General Line Protection

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General Line Protection

1. 1. Distance relays

Distance relays -

- basics

basics

2. 2. Operating

Operating characteristics

characteristics

3. 3. Effect

Effect of

of parallel

parallel line

line

4. 4. Phase

Phase selection

selection

5. 5. Power

Power swing

swing blocking

blocking

6. 6. Communication

Communication scheme

scheme

7. 7. Switch

Switch on

on to

to fault

fault

8. 8. Weak

Weak end

end infeed

infeed

9. 9. Supervision

Supervision fuse

fuse failure

failure

10. System supervision.

11. Fault locator

12. Stub protection

13. Earth fault protection

14. 14. Auto

Auto reclosing

reclosing systems

systems

List of Topics

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General Line Protection

1-Distance relay basics

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General Line Protection

1-Distance relay basics

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General Line Protection

Objective of relay

protection

•

• Protect persons and equipment in the surrounding of the

Protect persons and equipment in the surrounding of the

power system

•

• Protect apparatus in the power system

Protect apparatus in the power system

•

• Separate faulty parts from the rest of the power system to

Separate faulty parts from the rest of the power system to

facilitate the operation of the healthy part of the system

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General Line Protection

Electrical faults in the power system

• Transmission lines

85%

• Busbar

12%

• Transformer/ Generator

3%

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General Line Protection

Fault statistics

• Single phase to earth

80%

• Two phases to earth

10%

• Phase to phase faults

5%

• Three phase faults

5%

The probability of line faults caused by

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General Line Protection

Fault types

• Transient faults

– are common on transmission lines, approximately 80-85% – lightnings are the most common reason

– can also be caused by birds, falling trees,Forest growth, swinging lines, High velocity winds etc.

– will disappear after a short dead interval

• Persistent faults

– can be caused by a broken conductor fallen down – can be a tree falling on a line

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General Line Protection

Fault types on double circuit lines

• Simultaneous and Interline faults

– On parallel line applications a problem can occur with simultaneous faults.

– A full scheme relay is superior when the protection is measuring two different fault types at the same time.

L1

L3

L1

L2

~

Z< L2-N L1-N

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General Line Protection

Fault resistance

• multi-phase faults

consist only of arc resistance

• earth faults

consist of arc and tower footing resistance

L1

L3

L1

L2

Footing resistance

R

arc

=

28707 x L

_1.4

I

Warrington´s formula

L= length of arc in meters I= the actual fault current in A

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General Line Protection

Fault types

• Mid-span faults

– the fault resistance is out of control

– can be caused by growing trees, bushfire or objects

touching a conductor

– this type of high resistive faults can not be detected by

impedance protection

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General Line Protection

MAIN REQUIREMENTS ON LINE PROTECTION ARE:

• SPEED

• SENSITIVITY

• SELECTIVITY

• DEPENDABILITY

• SECURITY

• RELIABILITY

• MTBF

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General Line Protection

Measuring principles

• Overcurrent protection

• Over current & under voltage

combination

• Differential protection

• Phase comparison

• Directional- wave protection

• Distance protection

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General Line Protection

The principle of distance protection

Z<

Z

_K

=U

_k

/ I

_k

U

_k

=0

U

_k

Z

_k

I

_k

A B metallic fault

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General Line Protection

The principle of distance protection

• Power lines have impedances of size 0,3- 0,4 ohm/ km and normal

angles of 80 - 85 degrees in a 50Hz systems.

• The line impedance must be converted to secondary values with the

formula:

A Z< B Z<

Z

L

=R+jX

Z

sec

=

VT

sec

VT

prim

CT

sec

CT

prim

Z

prim x x

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General Line Protection

The principle of distance protection

t

l

A Z< B Z< Z< C Z<

t

t1 t2 t3

l

t1 t2 t3 f1 f2 f3

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General Line Protection

Measuring loop for earth faults

• The distance protection relays are always set

based on the phase impedance to the fault

Z

_s

_R

L

X

L

The measured Impedance is a function of

positive and zero sequence impedance

R

_N

X

N

IL1

UL1

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General Line Protection

Measuring loop for two- phase faults

• The distance protection relays are always set

based on the phase impedance to the fault

Z

_s

_R

L

X

L

UL1-L2

IL1

IL2

The measured impedance is equal to the

positive sequence impedance up to the fault

location

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General Line Protection

Measuring loop for three- phase faults

• The distance protection relays are always set

based on the phase impedance to the fault

The measured impedance is equal to the

positive sequence impedance up to the fault

location

Z

_s

_R

L

X

L

UL1

IL1

IL2

IL3

UL2

UL3

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General Line Protection

The earth fault measurement

U= I

₁

Z

₁

+I

₀

Z

₀

+I

₂

Z

₂

_Z

₁

_=Z

₂

U= Z

₁

( I

₁

+I

₂

+I

₀

) +I

₀

Z

0

-I

₀

Z

₁

I= I

1

+I

2

+I

0

U=I Z

₁

+I

₀

( Z

₀

- Z

₁

)

3I

0

=I

N

U=IZ

₁

+I

_N

(

Z

₀

- Z

₁

3 )

U=I Z

₁

+

I

N

3 ( Z

0

- Z

1

)

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General Line Protection

The earth fault measurement

• The current used is thus the phase current plus the residual

current times a factor K

_N

= (Z

₀

-Z

₁

) / 3Z

₁

, the zero sequence

compensation factor.

