibratesrapidly, the frequency of the wave ishigh. Because there are many oscilla-tions per second, the correspondingwavelength is short.

Conversely, if the original chargedparticle vibrates slowly, the frequencyof the wave is low and the correspon-ding wavelength is long.

What makes up the electromagnetic spectrum?

The whole range of frequencies andwavelengths is called the electromag-netic spectrum and different parts ofthe spectrum are given differentnames. These parts of the spectrumhave different properties and, conse-quently, they have different uses.

Therefore, it can be seen that there isthe need for the coexistence of allkinds of radio services, which use theelectromagnetic spectrum to conveyinformation, with technical processesand products emitting electromagneticenergy as an undesirable by-product.Furthermore, the problems of EMC arenot limited to interference with radioservices because electronic equipmentof all kinds is becoming more suscep-tible to malfunctions caused by externalinterference. This is particularlyrelevant in the case of electronic equip-ment that is required to continuerunning for economic or safetyreasons. Banking systems and aircraftcomputers are two notable examples.

103

100

10-3

10-9

10-12

106

109

1012

1015

1018

1021

Wavelength MFrequency Hz

long-wave radio

short-wave radio

microwaves

millimeter waves

infrared light

ultraviolet light

x rays

gamma rays

VISIBLE LIGHT

red orangeyellow green blue indigo violet

The Electromagnetic Spectrum

There is now the European Directive89/336/EEC, which specifically dealswith EMC. Like a number of otherdocuments produced by the EuropeanCommission this is a new approachdirective, which sets out the essentialrequirements that must be satisfiedbefore products can be marketedanywhere within the EC. It also sayshow evidence of conformity will beprovided.

In the case of EMC the essentialrequirements are that electrical andelectronic equipment shall beconstructed so that:

�

�

Electromagnetic Compatibility (EMC) and the law

Standards

The generic standards relating to EMCare divided into two sections, one forimmunity and one for emissions, eachof which has separate parts fordifferent environment classes.

The electromagnetic disturbance itgenerates does not exceed a levelallowing radio and telecommunica-tions equipment and other apparatusto operate as intended;

The apparatus has an adequatelevel of intrinsic immunity to electro-magnetic disturbance to enable it tooperate as intended.

The manufacturers or their authorisedrepresentative are required to attestthat the requirements of the Directivehave been met. This requires twothings:

�

�

Compliance

In essence, for goods to comply withthe EMC Directive they should betested but in reality this is difficultbecause laboratory conditions are notthe same as the real working environ-ment. Also it is quite possible thatnumerous types of other equipmentcould be connected to the goods and itis impossible to cover all possibleconfigurations.

However, where possible the goodsshould be tested either in house or bya competent body against the relevantstandards. A Technical ConstructionFile must be produced and be ready forinspection, if required.

A Declaration of Conformity must bekept and made available to theenforcement authority.

A CE mark must be affixed to theapparatus, or its packaging, instruc-tions or guarantee certificate.

Where does Electromagnetic Interference come from?

Electromagnetic interference (EMI) canmanifest in a variety of ways and theemission source is usually frequencydependent. The interference can beconducted, through mains cables andearthing connections, or radiated. Mostelectronic hardware contains elementswhich act in a similar manner to an

antenna, such as cables, pcb tracks,internal wiring and mechanical struc-tures. These elements can unintention-ally transfer energy via electric,magnetic or electromagnetic fields,which couple with other circuits.

DomesticCommercialLight Industrial

Industrial SpecialEN 50 081 Emissions

EN 50 082 Immunity

Part 1 Part 2 Part 3

Instead of designing a filter stage forevery new piece of electronic equip-ment that is manufactured, there is aconvenient solution available in theform of a ready made module that canbe connected between the mainssupply and the electronic unit. Thecomponents are selected by the filtermanufacturer to give the best reductionof mains conducted interference formost situations, across the frequencyspectrum, using the optimum selectionof components. More importantly filterscomply with the numerous safety rulesand the approval costs have beenspread over a large number of unitsbecause the filters can be universallyapplied.

