reactive power and increase gen capacity

8/13/2019 Reactive Power and Increase Gen Capacity

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from the Power department...Reactive Power

Posted by khan on 19 July, 2010 !"#0 amReal power of $enerator depends upon power input. when load on a $enerator increases,stator current increases. %ue to counter emf the speed is reduced which is a$ain attained

by openin$ of the fuel valve. %ue to increase in current terminal volta$e drops which arecorrected by increasin$ e&citation current. 'uestion is that the reactive load also re(uirecurrent due to which counter emf would increase then why only e&citation current isincreased to meet the )*R+ demand -as reactive power no effect on power inputReply to this post...

Posted by +* on 20 July, 2010 /"20 pm

like to always refer to the reactive capability curve provided with a synchronous$enerator. his curve represents the limits of operation of a particular $enerator, and inmy estimation, is useful in describin$ how the ener$y input to the $enerator can be splitor divided.

*s we all know, * power systems with real and reactive components can be representedwith a ri$ht trian$le. 3ne le$ of the trian$le represents watts4 the other side of the ri$htan$le represents )*rs4 and the hypotenuse represent the total ener$y, )*.

f the e&citation is sufficient to keep the $enerator terminal volta$e e(ual to the volta$e ofthe electrical system with which the $enerator is synchroni5ed to, then there is no reactivecomponent 6)*rs7 at the $enerator. *ll of the power, )*, is $oin$ out as watts, and noneas )*rs.

f e&citation is increased, which would try to increase the $enerator terminal volta$eabove the volta$e of the electrical system with which the $enerator is synchroni5ed, thenla$$in$ )*rs will be present at the $enerator terminal. f the tor(ue bein$ input to the$enerator are held constant as e&citation is varied, then the amount of watts will decreaseas the amount of )*rs increases in the la$$in$ direction as e&citation is increased.

he )* 6hypotenuse7 of the power trian$le isn8t chan$in$4 ust the division of ener$y between real and reactive components. +o, as the an$le of the hypotenuse increases above0 de$rees, if the len$th of the hypotenuse 6the total ener$y input to the $enerator7 remainsthe same, the len$th of the ad acent side of the power trian$le decreases, which means thereal power output 6watts7 decreases.

:ow, how all of that is affected, or not, by counter emf is unknown to me. ounter emfhas never been monitored on any synchronous $enerator have ever seen operatin$, evenones in the lab at university. t8s always a theoretical parameter, which is the domain of$enerator desi$ners and manufacturers.
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, as a technician, have to believe that any and all effects of emf and counter emf and back emf and air $ap and conductor si5in$ and conductor spacin$ and twists per turn andall of those thin$s which can8t be chan$ed durin$ operation were all properly accountedfor by the $enerator desi$ners and manufacturers and anyone choosin$ an e&citation

system 6*)R, *utomatic )olta$e Re$ulator7.

don8t know if increasin$ e&citation to chan$e the )*r component of the power trian$leactually chan$es the tor(ue input to the $enerator or not. know it doesn8t chan$e theener$y flow rate bein$ admitted to the prime mover. ;ut, also know it does have aneffect on the total power output of the $enerator.

3ne last thin$ about the reactive component of electrical power. our use of this site is sub ect to the terms and conditions set forth under ?e$al :otices

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from the *utomation ?ist department...What makes a generator increase load

Posted by kumarash on 10 *u$ust, 200! C"D9 pmf a $enerator is runnin$ at 100B< of a $as turbine rated 120B< and a command is

issued from Bark ) to increase load to 120B


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Posted by +* on 12 *u$ust, 200! 1"01 amsn8t it obvious t does so because it is commanded to do so, you said so yourself. *ll

$ood $enerators do as commanded, don8t they

+eriously, thou$h, and in as few words as possible, when an operator clicks on Raise+pdE?d or increases the Pre +elected ?oad ontrol setpoint when the unit is bein$operated in Pre +elected ?oad ontrol mode the fuel flow rate into the turbine isincreased, which increases the tor(ue bein$ produced by the turbine, which the $eneratorconverts to amps, which results in an increase in load.

