Methods for Power Factor Improvement

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The following devices and equipment are used for

The following devices and equipment are used for Power Factor Power Factor  Improvement. Improvement. 1

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"e #now that most of the industries and power system loads are inductive that ta#e "e #now that most of the industries and power system loads are inductive that ta#e lagging current which decrease the system power factor

lagging current which decrease the system power factor $See %isadvantages of &ow$See %isadvantages of &ow

Power factor'

Power factor' . For Power factor improvement purpose( Static capacitors are connected . For Power factor improvement purpose( Static capacitors are connected in parallel with those devices which wor# on low power factor.

in parallel with those devices which wor# on low power factor. Th

Thesese e ststatatic ic cacapapacicitotors rs prprovovidides es leleadadining g cucurrrrenent t whwhicich h neneututraralili)e )e $t$tototalally ly or or  appro*i

appro*imately' the lagging inductive component of mately' the lagging inductive component of load current $i.e. leading load current $i.e. leading componecomponentnt neutrali)e or eliminate the lagging component of load current' thus power factor of the neutrali)e or eliminate the lagging component of load current' thus power factor of the load circuit is improved.

These capacitors are installed in +icinity of large inductive load e.g Induction motors and transformers etc( and improve the load circuit power factor to improve the system or 

devises efficiency.

Suppose(here is a single phase inductive load which is ta#ing lagging current $I' and the load power factor is Cos, as shown in fig-1.

In fig-2( a Capacitor $C' has een connected in parallel with load. /ow a current $Ic' is flowing through Capacitor which lead 0 from the supply voltage $ /ote that Capacitor  provides leading Current i.e.( In a pure capacitive circuit( Current leading 0 from the supply +oltage( in other words( +oltage are 0 lagging from Current'. The load current is $I'. The +ectors comination of $I' and $Ic' is $I3' which is lagging from voltage at ,2 as shown in fig .

It can e seen from fig  that angle of ,2 4 ,1 i.e. angle of ,2 is less than from angle of  ,2. Therefore Cos,2 is less than from Cos,1 $Cos,25 Cos,1'. 6ence the load power  factor is improved y capacitor.

 !lso note that after the power factor improvement( the circuit current would e less than from the low power factor circuit current. !lso( efore and after the power factor  improvement( the active component of current would e same in that circuit ecause

capacitor eliminates only the re-active component of current. !lso( the  !ctive power $in "atts' would e same after and efore power factor improvement.

Advantages:

• Capacitor an# offers several advantages over other methods of power factor  improvement.

• &osses are low in static capacitors

• There is no moving part( therefore need low maintenance

• It can wor# in normal conditions $i.e. ordinary atmospheric conditions' • %o not require a foundation for installation

• They are lightweight so it is can e easy to installed Disadvantages:

• The age of static capacitor an# is less $7 8 1 years'

• "ith changing load( we have to 9/ or 9FF the capacitor an#( which causes switching surges on the system

• If the rated voltage increases( then it causes damage it • 9nce the capacitors spoiled( then repairing is costly

2.

Synchr

onous

Condenser

"hen a Synchronous motor operates at /o-&oad and over-e*ited then it3s called a synchronous Condenser. "henever a Synchronous motor is over-e*ited then it provides leading current and wor#s li#e a capacitor.

"hen a synchronous condenser is connected across supply voltage $in parallel' then it draws leading current and partially eliminates the re-active component and this way( power factor is improved. :enerally( synchronous condenser is used to improve the power factor in large industries.

Advantages:

• &ong life $almost 2; years' • 6igh <eliaility

• Step-less ad=ustment of power factor.

• /o generation of harmonics of maintenance • The faults can e removed easily

• It3s not affected y harmonics.

• <equire &ow maintenance $only periodic earing greasing is necessary' Disadvantages:

• It is e*pensive $maintenance cost is also high' and therefore mostly used y large power users.

•  !n au*iliary device has to e used for this operation ecause synchronous motor  has no self starting torque

• It produces noise

3.

Phase

Advancer

Phase advancer is a simple !C e*citer which is connected on the main shaft of the motor and operates with the motor3s rotor circuit for power factor improvement. Phase advancer is used to improve the power factor of induction motor in industries.

 !s the stator windings of induction motor ta#es lagging current 0 out of phase with +oltage( therefore the power factor of induction motor is low. If the e*citing ampere-turns are e*cited y e*ternal !C source( then there would e no effect of e*citing current on stator windings. Therefore the power factor of induction motor will e improved. This process is done y Phase advancer.

Advantages:

• &agging #+!< $<eactive component of Power or reactive power' drawn y the motor is sufficiently reduced ecause the e*citing ampere turns are supplied at slip frequency $fs'.

