eddy current brakes seminar report

7/24/2019 Eddy Current Brakes Seminar Report

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Seminar Report 2004 Eddy Current Brake

ABSTRACT

This is an electric braking system which works on the principle that eddy

current produced in it opposes the driing tor!ue" This opposing tor!ue is used to

brake the automobiles" #ainly this system is purely based on $araday%s laws o&

electromagnetic induction and 'en(%s law"

$or operating this a control switch is proided on the steering column in a

position &or easy manual" The skidding and comple)ity o& mechanical braking system

can be minimi(ed by this system" Also the wear and tear o& the ehicles can be

reduced"

Since researches are going on to eliminate some o& the disadantages o& this

system* we can accept it to be the norm one in a &ew years o& time"

+ept" o& Electrical , Electronics #"E"S"C"E* -uttippuram.


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C/TETS

." 1TR/+CT1/

2" 3R1C13'E /$ /3ERAT1/

" C/STRCT1/

4" 5/R-16

7" E++8 CRRET BRA-E 1 TRA1S

9" BRA-16 3/5ER CA'C'AT1/S

:" E++8 CRRET BRA-E RE;1RE#ETS

ATA6ES

.0" +1SA+>ATA6ES

.." A33'1CAT1/S

.2" C/C'S1/

." RE$ERECES

+ept" o& Electrical , Electronics #"E"S"C"E* -uttippuram2


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1TR/+CT1/

#any o& the ordinary brakes* which are being used now days stop the ehicle

by means o& mechanical blocking" This causes skidding and wear and tear o& the

ehicle" And i& the speed o& the ehicle is ery high* the brake cannot proide that

much high braking &orce and it will cause problems" These drawbacks o& ordinary

brakes can be oercome by a simple and e&&ectie mechanism o& braking system ?The

eddy current brake%" 1t is an abrasion@&ree method &or braking o& ehicles including

trains" 1t makes use o& the opposing tendency o& eddy current

Eddy current is the swirling current produced in a conductor* which is

subected to a change in magnetic &ield" Because o& the tendency o& eddy currents to

oppose* eddy currents cause energy to be lost" #ore accurately* eddy currents

trans&orm more use&ul &orms o& energy such as kinetic energy into heat* which is

much less use&ul" 1n many applications* the loss o& use&ul energy is not particularly

desirable" But there are some practical applications" Such an application is the eddy

current brake"

+ept" o& Electrical , Electronics #"E"S"C"E* -uttippuram


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3R1C13'E /$ /3ERAT1/S

Eddy current brake works according to $araday%s law o& electromagnetic

induction" According to this law* wheneer a conductor cuts magnetic lines o& &orces*

an em& is induced in the conductor* the magnitude o& which is proportional to the

strength o& magnetic &ield and the speed o& the conductor" 1& the conductor is a disc*

there will be circulatory currents i"e" eddy currents in the disc" According to 'en(%s

law* the direction o& the current is in such a way as to oppose the cause* i"e" moement

o& the disc"

Essentially the eddy current brake consists o& two parts* a stationary magnetic

&ield system and a solid rotating part* which include a metal disc" +uring braking* the

metal disc is e)posed to a magnetic &ield &rom an electromagnet* generating eddy

currents in the disc" The magnetic interaction between the applied &ield and the eddy

currents slow down the rotating disc" Thus the wheels o& the ehicle also slow down

since the wheels are directly coupled to the disc o& the eddy current brake* thus

producing smooth stopping motion"



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E++8 CRRET 1+CE+ 1 A C/+CT/R



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C/STRCT1/

Essentially an eddy current brake consists o& two members* a

stationary magnetic &ield system and a solid rotary member* generally o& mild steel*

which is sometimes re&erred to as the secondary because the eddy currents are

induced in it" Two members are separated by a short air gap* they%re being no contact

between the two &or the purpose o& tor!ue transmission" Conse!uently there is no

wear as in &riction brake"

Stator consists o& pole core* pole shoe* and &ield winding" The &ield

winding is wounded on the pole core" 3ole core and pole shoes are made o& east steel

laminations and &i)ed to the state o& &rames by means o& screw or bolts" Copper and

aluminium is used &or winding material the arrangement is shown in &ig" ." This

system consists o& two parts"