• The factor K

_N

is a transmission line constant and Z

₀

/ Z

₁

is

presumed to be identical throughout the whole line length.

• (1+K

_N

) Z

₁

gives the total loop impedance for the earth fault

loop for single end infeed.

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General Line Protection

Double end infeed

I1

I2

U

F

R

F

U

F

= R

F

( I1 + I2 )

R

F

( I1 + I2 )

R

F1

=

U1

U2

I

_Load

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General Line Protection

Measuring error at high resistive earth fault on a

line with double end infeed

X

ZL

Rf Load export Rf Load import

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General Line Protection

Remote faults

– Due to current contribution If2 and If3 in substation B, the

distance protection in station A will measure a higher

impedance than the "true" impedance to the fault.

– The relay will thus underreach and this means in practice it

can be diffcult to get a remote back-up.

Um= If1

x

ZL+ (If1+If2+If3)

x

ZF

Z< If1 If2 If3 If=If1+If2+If3 ZL ZF A B Um

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General Line Protection

Directional measurement

• When a fault occurs close to the relay location the

voltage can drop to a value where the directional

measurement can not be performed.

– Modern distance protection relays will instead use the

healthy voltage e.g. for L1- fault the voltage UL2-L3,

shifted 90 degrees compared to UL1. This cross

polarisation is used in different proportions between

healthy and faulty phases in different products.

– At three- phase fault close to the station all phase

voltages are low and cross polarisation is not of any use.

Instead a memory voltage is used to secure correct

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General Line Protection

Design of distance protection

• Switched scheme

– consists of a start relay to select (switch) the measuring

loop to the single measuring relay

• Full scheme

– has a measuring element for each measuring loop and

for each zone

~

Z<

L2-N L1-N

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General Line Protection

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General Line Protection

SHOULD COVER AS MUCH AS POSSIBLE OF PROTECTED CIRCUIT AND OF ADDITIONAL RESISTANCE.

• IN CASE OF Ph TO GROUND FAULT FOLLOWED BY RECLOSURE TO TRIPPING IN UNFAULTED PHASES.

• FAST OPERATION

• DIRECTIONAL DISCRIMINATION.

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General Line Protection

EXTENSION UPWARDS AND TO THE RIGHT SHOULD ENCLOSE AS MUCH OF LINE IMPEDANCE AND ADDITIONAL RESISTANCE WITHOUT OVERREACH.

• REACH IN RESISTIVE DIRECTION SHOULD BE LARGE ENOUGH TO COVER LARGE RESISTANCE AND TO GET GOOD DYNAMIC

PERFORMANCE BUT LIMITED TO AVOID UNWANTED TRIPPING IN CASE OF POWER SWINGS , OVERREACH IN ADDITIONAL RESISTANCE IS SEEN WITH LARGE CAPACITIVE REACTANCE , SHORT TIME OVERLOADING.

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General Line Protection

EXTENSION UPWARDS IS DECIDED BY IMPEDANCE OF PROTECTED LINE AND SETTING OF I ZONE OF ADJACENT LINES.

• IN MOST CASES R-AXIS REACH OF ZONE - II SAME AS ZONE -I

IS SATISFACTORY. IF ADDITIONAL RESISTANCES ARE EXPECTED WHICH ZONE - I IS NOT ABLE TO COVER THEN DIFFERENT SETTING FOR ZONE - II IS ADVANTAGEOUS.

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General Line Protection

THIS IS THE WIDEST OF ZONES IN WHICH TRIPPING CAN OCCUR AFTER LONGEST TIME DELAY.

• IS REQUIRED TO GIVE REMOTE BACKUP THOUGH IN

MANY CASES IT IS IMPOSSIBLE TO GET COMPEREHENSIVE REMOTE BACK UP.

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General Line Protection

DISTANCE PROTECTION ON SHORT LINES.

jX

R _F

X_F

R

• Low measured reactance

• Ratio between fault resistance

and resistance is high.

• Distance protection with

mho characteristic can not

see an average fault resistance.

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General Line Protection

DISTANCE PROTECTION ON SHORT LINES

jX

R _F

X_F _R

• Low measured reactance

• Ratio between fault

resistance and reactance is

high.

• Distance protection with

mho characteristic can not

see average fault resistance.

• Cross polarization has no

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General Line Protection

jX

R _F X_F

R

DISTANCE PROTECTION ON SHORT LINES

• Quadrilateral characteristic

improves sensitivity for

higher R

_F

/X

_F

ratio.

• It still has some limitations.

-The value of set R

_F

/ X

_F

ratio is

is limited by 5

- Remote infeed increases the

apparent value of fault resistance.

