Electrostatic precipitator

ESP Rectifer transormer

ESP Rectifer transormer

M.G.Morshad /

M.G.Morshad / ACM

ACM

Transformer Mtce / TPS II

Transformer Mtce / TPS II

Principle o operation

Principle o operation

••

_{Electrodes at high voltage create a corona effect (ionized atmosphere)}

_{Electrodes at high voltage create a corona effect (ionized atmosphere)}

surrounding them.

surrounding them.

•• This charges the passing particles. Once charged, particles are subject to

 This charges the passing particles. Once charged, particles are subject to

a transverse electrostatic force that pulls them toward the collecting plates.

a transverse electrostatic force that pulls them toward the collecting plates.

•• Plates are periodicall !rapped" (vibrated) to ma#e the collected particles

 Plates are periodicall !rapped" (vibrated) to ma#e the collected particles

fall down

Principle o operation

Principle o operation

••

_{Electrodes at high voltage create a corona effect (ionized atmosphere)}

_{Electrodes at high voltage create a corona effect (ionized atmosphere)}

surrounding them.

surrounding them.

•• This charges the passing particles. Once charged, particles are subject to

 This charges the passing particles. Once charged, particles are subject to

a transverse electrostatic force that pulls them toward the collecting plates.

a transverse electrostatic force that pulls them toward the collecting plates.

•• Plates are periodicall !rapped" (vibrated) to ma#e the collected particles

 Plates are periodicall !rapped" (vibrated) to ma#e the collected particles

fall down

Back corona

Back corona

-$ -$ -$ -$ -$ -$ -$ -$ -$ -$ -$ -$ -$ -$ -$ -$ -$ -$ -$ -$ -$

$ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $

$ $ $ $

$ $ $ $ $ $ $ $ $

$ $ $ $ $ $ $ $ $

$ $ $ $ $ $ $

$ $ $ $ $ $ $

$ $ $ $ $

$

$

$

Positively Positively chared chared collectin collectin plates plates

%

%

- - - -

-!ih !ih resistive resistive d"st d"st particles particles #eativel #eativel y chared y chared d"st d"st particles particles #eatively #eatively chared chared emittin emittin electrodes electrodes Spark $et%een Spark $et%een layers o d"st layers o d"st particles particles 



In case of high resistive dust ( dry dust) , dust l

In case of high

resistive dust ( dry dust) , dust layer creates an insulation beteen the

ayer creates an insulation beteen the

!ositively charged collecting !late

!ositively charged collecting !late and negatively charged dust !articles"

and negatively charged dust !articles"





 In such condition, s!ar# / arc ithin the layer of dust !article is formed ith the decrease of

 In such condition, s!ar# / arc ithin the layer of dust !article is formed ith the decrease of

$% (&')" This !henomena is #non as '$ '*+*"

$% (&')" This !henomena is #non as '$ '*+*"





 s a result of s!ar# / arc for

 s a result of s

!ar# / arc formation , field current

mation , field current (m

(m ) gets increas

) gets increased

ed ith substantial

ith substantial

decrease in field voltage $%

decrease in field voltage $% (&')"

(&')"





To avoid bac# corona, field voltage $%(&') has to be reduced sufficiently, but such

To avoid bac# corona, field voltage $%(&') has to be reduced sufficiently, but such

measures finally

'oltae ( c"rrent characteristics

$% ( &')

m ( &')

ac# 'orona 0one

*!erating 0one

1ield Short

2

*!erating 0one 3

4ith the increase of field voltage 5$% (&')6, field current (m) increases linearly and no s!ar# is emitted"

ac# 'orona 7one 3

S!ar# starts emitting causing decrease in field voltage $%(&') ith high increase in field current (m)

1ield short 3

S!ar# !ersist continuously causing field voltage $%(&') to become 7ero ith ma8imum flo of field current (m)

Parameters a)ect the perormance o ESP

&. 'as Temperature



ormally 9SP is designed to o!erate in the tem!erature range :;2- <22 &eg '"  At higher temperature, the quality of insulation deteriorate and flash over voltage limit decreases. In such condition operating voltage has to be brought down to avoid back corona that results in lower dust collecting efficiency .  t

tem!erature

belo the acid de !oint, de!osition of acid in the structure leads to faster corrosion "

. *oisture content 

Moisture content has a large influence on the performance of E!. Moisture increases the ioni"ation tendency and decreases the resistivity of the dust particles. As an effect of these factors dust collection efficiency increases with reduced back corona tendency .

