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EE 104 LECTURE 1 FUNDAMENTAL PRINCIPLES OF

POWER SYSTEM PROTECTION

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Fundamental Principles

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Outlin1! A"n#$%&liti' in P#($ S)'t%'

2! I''u'* Pu$+#' &n, Fun-ti#n' #. P#($

S)'t% P$#t-ti#n

3! D'in C$it$i& .#$ P$#t-ti#n S)'t%

4! P$in-i+l' #. #n' #. P$#t-ti#n

! P$in-i+l' #. P$i%&$) &n, &-u+ P$#t-ti#n

6! Mt5#,' #. Di'-$i%in&ti#n

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Abnormalities in Power System

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Overcurrent

3

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Abnormalities in Power System

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OvercurrentSources of Overcurrent

Overload

O+$&ti#n #. E7ui+%nt/C#n,u-t#$ in 8-'' n#$%&l .ull l#&, 9$&t,:

-&+&-it) (5i-5 (5n it +$'i't' .#$ & 'u..i-int lnt5 #. ti%* (#ul, -&u',&%& #$ ,&n$#u' 5&tin

Shunt Faults (Short Circuits and round Faults!

W5n & +5&' -#n,u-t#$ t#u-5' &n#t5$ +5&' -#n,u-t#$ &n,/#$ t5

$#un, -&u'in 8-''i; -u$$nt &n, $7ui$' i%%,i&t int$$u+ti#n #.

t5 -i$-uit

Series Faults (Open Circuits!

W5n #n #$ t(# +5&' -#n,u-t#$' #+n, -&u'in 8-''i; un"&l&n-

-u$$nt &n, $7ui$' i%%,i&t int$$u+ti#n #. t5 -i$-uit

"

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Abnormalities in Power System

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Overcurrent

Protection #ethods

Protective devices that can sense overcurrents and

isolate faulted circuits Fuses

Circuit brea$ers (and protective relays!

%eclosers and sectionali&ers

'

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Abnormalities in Power System

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round PotentialSources of round Potential

round faults throuh an unrounded e)uipment

*ouch potentials Step potentials

Protection #ethods

System roundin +)uipment roundin

,

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Abnormalities in Power System

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Sure .oltae

Sources of Sure .oltaes

/ihtnin stro$es

Switchin sures Switchin in a lon line or

cable

Capacitor switchin

0nductive current choppin

Currentlimitin fuseoperation

Ferroresonance

armonics

Protection #ethods

esin

40/ of apparatus Protective devices

roundin

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0ssues and Purpose of Power

System Protection

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Safety *o prevent in6ury to personnel

+)uipment amae

*o minimi&e damae to system components

Service 0nterruption *o limit the e7tent and duration of service

interruption

+conomics *o minimi&e costs (+7penses and conse)uence

of failures!

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Functions of Protective Systems

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R-#ni

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Functions of Protective Systems

Primary Function Secondary Function

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T# -&u' t5 +$#%+t

$%#;&l .$#% '$;i- #.

&n) l%nt #n & +#($')'t% (5n it 'u..$' &

.&ult #$ (5n it 't&$t' t#

#+$&t in &n &"n#$%&l

%&nn$ t5&t %i5t -&u',&%&' #$ #t5$(i'

int$.$ (it5 t5 ..-ti;

#+$&ti#n #. t5 $'t #. t5

')'t%

*o provide indication of

the location and type offailure9 *his assists in

e7peditin repair and

provides means for

analy&in theeffectiveness of the fault

prevention

1:

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Protective System esin Criteria

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19 %eliability

29 Speed

39 Selectivity

"9 Sensitivity

'9 +conomic

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Protective System esin Criteria

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19 %eliability

M&'u$ t5 ,$ #. -$t&int) t5&t t5

+$#t-ti; ')'t% (ill +$.#$% -#$$-tl)!

Rli&"ilit) ,n#t'= D+n,&"ilit) -$t&int) #. -#$$-t #+$&ti#n

S-u$it) &''u$&n- &&in't in-#$$-t #+$&ti#n

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Protective System esin Criteria

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29 Speed

R%#; .&ult .$#% t5 ')'t% &' 7ui-l) &'

+#''i"l

Cl&''i.i-&ti#n= In't&nt&n#u' n# intnti#n&l ti% ,l&)

>i5 '+, l'' t5&t 3 -)-l' 960 >< ')'t%:

Ti%,l&) intnti#n&l ti% ,l&) ".#$ t$i+&-ti#n

13

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Protective System esin Criteria

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39 Selectivity P$.#$%&n- #. +$#t-ti; ,;i-' t# 'l-t "t(n

t5#' -#n,iti#n' .#$ (5i-5 +$#%+t #+$&ti#n &n, t5#'

.#$ (5i-5 n# #+$&ti#n* #$ ti% ,l&) #+$&ti#n i'$7ui$,

I'#l&t .&ult, -i$-uit $'ultin in %ini%u% int$$u+ti#n'!