- Requirements on current

instrument transformers are

stringent.

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General Line Protection

DISTANCE PROTECTION ON SHORT LINES.

jX

R R _F

X_F

• Teleprotection schemes improve

the total system behavior.

• Overreaching permissive schemes

increase the sensitivity.

• Weak infeed logic for very high

fault resistance.

• Requirements on CT’s are

decreased.

• Independent underreaching

zone 1 is sometimes an

additional advantage.

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General Line Protection

jX

R

DISTANCE PROTECTION ON LONG LINES

• Load impedance limits the

reach in resistive direction.

• High value of R

_F

/ X

_F

ratio is

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General Line Protection

DISTANCE PROTECTION ON LONG LINES

R

• Load impedance limits the reach in resistive direction.

• High relay of R _F/ X_Fratio is generally not necessary

• Circular (mho) characteristic - has no strictly defined reach

in resistive direction.

- needs limitation in resistive direction (blinder)

• Influences of heavy load current at phase to earth faults.

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General Line Protection

• AT THE ORIGIN DIRECTIONAL DISCRIMINATION REQUIRED BY LINE PASSING THROUGH 2nd _{QUADRANT , 4}th_QUADRANT

AND ORIGIN.

• THE DIRECTIONAL MEASUREMENT IS BASED ON THE USE OF + VE SEQUENCE VOLTAGE FOR THE RESPECTIVE FAULT LOOP. •VOLTAGE USED FOR R _PH ELEMENT IS

0.8 U_1R + 0.2 U_1RM

WHERE U_1RM IS MEMORY VOLTAGE (+VE SEQUENCE)

THIS WILL ENSURE CORRECT DIRECTIONAL DISCREMINATION. EXTENSION IN 2nd _{AND 4}th _{LIMITED TO AVOID OPERATION OF}

UNFAULTED PHASE AN ALSO DURING SWINGS YET GIVE GOOD DYNAMIC PERFORMANCE.

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General Line Protection

LOAD CURRENT INFLUENCES THE IMPEDANCE MEASUREMENT.

L i n e i m p e d a n c e

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General Line Protection

Characteristic with out load compensation The same fault position Equal fault resistance LOAD CURRENT INFLUENCES THE IMPEDANCE MEASUREMENT.

L i n e i m p e d a n c e

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General Line Protection

∼

ILOAD

_∼

E_A E_B A B R _F I_FA _I FB Z_L EXPORTING END OVERREACHING IMPORTING END OVERREACHING ZM = Z_L + R _F

(

1 + I_FB I _FA

)

Note : Currents and voltages are phasors

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General Line Protection

Characteristic with out load compensation The same fault position Equal fault resistance LOAD CURRENT INFLUENCES THE IMPEDANCE MEASUREMENT.

Load compensated characteristic

L i n e I m

p d e a n c e

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General Line Protection

IT IS NOT WHAT MANY HOPE IT IS

•RCALC is an interactive PC based program,

which helps the users in determination of

optimum settings of distance protection.

•Its operation is based on real algorithms

used in the distance protection.

•It includes measuring characteristics for :

-RAZOA and RAZFE

-REZ 1

and REL 100

-distance protection in REL 5XX

R C

A L

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General Line Protection

IT IS NOT WHAT MANY HOPE IT IS

•It presents the operation areas of distance

protection zones in impedance ( R- X ) plane

• Simulates two machine system :

-single line.

-double circuit line with zero

sequence mutual coupling.

-remaining network (line)

between two busbars.

-load conditions

-changing fault resistance.

R C

A L

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General Line Protection

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General Line Protection

Zero- sequence mutual coupling on parallel lines

ZA< overreaching ZB< underreaching

Z

L

~

Z

OM

Z

L

~

ZA< ZB<

~

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General Line Protection

Zero- sequence mutual coupling on parallel lines

• In double circuit lines and parallel lines the zero sequence coupling

will result in measuring errors, specially at ground faults.

• The mutual impedance will either cause an extension or reduction of

the set reach on the relay.

• Maximum overreaching will occur when the parallel line is out of

service and grounded at both ends.

• The overreaching caused by the grounded parallel line can be

avoided at the setting of the relay, by the K

_N

factor.

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General Line Protection

EFFECT OF MUTUAL COUPLING ON DISTANCE

RELAYS

∼

∆

_∼

PARALLEL LINE EARTH CURRENT = IEP= 3IOP

INDUCED VOLTAGE IN THE FAULT LOOP = IEP • ZOM

/

3

DISTANCE RELAY PH- EARTH UNIT MEASURES

Z = VPH- E

/ (

I PH + K OIE

)

WHERE K O = ZOL- ZL

/

3ZL = ZL •IPH

+ (

ZOL- ZL

)

IE

/

3ZL

+

IEP •ZOM

/

3ZL IPH + K O IE = ZL

[

1 + K OM •IEP

/

IPH + K O IE

]

WHERE K OM = ZOM

/

3ZL ZOM ERROR

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General Line Protection

EFFECT OF MUTUAL COUPLING ON DISTANCE RELAYS

- THE ERROR IS

α

MUTUAL COUPLING FACTOR ZOM / 3ZL .