1. Stator

2. Rotor

Stator:-

1t is supported &rame members o& the ehicle chassis" 1t has introduced

magnetic poles energi(ed by windings" Current is supplied to the winding &rom the

battery"

Rotor:-

1t is a rotating disc* which is &itted on the line o& cranksha&t with small air gap to

stator" 5hen disc rotates a &lu) change occur in the section o& the disc passing the

poles o& stator" +ue to the &lu) change there is a circulatory or eddy current in the



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disc around the magnetic lines o& &orce" The e&&ect o& this eddy current induces ?%

and ?S% poles at the sur&ace o& the disc" Then there will be a ?drag% or braking e&&ect

in between eddy current induced poles and magnetic poles in the stator" By

changing current &rom the battery we can change the braking &orce" 1n this breaking

system kinetic energy o& the ehicle is conerted to heat and this heat is dissipated

through the rotating disc"

Total resistance o& &ield winding

R 'A

where* ' total length o& &ield winding in meter"

Resistiity o& the wire in ohm meter

A the area o& cross section o& &ield winding in m2

Total noD o& terms total length mean length o& one term

The rotor is a rotating disc on sha&t* which is placed ery near to the stator

with small air gap . mm to 2 mmF" Rotating disc may be one or both side o& stator"

The two units hae common ring member* poles cores on which winding are

proided being &i)ed to ring number" 1& a malleable casting is employed* then the pole

core could be cast integrally with the right" A&ter &itting the windings on the cores*

poles shoes are &itted to proide pole &aces o& appropriate shape and area" The rotor

disc should be proided with properly designed &ins &or &aster heat remoal" The

magnetic circuits o& the two units are substantially the same* non@undue and thrust

would be imposed on the motor bearings" Slight a)ial displacement o& rotor could

howeer* cause !uite appreciable discrepancy* the air gap o& two units" The e&&ect

would be to increase the magnetic pull in one air gap and diminish it on other which

could gie to rise to e)cessie and thrust on rotor bearing to oercome the inherent

de&ect* the air gaps o& both units could be put in series by making the central number

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non magnetic and proiding a continues pole core &or each pair a)ially opposite poles"

This modi&ication could possibly reduce the length o& the combined pole course or

permits a larger winding length"

The ma)imum diameter o& the eddy current brake is decided by

." The spacing o& ehicle chassis &rame"

2" >ehicle &loor clearance

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5/R-16

5hen the ehicle is moing* the rotor disc o& eddy current brake which is

coupled to the wheels o& the ehicle rotates* in close pro)imity to stationary magnetic

poles" 5hen we want to brake the ehicle* a control switch is put on which is placed

on the steering column in a position &or easy operation"

5hen the control switch is operated* current &lows &rom a battery to the &ield

winding* thus energi(ing the magnet" Then the rotating disc will cut the magnetic

&ield" 5hen the disc cuts the magnetic &ield* &lu) changes occur in the disc which is

proportional to the strength o& the magnetic &ield" The current will &low back to the

(ero &ield areas o& the metal plate and thus create a closed current loop like a whirl or

eddy" A &low o& current always means there is a magnetic &ield as well" +ue to 'en(%s

law* the magnetic &ield produced by the eddy currents works against the moement

direction" Thus instead o& mechanical &riction* a magnetic &riction is created" 1n

conse!uence* the disc will e)perience a GdragH or the braking e&&ect* and thus the disc

stops rotation" The wheels o& the ehicle* which is directly coupled to the disc* also

stop rotation" $aster the wheels are spinning* stronger the e&&ect* meaning that as the

ehicle slows* the braking &orce is reduced producing a smooth stopping action"

The control switch can be set at di&&erent positions &or controlling the

e)citation current to seeral set alues in order to regulate the magnetic &lu) and

conse!uently the magnitude o& braking &orce" i"e" i& the speed o& the ehicle is lpw* a

low braking &orce is re!uired to stop the ehicle" So the control switch is set at the

lowest position so that a low current will be supplied to the &ield winding" Then the

magnetic &ield produced will be o& low strength* so that a re!uired low braking &orce

is produced"

