General Line Protection

General Line Protection List of Topics 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.

Distance relays - basics Operating characteristics Effect of parallel line Phase selection Power swing blocking Communication scheme Switch on to fault Weak end infeed Supervision fuse failure System supervision. Fault locator  Stub protection Earth fault protection Auto reclosing systems

General Line Protection

1-Distance relay basics

General Line Protection

1-Distance relay basics

General Line Protection Objective of relay protection • Protect persons and equipment in the surrounding of the power system • Protect apparatus in the power system • Separate faulty parts from the rest of the power system to facilitate the operation of the healthy part of the system

General Line Protection

Electrical faults in the power system • Transmission lines

85%

• Busbar

12%

• Transformer/ Generator

3%

Total

100 %

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 lightnings are 0,2-3 faults/ 100 km and year 

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  – must be located and repaired before normal service

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.

~

Z<

L1-N

L2-N

~

L3

L1

L1

L2

L2

L3

General Line Protection Fault resistance • multi-phase faults consist only of arc resistance

• earth faults

L3

L1

L1

L2

L2

L3

consist of arc and tower  footing resistance

Warrington´s formula

Rarc =

28707 x L

L= length of arc in meters

1.4

I

I= the actual fault current in A

Footing resistance

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

General Line Protection

MAIN REQUIREMENTS ON LINE PROTECTION ARE: • SPEED • SENSITIVITY • SELECTIVITY • DEPENDABILITY • SECURITY • RELIABILITY • MTBF

General Line Protection Measuring principles • Overcurrent protection • Over current & under voltage combination • Differential protection • Phase comparison • Directional- wave protection • Distance protection

General Line Protection The principle of distance protection

ZK=Uk / Ik Uk

Uk=0 metallic fault

Zk

A

Z<

Ik

B

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. A

B

ZL=R+jX

Z<

Z<

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

VTsec Zsec= VTprim

x

CTprim CTsec

x

Zprim

General Line Protection The principle of distance protection

t t3 t2 t1

l

A

B f1

Z<

C f3

f2

Z<

Z<

Z<

t t3 t2

l

t1

General Line Protection Measuring loop for earth faults • The distance protection relays are always set based on the phase impedance to the fault Zs

IL1

RL

XL

IN

RN

XN

UL1

The measured Impedance is a function of  positive and zero sequence impedance

General Line Protection Measuring loop for two- phase faults • The distance protection relays are always set based on the phase impedance to the fault Zs

IL1 UL1-L2

RL

XL

IL2

The measured impedance is equal to the positive sequence impedance up to the fault location

General Line Protection Measuring loop for three- phase faults • The distance protection relays are always set based on the phase impedance to the fault Zs

IL1 UL1 UL2

RL

XL

IL2 IL3

UL3

The measured impedance is equal to the positive sequence impedance up to the fault location

General Line Protection The earth fault measurement U= I1Z1+I0Z0+I2Z2

Z1=Z2

U= Z1( I1+I2+I0 ) +I0Z0 -I0Z1

I= I1+I2+I0 3I0=IN

U=I Z1+I0 ( Z0 - Z1 )

U=I Z1+

IN 3

( Z0 - Z1 )

U=IZ1+IN

(

Z0 - Z1 3

)

General Line Protection The earth fault measurement • The current used is thus the phase current plus the residual current times a factor KN = (Z0-Z1) / 3Z1, the zero sequence compensation factor. • The factor KN is a transmission line constant and Z0 / Z1 is presumed to be identical throughout the whole line length. • (1+KN) Z1 gives the total loop impedance for the earth fault loop for single end infeed.

General Line Protection Double end infeed I1

I Load

I2 U2

U1 UF

RF

UF = RF ( I1 + I2 ) RF ( I1 + I2 ) RF1=

I1

General Line Protection Measuring error at high resistive earth fault on a line with double end infeed X

Rf Load import

ZL Rf Load export

R

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.

A

ZL Um

If1 B If2 If3

ZF

If=If1+If2+If3

Z<

Um= If1 x ZL+ (If1+If2+If3) x ZF

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 measurement.

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<

L1-N

L2-N

~

General Line Protection

2- Operating characteristic

General Line Protection THE FIRST ZONE CHARACTERISTIC 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.