Filters work by providing an impedancemismatch between the power line andthe equipment, which reflects thegenerated noise back to its source. Inorder to maximise the impedancemismatch the choice of filter circuitshould take into account the imped-ances of the source and load.

The main components inside the filterare chokes, capacitors and resistors.

( asymmetrical interference )

( Symmetrical Interference )

Earth Current

Cp = parasitic capacitance

Common Mode

Differential Mode

Source Load

EMC Filters

The filter circuit is designed to contendwith two types of noise. There isCOMMON MODE NOISE, whichmanifests itself as a current in phase inthe live and neutral conductors andreturns via the safety earth. Thisproduces a noise voltage betweenlive/neutral and earth. It is often causedby capacitive coupling to the caseearth. The other is DIFFERENTIALMODE NOISE produced by currentflowing along either the live or neutralconductor and returning by the other.This produces a noise voltage betweenthe live and neutral conductors.

The chokes fall into two groups; currentcompensated or common mode andseries or differential mode types. Thecurrent compensated choke has two orthree windings on a toroidal core. Thedirection of each winding is chosen togive an opposing current flow, hencebalancing the flux. The result is that amuch smaller choke can be used.Furthermore, the common modecurrents, which are in phase in the twoor three conductors, have an additiveeffect, thus presenting higher imped-ance against the common mode noise.

The capacitors oppose the AC flow ofelectrons more at lower frequenciesand less at higher frequencies.Inductors on the other hand reactagainst the rate of change of current;they are more effective at opposing ACflow of electrons at higher frequencies.Therefore, a combination of seriesconnected inductors and shuntconnected capacitors is chosen toprovide suppression over a widefrequency spectrum. The resistorsserve to discharge the capacitors whenthe supply is disconnected and fordamping resonances. The enclosure isnormally produced from metal toprovide good earth bonding.

A typical REO filter built into metal enclosure(lid removed). The main components; capaci-tors and inductors can be clearly seen.

Cx 1 Cx 2

Cy

Cy

LSymmetrical Interference current

Asymmetrical Interference current

The differential mode chokes are largerdue to the higher current handlingrequirement. Using a core made from ahighly permeable material will reduceits size.

Capacitors also fall into two groups; XClass and Y Class. The X Class capac-itors are connected between live andneutral, or between phases, to reducedifferential noise. They are tested towithstand mains voltage. Y Classcapacitors on the other hand are morecritical because they are connectedbetween live/neutral and earth toreduce common mode noise. Becauseof this they have to be tested to ensurethat they cannot fail to short circuit.Needless to say they are more expen-sive.

For higher levels of attenuation, severalstages of chokes and capacitors canbe added and this is known as a multi-stage filter.

Another important factor is the earthleakage current. The larger the Y Classcapacitor the more the 50 Hz currentthat will leak to earth, raising the poten-tial of the filter enclosure. Themaximum permissible leakage currentdepends on the application but to givean indication the maximum earthleakage for double insulated equip-ment, such as hedge trimmers and

drills, is 0.25 mA. Equipment that ispermanently connected to the mainssupply may have a leakage current ofup to 5mA. Industrial equipmentnormally has higher leakage currentlimits but in each case particular caremust be taken to ensure that earthingregulations are observed.

The frequency range of interest foremissions from most products is150kHz to 30MHz. The emissions aremeasured using a spectrum analyserand then they are compared with theClass B limits for domestic or lightindustrial applications or Class A limitsfor industrial applications (Standard EN55 022). The spectrum analyser willgive a sweep of the entire spectrumrange and indicate the emission levels,usually as a print-out. The limits arealso indicated and frequencies withunacceptable emission levels arehighlighted.

The picture shows a screen capturefrom a spectrum analyzer. Note thatthe sweep range is 150 kHz to 30 MHzand the red line (quasi-peak) andpurple line (average) indicating thelimits for light industrial and domesticuse (Class B). The two frequencycurves for the equipment under test arequasi peak in blue and average ingreen. The vertical scale is in dB�V. Inorder to conform the curves should notexceed their corresponding limits.Thisis the format for the results asprescribed in EN 50 081-1 forconducted emissions.

