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INTELIGENT LOADSHEDDING(ILS)A N E F F E C T IV E A P P R O A C H T O LO A D
S H E D D IN G
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INTRODUCTION
Load shedding is a process in whicha suitable amount load is thrownoff in order to maintain system
stability during over loadedcondition
Generation- load unbalance problems
Load shedding in industrial units
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Problems of frequency decay
Frequency is propotional to speed
Gas turbines are sensitive to frequency
Low frequency problem with thermal
power plants Frequency decay affects quality of
industrial products
Frequency below 49.5Hz make s/munstable
Is load shedding necessary
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Breaker interlock loadshedding
Load sheddingbased on hard-wire signal
&circuit-breakers Fast load shedding
Load sheddingbased on worstcase scenario
Only one stageload shedding
Excessive loadshedding
Modificationcostlier
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Under frequency relay loadshedding
Used to drop loadautomatically inaccordance withthe pre
determinedschedule
Fixed load reductionat fixed frequencylevel
Upon reaching theset point &pre-specified timedelay the relaytrips load breakers
Cycle repeats until
Slow responsetime
Incorrect orexcessive loadshedding
Analysis knowledgeis lost
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PLC based load shedding
Load sheddingbased on Loadvsnum ofgeneratoronline orunder frequencydetection
Shed a preset
sequence ofload
Use of distributedn/w via power
managements/m
Monitoring ofpower s/m islimited to portionof n/w
s/m wide operatingcondition ismissing fromdecision makingprocess result inincorrect loadshedding
Priority load list
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INTELLIGENT LOADSHEDDING
Requirements of ILS s/m1.Pre-disturbance operating conditions
2.post-disturbance operatingconditions3.Nature and duration of disturbance
4.s/m transient response to adisturbance
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ILS block diagram
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Functions of blocks
Knowledgebase-possess s/m dynamicbehavior
Advanced Monitoring
Network Models Trigger List
Load Shed Optimizer- computes optimal
load shedding tables corresponding to system
changes.
Distributed Controls -utilize PLCs to
rapidly execute the load shedding
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, W ith th e a rch ite ctu re d e scrib e d a b o v e a nILS
sch e m e p ro v id e s th e fo llo w in g b e n e fits:
- ,Tim e v a ria n t lo a d sh e d d in g ta b le s w h ichre fle ct
,tru e sta tu s a n d lo a d in g co n d itio n s fo r th e
.sh e d d a b le lo a d s
O p tim a l co m b in a tio n o f sh e d d a b le lo a d s to.m a x im ize lo a d p re se rv a tio n
(Fa st re sp o n se to d istu rb a n ce trig g e rs le ssthan
).1 0 0 m s in m o st case s
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O n e lin e d ia g ra m o f o il re fin e ry
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T h e in te rn a l e le ctrica l n e tw o rk su p p lie s a to ta llo a d
,o f a b o u t 4 5 M W a n d is con stitu te d b y th e:fo llo w in g
S u b sta tio n in te rco n n e ctin g th e in te rn a le le ctrica l
, -syste m to th e p o w er g rid b y tw o th re e w in d in g. / . ,tra n sfo rm e rs 3 4 5 1 3 8 kV ra te d a t 2 0 M V A
.su p p ly in g th re e m a in sw itch b o a rd s
In te rn a l d istrib u tio n syste m o p e ra tin g a t 6 0h e rtz
,o rg a n ize d in to m a in d istrib u tio n sw itch b o a rd s. . ,ra te d a t 1 3 8 kV a n d 4 1 6 kV w h ich su p p lies
/la rg e M V m o to rs a n d o r d istrib u tio n fe e d e rs a sw e ll a s se ve ra l lo w v o lta g e d istrib u tio n
.sw itch b o a rd s To ta lg e n e ra tio n o f 1 5 M W o b ta in e d fro m o n e
( ).g en erator G en set C T h e p la n t is n o rm a lly im p o rtin g 2 3 M W fro m th e
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H a rd w a re co n fig u ra tio n o f P LC/b a se d S m
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TABLE ISHEDDABLE LOAD PRIORITY LIST
Load ShedPriority Load ID
MW Shed- ( )1 Aux B Pump
.1 20( % )MCC24AB 30 Load
.2 55( )Aux A Pump
.2 00( % )MCC24AB 30 Load
.2 55#Desalter 1
.4 25#2 Distillation Unit 1
.3 40#Distillation Unit 3
.2 55#Desalter 2
.4 25( % )3 MCC24AB 40 Load
.4 25#Distillation Unit 5
.2 55 Total Load Shed
.29 55
Frequency response
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ILS communication architecture
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TABLE IILOADS SHED BY ILS SCHEMELoad Shed
Priority Load ID MW Shed
- ( )1 Aux B Pump.1 20( )MCC24AB LV Motors 1
.2 55 ( )Aux A Pump.2 00( )MCC24AB LV Motors
.2 55
#Desalter 1.4 25 2 Distillation
# .Unit 1 3 40 Distillation Unit
# .3 2 55
#3 Desalter 2
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conclusion
ILS is better than any of theconventional load shedding scheme
ILS is essential for indusrialapplication
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