+.ust particle size

#he collecting efficiency increases with increase in particle si"e since the larger particles receive charge more quickly and attains migration velocity. $Migration velocity is proportional to diameter when d%&pm and is independent when d'&(m). *ence , collection efficiency decreases with the increase of fineness of the dust particles+.

-. ust resistivel

ust resistivity increases with the increase of dryness of dust and quality of fuel. At higher dust resistivity , internal spark over between two layers of dust takes place as a result of potential difference created by the high resistance of dust. #his phenomena is called -ack orona. /nce the back corona starts , field intensity $ 01 ) start reducing with increase of field current . #his reduces the collecting efficiency of the E!.

. /apping fre0uenc 

2henever the electrode surface is sub3ected to rapping shock, re4entertainment of particles takes place in the main flow path and carried away by the gas causing increase in emission level . #o reduce the re4 entertainment to a minimum level, it must be allowed to form a layer of significant thickness of dust so that when it is dislodged by rapping, the layer breaks into agglomerate masses, sufficiently large to

Components o rectifer transormers

*icroprocessor based

1oltage controller 

2ontrol panel =

:" nalog Meters for >uic# visual indication of o!erating level" <" 9lectronic 'ontroller for 'ontrolling !oer ($% and m)

delivered to the T+"

?" S'+ Module ith .eat Sin#s under control of the 9lectronic 'ontroller for Phase 'ontrol of the ' 1eed to the T+"

@" 'ircuit rea#er, 'ontactor and Misc" control and interloc# relays Phase control Thyristor,

Transformer unit =

:"Series reactor, <"Transformer coil, ?"+ectifier bridge, @"+esistor assembly A".1 cho#e" B"Insulating oil C"D%  .% ushing

SCR controller



The single !hase in!ut voltage of @;2 % is a!!lied across the S'+ assembly hich is

made u! of to S'+s connected in a reverse !olarity !arallel configuration "



The !rimary voltage of transformer is controlled by changing the conduction angle of

the S'+ ith the hel! of feed bac# signal ( m  $%) ta#en from &' side of the secondary



The S'+s are !rotected from dv/dt damage by a resistor ca!acitor snubber netor#

consist of metal o8ide varistor and fuse to !rotect against over current conditions"

 *ransormer +nit

+ectifier

ridge



&' %olt / 'urrent

-32 4nput 5 -& 1,663

32 Out put 5 +76 1, &.-6 3 %oltage

+atio :3:@?"@<

*ut!ut &' %oltage E A?AC2 8 (:"@:@/:"2;) E C2$% *ut!ut &' current E :"@2 / :"@:@E 2"FF2 

*ut!ut $4r E % 8 I E C2 82"FF2 E BF"?$4

In!ut $% E ?C?"A 8 <22 E CA$% In!ut $4 E CA$% 8: E CA$4



Single !hase transformer ith higher voltage

ratio is used to create high voltage at secondary

terminal



Transformer is o!erated ith < !hase su!!ly for

achieving natural commutation of rectifier

bridge"



Transformer $% is controlled by controlling the

voltage  current ith the hel! of S'+ controller



.eat generation during o!eration is e>ual to

(In!ut CA $4 = *ut!ut BF"? $4 ) A"C $4 is

carried aay by the silicon oil to maintain the

tem!erature"



Gas generation due to high tem!erature is

detected by H'.*DT0 relay

Various capacity of transformer

C"rrent ,imitin Reactor

+ectifier unit

D

%

.

