Isochronous vs Droop_mode

1.

Great explanation on isochronous vs droop

Original thread : http://www.control.com/thread/1026221805 Whenever two governors are in Isoch mode (withot some !ind o" Isoch #oad $haring scheme% the& will '"ight each other to control the "re)enc&. *hat+s *hat+s their natre, and the&+re not disposed to sharing the load. -ach governor wants to control "re)enc& and so each will respond to an& change in "re)enc& (which reslts "rom a change in load, s&stem load%. n Isochronos #oad $haring scheme will allow the two nits to 'split or 'share the load etween them depending on how the scheme/controller is programmed. It will allow more than one governor to e operated in Isoch mode and will redce and  possil& even eliminate "re)enc& swings as a reslt o" load changes. Whether Whether or not two governors need to e operated simltaneosl& in Isoch mode is a "nction o" man& "actors, and to cover all the possiilities wold ta!e the e)ivalent o" several chapters in a tetoo!. Imagine two people riding on a tandem ic&cle, each with pedals to contrite to the tor)e re)ired to move the ic&cle and an& load the& might e carr&ing. Imagine the& have to maintain a constant speed (which in an  s&stem speed is directl&  proportional to "re)enc&%. *he *he two riders are each prime movers providing tor)e to the ic&cle, st as trines provide tor)e to generators. It ta!es a certain amont o" tor)e to maintain a certain speed (on a "lat and level road% when there is no load on the ic&cle (pac!ages, etc.% and more tor)e to maintain that same speed when there are pac!ages and possil& a passenger on that same "lat and level road. #et+s "rther sa& that the nmer and weight o" the pac!ages can e variale, that the& can e dropped o"" the ic&cle and added to the ic&cle at random times and intervals while the ic&cle is moving, meaning that the tor)e re)ired to maintain a constant speed is going to change as the nmer o" pac!ages and the weight o" the pac!ages change. I" oth riders are each wor!ing to independentl& control the speed o" the ic&cle as the load changes, it+s ver& li!el& that the speed o" the ic&cle won+t e ver& constant. I" the& oth appl& more tor)e as a pac!age or pac!ages are added to the ic&cle the speed might increase aove the desired rate, and i" the& oth decrease their tor)e at the same time to slow the i!e down then the speed might decrease elow the desired rate. 3t, i" the& decided that one rider will pedal with a "airl& constant tor)e and the other  rider will var& his tor)e otpt to maintain the desired speed as the nmer and weight o" the pac!ages changes, then it+s more li!el& that the speed o" the ic&cle (and it+s load% will remain "airl& constant.

We+ll call the rider who+s maintaining a relativel& constant tor)e '4roop and the rider who+s var&ing his otpt as a "nction o" load 'Isoch. #et+s sa& that 4roop is sppl&ing a constant tor)e to the pedals e)al to 50 o" his ailit& while the ic&cle is moving and pac!ages o" var&ing weight are eing dropped o"" and pic!ed p. *his means that Isoch+s otpt is var&ing as necessar& to maintain the desired speed as the load on the ic&cle is changing. 3*, i" the load eceeds Isoch+s ailit& to prodce tor)e, then the speed o" the ic&cle will slow down,  ecase 4roop is onl& ptting ot 50 o" his otpt. $o, Isoch can as! 4roop to increase his tor)e to help get the ic&cle ac! to desired speed. nd in so doing, as 4roop increases his tor)e the amont o" tor)e that Isoch is prodcing will e decreased as the desired speed is reached. 4roop shold increase his tor)e otpt sch that an& anticipated load increase can e handled & Isoch so that the speed will remain constant as epected load changes occr.  7ow let+s sa& that the load on the ic&cle has dropped signi"icantl& (a lot o" the  pac!ages have een dropped o"" the i!e%, and the amont o" tor)e that Isoch has to  provide is down to near ero (he+s st 'coasting% to maintain the desired speed. I" even more pac!ages are removed "rom the i!e, then the speed will start to increase. nd, so 4roop will have to decrease his tor)e otpt to redce the speed o" the  ic&cle. 4roop shold redce his tor)e otpt sch that Isoch has to increase his tor)e otpt aove that re)ired "or the loss o" an& additional pac!ages in order to maintain the desired speed.  generators (alternators% with prime movers are identical to this eample. *he& have to operate at a constant speed ("re)enc&% and the& have to var& their tor)e otpt in order to control speed ("re)enc&% when load is changing when the& are  eing operated 'o""9grid, or in 'island mode. 3t, i" two governors are oth tr&ing to control the speed ("re)enc&% the& will generall& "ight each other which will case the "re)enc& to e nstale, and the loads on the two generators to e nstale. We have no wa& o" !nowing what the load is when the two nits are separated "rom the grid. #et+s presme the two nits are rnning at 10 W and 20 W in parallel with the tilit&. nd sddenl&, the tie rea!er opens, and the ' island load drops to 12 W. #et+s "rther presme that one (onl& one% o" the 505- controllers will switch to Isoch mode when the tie rea!er opens, and let+s sa& it+s the nit rnning at 20 W (which we+ll call '3ig%. $o, when the tie rea!er opens 3ig will switch to Isoch mode and the other nit (we+ll call it '#ittle% sta&s in 4roop control mode. 3ecase the power otpt o" the two nits at the instant the tie rea!er opens eceeds that re)ired "or the 'island load, the "re)enc& will start to increase ver& )ic!l&, and 3ig will redce it+s load (hope"ll& ver& )ic!l&;% to aot 2 W, which in comination with the load on #ittle (10 W% shold reslt in a stale "re)enc&. (What will reall& happen is that the "re)enc& will increase and #ittle+s load shold decrease ecase o" 4roop action and as 3ig+s load comes down #ittle+s load will increase ac! to 10 W as "re)enc& retrns to normal.%
control also has to redce "iring rate prett& )ic!l& to tr& to help redce steam pressre  ecase o" the redced steam "low to 3ig.% 3ig, eing the Isoch nit, will now respond to an& load changes in the 'island load. (*his presmes #ittle is in 'straight 4roop speed control with no load setpoint.% it will actall& ma!e the "re)enc& prolem worse, ecase instead o" changing it+s otpt to help maintain the "re)enc& se tpoint & increasing or decreasing load as necssar&, it will & tr&ing to !eep its load constant which will ma!e the "re)enc& prolem worse. I" &o want to operate oth nits in Isoch mode (and there ma& e compelling reasons to do that, we don+t and can+t !now that "rom the in"ormation &o have provided% &o shold seriosl& consider investing in an Isoch #oad $haring modle. 3t, it sholdn+t  e necessar&, nless &or operators can+t respond to load changes and adst the otpt o" #ittle to !eep 3ig in a range o" otpt that wold allow it to control "re)enc& as load changes. $team trines don+t generall& ma!e great Isoch machines, ecase the "iring rate o" the oiler can+t sall& e changed ver& )ic!l& i" load changes )ic!l&. It+s not that the& can+t e tned to e good Isoch nits, it+s st that it sall& ta!es tning o" oth the governor and the oiler control to achieve smooth "re)enc& control, and then onl& "or epected load changes. I" the load changes mch more than epected "or some reason, then the& generall& won+t respond as )ic!l& as necessar&. =osted 2 &ears ago

Ingat 5 =er!ara $eelm 5 =er!ara. $ihat $eelm $a!it. da $eelm *a. #apang $eelm $i!. ?a&a $eelm is!in.
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