- ERROR INCREASES WITH IEP IN RELATION TO THE RELAY CURRENT IPH + KO IE

- THE RELAY UNDER REACHES WHEN IEP IS IN PHASE WITH IPH AND IE

- THE RELAY OVER REACHES WHEN IEP , IPH AND IE HAVE OPPOSITE SIGNS.

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General Line Protection

EFFECT OF MUTUAL COUPLING ON DISTANCE RELAYS

∆

∼

∆

Z = - ZL

K

OM

• Z

OM

/ Z

OL

1 + K

O

• = - 0.23 Z

L

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General Line Protection

EFFECT OF MUTUAL COUPLING ON DISTANCE RELAYS.

∆

Z =

∼

∆

D

K

OM

1 + K

O

• Z

L

= 0.38 Z

L

K

O =

Z

OL -

Z

L

3 Z

L

= 0.864

K

OM =

Z

OM

/ 3Z

L =

0.716

R 1+ j X1= 0.0289 + j 0.307

Ω

/

KM R O+ j X0= 0.276 + j 1.0715

Ω

/

KM R MO1+ j XMO= 0.228 + j 0.622

Ω

/

KM

∴

ZL = 0.308

Ω

/

KM ZOL =1.106

Ω

/

KM ZOM =0.662

Ω

/

KM

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General Line Protection

SETTING OF DISTANCE ZONE FOR PARALLEL LINES.

• SETTING OF ZONE 1.

SETTING OBJECTIVE IS TO AVOID OVERREACH BEYOND THE REMOTE END IN CASE SHOWN BELOW. ALSO SETTING SHOULD COVER AS

MUCH OF THE LINE AS POSSIBLE ( MIN 50 % + SAFETY MARGIN )

∼

D

PH- E 1 +

(

ZOL - ZL 3ZL

-

K OM • ZOM ZOL

)

1 + K O

Z = X Z

L

• ∴

SET

K

O

=

[

ZOL - ZL 3ZL

-

K OM ZOM ZOL

]

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General Line Protection

WITH THE ABOVE FOR OTHER CASES VIZ PARALLEL LINES

SWITCHED OFF AND NOT EARTHED & BOTH LINES IN SERVICE THE REACH WILL REDUCE AS GIVEN BELOW.

-

PARALLEL LINE SWITCHED OFF AND NOT EARTHED - 69%

- BOTH LINES IN SERVICE

- 60%

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General Line Protection

SETTING OF DISTANCE ZONES FOR PARALLEL LINES

• SETTING OF ZONE 2

SETTING OBJECTIVE IS RELAY MUST SAFELY COVER 100 % OF THE LINE WITH SAFTEY MARGIN OF 20 % FOR THE MOST

UNFAVOURABLE CONDITION.

∼

PH - E

Z = Z

L 1 +(ZOL - ZL )

/

3ZL+ K OM 1 + K O

[

]

∴

SET K 0

=

ZOL - ZL 3 ZL + K OM AND REACH TO 120 %

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General Line Protection

FOR OTHER CASES VIZ PARALLEL LINE SWITCHED OFF AND EARTHED AT BOTH LINE ENDS IT MUST BE ENSURED THAT THIS DOES NOT OVERLAP WITH THE ZONE 2 OF THE

FOLLOWING LINE.

Z

_Z

Z

L

0. 44

THIS MEANS IN THE CASE OF 2nd ZONE SET TO 120 % OF ZL

WOULD HAVE A REACH OF 173 % OF ZL.

IN NORMAL PRACTICE THIS PROVIDES NO PROBLEMS AS OVERRECH IN TO FOLLOWING LINE IS REDUCED BY

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General Line Protection

THE INFLUENCE OF ZERO SEQUENCE MUTUAL COUPLING CAN BE COMPENSATED IN NUMERICAL RELAYS IN TWO DIFFERENT WAYS

ALT 1

-BY USING POSSIBILITY OF DIFFERENT VALUES OF EARTH RETURN COMPENSATING FACTOR K FOR DIFFERENT ZONES WITHIN THE SAME GROUP OF SETTING PARAMETERS.

ALT 2

-BY USING DIFFERENT GROUPS OF SETTING PARAMETERS FOR DIFFERENT OPERATING CONDITIONS OF PROTECTED DOUBLE CIRCUIT LINE.

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General Line Protection

ALTERNATIVE 1

K

N1

₌

[

ZOL

-

ZL 3ZL

-

K OM ZOM ZOL

]

=

[

ZOL

-

ZL 3ZL

+

K OM

]

=

[

ZOL

-

ZL 3ZL

]

K

N2

K

N3 WHERE K OM = ZOM

/

3ZL

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General Line Protection

ALTERNATIVE 2

=

[

ZO L - ZL 3 ZL - K O M ZO M ZO L

]

CASE 1 - PARALLEL LINE SWITCHED OFF WITH BOTH ENDS

EARTHED.

