oc relay cordination

8/10/2019 Oc Relay Cordination

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Basic InformationO/C E/F Relay & Time Coordination 1

O/C E/F Relay &Time Coordination

BasicInformation


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O/C E/F Relay & Time Coordination 2

General Circuit Diagram200/1 Amp

R Ph O/C (51R)

E/F (51N)

B Ph O/C ( 51B)

150 Amp

150 Amp

150 Amp

0.75 Amp

0.75 Amp

0.75 Amp

0.0 Amp

C11

C31

C51

C71

S1

S1

S1

S2

P1 P2


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O/C E/F Relay & Time Coordination 31S1R1S2R1S3R1S1Y1S2Y

1S3Y1S1B1S2B1S3B2S1R2S2R2S3R

2S1Y2S2Y2S3Y2S1B2S2B2S3B3S1R

3S2R3S3R3S1Y3S2Y3S3Y3S1B3S2B

3S3B

R Ph CT

Y Ph CT

B Ph CT

Core-1Core-2Core-3

Core-1Core-2Core-3

Core-1Core-2Core-3

A11

A31

A51

A71

C11

C31

C51

C71D71

D11

D31

D51

Yard MB Wiring


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O/C E/F Relay & Time Coordination 41S1R1S2R1S3R1S1Y1S2Y

1S3Y1S1B1S2B1S3B2S1R2S2R2S3R

2S1Y2S2Y2S3Y2S1B2S2B2S3B3S1R

3S2R3S3R3S1Y3S2Y3S3Y3S1B3S2B

3S3B

R Ph CT

Y Ph CT

B Ph CT

Core-1Core-2Core-3

Core-1Core-2Core-3

Core-1Core-2Core-3

A11

A31

A51

A71

C11

C31

C51

C71D71

D11

D31

D51

Yard MB Wiring


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Terminal Diagram of MiComP141O/C E/F Relay & Time Coordination 5


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Single Line to Ground Fault200/1 Amp

R Ph O/C (51R)

E/F (51N)

B Ph O/C ( 51B)

1500 Amp

7.5 Amp

7.5 Amp

C11

C31

C51

C71

S1

S1

S1

S2

P1 P2


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Electromagnetic Induction relays

50%75%

100%125%150%

200%

1 2


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Relay Operation Time - 1O/C E/F Relay & Time Coordination 8

E/F PSM 30% i.e. 0.3 Amp

E/F Relay Current 7.5 AmpE/F Relay Current is 7.5/0.3 = 25 Timesits operating currentFrom Graph for 25 Times relay operatingcurrent for TMS = 0.15 relay time ofoperation would be @ 0.35 Sec

O/C PSM 100%O/C Relay Current 7.5 AmpIt is 7.5 times relay operating currentFrom graph for 7.5 Times relay operatingcurrent and for TMS = 0.1 time ofoperation for the relay would be 0.35 Sec

( Zoom out Graph )
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Relay Operation Time - 2O/C E/F Relay & Time Coordination 9

Actually our problem is to decide relay settings and not relay time of

operations as shown previously

Hence Unknowns areRelay PSMRelay TMS

Whereas known facts areRelay placement and purpose of useRelay current during fault ( i.e. CT secondary current during fault. )Relay desired time of operation.

General Steps1) Decide PSM2) Find out fault current3) Find out multiple of relay set current as per decided PSM in step-14) Find out time of operation for above multiple of current and TMS=1 usingrelay characteristic curve5) Decide relay time of operation as per protection needs6) Find out TMS = Required Time of operation /Time of operation with TMS =1


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Basic Information Selection of PSMO/C E/F Relay & Time Coordination 10

E/F PSM generally selected as 30% ( Other than 30% settings may also be selected but about thisdiscussed somewhere else in the presentation)