General Line Protection THE FIRST ZONE CHARACTERISTIC(Contd..) 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.

General Line Protection THE SECOND ZONE CHARACTERISTIC

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.

General Line Protection THE THIRD ZONE CHARACTERISTIC

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.

General Line Protection DISTANCE PROTECTION ON SHORT LINES.  jX

• Low measured reactance • Ratio between fault resistance and resistance is high. • Distance protection with mho characteristic can not see an average fault resistance. R F XF

R 

General Line Protection DISTANCE PROTECTION ON SHORT LINES • Low measured reactance  jX

• Ratio between fault resistance and reactance is   high. • Distance protection with mho characteristic can not see average fault resistance. • Cross polarization has no significant effect.

R F XF

R 

General Line Protection DISTANCE PROTECTION ON SHORT LINES • Quadrilateral characteristic improves sensitivity for higher R F/XF ratio.

 jX

• It still has some limitations. -The value of set R F/ XF ratio is is limited by 5 - Remote infeed increases the apparent value of fault resistance. - Requirements on current instrument transformers are   stringent.

R F XF

R 

General Line Protection DISTANCE PROTECTION ON SHORT LINES.  jX

R F XF

R 

•

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.

General Line Protection  jX

DISTANCE PROTECTION ON LONG LINES

• Load impedance limits the reach in resistive direction. • High value of R F / XF ratio is generally not necessary.

R 

General Line Protection DISTANCE PROTECTION ON LONG LINES • Load impedance limits the reach in resistive direction. • High relay of R F/ XF ratio 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. • Sensitivity for low currents. R 

General Line Protection • AT THE ORIGIN DIRECTIONAL DISCRIMINATION REQUIRED BY LINE PASSING THROUGH 2nd QUADRANT , 4th  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 U1R + 0.2 U 1RM WHERE U1RM IS MEMORY VOLTAGE (+VE SEQUENCE) THIS WILL ENSURE CORRECT DIRECTIONAL DISCREMINATION. EXTENSION IN 2nd AND 4th LIMITED TO AVOID OPERATION OF UNFAULTED PHASE AN ALSO DURING SWINGS YET GIVE GOOD DYNAMIC PERFORMANCE.

General Line Protection LOAD CURRENT INFLUENCES THE IMPEDANCE MEASUREMENT.

       c e          an        ed       p              im      e             in          L

General Line Protection LOAD CURRENT INFLUENCES THE IMPEDANCE MEASUREMENT.

The same fault position Equal fault resistance    e    c        n    a          d    e        p                im    e               in      L

Characteristic with out load compensation

General Line Protection A

∼

B

ILOAD

∼

ZL R F

EB EA IFA

IFB

EXPORTING END OVERREACHING

ZM = Z L + R F

 Note : Currents and voltages are phasors

(

1+

IFB I FA

)

IMPORTING END OVERREACHING

General Line Protection LOAD CURRENT INFLUENCES THE IMPEDANCE MEASUREMENT.

The same fault position Equal fault resistance        c e        a n         e d      p            I m      e           i n     L

Characteristic with out load compensation

Load compensated characteristic

General Line Protection IT IS NOT WHAT MANY HOPE IT IS

   C    L    A    C    R

•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

General Line Protection IT IS NOT WHAT MANY HOPE IT IS

   C    L    A    C    R

•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.

General Line Protection

3- Effect of parallel line

General Line Protection Zero- sequence mutual coupling on parallel lines ZL

~

ZOM ZL

~

ZA< overreaching

~

~

ZA<

ZB< ZB< underreaching

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.

General Line Protection EFFECT OF MUTUAL COUPLING ON DISTANCE RELAYS

∼

∆

∆

ZOM

∼

PARALLEL LINE EARTH CURRENT = IEP = 3IOP INDUCED VOLTAGE IN THE FAULT LOOP = I EP • ZOM / 3 DISTANCE RELAY PH- EARTH UNIT MEASURES Z = VPH- E / = ZL • IPH

( I PH + K O IE ) WHERE K O = ZOL - ZL / 3ZL + ( ZOL - ZL ) IE / 3ZL + IEP • ZOM / 3ZL IPH + K O IE

= ZL

[

 1 + K OM • IEP / IPH + K O IE ERROR 

]

WHERE K OM = ZOM / 3ZL

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.