Testing

The electromagnetic field strengthsassociated with the emissionsmeasurements range from a fewmillionths of a volt per meter to a fewthousandths of a volt per meter. It isdifficult to represent this scale in alinear manner and so a logarithmicscale is adopted. The spectrumanalyser plot has decibels as the unitof measurement along its vertical axis.A decibel is a ratio of two powervalues, which in this case is theincrease in power caused by theemission compared with the power ofthe reference voltage. For conven-ience, because power is proportional tothe square voltage, the ratio of thevoltages is squared instead ofmeasuring power.

Screen capture from a spectrum analyzer

Relative Humidity95% 21 days/year

The performance and hence quality ofa filter may be assessed by looking atits insertion loss characteristics. Thisdata is published by all reputable filtermanufacturers and the following is anexample.

The curves can be used to assesswhether a particular filter will providesufficient suppression for a knowninterference pattern. However, preciseperformance can only be establishedby testing under real conditions. Thehigher the dB value the greater thedegree of suppression achieved.

Points to consider when selecting a filter

The current rating is also very impor-tant especially in instances where theload produces high peak currents andthe RMS is not a true indication of thereal current. Higher than expectedcurrents can cause core saturation, inthe inductors, thus drastically reducingthe filter s effectiveness. Most filtermanufacturers will take this intoaccount when designing a filter but thisdata is not normally published.

The acceptable level of earth leakagecurrent for the installation must also beknown and the filter selected, accord-ingly.

The components in a filter are classi-fied for a range of climatic andmechanical requirements, includinglower temperature limit, over tempera-ture limit and relative humidity. Unlessotherwise stated REO filters conformwith Environment Category IEC 68-1.

The current has to be derated forambient temperatures of greater than40�C

� = � � √(85-�)/40The permissible current rating issubject to ambient temperature. Below40�C a filter can be used at its ratedcurrent. The current reduces for highertemperatures. At 85�C the current isreduced to zero. (For 25/85/21 )

Lower temperature limit - 25�C

Over temperature limit + 85�C

25/85/21�

� �

� Ambient

40�C 85�C

Frequency [MHz].15 1 10 30

0

20

40

60

80

100[dB]Damping symmetrical

asymmetrical

All REO filters are built to the followingstandards:-

VDE 0565 Part 1 - 3DIN EN 133200IEC 68-1

Standards

All materials are UL listed and in manycases filters are UL approved, orapproval can be obtained in a shorttime.

� 2�[�2]

A filter should be positioned as closeas possible to the connection to thesupply; ideally before the mains switchin the front panel and fuses. Otherwisethe connecting cables could provide acoupling path via stray induction to theunfiltered cables.

Wiring on each side of the filter shouldbe well separated and extend straightout from the filter s terminals. If this isnot practical the output cables shouldbe run at 90 degrees to the inputcables to reduce the likelihood ofcoupling.

The filter should be correctly rated forthe local supply voltage.

A good ground connection is requiredbetween the filter casing and earth.The ground connections must havelarge contact surfaces and be madeonto bare metal, not painted.

Installation

CNW 101

Single phase, 250 V, costeffective unit for generalpurpose.

Standard Filters - Single Phase

Type

CNW 101/3CNW 101/6CNW 101/10CNW 101/16CNW 101/20

3 A6 A

10 A16 A20 A

8080929292

4545505050

3030303030

CurrentSize (inc terminals)

L W H

CNW 102

Single phase, 250 V, highperformance unit suitablefor most applications.

Type

CNW 102/3CNW 102/6CNW 102/10CNW 102/16CNW 102/20

3 A6 A

10 A16 A20 A

939393118118

5050505050

4040404040


L W H

CNW 201

230V / 440V 2 linebookcase style filter.

Type

CNW 201/16CNW 201/30CNW 201/50CNW 201/63

16 A30 A50 A63 A

255255255255

50505050

126126126126


L W H

PE

L

N(L2)

R

L

C y

C y

L'

N'(L2')

Cx1Cx2

CNW 116

Single phase, 250 V,optimised unit for use withmotor drives.