%

Series +eactor _{?C?"A %} Su!!ly Im!edance (0) E %/I (' +esistance)

 0 E %/I E D 8 <f *hms  J 0 E 5(D 8 <f 8 I) / % 6 8 :22 *hms  D E (% 8 J0) 8 (I 8 <f ) .enry 'D+ reactance (D) E :"A m. 'D+ resistance ( + ) EF mK  Im!edance of 'D+ E<@"B@J T+ im!edance E :2J System im!edance E ?@ "B@J

  system im!edance of A2J limits the ma8imum ' current to tice the rated current" t ??J the limit is three times the rated current

:" The !rimary !ur!ose of the 'D+ is to limit the surge current that is !roduced due to

generation of s!ar#  arc in the 9SP field " The ty!ical 'D+ value is selected in such a ay

that it can limit the current surge, ithin a ;"? msec (Dine L 'ycle) to a!!ro8imately < = @

limitation is re>uired because the S'+ controller cannot res!ond (turn off) until the end of

the line cycle"

<" The secondary !ur!osed of the 'D+ is !rovide a means for decreasing m and $% ri!!le

on the &' Poer delivered to the 9SP" The reduced +i!!le results in increased average $%

levels, and increased 9SP !erformance (efficiency)

@:A % Su!!ly

Rectifer -iode assem$ly

•

 The diode assembly is used to convert the high voltage ' out!ut of the transformer to a &' signal"

 The diode assembly is made u! of a series string of many diode unctions" This series string of diodes should be ca!able of bloc#ing at least tice the !ea# out!ut voltage of the T/+" i"e" (< 8 C2 $%! E :A2 $%)

 1or obtaining high bloc#ing voltage s!ecial measures are em!loyed to assure !ro!er voltage sharing"

 Im!ro!er voltage sharing is caused by variation of the reverse lea#age of individual diode unctions" This variation results in an uneven distribution of the PI% among the diodes" In such case the diodes ill fail in a NdominoO fashion

!& Choke

 .igh 1re>uency 'ho#e / ir 'ore +eactor ('+) is an electric coil that is connected beteen the rectifier bridge and .% bushing for !rotecting the T+ +ectifier ridge from high fre>uency, high voltage s!i#es and disturbances that occur ithin the s!ar#ing 9SP"

 '+s used in modern T/+s are rated from <2 to A2 (m.) and must be ca!able of ithstanding u! to < times !ea# rated voltage"

 s the 9SP s!ar#s and arcs, the full 9SP voltage ill be im!ressed across the '+"

 '+ design must !rovide sufficient layer insulation and clearance to accommodate such voltage"

 Ty!ical failure mode for '+s is a s!ar# over of t he layer insulation" Since the '+ is !hysically much smaller than the transformer secondary coil, it is subect to e8treme voltage stress"

Resistance $oard assem$ly

( eed $ack sinal or control  monitorin

&. m3 feed bac#

This signal is used for 'ontrol and monitoring"

The m 1eed bac# is im!lemented by a !oer resistance of a!!ro8imately :2 *hms" It is used to !rovide a :2 %olt &' signal that ill corres!ond to a :222 ma T+ out!ut" *ther resistor values may be used for other ratios"

The ma feed bac# is electrically connected beteen the Positive () leg of the .% ridge and 9arth Ground"

The +esistor must be of .igh +eliability +ating and also bac#ed u! by a !rotective .% &evice"

If this com!onent fails the rated .igh %oltage is im!osed u!on this feed bac# ire"

. 81 9eed bac# signal

The $% signal is im!lemented through use of a high voltage divider ith a ty!ical ratio ;,222 to :"

The ratio uses an ;2 Meg *hm resistor on the high end and a :2$ *hm resistor on the lo end, thus !roducing a feedbac# of ; $% !er volt" :<2 Meg dividers are sometimes used for higher voltage T+s"

Ty!ical $% 1eed ac# systems are not fre>uency com!ensated, yet !rovide a reasonable re!resentation of the 9SP signal"

*ne of the most im!ortant feedbac# signals is secondary voltage or #%" lthough this is one of the most commonly inaccurate signals found in many installations, inaccuracies in $% feed bac# can be calculated by the folloing formula 3 01 $  ) 5 $!rimary current x !rimary 1oltage 6 788) 9 econdary mA