For O/C PSM is selection depends upon place and purpose of use for example 1.Transformer O/C protection

a) Transformer HV or LV side O/C relay PSM settings should be in commensuration with transformerfull load current and respective CT ratio such that PSM = T/F Full load current / CT ratio ( Generallyexpressed in %)

b) For example for a 25 MVA transformer HV side full load current is 109 A if HV CT ratio is 200/1 Ampthen PSM =109/200 55% ( exact value 54.5%)

c) For old type numerical relay it was not possible to go as near as possible to value calculated fromabove formula due to large steps available

d) Under such condition it is decision as per local condition to select higher or lower nearest PSMe) In above example it is customary to select 50%, however due to this selection there is apparent

loss of about 10% capacity of the T/Ff) It is also possible to select 75% but load on transformer is to be monitored carefully ( and manually

)2.For 220-132 kV feederHere generally it is customary to select relay PSM as per-

a) Line conductor allowable loading limitb) CT primary normal currentc) Substations capacity/normal load feed by the lined) Considering above facts it is very common to select 100% PSM for 132kV lines with CT ratio 400/1

Ampe) For 220kV lines with CT ratio 800/1 amp and conductor 0.4 ACSR or 0.525 AAAC it is 100%

a)For 33-11kV feedera) As per local feeder condition, load pattern and needs ranging between 50% to 100%


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Relay Operation Time - 3

Desired time of operation will depend upona) Equipment being protectedb) Time discrimination from down stream protection (150 ms 250 ms)c) Time of operation of main protection etc.

For transformer LV side protection it is common to adopt 250 ms asoperating time.

This is so as to have 150 ms time discrimination from 100 ms relaytime of operation for lower (feeder) protection.

When relays are used as backup protection of 132kV lines its time

of operation shall be equal to Z-2 time of operation (300 350 ms). Once these two things decided there remains only mathematical

part



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Worked out ExampleO/C E/F Relay & Time Coordination 12

400/1 A

132 kV 33 kV400/1 A

25 MVA

33kV Bus fault level

1Ph 170 MVA , 3Ph 210 MVARelay current during fault1Ph 7.43 Amp, 3 Ph 9.18 AmpRelay PSME/F 30% , O/C 100 %Multiple of relay currentE/F 25, O/C 9.Time of operation with TMS = 1E/F 2.2 s, O/C 3.0 SecDesired time of operationE/F 250 ms , O/C 250 msTMS E/F 0.114, O/C 0.083Roundup toE/F 0.125 , O/C 0.1


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More InformationO/C E/F Relay & Time Coordination 13


MoreInformation


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Introduction

Fuse wire is simplest protection Fusing ampere of copper wire of diameter d

expressed in Cm is given by the formula A =2530*d 3/2

Time taken by fuse to blow off depends up onfusing amperes



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Introduction

For a wire of length L carrying current I

and diameter d heat produced is H = I 2R H = I 2 (L/A) H = I 2 ( L/( d2/4)) Heat dissipated = K ( d)L ( i.e.

proportional to surface area where K

is constant of proportionality) Temperature will be steady state if

heat generated is equal heatdissipated or

I2 ( L/( d2/4)) = K ( d)L I2 ( 1/(d 2/4)) = K d

I2 = K d3 I = K d 3/2 And by experiments for normal

ambient temperature value of K forcopper is determined as 2530 for dexpressed in Cm.


SWG D in mm D in Inch Amp FusingAmp

Fusing Ampby Formula

40 0.122 0.0048 1.5 3 3.41

39 0.132 0.0052 2.5 4 3.84

38 0.152 0.006 3 5 4.74

37 0.173 0.0681 3.5 6 5.76

36 0.193 0.0076 4.5 7 6.78

35 0.213 0.0084 5 8 7.8634 0.234 0.00921 5.5 9 9.06

33 0.254 0.01 6 10 10.24

32 0.274 0.0108 7 11 11.47

31 0.29464 0.0116 8 12 12.80

30 0.315 0.0124 8.5 13 14.14

29 0.345 0.0136 10 16 16.21

28 0.376 0.0148 12 18 18.45

27 0.416 0.0164 13 23 21.47

26 0.457 0.018 14 27 24.72

25 0.508 0.02 15 30 28.97

24 0.559 0.022 17 33 33.44

23 0.61 0.024 20 38 38.12 More
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Simplest Protection Fuse

