Oc Relay Ion

7/29/2019 Oc Relay Ion

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Basic Information

O/C E/F Relay & Time Coordination1

O/C E/F Relay &Time Coordination

Basic

Information


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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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1S1R

1S2R

1S3R

1S1Y

1S2Y

1S3Y1S1B

1S2B

1S3B

2S1R

2S2R

2S3R

2S1Y2S2Y

2S3Y

2S1B

2S2B

2S3B

3S1R

3S2R3S3R

3S1Y

3S2Y

3S3Y

3S1B

3S2B

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

C71

D71

D11

D31

D51

Yard MB Wiring


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1S1R

1S2R

1S3R

1S1Y

1S2Y

1S3Y1S1B

1S2B

1S3B

2S1R

2S2R

2S3R

2S1Y2S2Y

2S3Y

2S1B

2S2B

2S3B

3S1R

3S2R3S3R

3S1Y

3S2Y

3S3Y

3S1B

3S2B

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

C71

D71

D11

D31

D51

Yard MB Wiring


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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 - 1


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 Times

its operating current

From Graph for 25 Times relay operating

current for TMS = 0.15 relay time of

operation would be @ 0.35 Sec

O/C PSM 100%

O/C Relay Current 7.5 Amp

It is 7.5 times relay operating current

From graph for 7.5 Times relay operating

current and for TMS = 0.1 time of

operation for the relay would be 0.35 Sec

( Zoom out Graph)
http://localhost/var/www/apps/conversion/tmp/scratch_1/IEC-A%20Normal%20Inverse%20jpeg.jpghttp://localhost/var/www/apps/conversion/tmp/scratch_1/IEC-A%20Normal%20Inverse%20jpeg.jpg


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

operations as shown previously

Hence Unknowns are

Relay PSM

Relay TMS

Whereas known facts areRelay placement and purpose of use

Relay current during fault ( i.e. CT secondary current during fault. )

Relay desired time of operation.

General Steps

1) Decide PSM2) Find out fault current

3) Find out multiple of relay set current as per decided PSM in step-1

4) Find out time of operation for above multiple of current and TMS=1 using

relay characteristic curve

5) Decide relay time of operation as per protection needs

6) Find out TMS = Required Time of operation /Time of operation with TMS =1


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Basic Information Selection of PSM


E/F PSM generally selected as 30% ( Other than 30% settings may also be selected but about this

discussed 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 transformer

full load current and respective CT ratio such that PSM = T/F Full load current / CT ratio ( Generally

expressed in %)

b) For example for a 25 MVA transformer HV side full load current is 109 A if HV CT ratio is 200/1 Amp

then 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 PSM

e) 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/F

f) It is also possible to select 75% but load on transformer is to be monitored carefully ( and manually

)

2.For 220-132 kV feeder

Here generally it is customary to select relay PSM as per-

a) Line conductor allowable loading limit

b) CT primary normal current

c) Substations capacity/normal load feed by the line

d) Considering above facts it is very common to select 100% PSM for 132kV lines with CT ratio 400/1

Amp

e) 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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Desired time of operation will depend upon

a) Equipment being protected

b) 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 relay

time 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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14


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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*d3/2

Time taken by fuse to blow off depends up onfusing amperes



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Simplest Protection - Fuse

Log scale graph are

use full tool where

range of values varies

very widely

This variation in rangeis generally 10,000

times

It does not affect

overall accuracy of

selecting proper value

manually


O/C / & C19


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General mathematical formula for timecharacteristic of the relay as per IEC

Standards

K

Time Of Operation = ---------------------

( ( Is/Ib) - 1 )



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O/C E/F R l & Ti C di ti22


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Use of Log Scale-2



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Use of Log Scale-4




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Transformer Protection Damage Curve

Damages to the equipment due

to fault current flowing through itare mainly due to heating effect

of the current ( I2Rt)

Hence fuse time characteristic

initially suited very well to the

equipments in the power system

This figure shows protection of

transformer with the help of relay

and breaker

This also indicates how inverse

characteristic of O/C Relay is

suitable to protection of powersystem equipments

( More about Transformer

Damage Curves)

( More about this figure )

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Protection of Transformer by O/C Relay


Trafo Damage

Curve

Long Time

Inverse

Extremely Inverse

Normal Inverse



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End of More Information


After understanding basics of relaycharacteristic curves and its selection

according to protection needs we will

turn to allied information about O/C E//Frelaying

This allied information will prove helpful

in overall understanding aboutdevelopment of protective relays and its

use in power system



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Basic Information

O/C E/F Relay & Time Coordination

O/C E/F Relay &Time Coordination

Allied

Information



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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




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Early Development of Protective Schemes

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

power systems

As the complexity of power system

increased other technique get introduced

like breaker, relay DC battery etc. (How?)


http://localhost/var/www/apps/conversion/tmp/scratch_1/LINK-History%20of%20protection.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/LINK-History%20of%20protection.pdf


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Early development of power system

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

it self

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

during 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 system

continuous to be there however main principles of power

system protection are 3S and 1R remained same.




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General Requirements of Protective Scheme

For any protective device following Functional

Characteristic are important.

Sensitive

Selectivity

Speed

Reliability

( Note:- 3 S & 1 R)

As a improvement over simple fuses (in aboveareas) other protective devices get developed

with 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 bedisconnected detected by SELECTIVE system then there comes the

SPEED.

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 from

design and commissioning of the protection system.




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Changing Trend In Protective Relaying

Protection relay is a tool for

protection engineer

During last 30 years relay

operating principles changed

very drastically

Electromagnetic Relays

Static Relays

Digital Relays

Numerical Relays

Though it is not required to

design a relay or repair a relay

at site it is customary to havesome working knowledge of

these relays for better

understanding and use of it



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Electromagnetic Induction relays



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Static Relays


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Numerical Relay

FunctionsAvailableinNum

ericalO/C

Relay


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Introduction


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 is

used 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 should

act 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 its

damage curve and decide parameters of protection

system 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 the

protective system




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Role of Over Current Protection in Selective Tripping

It is obvious that only that part of the power system

should get disconnected where the fault exists

Hence proper time co-ordination should be there so as to

let the down stream protection should act fast enough

and up-stream protection should give sufficient time for

down stream protection to act

Otherwise un-necessary larger area get affected




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y &

Backup Protection

When ever main protection fails to separate the

faulty section backup protection take up this role As such there is inherent time delay in operation

of 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 Coordination 47


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y

Backup Relay Time Coordination

A C

E

F

X Y

Z

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