 Di#e the ma 1eed ac#"" This signal must be !rotected since the full out!ut voltage of the T+ can be im!osed on this ire

ns"latin oil

The &ielectric 1luid is used to !rovide cooling for the T+ internal com!onents as ell as to !rovide high voltage insulation"

Mineral *il, Silicone *il and +-Tem! *il are fluids used"

P' fluid - s#eral (Prior to :FC2) ,Silicon 1luid , +-Tem! ty!e fluids are having higher fire !oint and therefore they are used here fire is of greater concern"

 Silicon fluid is more viscous than mineral oil at tem!eratures above :2 &eg c and therefore re>uires additional radiator or bigger tan# for !ro!er cooling"

 Silicone fluid has a greater affinity for ater absor!tion com!ared to Mineral oil

$2ater saturation point for Mineral oil is approx 78 ppm while silicone can be as high as :88 ppm) "

 Silicone fluid can maintain a higher dielectric !ro!erties at high ater concentrations"

 The solid insulation of silicon oil filled transformer gets contaminated ith ater easily since the Silicone fluid has a greater affinity for ater absor!tion and about F2J of the ater !resent in oil is absorbed by the insulation due to natural migration of moisture" .ence .*' is re>uired fre>uently in silicon fluid for #ee!ing the solid insulation dry"

 &ecom!osition of Silicon fluid due to internal arcing generates gases and carbon !articles" 4hen ucholt7 relay is actuated by gases, carbon !articles contaminated the oil as ell as gets attracted to the transformer indings hich finally causes the failure of the transformer due to insulation failure" .ence to remove the contamination from the oil , !ro!er oil filtration or total oil re!lacement is re>uired before installing the transformer after re!air and rectification"

Principle o operation

&e!ending u!on gas tem!erature, dust resistivity and gas velocity folloing !arameters are

set-:"uni !ulse mode/ Semi !ulse mode , <"!ea# mode ,

?"charge ratio,

@"s!ar# control rate ( S  T) A"secondary &' current limit

m

Time 'urrent limit

Ma8 'urrent at hich s!ar# occur

<2ms loc#ing time S

T

 4ith sitching on !rimary , S'+ controller increase the conduction angle de!ending u!on the &' feed bac# signal (m  $%) till it reaches the set current"

 &uring the current rise henever the secondary encounters ith s!ar#s hich is detected by lo voltage and high current &' feed bac# signal , S'+ controller immediately sto!s conduction"

 S'+ controller restarts conduction after <2 ms ith slo! less than AJ

 This !rocess goes on continuously to #ee! the field in energi7ed condition ith negative !olarity ithout any s!ar#"

+ni p"lse / Semi p"lse mode

In uni !ulse mode of o!eration fields are in continuous charging state ith all half

cycle of sinusoidal in!ut ( 'harge ratio E :)" This results in im!osing of high !ea#

voltage and high average current on the field hich causes higher !oer

consum!tion, loer dust collecting efficiency due to fre>uent occurrence of ac#

'orona 9ffect in the field"

In semi !ulse mode of o!eration fields are in intermittent charging state ith only

!reset half cycle of sinusoidal in!ut ( 'harge ratio Q:)" This results in im!osing of

high !ea# voltage and loer average current on the field hich causes Doer

!oer consum!tion, .igher dust collecting efficiency due to com!lete avoiding of

ac# 'orona 9ffect in the field"

% I

% I

S'+ controller +ectifier   Hni !ulse

Semi !ulse Sinusoidal in!ut

Chare Ratio



To avoid bac# corona , o!timi7ation of field voltage $% (&') is needed and It is achieved by

increasing the time ga! beteen the consecutive voltage !ulse hich is denoted as charge

ratio"



1or higher dust resistivity, higher charge ratio is re>uired so that field voltage is im!osed

after a sufficient interval to avoid bac# corona



 To maintain the sufficient average field current for increasing collection efficiency , field

current is to be set at <22J for charge ratio more than :



 Poer consum!tion reduces ith the increase of charge ratio



 1or setting field current at <22J , .% coil is fre>uently e8!osed to high current that may lead

to failure of coil"



Since lignite ash is lo resistive dust ( 4et dust), system can be set for charge ratio beteen

Hni !ulse mode

Semi !ulse mode 'harge +atio :

'harge +atio ?