K

N1

K N2 , K N3 IDENTICAL TO ALT 1

CASE 2 - DOUBLE CIRCUIT PARALLEL LINE IN OPERATION.

=

[

ZOL

_-

_ZL 3ZL

+

K OM

]

K N2 , K N3 IDENTICAL TO ALT 1

K

N1

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General Line Protection

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General Line Protection

AN INDEPENDENT PHASE SELECTION FUNCTION OPERATES

AS A COMPLEMENT TO THE IMPEDANCE MEASURIING ELEMENT SO AS TO SECURE CORRECT PHASE SELECTION IN CASE

OF SINGLE PH TO EARTH FAULTS ON HEAVILY LOADED LONG TRANSMISSION LINES AND ALSO MULTI CIRCUIT.

IT IS NOT NECESSARY TO SET THESE TO COVER ALL

ZONES. IT IS ENOUGH IF IT COVERS FIRST OVERREACHING ZONE ( ZONE 2 ) MEASURING ELEMENT FOR DIFFERENT FAULT LOOPS BUT FOR PHASE INDICATIONS.

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General Line Protection

PHASE SELECTION

• I PH FAULTS

.

Characteristic of phase selector for single-phase faults.

jX XNPh RNPh R RN2 2 . ( 1 + Kn )

U

R

I

R

<

R

N4

+ j x

N4

Us

Is

R

N4

+ j x

N4

<

U

T

I

T

R

N4

+ j x

N4

<

ALSO

3I

o

> 0.1 I

n

&

3I

o

>

0.2 I

pHMAX

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General Line Protection

PHASE SELECTION

_{• 2 PH FAULTS.}

jX R XPh RPh 2. X2 2.R2 70•

α

∂

U

R -

U

T

I

R

<

R

4

+

j X

4

R

4

+ j x

4

R

4

+ j x

4

U

s -

U

R

_<

I

S

U

T -

U

R

I

T

<

ALSO

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General Line Protection

Characteristic of phase selectors at three phase faults.

jX

R

100• RPh 2/

√

3 2.X2 2. R2 XPh .2/

α

δ

jX’ R’

PHASE SELECTION

• 3 PH FAULTS. THIS IS SIMILAR TO PH - PH FAULTS WITH FOLLOWING DEVIATIONS. - ROTATED ANTICLOCKWISE BY 30 DEGREES. - REACH 2/

√

3 TIMES THAT OF FOR PH - PH FAULTS.

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General Line Protection

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General Line Protection

Power Swing Blocking (PSB) function

• A power swing can be started by sudden load change due to

a fault somewhere in the network.

• Close to the centre of the power swing, low voltage and thus

low impedance will occur.

• A distance protection relay must then be blocked during the

power swing.

• This can be done by mesuring the transit time of the

impedance locus passing two dedicated impedance zones.

• Normally the time used is 35-40 ms.

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General Line Protection

POWER SWING BLOCKING FUCTION

•WHEN POWER SWING DETECTION UNIT OPERATES ANY IMPEDENCE ZONE CAN BE SELECTED TO BE BLOCKED OR NOT AS REQUIRED.

•OPERATION OF POWER SWING DETECTION UNIT IS INHIBITED WHEN ZERO SEQUENCE CURRENT IS DETECTED. THIS FEATURE IS

INCLUDED TO ENSURE TRIPPING OF HIGH RESISTANCE EARTH FAULTS WHERE FAULTS WHERE FAULT RESISTANCE CAN DECREASE SLOWELY. •THE RESIDUAL CURRENT INHIBIT CONDITION ENSURE PSD

WILL NOT BLOCK DUE TO UNBALANCED LOAD OR

RESIDUAL CURRENT EXPERIENCED WITH UNTRANSPOSED TRANSMISSION LINES.

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General Line Protection

Power Swing Blocking function

∆

t

∆

t = 40 ms

X

R

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General Line Protection

EFFECT OF VOLTAGE COLLAPSE ON DISTANCE RELAYS.

• APPARENT IMPENDANCE PRESENTED TO A DISTANCE RELAY

AS THE LOAD VOLTAGE VARIES DEPENDS ON VOLTAGE CHARACTERISTIC OF THE LOAD. • FOR A MOTOR P = 0.35 ( 0.75 + O.25 V )2

X

R

V = 0.8PU• •V = 1.1 PU

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General Line Protection

• SIMPOW IS A COMPUTER PROGRAMME DEVELOPED BY ABB POWER SYSTEM AB

• FOLLOWING STUDIES CAN BE DONE BY SIMPOW

- STEADY STATE (POWER FLOW , FAULT CURRENT , HARMONICS). - ELECTRO MECHANICAL TRANSIENTS ( LONG TERM DYNAMICS ,

SHORT TERM DYNAMICS , MACHINE TRANSIENTS).

- ELECTRO MAGNETIC TRANSIENTS (SATURATION AND RESONANCE SWITCHING TRANSIENTS , LIGHTNING TRANSIENTS).