For the e&act details of what8s happenin$, read on.

f one wants to make somethin$ spin, one needs to supply some force to it. hat force isusually referred to as tor(ue. he more tor(ue applied to somethin$, the faster it willusually spin. %ecrease the tor(ue applied to somethin$, and it will usually slow down.

* $as turbine is a device that produces tor(ue, and the amount of tor(ue bein$ producedcan be varied, and is in direct proportion 6usually7 to the amount of fuel bein$ burned inthe combustor6s7 of the $as turbine. ncrease the fuel flow rate, and the amount of tor(ue

bein$ produced by the turbine will increase. %ecrease the fuel flow rate, and the amountof tor(ue bein$ produced by the turbine will decrease.

he $enerator 6more correctly called an alternator7 used with GH desi$n heavy duty $asturbines is a synchronous $enerator. t is the nature of synchronous $enerators bein$operated in parallel with other synchronous $enerators on an * $rid to supply a loadwhich is much $reater than any sin$le $enerator that they will all be runnin$ at the samespeed, and no sin$le $enerator and its prime mover 6the $as turbine in your case7 canoperate at speeds hi$her or lower than the other $enerators with which is it connected,

because they are synchronous $enerators 6alternators7.

here is a formula that describes the relationship between the fre(uency of an * systemand the speed and type of synchronous $enerators connected to the system" F I 6P

:7E120, where F is the fre(uency 6in -ert57 of the $rid, P is the number of poles of the$enerators 6an even number never less than two, and the number of poles of any$enerator is usually fi&ed and can8t be chan$ed while the $enerator is runnin$7, and : isthe speed of the $enerator rotor, usually the field 6in RPB7. he 6synchronous7 $eneratorsused with Frame 9H GH desi$n heavy duty $as turbines are two pole $enerators and aredirectly connected to the turbines 6i.e., there is no reduction $ear between the turbine andthe $enerator, and the $enerator is not connected to a free turbine which spinsindependently of the a&ial compressor of the turbine7, so that8s why the 100K speedratin$ of the turbine is C000 RPB because the $rid the $enerator is connected to is a #0-5 system 6nominally7. 6:ote there are no appro&imations in this formula, and note thatspeed and fre(uency are directly proportional. ncrease the speed of a synchronous$enerator and it8s fre(uency will increase4 decrease the fre(uency of a $rid to which a$enerator is connected and the $enerator speed will decrease proportionally4 speed and


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fre(uency are directly related.

+o, we8ve established that when a two pole 6synchronous7 $enerator is connected to a #0-5 $rid with other $enerators that it will be operatin$ at C000 RPB 6: I 6120 #07E2 IC000 RPB7, and when the prime mover 6the turbine7 is directly coupled to the $enerator

that it, too, will spin at C000 RPB. *$ain, this is because the $enerator rotor is lockedinto the same speed 6in synchronism with7 the other $enerators at a speed that is dictated by the fre(uency of the $rid and the number of poles of the $enerator 6which neverchan$es7, and the turbine shaft is directly connectedEcoupled to the $enerator rotor.

Further, it is the nature of most * $rids that there are so many $enerators, of variousnumber of poles, so many all supplyin$ such a lar$e load that any one sin$le $eneratorand its prime mover can8t usually have any appreciable effect on the fre(uency of all theother $enerators and the speeds of their prime movers 6unless the prime mover bein$loaded or unloaded has a very lar$e power ratin$Ecapacity in relation to all the other$enerators and the load7.


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I ) 6CL60.#77 PF, where, CL60.#7 is the s(uare root of three 6a fi&ed value, 1.MC2, think7, and PF is the power factor of the $enerator 6which is a number never $reater than1.0, and which we will presume to be 1.0 for the purposes of our discussion7.

oincidentally, the terminal volta$e of most synchronous $enerators is almost a fi&edvalue, as well, and doesn8t usually vary by more than appro&imately NE #.0K, which on

an 11,0000 )olt $enerator is only about ##0 )olts 6out of 11,0007.