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5hen the control switch is operated during the standby position o& the

ehicle* the magnet will be energi(ed and magnetic &ield is created" But since the

wheels are not moing* magnetic lines o& &orce are not cut by it* and the brake will not

work" Ioweer* a warning lamp is proided on the instrument panel to indicate

whether the brake is energi(ed" This proides a sa&e guard &or the drier against

leaing the unit energi(ed"

5hen control switch is put in any one o& the operating positions* the

corresponding conductor in the contractor bo) is energi(ed and current &lows &rom the

battery to the &ield winding to the contractor bo)" This current magneti(es the poles

in stator* which placed ery near to the rotor" 5hen rotor rotates it will cut magnetic

lines and eddy current will set up in the rotor" The magnetic &ield o& this eddy current

produces a breaking &orce or tor!ue in the opposite direction o& rotation disc" This

kinetic energy o& rotor is conerted as heat energy and dissipated &rom rotating disc

to surrounding atmosphere" Current in the &ield can change by changing the position

o& the controls switch" Thus we can change the strength o& the braking &orce"

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E++8 CRRET BRA-E 1 TRA1S

1n the case o& trains* the part in which the eddy current is induced is rail" The

brake shoe is enclosed in a coil* &orming an electromagnet" 5hen the magnet is

energi(ed* eddy currents are induced in the rail by means o& electromagnetic

induction* thereby producing braking action"

E++8 CRRET BRA-E 1 TRA1S

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+1STR1BT1/ /$ #A6ET1C $'J +ES1T8



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T83ES /$ E++8 CRRET BRA-ES

There are two types o& eddy current brakes according to the method o&

e)citation"

."Electrically e)cited eddy current brake

2"3ermanent magnet eddy current brake

."E'ECTR1CA''8 EJC1TE+ E++8 CRRET BRA-E

Electrically e)cited eddy current brakes are abruption@&ree method &or

braking" 1n high@speed trains they o&&er a good alternatie to the mechanical rail

brakes which are being used now a days" +uring braking* the brake comes in contact

with the rail* and the magnetic poles o& brakes are energi(ed by a winding supplied"

#agnetic poles o& brakes are energi(ed by a winding supplied with current &rom the

battery" Then the magnetic &lu) is distributed oer the rail" The eddy currents are

generated in the rail* producing an electromagnetic braking &orce" This types o&

braking need an additional sa&ety power supply when there are breakdowns in the

electrical power supply"



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E'ECTR1CA''8 EJC1TE+ E++8 CRRET BRA-E



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2" 3ER#AET #A6ET E++8 CRRET BRA-E

Recently* permanent magnet eddy current brakes hae been deeloped &or

subways* trams and local trains" These brakes need a mechanical actuator to turn the

magnets n an on and o&& position" The main adantage o& this type o& brake is sa&ety"

i"e" it does not need electrical power supply to energi(e the magnet"



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BRA-16 3/5ER CA'C'AT1/S

Sophisticated calculation methods &or the determination o& braking &orces o&

eddy current brakes are important &or the design o& the brakes"

$or a simple eddy current brake employing a thin non@magnetic disc as

copper the drag or braking &orce on the disc

where

I #agnetic &ield strength in 5ebers"

A 3ole &orce area in cm2"

> >elocity in cmsec o& mean radius o& disc under the poles"

T disc thickness in cm"

speci&ic resistance o& disc material at its operating temperature in micro

ohmscm"

Tor!ue $ K R m

5here R mean pole radius in meter"

3ower 3 2 T90 watts"



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E++8 CRRET BRA-E RE;1RE#ETS

An eddy current brake is an energy conerter &unctions is to conert the

kinetic energy o& a ehicle into heat and dissipate it such a rate to maintain the

temperature o& unit with in reasonable limits under ma)imum and prolonged braking

conditions" The energy absorbed by the brake is trans&ormed into heat by the currents

induced in the motor* and this is heat manly dissipated in surrounding air through the

medium o& suitable designed &ins the rotating member"