I%+l%nt, t5$#u5 #$one o% &rotection'

"9 Sensitivity Rl&)in 7ui+%nt %u't " 'u..i-intl) 'n'iti; '#

t5&t it (ill #+$&t (5n $7ui$,! Mu't ,i'-$i%in&t n#$%&l .$#% &"n#$%&l -#n,iti#n'!

1"

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Protective System esin Criteria

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'9 +conomics

Rl&)' 5&;in -l&$l) ,.in'

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;one of Protection

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Ri#n' 9

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;one of Protection

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;one of Protection

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9": Li;t&n -i$-uit "$&$ (it5

.$'t&n,in CT!

9&: D&,t&n -i$-uit "$&$ (it5

"u'5in CT?'!

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;one of Protection

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9&: Li;t&n -i$-uit "$&$ (it5 .$'t&n,in CT!

9": D&,t&n -i$-uit "$&$ (it5 "u'5in CT'

9-: Li;t&n ,'in

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P$i%&$) &n, &-u+ P$#t-ti#n

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Provision must be made to clear the fault by

some alternate protection system should the

protection system fail to operate (fail to

clear the fault!

Primary Protection %&in +$#t-ti#n ')'t% .#$ &

i;n

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Primary and 4ac$up Protection

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Primary and 4ac$up Protection

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Mt5#,' #. Di'-$i%in&ti#n

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19 #ethod 4ased on /ocation of Fault

&: Di'-$i%in&ti#n ") ti%

": Di'-$i%in&ti#n ") -u$$nt %&nitu,

-: Di'-$i%in&ti#n ") ,i't&n- %&'u$%nt,: Di'-$i%in&ti#n ") ti% &n, ,i$-ti#n

: Di'-$i%in&ti#n ") ti% &n, -u$$nt %&nitu,

.: Di'-$i%in&ti#n ") ti% &n, ,i't&n-

: Cu$$nt"&l&n- ,i'-$i%in&ti#n5: P#($,i$-ti#n -#%+&$i'#n ,i'-$i%in&ti#n

i: P5&' -#%+&$i'#n ,i'-$i%in&ti#n

23

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#ethods of iscrimination

iscrimination by *ime

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Add time la featuresto the controllin relays

of a number of circuit

brea$ers to trip the

brea$er nearest the fault

prior to those farther offthe point of fault

2"

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#ethods of iscrimination

iscrimination by Current#anitude

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%elays are set to pic$up

at a proressively hiher

current towards the

source

2'

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#ethods of iscrimination

Di'-$i%in&ti#n ") Di't&n-

M&'u$%nt

Di'-$i%in&ti#n ") Ti% &n,

Di$-ti#n

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#ethods of iscrimination

Di'-$i%in&ti#n ") Ti% &n,

Cu$$nt M&nitu,

Di'-$i%in&ti#n ") Ti% &n,

Di't&n-

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#ethods of iscrimination

Cu$$nt &l&n-

Di'-$i%in&ti#n

P#($Di$-ti#n

C#%+&$i'#n Di'-$i%in&ti#n

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#ethods of iscrimination

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P5&' &nl #. -u$$nt &t

t5 n,' #. t5 +$#t-t,

'-ti#n i' -#%+&$,* (5i-5i;' in,i-&ti#n (5t5$

t5 .&ult i' internal #$

e7ternal

Phase Comparison iscrimination

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#ethods of iscrimination

29 #ethods based on

*ype of Fault

39 Combination of #ethodsSensitive to /ocation and

*ype of Fault

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&: $# +5&' '7un-

nt(#$

": N&ti; +5&' '7un-

nt(#$'

Phase and earth fault

protection

3:

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Assinment

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1! W5&t &$ t5 &"n#$%&liti'

in P#($ S)'t%@ >#( ,#

( +$;nt t5%@2! W5&t i' t5 +u$+#' #.

$#un,in@ W5) i' it

i%+#$t&nt@

3! W5&t i' t5 ,i..$n-

"t(n #;$l#&, -u$$nt&n, .&ult -u$$nt@

"9 For the system shown in the fiure

below< the fault F produces these different

responses at various times=

(a! %1 41and %2< 42operate>

(b! %1 41