- ANALYSIS (FREQUENCY SCANNING , EIGEN VALUES AND VECTORS, MODEL ANALYSIS).

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General Line Protection

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General Line Protection

COMMUNICATION EQUIPMENT

∼

×

∼

A A BB

IN THE ABSENCE OF COMMUNICATION LINK

-THE OPERATION ZONE OF END ZONE FAULT IS LONGER.

-AUTO RECLOSING IS NOT POSSIBLE.

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General Line Protection

Communication equipment

•• Powe

Power li

r line ca

ne carrier

rrier (PLC

(PLC) eq

) equipme

uipment is

nt is base

based on

d on a cap

a capaciti

acitive

ve

connection of signals with frequency in the range 50- 500 kHz

connection of signals with frequency in the range 50- 500 kHz on the

on the

power line.

•• Radio

Radio link

link is a

is a good a

good and rel

nd reliable

iable commu

communicat

nication e

ion equime

quiment, bu

nt, but is

t is

rarely used due to the high cost.

•• Opti

Optical fi

cal fibres h

bres have th

ave the adva

e advantage

ntage to be i

to be insen

nsensitiv

sitive to no

e to noise an

ise and can

d can

transmit a huge amount of information.

(142)

(143)

General Line Protection

RELAY SETTING AND THE WAY SIGNALS ARE USED IS GIVEN RELAY SETTING AND THE WAY SIGNALS ARE USED IS GIVEN BELOW.

BELOW.

FIRST ZONE REACH FIRST ZONE REACH

• UNDER REACHING (0.8 TO 0.9 Z AB ) • UNDER REACHING (0.8 TO 0.9 Z AB ) • OVER

• OVER REACHING REACHING ( ( 1.2 Z 1.2 Z AB)AB) USE OF RECIVED SIGNAL

USE OF RECIVED SIGNAL

• OPERATION OF CB IF LOCAL RELAY HAS PICKED UP • OPERATION OF CB IF LOCAL RELAY HAS PICKED UP •

• AS INFORMATIAS INFORMATION REGARDINON REGARDING DIRECTION G DIRECTION OF FAULTOF FAULT -

- FOR FOR COMPARISON COMPARISON WITH WITH LOCAL LOCAL ENDEND -

- TO TO EXTEND EXTEND ZONE ZONE I I REACHREACH -

- TO TO BLOCK BLOCK RELAY RELAY OPERATIONOPERATION

COMMUNICATION EQUIPMENT

(144)

(145)

General Line Protection

Permissive communication schemes

– Communication signal carrier send (CS) is sent to remote end

when the fault is detected in forward direction. Tripping is achieved

when the commmunication signal carrier receive (CR) is received

and the local relay has detected a forward fault.

– In a permissive underreaching scheme the communication signal is

sent from a zone that underreaches the remote end.

– In a permissive overreaching scheme the communication signal is

sent from a zone that overreaches the remote end.

A

Z< _Z< B

Carrier send CS = Z< forward, under or overreach Trip = ZM1 + ZM2 (t2 + CR) + ZM3 x t3

(146)

(147)

General Line Protection

PERMISSIVE OVERREACHING SCHEMES

PERMISSIVE OVERREACHING SCHEMES ARE ARE ADOPTED FOR ADOPTED FOR SHORTSHORT LINES

LINES (

( ALSO ALSO CALLED CALLED DIRECTIONAL DIRECTIONAL COMPARISON COMPARISON SCHEMES)SCHEMES) ADVANTAGES

ADVANTAGES AREARE •

• BETTER PERFORMANCBETTER PERFORMANCE FOR HIGH E FOR HIGH RESISTANCE FAULTS.RESISTANCE FAULTS. •

• SUPERIOR TO PILOT SUPERIOR TO PILOT WIRE AS WIRE AS DIGITAL DECISIONS AREDIGITAL DECISIONS ARE EXCHANGED

EXCHANGED AND AND NOT NOT ANALOGUEANALOGUE • SUPERIOR

• SUPERIOR TO PHASE TO PHASE COMPARISON WHICH REQUIRESCOMPARISON WHICH REQUIRES FAITHFUL

FAITHFUL TRANSMISSION TRANSMISSION OF OF PHASE PHASE INFORMATION.INFORMATION.

PERMISSIVE COMMUNICATION SCHEMES

(148)

(149)

General Line Protection

Blocking communication schemes

–

– Communication

Communication signal (CS) i

signal (CS) is sent to rem

s sent to remote end when

ote end when the

the

fault is detected in the

fault is detected in the reverse direction. Tripping is achieved

reverse direction. Tripping is achieved

when this blocking signal is not received within a time T0

(20-40 ms) and the local relay has detected a fault in the forward

40 ms) and the local relay has detected a fault in the forward

direction.