+o, since one of the terms of the three phase power formula is a fi&ed value 6the s(uareroot of three7, and we are presumin$ one of the terms 6PF7 to be fi&ed and e(ual to 1.0,and the $enerator terminal volta$e is, for all intents and purposes, a fi&ed value, the waythat a $enerator produces more power is to increase the number of amps flowin$ in thestator. he way that amps are increased in the $enerator stator is by providin$ moretor(ue from the turbine into the $enerator4 more tor(ue e(uals more amps. ?ess tor(uee(uals less amps. 6


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n turbine leadin$ mode, turbine8s controller is controllin$ power output by ad ustin$control valves. hat, inevitably, leads to steam8s pressure chan$in$. n such case, boilercontroller is increasin$ or decreasin$ coal feeders speed. Bore speed means more coal inthe boiler. Bore coal in the boiler means more heat, more heat means hi$her pressure 6ormore steam= =7.

*m on the ri$ht track

hanks.Reply to this post...

Posted by electrics on 12 June, 2009 2"0# pm-ello,

ponder on this issue for a lon$ time, there are a few (uestions if you allow me to ask sir.

now, if we increase the load of a syn. $enerator while opeatin$ under normal conditionsand doesn8t increase the fuel so what happens i think if we don8t increase the fuel any sothe $enerator will be$in to slow and it will stop till the kinetic ener$y of the primemoverand alternator is consumed totally and the $enerator will have so bi$ currents true butthis is ust a amateurish $uess pls tell me what happens if fre(uency controller doesntintervene with the load incrase in theory now the load is not e(ual the power bein$

produced so what happens this is my first (uestion.

my second (uestion is, they always say that the $enerator speed $ets slower if loadincreases, so this is a matter rea$rdin$ fre(uency controller or the nature of a sync.$enerator

he mechanical source of power for the $enerator is a prime mover such as dieselen$ines or steam, $as, water, and wind turbines. *ll prime movers behave in a similarfashion. *s the power drawn from them increases, the rotational speed decreases. n$eneral, this decrease in speed is nonlinear. -owever, the $overnor makes this decreasein speed linear with increasin$ power demand. for e&ample this is a passa$e from a

book, so pls tell me how can a sync. $en can $et slower as load increases what makes itto slow down

also wanna ask you as third (uestion, a diesel $enerator has a sli$htly hi$her fre(uencythan #0 h5 while workin$ no load true so does it make difference between workin$

alone and workin$ in synchronisation with an infinite $rid if true why need to be a bithi$her than #0

pls en$lihten me sir...Reply to this post...

Posted by HnricO $n on 12 *u$ust, 200! 2"CD am
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n essence, you are increasin$ the tor(ue applied on the $enerator shaft 6power, but speedis constant7 *nd this increases the an$le between Ho 6induced volta$e in stator7 and thevolta$e at output terminals 6theoretical A and f, constants, and connected to an infinite

power net7. his an$le is tor(ue dependant 6called tor(ue an$le7 more an$le more power delivered more power drained from drivin$ machine. f the $enerator is workin$

as a motor, this an$le is ne$ative. f the machine is under no load condition 6open circuit7this an$le is 0.Reply to this post...

Posted by QushwahaOrOk on 2M 3ctober, 200! D"12 pmt8s true that more fuel to prime mover increases the tor(ue, which increases the load

an$le in the $enerator. t8s also true that ma$netic field stren$th of rotor increases as loadan$le increases, which causes to increase the current throu$h stator windin$s thus theB


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+o, one does not usually chan$e the load 6B


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rotatin$ clock wise in the Fast direction7.


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;est Re$ards++)Reply to this post...

Posted by ;ruce %urdle on C1 Barch, 2010 C"0# pm

By basic mechanics te&t says that tor(ue I Force & radius of action. *nd increasin$drive tor(ue will increase the an$ular displacement by which the rotor field leads thestator field up to 90 de$rees or so.

;ruce.Reply to this post...

Posted by Jesus +antos on 12 *u$ust, 200! 2"C/ am


12/13

Reply to this post...

Posted by Gre$ : on 29 June, 2010 !"DC pm have the same (uestion, but what if the $enerator is only rated for 100B

reactive power and increase gen capacity

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