'harge +atio A Semi !ulse mode

: < ? @ A B C ;

: < ? @ A B C ;

spark control rate

0 S  * control1



The s!ar# rate is determined by the settings of S-control and T-control"



  Su!!ose T-'ontrol is set at <2J , the time re>uired by the rectifier to reach the rated

current after a s!ar#, from 7ero current ill be < minutes"



 Su!!ose S-'ontrol is set AJ of the rated current, the time from S-'ontrol brea# !oint to

ne8t s!ar# ill then be AJ of the T-'ontrol time (AJ of < minutes), that is B seconds"



 If e do not account for the thyristor bloc# time (<2mS) then B seconds is the statistical

interval beteen s!ar#s in the 9SP"



  S-'ontrol  T-'ontrol are affected neither by the absolute value of current nor of the

voltage at hich a s!ar# occurs, the s!ar# rate is constant"

AJ

FAJ S

&ield c"rrent settin

Formula Field I Field II Field III

Field IV Field V Field VI  Secondary DC Current mA 100.00 200.00 500.00 500.00 700.00 700.00  Secondary AC Current ₂ 3 0mA 4 5.65651/5777 7.56 7.28 7.95 7.95 7.:: 7.::  Secondary DC Voltage ;'p 3 097 4 mA1/5777 9.77 56.77 <=.77 <=.77 6:.77 6:.77  Secondary AC Voltage ;'₂ 3 0;'p 4 5.781/5.656 =.<= 57.>: 2>.9< 2>.9< <9.62 <9.62  Out Put K ;%o 3 0mA4;'p1/5777 7.97 2.87 59.=7 59.=7 <6.<7 <6.<7  !r"o #oltage ratio R 56<.62 56<.62 56<.62 56<.62 56<.62 56<.62

D

%

.

_%

'D+ .1' m $%! $ Positive % :egative $%< I_< I: %_: @:A % su!!ly

Specifcation ( Stae  transormers

Name Rectifier Transformer

Supply Voltage 415 V AC two phase

Make !"#

#ocation Stage $$ "S% roof top

Capacity &5 'VA

Rate( primary Voltage ) #V* +&+,5 V

Rate( primary current )* -..,/ A

Rate( secon(ary 0oltage )!V* 5+5&. V

Rate( secon(ary current )!V* 1,4 A

Voltage ratio

14+,4-il Capacity 4.. #iters ) - arrels*

Type of oil Silicon oil

,ocation ( stae  transormers

A

:

<

?

@

B

::

C

; 

F 

:2

:< 

A

:

<

?

@

B

::

C

; 

F 

:2

:< 

'lean gases to chimney

 *ransormer connection / Stae 

HF Choke H.V Resistance

a5

av

a<

,'

ACR

!'

AR

AS

2

AS

5

A2

A5

Protection diode Diode Stack 

Terminal;Parts Purpose

a+ % av  ' series +eactor to restrict !rima ry current incase of shorted secondary ( +esistance F"?< m *hms) av% a& inding terminal ( +esistance :@"B m *hms)

4nternal Terminal .% inging terminal (+esistance @A@ *hms)

a+ < a& To !hase ' in!ut terminal (+esistance <@";@ m *hms) 3& egative terminal to create negative !otential in the fields

3 Positive terminal earthling !oint to create !ositive !otential in the structure 3= < 3/ &' feed bac# voltage measuring terminal

>9 2ho#e To reduce s!ar#ing rate at .% terminal ( Inductance A2m., B"C@ *hms) iode =tac# 1ull ave bridge rectifier for converting ' to &'

pen circ"it test  B!E, *ransormer

1oltage 3pplied on ?1 terminals @sing 1ariac (1olt)

*agnetizing current measured on ?1 terminals (3mps)

2 feed Aac# voltage measured between 3=B3/ (1) A2 0.116 20.20 :22 0.176 41.00 :A2 0.190 58.20 <22 0.280 77.20 <A2 0.490 96.50 ?22 2.460 116.00 ?A2 .110 1.00 ?C@ 4.240 140.50