1n mountains area* continues braking &orce is needed &or a long time say

about hal& an hourF* at this condition* eddy current braking is more suitable to &unction

without oer heating" The use o& these retarders is by no means limited to mountain

on country" They can be adantageously employed on public serice ehicles on city

routes without &re!uent stops" But in this braking system there with out be any

braking &orce in the ehicle is rest" So the eddy current brake is used as an au)iliary

heay@duty retarder" By using au)iliary retarder ery smooth retardation is assumed

and likely hood o& skidding on slippery roads sur&aces is minimi(ed" Smooth braking

action cuts down tier were and since brake is used as an au)iliary heay@duty retarder"

By using au)iliary retarder ery smooth retardation is assumed and likely hood o&

skidding on slippery roads sur&aces is minimi(ed" Smooth braking action cuts down

tier were and since the conentional brakes are relieed o& heay duty being re!uired

only to bring ehicles to rest"

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#/T16 A+ 1STA''AT1/

A typical mounting o& an eddy current brake consists o& two discs in which

pole salient type* supported between the &rame numbers o& a ehicle chassis" Rotor is

coupled to road wheels being o&ten mounted on a sha&t that is interposed between the

gearbo) and propeller sha&t and stator is mounted on the &rame o& the ehicle"

The drier who can select one or &our e)citation settings according to the

breaking e&&ect re!uired mounts a control switch on a steering column in a position

&or easy operation" 1n the operatie positions o& this switch .* 2* * 4 contractors are

energi(ed to supply current to the e)citation windings o& the retarder" 5arning lamp is

also proided on the instrument panel to indicate when the retarder is energi(ed" This

proides a sa&e guard &or the drier against leaing the unit energi(ed when the

ehicle is stationary"



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A+>ATA6ES

'ess maintenance

5ide range o& braking &orce aailable within the temperature limit

3rolonged braking is possible

'ong li&e

'ess strain to the operation

Smooth retardation* which cuts down* the tire wears

Eddy current brakes o&&er smooth retardation o& ehicles without skidding" 1t

is totally &ree o& wear and tear" So it has long li&e compared to ordinary brakes" These

need less maintenance"

1n mountain areas continuous braking is needed &or a long time" At this

condition* eddy current braking is more suitable to &unction without oerheating"

By changing the e)citation current to the &ield winding* i"e" by adusting the

position o& the control switch* we can ary the braking &orce to re!uired range" The

operation o& eddy current brake is ery simple" i"e" the control switch is a so&t switch

which can be operated without any strain"

Eddy current brakes works een under the toughest enironmental conditions"

$or e)ample* in larger water slides and water coasters where the humidity would

immediately result in reduction o& &riction and thus impair the e&&ectieness o&

ordinary brakes" 1t works een in highly corrosie enironments and heaily

contaminated areas"

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+1SA+>ATA6ES

o breaking &orce at rest

eed o& electric power

The main disadantage o& the edyy current brake is that it needs electric power

to work" Researches are going on to oercome this disadantage by making the brake

regeneratie i"e" by conerting the kinetic energy o& the ehicle into electric energy

and storing it back into the battery"



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A33'1CAT1/S

$or additional sa&ety on long decants in mountain area

$or high speed passenger and goods ehicle

Eddy current brakes are best substitutes &or ordinary brakes* which are being

used nowadays in road ehicles een in trains* because o& their erk@&ree operation" 1n

mountain areas where continuous braking &orce is needed* &or a long time* the eddy

current braking is ery much use&ul &or working without oerheating" Eddy current

brakes are ery much use&ul &or high@speed passengers and good ehicles" 1t can also

be used to slow down the trolleys o& &aster roller coasters"

+ept" o& Electrical , Electronics #"E"S"C"E* -uttippuram2.


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C/C'S1/

Eddy current brakes are the best choice when demands &or reliability and

sa&ety are the highest" They work een in the toughest enironmental conditions" Een

the strike o& lightning will not result in the loss o& the braking &orce"

Eddy current braking system is not popular now a days" But we hope that the

eddy current braking system which is simpler and more e&&ectie will take the place o&

the ordinary braking system and we can do e)pect it to be the norm one in &ew years

o& time"



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RE$ERECES

." #anual . 6on(ale(* >olume 27*1ssue 4*Luly 2004

2" 1EEE Transactions on magnetics* >olume 4* 1ssue 4* Luly .==

eddy current brakes seminar report

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