Thesecharacteristicgraphs aregenerally doublelog graph

This is due toincluding from verysmall to very largevalues on both axis


18


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Simplest Protection - Fuse

Log scale graph areuse full tool whererange of values variesvery widely

This variation in rangeis generally 10,000times

It does not affectoverall accuracy ofselecting proper valuemanually


19


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General mathematical formula for timecharacteristic of the relay as per IECStandards

KTime Of Operation = ---------------------

( ( Is /Ib) - 1 )


20


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General mathematical formula for timecharacteristic of the relay shown onprevious slide, with parameter values fordifferent curves are shown here


Characteristic K

Normal Inverse 0.02 0.14

Very Inverse 1 13.5

Extremely Inverse 2 80

Long Time Inverse 1 120

21


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Use of log scale-1O/C E/F Relay & Time Coordination 21

22


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Use of Log Scale-2O/C E/F Relay & Time Coordination 22

23


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l d 24


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O/C E/F R l & Ti C di i 25


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Transformer Protection Damage Curve

Damages to the equipment due

to fault current flowing through itare mainly due to heating effectof the current ( I 2Rt)

Hence fuse time characteristicinitially suited very well to theequipments in the power system

This figure shows protection oftransformer with the help of relayand breaker

This also indicates how inversecharacteristic of O/C Relay is

suitable to protection of powersystem equipments ( More about Transformer

Damage Curves ) ( More about this figure )


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Transformer Protection Damage Curve

Transformer damage curve as per

IEEE 57.109 for class IIItransformers ( 5 MVA to 30 MVA )




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Protection of Transformer by O/C RelayO/C E/F Relay & Time Coordination 27

Trafo DamageCurve

Long TimeInverse

Extremely Inverse

Normal Inverse

O/C E/F R l & Ti C di ti 28


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End of More InformationO/C E/F Relay & Time Coordination 28

After understanding basics of relaycharacteristic curves and its selectionaccording to protection needs we will

turn to allied information about O/C E//FrelayingThis allied information will prove helpful

in overall understanding aboutdevelopment of protective relays and itsuse in power system



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Basic InformationO/C E/F Relay & Time Coordination 29


AlliedInformation



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Disadvantages of fuses

Though simple less accurate ( If Rewirable) Because of previous heating effect Ambient Temperature In consistencies in material Limitations for breaking capacities hence suitable for LV and to

some extent MV HRC Fuses

More accurate Higher rupturing capacities Requires time for replacement Suitable for LV and to some extent MV

O/C E/F Relay & Time Coordination



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Early Development of Protective Schemes

This simple device (Fuse) played a veryvital role during early development ofpower systems

As the complexity of power systemincreased other technique get introducedlike breaker, relay DC battery etc. ( How? )


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Early development of power system

History of power system protection dates back nearly to the start of development of power systemit self

In real sense power system started growing due to invention of incandescent lamp by Edisonduring 1880

Edison was promoter of DC power system ( Why ? ) General Electric founded by him was main supplier of electricity in Newyork. Washington first introduced AC system with the advancement in transformer during 1887 During 1890 charls introduced symmetrical component analysis which helped in analyzing 3 ph.

Power system and there by possible to design larger machines and power systems. Modern day power system came into existence from 1890 One of the patent of fuse is in the name of Edison Development of relays breakers and instrument transformers took place during 1890 to 1920 and

modern day protection system came into existence. And during last century development of power system continuous to be there however main

principles of power system protection are 3S and 1R remained same.

Development of relays breakers and instrument transformers took place during 1890 to 1920 andmodern day protection system came into existence.

And during last century development of power systemcontinuous to be there however main principles of powersystem protection are 3S and 1R remained same.