• The phase advancer can e easily used where the use of synchronous motors is >nacceptale

Disadvantage:

• >sing Phase advancer is not economical for motors elow 2 6.P. $aout 1;#"'

METHODS OF REACTIVE POWER SHUNT COMPENSATION

• Shunt compensation-- Hee the !e"ice is connecte! in paa##e# $ith the tansmission #ine% A shunt compensato is a#$a&s connecte! in the mi!!#e o'  the tansmission #ine ()* a#on+ $ith eithe a cuent souce, "o#ta+e souce o a capacito% It supp#ies eacti"e po$e to the s&stem% The "o#ta+e euation is +i"en as. P / 01 2 -03V456-cos789:8; Since the ea# pat o' the po$e is <, thee'oe the eacti"e po$e in the s&stem is a!!e! =& shunt compensato% Shunt-connecte! eactos ae connecte! in the s&stem to conto# the eacti"e po$e% >& consumin+ the eacti"e po$e shunt connecte! eactos !ecease the o"e "o#ta+es in the tansmission #ine% The capacitos connecte! in paa##e# $ith tansmission #ine ae a#so use! to e+u#ate the "o#ta+e #e"e# =& conto##in+ the eacti"e po$e to the tansmission #ine% Fi+ue 6. Tansmission #ine $ith shunt compensation

Fi+ue 6. Tansmission #ine $ith shunt compensation

• Seies compensation Hee a !e"ice

is connecte! in seies $ith the tansmission #ine(?* Thus it is ca##e! a seies compensato% Thee ae t$o mo!es o' opeation @ capaciti"e mo!e o' opeation an! in!ucti"e mo!e o' opeation% A simp#ie! mo!e# o' a tansmission s&stem $ith seies compensation is sho$n in Fi+ue 9 %The "o#ta+e ma+nitu!es o' the t$o =uses ae assume! eua# as V, an! the phase an+#e =et$een them is B%

Fi+ue 9. Tansmission #ine $ith seies compensation

• Static VAR compensatos A static VAR compensato 5o SVC: is set o' 

e#ectica# !e"ices 'o po"i!in+ 'ast-actin+ eacti"e po$e on tansmission net$os (66*% The SVCs ae pat o' e;i=#e AC tansmission s&stem !e"ice 'ami#& e+u#atin+ "o#ta+e, po$e 'acto, hamonics an! sta=i#iin+ the s&stem%

SVC is a shunt connecte! static VAR +eneato o a=so=e $hose output is a!0uste! to e;chan+e capaciti"e o in!ucti"e cuent so as to maintain o conto# specic paametes o' the e#ectica# po$e s&stem%SVC is =ase! on th&istos $ithout +ate tun-o capa=i#it&% The opeatin+ chaacteistics o'  th&istos sho$s "aia=#e eacti"e impe!ance o' SVC% It inc#u!es 9 main components an! thei com=inations ae- 6: Th&isto conto##e! an! th&isto s$itche! eacto 5 TCR G TSR: 9: Th&isto s$itche! capacito5TSC: When TSC is s$itche! on the eacti"e po$e in SVC inceases% This in!icates that SVC supp#ies eacti"e po$e to the AC po$e souce% Simi#a#& $hen TCR in+ an+#e is !ecease! eacti"e po$e in SVC inceases% This in!icates that SVC a=so=s moe an! moe eacti"e po$e 'om AC po$e souce%

Fi+ue . Th&isto s$itche! eacto

• Se#' commutate! VAR compensato The& contain s$itche! "a#"e !e"ices such

as TOs5ate tun-o th&isto:G I>Ts5Insu#ate! ate >ipo#a  Tansistos:%Static s&nchonous compensatos, unie! po$e o$ conto##es etc% opeate on the pincip#e o' se#' commutate! VAR compensato% The& can +eneate o a=so= eacti"e po$e as pe euiement in the s&stem%

• Static S&nchonous Compensato5STATCOM: It is a mem=e o' FACTS 'ami#& o' 

!e"ices% It is a e+u#atin+ !e"ice use! on a#tenatin+ cuent e#ecticit& tansmission net$o% It is =ase! on po$e e#ectonics "o#a+e souce con"ete an! can act as eithe a souce o sin o' eacti"e AC po$e to an e#ecticit& net$o% A STATCOM is a "o#ta+e souce con"ete5VSC: =ase! !e"ice $ith the "o#ta+e souce =ehin! a eacto% The "o#ta+e souce is ceate! 'om a DC capacito% The eacti"e po$e at the temina#s o' the STATCOM !epen!s upon amp#itu!e o' "o#ta+e souce% Fo e;amp#e i' the

temina# "o#ta+e o' VSC is hi+he than AC "o#ta+e at the point o' connection the STATCOM +eneates eacti"e cuent con"ese#& $hen temina# "o#ta+e o'  VSC is #o$e than AC "o#ta+e it a=so=s eacti"e po$e%

Fi+ue 3. VI chaacteistics o' SVC an! STATCOM

• S&nchonous Con!ense It is a s&nchonous machine $hich uns

$ithout pime mo"e o a mechanica# #oa! an! connecte! to impo"e the po$e 'acto o' the e#ectica# s&stem%I' the e#! e;citation o'  s&nchonous con!ense is conto##e! it can +eneate o a=so= eacti"e po$e% When the& ae o"e-e;cite! the& supp#& eacti"e po$e an! $hen un!e-e;cite! the& a=so= eacti"e po$e% When the eacti"e po$e is supp#ie! =& s&nchonous con!ense cuent in the s&stem is e!uce!% Thus the #osses +et !ecease! an! it po"i!es a =ette eJcienc&% Due to this #a+e amount o' po$e can =e !e#i"ee! to the #oa!%