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INTELIGENT LOADSHEDDING(ILS) A N E F FE 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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Conventional load sheddingschems
1.Breaker interlock load shedding
2.Under frequecy relay load shedding
3.PLC based load shedding
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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 of generatoronline orunder frequencydetection
• Shed a preset
sequence of load
• Use of distributedn/w via power
managements/m
• Monitoring of power 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 n
ILS
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 ich
re 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 ss
than
).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 l
lo 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 0
h 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 s w 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 I SHEDDABLE LOAD PRIORITY LIST
Load Shed Priority 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 II LOADS SHED BY ILS SCHEME Load 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