A A BB Z< Z< _Z<_Z<

Carrier send CS = Z< reverse zone

Trip = ZM1 + ZM2 (t2 + CR x T0) + ZM3 x t3

(150)

(151)

General Line Protection

BLOCKING COMMUNICATION SCHEMES

BLOCKING SCHEMES ARE USED WHEN COMMUNICATION SIGNALS BLOCKING SCHEMES ARE USED WHEN COMMUNICATION SIGNALS SHALL NOT BE TRANSMITTED OVER FAULTY LINE FOR RELIABILITY SHALL NOT BE TRANSMITTED OVER FAULTY LINE FOR RELIABILITY REASONS

REASONS

Ex : BOOSTING OF SIGNAL NOT PERMITTED. Ex : BOOSTING OF SIGNAL NOT PERMITTED.

(152)

(153)

General Line Protection

(154)

(155)

General Line Protection

Current reversal logic

~

A:1 B:1 A:2 B:2 A:1 B:1 A:2 B:2

Permissive overreaching schemes

can trip healthy line without C.R.L

1 Fault occurs on line 1

Fault detection by protection A:1 B:1 and A:2 2 Relay B:1 trips CB and sends carrier to A:1 Relay A:2 sees fault in forward direction and sends carrier to B:2

3 Fault cleared at B:1, current direction changed on line 2

4 Carrier from A:2 and forward looking measuring element in relay A:2 does not reset before relay B:2 detects the fault in forward direction and

trips, also relay A:1 will trip when receiving carrier from B:1

C.R.L allows slowly resetting

(156)

(157)

General Line Protection

(158)

(159)

General Line Protection

Switch On To Fault (SOTF)

• When energizing a power line onto a forgotten earthing no

measuring voltage will be available and the directional measuring

can thus not operate correctly.

– A special SOTF function is thus provided. Different principles

can be used, from one phase current to undirectional

impedance measuring.

Z<

U=0 V

SOTF conditon can either be

taken from the manual closing

signal activating the (BC) input

or it can be detected internaly by

a logic.

(160)

(161)

General Line Protection

(162)

(163)

General Line Protection

Weak end infeed

Weak end infeed is a condition which can occur on a transmission

line, either when the circuit breaker is open, so there is no current

infeed from that line end, or when the current infeed is low due to

weak generation behind the protection.

CS = ZM2

TRIP = ZM1 + ZM2(CR + t2)

CS (echo)=CR x low voltage x no start forward or reverse

l

t1 t2 t3 Z< _Z< CS CS (echo) CR CR

(164)

(165)

General Line Protection

WEAK END INFEED

• IN PERMISSIVE OVER REACH SCHEMES BOTH CBS MAY FAIL TO TRIP INSTANEOUSLY DUE TO NO CARRIER SEND SIGNAL AND NO RELAY OPERATION IN WEAK END.

• IN PERMISSIVE UNDERREACH SCHEMES FAST FAULT CLEARENCE OF WHOLE LINE SECTION WILL NOT BE THERE BECAUSE NO

SIGNALS WILL BE SENT FROM THE WEAK END.

• IN BLOCKING SCHEME OR PERMISSIVE UNDERREACH SCHEME THE LOW INFEED END WILL FAIL TO TRIP INSTANTANEOUSLY.

(166)

(167)

General Line Protection

WEAK END INFEED.

THE LOGIC DESCRIBED FOR PERMISSIVE OVERREACH SCHEME CAN BE USED IN TWO MODES.

-ECHO FOR COMMUNICATION SIGNAL ONLY.

-ECHO OF COMMUNICATION SIGNAL AND TRIP OF LOCAL CB.

IN CASE OF PERMISSIVE UNDERREACH SCHEME THE LAST 10-20 % TOWARDS WEAK END WILL BE CLEARED IN ZONE II TIME .

IF THIS IS NOT ACCEPTABLE OVERREACH SCHEME SHOULD BE USED. IN BLOCKING SCHEME WEAK END CB CANNOT BE TRIPPED .

IN SUCH CASE DIRECT TRIPPING FROM ZONE I AND ACCLERATED ZONE MUST BE USED.

(168)

(169)

General Line Protection

(170)

(171)

General Line Protection

THIS FUCTION IS BASED ON CONDITION

3U_O> 20 % OF U_n/

√

3 AND 3I_O < 20 % OF I_n

IT CAN BE SELECTED TO BLOCK PROTECTION AND GIVE ALARM OR JUST TO GIVE ALARM.

FUSE FAIL SUPERVISION IS BLOCKED FOR 200ms FOLLOWING LINE ENERGISATION IN ORDER NOT TO OPERATE FOR UNEQUAL POLE CLOSING AND ALSO DURING AUTORECLOSING.

MCB CAN ALSO BE USED.

(172)

(173)

General Line Protection

(174)

(175)

General Line Protection

SYSTEM SUPERVISION

.

• OVER LOAD SUPERVISION GIVES ALARM IF CURRENT EXCEEDS FOR 10 SECS.

• UNSYMMETRICAL LOAD CONDITION CHECK GIVES ALARM WHEN ANY PH CURRENT IS LOWER THEN 80% OF LARGEST PH CURRENT. ALSO

LARGEST PH CURRENT MUST BE > 15% OF NOMINAL CURRENT.

