Basic Information O/C E/F Relay & Time Coordination 1 O/C E/F Relay & Time Coordination Basic Information

Basic Information

O/C E/F Relay & Time Coordination 1

O/C E/F Relay & Time Coordination

Basic Information


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


1S1R

1S2R

1S3R

1S1Y

1S2Y

1S3Y

1S1B

1S2B

1S3B

2S1R

2S2R

2S3R

2S1Y

2S2Y

2S3Y

2S1B

2S2B

2S3B

3S1R

3S2R

3S3R

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


1S1R

1S2R

1S3R

1S1Y

1S2Y

1S3Y

1S1B

1S2B

1S3B

2S1R

2S2R

2S3R

2S1Y

2S2Y

2S3Y

2S1B

2S2B

2S3B

3S1R

3S2R

3S3R

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

Terminal Diagram of MiComP141



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


Electromagnetic Induction relays

50%75%

100%125%150%

200%

Φ 1 Φ 2

Relay Operation Time - 1


E/F PSM 30% i.e. 0.3 AmpE/F Relay Current 7.5 AmpE/F Relay Current is 7.5/0.3 = 25 Times its operating currentFrom 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 AmpIt is 7.5 times relay operating currentFrom 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)



Actually our problem is to decide relay settings and not relay time of operations as shown previously

Hence Unknowns are Relay 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 using

relay characteristic curve5) Decide relay time of operation as per protection needs6) Find out TMS = Required Time of operation /Time of operation with TMS =1

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 from above 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/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%


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 as operating 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 it’s 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


Worked out Example


400/1 A

132 kV 33 kV400/1 A

25 MVA

33kV Bus fault level 1Ph 170 MVA , 3Ph 210 MVARelay current during fault 1Ph 7.43 Amp, 3 Ph 9.18 AmpRelay PSM E/F 30%, O/C 100 %Multiple of relay currentE/F 25, O/C 9.Time of operation with TMS = 1 E/F 2.2 s, O/C 3.0 SecDesired time of operation E/F 250 ms, O/C 250 msTMS E/F 0.114, O/C 0.083Roundup to E/F 0.125, O/C 0.1

More Information



More Information

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 on fusing amperes


Introduction

• For a wire of length L carrying current I and diameter d heat produced is

• H = I2R • H = I2σ (L/A)• H = I2σ ( L/(πd2/4))• Heat dissipated = K’ (πd)L ( i.e.

proportional to surface area where K’ is constant of proportionality)

• Temperature will be steady state if heat generated is equal heat dissipated or

• I2σ ( L/(πd2/4)) = K’ (πd)L• I2σ ( 1/(d2/4)) = K’ d• I2 = K’’ d3

• I = K d 3/2

• And by experiments for normal ambient temperature value of K for copper is determined as 2530 for d expressed in Cm.


SWG D in mm D in Inch Amp Fusing Amp

Fusing Amp by 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 7.86

34 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 MoreMore

Protection of transformer by a fuse


For T/F with normal load of 100 AmpFuse Transformer

CurrentFusing Time

Current

Safe Operation Time as per IEEE

Safe Operation Time With FOS 2.5

200 10000 200 1800 720430 5 300 300 120

1200 0.4 475 60 241800 0.2 630 30 122800 0.1 1130 10 4

2500 2 0.8

Simplest Protection – Fuse

• These characteristic graphs are generally double log graph

• This is due to including from very small to very large values on both axis


Simplest Protection - Fuse

• Log scale graph are use full tool where range of values varies very widely

• This variation in range is generally 10,000 times

• It does not affect overall accuracy of selecting proper value manually


• General mathematical formula for time characteristic of the relay as per IEC Standards

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

( ( Is/Ib) α - 1 )


• General mathematical formula for time characteristic of the relay shown on previous slide, with parameter values for different curves are shown here


Characteristic α K

Normal Inverse 0.02 0.14

Very Inverse 1 13.5

Extremely Inverse 2 80

Long Time Inverse 1 120

Use of log scale-1


Use of Log Scale-2


Use of Log Scale-3


Use of Log Scale-4


Transformer – Protection – Damage Curve

• Damages to the equipment due to fault current flowing through it are 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 power system equipments

• ( More about Transformer Damage Curves)• ( More about this figure )


Transformer – Protection – Damage Curve

• Transformer damage curve as per IEEE 57.109 for class – III transformers ( 5 MVA to 30 MVA )


Protection of Transformer by O/C Relay


Trafo Damage Curve

Long Time Inverse

Extremely Inverse

Normal Inverse

End of More Information


After understanding basics of relay characteristic curves and its selection according to protection needs we will turn to allied information about O/C E//F relayingThis allied information will prove helpful in overall understanding about development of protective relays and its use in power system

Basic Information



Allied Information

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


Early Development of Protective Schemes

• This simple device (Fuse) played a very vital 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?)


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 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.


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 above

areas) other protective devices get developed with the advancement of power system


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 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.



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 have some working knowledge of these relays for better understanding and use of it


Electromagnetic Induction relays


Static Relays


Digital Relay


Numerical Relay

Fu

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s A

vaila

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in N

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al O

/C R

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Introduction


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 see a) 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 shall operate at expected time

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

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

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


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 of equipment due to fault current through it.

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

• Obviously Transformer is most costliest and delicate (for fault 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


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



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, but invariably it is employed as a separate relay to ensure it’s operation even if failure of quantities/links which are common to both functions such as-– DC Source– PT supply– Relay hardware– Main CTs


Back up protection

• EHV line faults are of sever nature from power system security and stability point of view. Hence must be cleared instantaneously

• For this purpose distance relays which operates instantaneously (Z1) are employed for protection of EHV lines

• For protection of EHV transformers differential and REF relays are employed which are also instantaneous


Backup Relay Time Coordination

A C

E

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X Y

Z

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Documents

Basic Information O/C E/F Relay & Time Coordination 1 O/C E/F Relay & Time Coordination Basic Information