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General Requirements of Protective Scheme

For any protective device following FunctionalCharacteristic are important. Sensitive Selectivity

Speed Reliability

( Note:- 3 S & 1 R )

As a improvement over simple fuses (in aboveareas) other protective devices get developedwith the advancement of power system


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3S & 1R

Sensitivity is that property of protection system which enables it to

distinguish between fault and no fault condition very correctly. As if we say that some animals are more sensitive than humans to

natural disasters like earthquake. Where as selectivity is that property of the power system which

enables it to isolate only the faulty part from healthy part. In this sense differential protection is most selective protection Once the fault detected by SENSITIVE system and area to be

disconnected detected by SELECTIVE system then there comes theSPEED.

This faulty section should be get cleared as early as possible. For EHV system Faults are once in blue moon. Hence this all above

said things should happen RELIABELY even after 5-10 years fromdesign and commissioning of the protection system.




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O/C E/F Relay & Time CoordinationChanging Trend In Protective Relaying

Protection relay is a tool forprotection engineer

During last 30 years relayoperating principles changedvery drastically Electromagnetic Relays Static Relays Digital Relays Numerical Relays

Though it is not required todesign a relay or repair a relay

at site it is customary to havesome working knowledge ofthese relays for betterunderstanding and use of it



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O/C E/F Relay & Time CoordinationElectromagnetic Induction relays



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O/C E/F Relay & Time CoordinationStatic Relays



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O/C E/F Relay & Time CoordinationDigital Relay



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O/C E/F Relay & Time CoordinationNumerical Relay

F u n c t

i o n s

A v a

i l a b l e i n N u m e r i c a

l O / C R e

l a y



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IntroductionO/C E/F Relay & Time Coordination

R3 R2 R1

A B C

110 ms350 ms500 ms

1) Consider a representative part of a power system as shown above.

2) It is being protected by over current relay

3) Typical expected time of operation for over current relays are as shown

4) In next couple of hour we will seea) What is mean by relay characteristics curveb) How relay characteristic curve suites our protection needsc) How it helps us in deciding relay time of operation

d) Workout relay settings so that they shalloperate at expected time

e) Methodology being adopted for selective tripping by over currentrelay including directional relay



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IntroductionO/C E/F Relay & Time Coordination

R3 R2 R1

A B C

10 sec.25 sec.40 sec.

R3 R2 R1

A B C

200 ms220 ms180 ms

R3 R2 R1

110 ms350 ms500 ms

S

S

S



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Study of Time Co-ordination and its role in design of protection scheme.

Over Current and Earth Fault Protection isused for Protecting a equipment Selective tripping of faulty section of the

power system Backing up the main protection




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Role of Over Current Relay in Protecting the Equipment

It is obvious that over current protective system shouldact and interrupt the fault current before to damage ofequipment due to fault current through it.

Power system equipments include Line, Isolator, CT,Breaker, Transformer

Obviously Transformer is most costliest and delicate (forfault currents) equipment first we will consider itsdamage curve and decide parameters of protectionsystem so that it should act fast enough to protect the

transformer This can be ascertained with the help of Damage Curve

of the transformer and time-current curve of theprotective system




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Role of Over Current Protection in Selective Tripping

It is obvious that only that part of the power systemshould get disconnected where the fault exists

Hence proper time co-ordination should be there so as tolet the down stream protection should act fast enoughand up-stream protection should give sufficient time fordown stream protection to act

Otherwise un-necessary larger area get affected




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O/C E/F Relay & Time CoordinationBackup Protection

When ever main protection fails to separate thefaulty section backup protection take up this role

As such there is inherent time delay in operationof backup protection

This backup protection can be employed in main

protection itself as additional function, butinvariably it is employed as a separate relay toensure its operation even if failure ofquantities/links which are common to bothfunctions such as- DC Source PT supply Relay hardware Main CTs



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O/C E/F Relay & Time CoordinationBack up protection

EHV line faults are of sever nature frompower system security and stability pointof view. Hence must be clearedinstantaneously

For this purpose distance relays whichoperates instantaneously (Z1) areemployed for protection of EHV lines

For protection of EHV transformersdifferential and REF relays are employedwhich are also instantaneous



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yBackup Relay Time Coordination

A C

E

F

X Y

Z

M

oc relay cordination

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