Type

CNW 116/8CNW 116/12CNW 116/20CNW 116/30

8 A12 A20 A30 A

120120140140

105105105105

57575757


L W H

For details of our full range of EMCfilters and custom design solutionsplease;

Call 01588 673411

Email [email protected]

Visit our website www.reo.co.uk

CNW 103

3 phase, 3 x 440 V, 3 line mains filter withhigh attentuation.

Type

CNW 103/3CNW 103/6CNW 103/10CNW 103/16CNW 103/25CNW 103/36CNW 103/50CNW 103/80CNW 103/120CNW 103/150

3 x 3 A3 x 6 A

3 x 10 A3 x 16 A3 x 25 A3 x 36 A3 x 50 A3 x 80 A

3 x 120 A3 x 150 A

118118118170170290290320320320

5353539898

148148168168168

40404070707070110110110


L W H

L1 L2 L3 PE

L1' L2' L3' PE'

R

Cx1

L

Cx2 Cy1

Cy2

LIN

E

LOA

D

L1 L2 L3 PE

L1' L2' L3' PE'

R

Cx1

L

Cx2 Cy1

Cy2

LIN

E

LOA

D

CNW 106

3 phase, 3 x 440 V, 4 line mains filter with veryhigh attentuation.

Type

CNW 106/6CNW 106/10CNW 106/16CNW 106/25

4 x 6 A4 x 10 A4 x 16 A4 x 25 A

240240240240

150150150150

65656565


L W H

L1 L2 L3

L1' L2' L3'

N

PE PE'

N'

Cx1 Cx2 Cx3

Cy1 Cy2

R

L1 L2

LIN

E

LOA

D

Standard Filters - Three Phase

CNW 104

3 phase, 3 x 440 V, 3 line mains filter withvery high attentuation.

Type


3 x 3 A3 x 6 A

3 x 10 A3 x 16 A3 x 25 A3 x 36 A3 x 50 A3 x 80 A

3 x 120 A3 x 150 A

170170170170170290290350350350

9898989898

168168168168168

7070707070110110140140140


L W H

CNW 105

3 phase, 3 x 440 V, 4 line mains filter withhigh attentuation.

Type


4 x 3 A4 x 6 A

4 x 10 A4 x 16 A4 x 25 A4 x 36 A4 x 50 A4 x 80 A

4 x 120 A4 x 150 A

118118118170170290290320320320

5353539898

148148168168168

40404070707070110110110


L W H

L1 L2 L3 PE

L1' L2' L3' PE'

R

Cx1

L1

Cx2

L2

Cx3

Cy1

Cy3

Cy2

LIN

E

LOA

D

L1 L2 L3

L1' L2' L3'

N

PE PE'

N'

Cx1

Cy

Cx2

RL

LIN

E

LOA

D

CNW 204

3 phase, 3 x 480 Vbookcase style filters, withvery high attentuation.

Type

CNW 204/7CNW 204/16CNW 204/30CNW 204/42CNW 204/55CNW 204/75CNW 204/100CNW 204/130CNW 204/180

3 x 7 A3 x 16 A3 x 30 A3 x 42 A3 x 55 A3 x 75 A

3 x 100 A3 x 130 A3 x 180 A

255305335330330330380440440

50556070808090110110

126142150185185220220240240


L W H

CNW 203

3 phase, 3 x 480 V bookcase style filters, with very high attenuation.

Type

CNW 203/16/SECNW 203/25/SECNW 203/36/SECNW 203/50/SE

3 x 16 A3 x 25 A3 x 36 A3 x 50 A

230230280330

50506056

8080

150150


L W H

L1

L2

L3

PE PE

L2'

L3'

L1'L

Cx1Cx2

R

Cy

LOA

D

LIN

E

CNW 703

Over voltage protection device,3 x 440V for easy installationinto new or existing equipment.Efficient protection against highvoltages, lightning strikes andtransients. Attenuation of inter-ference down to approximately50dB at 1MHz.

Type

CNW 703 80 205 90 75

Max. SurgeCurrent kA

Size (inc terminals)L W H

EMC Filters Guide - EMCIA - EMC Industry Association ... Filters Guide.pdf · EMC Filters Guide REO(UK) LTD Units 8 -10 Long Lane Industrial Estate, Craven Arms, Shropshire SY7 8DU

Documents