• LOSS OF VOLTAGE SUPERVISION CAN TRIP OR GIVE ALARM WHEN ALL 3 PH VOLTAGES ARE LOW FOR MORE THEN 7 SECS.

SYSTEM SUPERVISION CONSISTS OF FEATURES TO GIVE ALARM FOR UNNATURAL CONDITIONS VIZ.

- OVERLOAD SUPERVISION - BROKEN CONDUCTER - LOSS OF VOLTAGE

(176)

(177)

General Line Protection

(178)

(179)

General Line Protection

FAULT LOCATOR

×

R _F

P

U

_A IFA

D

A

I

A

×

p

Z

L

I

R

F

U

A

= I

A

×

P

Z

L

+

I

FA

D

A

×

R

F

P

2

- p

×

k

1

+ k

2

- k

3

×

R

F

= 0

(180)

(181)

General Line Protection

FAULT LOCATOR

∼

-+

L

F

A

B

I

A

I

F

I

B

Z

A

Z

B

R

F p

Z

L

( I - p )Z

L p

Z

L

( 1- p ) Z

L

Z

A

Z

B

Fault Locator Measuring Principle

U_A=I_AX _PZ_L+ I_FAX R _F D_A

D_A =

(I-_P) Z_L+Z_B Z_A+Z_L+Z_B

(182)

(183)

General Line Protection

FAULT LOCATOR

For Double Circuit Lines.

U

A

= I

A

. pZ

L

+

I

FA

D

A

.

_R

_F

_{+ I}

_OP

_{. Z}

_OM

p

2

-

p k

1

+ k

2

- k

3

R

F

=

0 D

_A

=

(1-p) ( Z

1A

+ Z

1L

+ Z

1B

)

2 Z

_1A

+ Z

_IL

+ 2Z

_1B

WHERE

I

_A

Z

_1L

Z

_1L

+ Z

_ADD

K

₁

=

U

A

+

Z

1B

+ 1

K

2

=

I

_A

Z

_1L

Z

_1L

+ Z

_ADD

U

_A

Z

_1B

(

+ 1

I

_A

Z

_1L

Z

_1L

+ Z

_ADD

K

₂

=

I

FA

(

Z

1A +

Z

1B

+ 1

,

)

(184)

(185)

General Line Protection

(186)

(187)

General Line Protection

Stub protection function

It is not possible for the distance protection relay to measure

impedance when the line

disconnector is open. Not to risk incorrect operation the distance protection must be blocked and a Stub protection is released.

The Stub protection is a simple current relay. line disc open I STUB > & trip 25ms Bus A Bus B > Z +

(188)

(189)

General Line Protection

(190)

(191)

General Line Protection

Earth fault current in solidly grounded system

Reverse operation Forward operation Upol -3U0 3I0D 0.6 3I0Dx

3I

0

>

3I0 X cos(65-

φ

)=3I0D

φ

= the characteristic angle of zero sequence source impedance

(192)

(193)

General Line Protection

• HIGH FAULT RESISTANCE CAN BE DIFFICULT TO DETECT THROUGH DISTANCE RELAYS.

• THIS CAN BE OVERCOME BY E/F O/C PROTECTION EITHER NON DIRECTIONAL OR DIRECTIONAL.

• PROVIDED WITH SECOND HARMONIC CURRENT RESTRAINT WHICH BLOCKS OPERATION IF RESIDUAL CURRENT CONTAINS 20% OR MORE OF SECOND HARMONICS.

• POLARIZING VOLTAGE CAN HAVE HIGH AMOUNT OF HARMONICS WHEN OUTPUT VOLTAGE IS LOW PARTICULARLY WHEN CVTS ARE PROVIDED. THEREFORE RELAY MUST HAVE BAND PASS FILTER. BAND PASS FILTER PROVIDES SECURE OPERATION DOWN TO 1% OF NOMINAL VOLTAGE.

EARTH FAULT CURRENT IN SOLIDLY

GROUNDED SYSTEM.

(194)

(195)

General Line Protection

(196)

(197)

General Line Protection

1.0 GENERAL

• The auto-reclosing of power lines has become a generally accepted practice.

• Reports from different parts of the world show that in

certain networks in region subject to a high lightening intensity only about 5% of the faults are permanent.

• Auto reclosing therefore provides significant advantages.

• Outage times will be short compared to where station personnel have to re-energize the lines after a fault.

• In interconnected networks auto-reclosing helps in maintaining system stability

(198)

(199)

General Line Protection

1.1 Recommendations for provisions of auto-reclosing 1.1 Recommendations for provisions of auto-reclosing

• Presently 1 phase high speed auto-reclosure (HSAR) at 400kV and 220kV level is widely practised including on lines emanating from Generating Stations and the same is recommended for adoption. • If 3-phase auto-reclosure is adopted in future the application of the

same on lines emanating from generating stations should be studied and decision taken on case to case basis.

(200)