aptd- tcbr.docx

8/18/2019 APTD- TCBR.docx

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The "est location or a TCBR is near a generator that would need "raking during transient insta"ilityconditions.Transor$er tertiary at or near the generator "us would "e desira"le.

The three !hase legs $ay "e connected in wye or delta, although delta connection would "e $orecon%enient since the ground !ath would not "e needed.


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e is electric !ower ro$ the generator reuiring a rotor-stator angle (!ower angle) . t steady state, the

$echanical in!ut !ower $ . is eual to the electrical !ower, neglecting losses. hen a ault occurs on a line,the electrical out!ut is greatly decreased during the ault and $ay e%en reach #ero or a ault close to thegenerator. ssu$ing that the $echanical !ower re$ains constant during the irst transient swing, the

electric !ower during the ault dro!s to !/0, #nd the e1cess $echanical !ower 2 - a (shaded area) "egins

to accelerate the tur"ine generator. s the $achine s!eed increases, the rotor-stator angle also increases. Theangle increases to d# at the instant o ault clearing. Following the ault clearing, including re$o%al o theaulted line, the electric !ower is restored through alternate trans$ission !aths. The !ower angle ollows a newlower cur%e o 6, deter$ined "y the new %alue o ElE#l 3, which is lower "ecause o increased i$!edance"etween the generator and the re$ote syste$.

Following the ault clearing, the electrical !ower e1ceeds the $echanical !ower "ecause o the increase in the

!ower angle. s a conseuence o the e1cess electrical !ower, the generator starts to decelerate. hen the!ost-ault shaded area o the e1cess electrical energy euals the !re-ault shaded area o e1cess $echanical

energy, the $achine angle reaches its transient $a1i$u$ 4 and its s!eed euals the synchronous

s!eed. The rotor then starts to turn "ack, accelerate and the angle decreases. 5 the e1cess electrical energy

ollowing the ault did not eual the e1cess $echanical energy, it would "e too late and the angle would takeo (continue to increase). The generator connection to the syste$ would "e se%ered "y the !rotecti%e $eans inorder to sa%e the generator and the syste$ ro$ high o%er-current. This also $eans that adeuate $arginhas to "e a%aila"le or o!eration during the steady state o!eration, so that the generator does not all out o ste! as a result o the $ost se%ere ault.

&uring the ault the resistor !ower, though s$all, hel!s to decrease the accelerating !ower and ater the ault

clearing it is $uch $ore eecti%e in increasing the decelerating !ower. The $a1i$u$ angle i in now s$aller than the case without the TCBR. E1tra $argin a%aila"le de!ends on the !ower rating o the TCBR and itis not hard to i$agine that this $ay "e the $ost cost-eecti%e and si$!lest way to enhance transient

sta"ility, i it ha!!ens to "e the li$iting criteria or the generated !ower.

By Speed Deviation


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The resistor is switched on when the iltered s!eed de%iation ro o a !articular oscillation to "e da$!ed is

!ositi%e, and the TCBR is switched o when the s!eed de%iation is negati%e.

*ince the resistor only consu$es !ower and does not su!!ly !ower, it hel!s to ser%e as a "rake when thes!eed is higher than nor$al "ut cannot hel! to counter increase in s!eed when the s!eed is lower thannor$al. This is not a deiciency "ut rather is an o!erating eature o this Controller.

+nce the generator is drawn "ack with the hel! o the TCBR ro$ the irst transient acceleration, the

TCBR will also eecti%ely assist in ra!id da$!ing o the dyna$ic oscillations.

5 the o"ecti%e is to control !ower syste$ swing oscillations, the s!eed de%iation deri%ed ro$ the tur"ine-

generator !lant can "e iltered through a low-!ass ilter to deri%e the low-reuency signal or controlling

the low-reuency oscillations.

i the o"ecti%e o a TCBR is to control the su"synchronous torues, whether to counter the i$!act o seriesca!acitor co$!ensation or to utili#e high-s!eed reclosing without high-torsional torues on the shatsyste$, the s!eed de%iation signal can "e lltered through a high-!ass ilter designed to o"tain signal or the entire su"synchronous s!eed de%iation.

For the co$!osite su"synchronous s!eed de%iation, the on-o seuence o the TCBR is shown "y Figure9.9(d). This strategy results in shorter TCBR load !ulses corres!onding to the su"synchronous oscillations.

Figure 9.9(c) shows the load !ulses corres!onding to the unlltered s!eed de%iation in!ut.

The !reerred a!!roach would "e to irst sa%e the tur"ine-generator ro$ the irst transient swing and

then switch to assisting da$!ing o the su"synchronous oscillations.

The s!eed de%iation signal is essential to the correct e1!loitation o the TCBR. This can "e o"tained ro$

a%aila"le $easure$ent techniues o directly $easuring the s!eed de%iation o the tur"ine-generator shat.

7owe%er, it is uite easi"le to deri%e such a signal ro$ the generator out!ut %oltage or the %oltage at theTCBR location.


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t h e f u n c t i o n o f T C B R t o d a m p s u bs y n c h r o n o u s o s c i l l a t i o n s

it is i$!ortant to a!!reciate the nature o load switching "y thyristor switches.

TCBR $ay "e "ased on thyristors switched hal-cycle "y hal-cycle without iringangle control. 8i%en a three-!hase TCBR, it in%ol%es si1 actions o !ower change !er cycle.

5t is seen that "ecause a thyristor will turn o only when itscurrent reaches #ero,the TCBR conduction will last or a"out a hal-cycle longer withdecreasing !ower during that e1tended !eriod "eyond ti$e ts. This is o no signiicance

when the o"ecti%e is to da$! !ower syste$ swings o low reuency, "ecause theturn-on ti$e would "e relati%ely %ery long. 7owe%er, i the reuired !ulses are short.it would lead to less than o!ti$u$ use o TCBR or da$!ing higher su"synchronousreuency torues.

+ne a!!roach to o!ti$u$ use o TCBR would "e to select the !ulsewidth to "e so$ewhat less than the hal-cycle !eriod o the indi%idual s!eed de%iation reuency to "e da$!ed.

8i%en that the thyristors are already there, additional cost o thyristor switches$ay result ro$ higher switching losses, "ut gi%en the short ti$e duty this cost should

not "e signiicant. ith turn-on control the load current can "e controlled as shown"y the wa%eor$s or the 9 degree delay and 0 degree delay in Figure 9.("), or the sa$e turn on ti$e ls as or the thyristor-switched resistor.


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Turn-on angle control will "e useul or reducing the da$!ing and the dissi!ation in resistors when theoscillation $agnitude is low.

Considering the transient and dyna$ic reuire$ent o a ty!ical syste$, a TCBRrating would generally ha%e high :;:7rs ratio. For e1a$!le, : rating $ay

"e -0 : or a : !ower !lant, and its energy duty reuire$ent !er

e%ent would "e in the range o -0 :< or a series-co$!ensated line. 5 the dutyreuired includes su!!ressing the irst transient swing and low-reuency dyna$ics,

the : reuire$ent $ay "e in the range o =-4>o o the generator rating or se%eral seconds. +n the other hand, i there is no series ca!acitor co$!ensation, andthe o"ecti%e is to only acilitate high-s!eed reclosing and synchroni#ing, then the :

reuire$ent $ay "e only *>o o the generator rating or .?-. second. 5t is uitereasona"le to consider s$all continuous duty as well, say a ew !ercent o the TCBRrating to da$! s$all signal low-reuency and su"synchronous oscillations.

aptd- tcbr.docx

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