General Line Protection EFFECT OF MUTUAL COUPLING ON DISTANCE RELAYS

∼

∆

∆

∆Z = - ZL  •

K OM • ZOM / ZOL

= - 0.23 ZL

1 + K O

∼

General Line Protection EFFECT OF MUTUAL COUPLING ON DISTANCE RELAYS.

∼

∆ D K OM

∆Z = 1 + K O

• ZL

= 0.38 ZL

ZOL - ZL K O =

3 ZL

= 0.864

 K OM = ZOM / 3ZL = 0.716 R 1 + j X1 = 0.0289 + j 0.307 Ω / KM

∴ ZL = 0.308 Ω / KM

R O + j X 0 = 0.276 + j 1.0715 Ω / KM

ZOL = 1.106 Ω /KM

R MO1 + j XMO = 0.228 + j 0.622 Ω / KM

ZOM = 0.662 Ω/ KM

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 )

PH- E

∼ D 1+

Z = X ZL •

(

ZOL - ZL 3ZL

- K OM •

ZOM

)

ZOL

 1 + K O

∴ SET K O =

[

ZOL - ZL  3ZL

 - K OM

ZOM  ZOL

]

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%

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 = ZL

∴ SET

[

1+

K 0

(ZOL

=

ZL ) / 3ZL + K OM 1 + K O -

ZOL - ZL 3 ZL

+ K OM

] AND REACH TO 120 %

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 ZL

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 INTERMEDIATE INFEEDS AT REMOTE STATION.

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.

General Line Protection ALTERNATIVE 1

K  N1 =

K  N2 =

-

[

ZOL

[

ZOL

K  N3 =

WHERE

ZL

3ZL

-

ZL

3ZL

[

ZOL - ZL

K OM

3ZL

=

ZOM

-

+

] / 3ZL

K OM

ZOM ZOL

K OM

]

]

General Line Protection ALTERNATIVE 2 CASE 1 - PARALLEL LINE SWITCHED OFF WITH BOTH ENDS   EARTHED.

K  N1

[

=

ZOL

-

ZL

3ZL

K O M

-

ZOM ZOL

]

 N3 IDENTICAL TO ALT 1 K  N2 ,  K 

CASE 2 - DOUBLE CIRCUIT PARALLEL LINE IN OPERATION.

K  N1

=

[

ZOL - ZL 3ZL

+

K OM

K  N2 , K  N3 IDENTICAL TO ALT 1

]

General Line Protection

4-Phase selection

General Line Protection PHASE SELECTION. 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.

General Line Protection .

PHASE SELECTION

• I PH FAULTS

 jX

UR 

XNPh

IR 

< R  N4 + j x  N4

2 . ( 1 + Kn )

Us Is UT IT RN2

RNPh

R 

< R  N4 + j x  N4 < R  N4 + j x  N4 ALSO 3Io > 0.1 In

& 3Io > 0.2 I pHMAX

Characteristic of phase selector for single-phase faults.

General Line Protection PHASE SELECTION

• 2 PH FAULTS.

 jX

UR - UT < IR 

XPh 2. X2

R 4 + j X4

Us - UR  < R 4 + j x4 IS

α

UT - UR  IT

•

70

2.R2

∂

R  RPh

< R 4 + j x4

ALSO 3Io < 0.2 I N & 3Io < 0.4I pHMAX

General Line Protection  jX’

 jX

PHASE SELECTION

2.X2

R’

XPh .2/

• 3 PH FAULTS.

RPh 2/√3

α 2. R2

δ

Characteristic of phase selectors at three phase faults.

THIS IS SIMILAR TO PH - PH FAULTS WITH FOLLOWING DEVIATIONS.

100 •

R 

- ROTATED ANTICLOCKWISE   BY 30 DEGREES. - REACH 2/ √ 3 TIMES THAT OF FOR PH - PH FAULTS.

General Line Protection

5- Power swing blocking

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.

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.

General Line Protection Power Swing Blocking function X Power swing locus

R

∆t

∆t = 40 ms

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 2 P = 0.35 ( 0.75 + O.25 V )

X

V = 0.8PU•

•V = 1.1 PU

R 

General Line Protection SIMPOW ( SIMULATION OF POWERSYSTEMS ) • 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).

General Line Protection

6- Communication scheme

General Line Protection COMMUNICATION EQUIPMENT A

∼

B

× × × ××

×

IN THE ABSENCE OF COMMUNICATION LINK 

-THE OPERATION ZONE OF END ZONE FAULT IS LONGER. -AUTO RECLOSING IS NOT POSSIBLE.

∼

General Line Protection Communication equipment • Power Power line line carrier carrier (PLC) (PLC) equipme equipment nt is based based on a capaciti capacitive ve connection of signals with frequency in the range 50- 500 kHz on the power line. • Radio link is a good and and reliable reliable communicat communication ion equime equiment, nt, but but is rarely used due to the high cost. • Optical Optical fibres fibres have have the the advantage advantage to be insen insensitiv sitive e to noise noise and and can transmit a huge amount of information.

General Line Protection COMMUNICATION EQUIPMENT RELAY SETTING AND THE WAY SIGNALS ARE USED IS GIVEN BELOW. FIRST ZONE REACH • UNDER REACHING (0.8 TO 0.9 Z AB ) • OVER REACHING ( 1.2 Z AB) USE OF RECIVED SIGNAL • OPERATION OF CB IF LOCAL RELAY HAS PICKED UP • AS INFORMATION INFORMATION REGARDING REGARDING DIRECTION OF FAULT - FOR COMPARISON WITH LOCAL END - TO EXTEND ZONE I REACH - TO BLOCK RELAY OPERATION

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

B

Z<

Z<

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

General Line Protection PERMISSIVE COMMUNICATION SCHEMES  

PERMISSIVE OVERREACHING SCHEMES ARE ADOPTED FOR SHORT LINES ( ALSO CALLED DIRECTIONAL COMPARISON SCHEMES) ADVANTAGES ARE • BETTER PERFORMANCE PERFORMANCE FOR HIGH RESISTANCE FAULTS. • SUPERIOR TO PILOT WIRE AS DIGITAL DECISIONS ARE EXCHANGED AND NOT ANALOGUE • SUPERIOR TO PHASE COMPARISON WHICH REQUIRES FAITHFUL TRANSMISSION OF PHASE INFORMATION.

General Line Protection Blocking communication schemes  – Communication signal (CS) is is sent to remote remote end when the fault is detected in the reverse direction. Tripping is achieved when this blocking signal is not received within a time T0 (2040 ms) and the local relay has detected a fault in the forward direction. A

B

Z<

Z<

Carrier send CS = Z< reverse zone Trip = ZM1 + ZM2 (t2 + CR x T0) + ZM3 x t3

General Line Protection BLOCKING COMMUNICATION SCHEMES

BLOCKING SCHEMES ARE USED WHEN COMMUNICATION SIGNALS SHALL NOT BE TRANSMITTED OVER FAULTY LINE FOR RELIABILITY REASONS Ex : BOOSTING OF SIGNAL NOT PERMITTED.

General Line Protection

7- Current reversal logic

General Line Protection Current reversal logic

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

~

A:1

A:2

~

B:1

2 Relay B:1 trips CB and sends carrier to A:1

~

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

B:2

A:1

B:1

A:2

B:2

Relay A:2 sees fault in forward direction and sends carrier to B: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 communication equipment without risk

General Line Protection

8- Switch on to fault

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.

U=0 V Z<

SOTF conditon can either be taken from the manual closing signal activating the (BC) input or it can be detected internaly by a logic.

General Line Protection

9- Week end infeed

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.

CR Z< t3 t2

CS (echo)

CS

t1

CR

Z<

l

CS = ZM2 CS (echo)=CR x low voltage x no start forward or reverse TRIP = ZM1 + ZM2(CR + t2)

General Line Protection WEAK END INFEED DUE TO WEAK END INFEED FOLLOWING WILL HAPPEN. • 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.

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.

General Line Protection

10- Supervision of fuse failure

General Line Protection FUSE FAIL SUPERVISION THIS FUCTION IS BASED ON CONDITION 3UO > 20 % OF Un / √ 3 AND 3IO < 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.

General Line Protection

11- System supervision

General Line Protection SYSTEM SUPERVISION. SYSTEM SUPERVISION CONSISTS OF FEATURES TO GIVE ALARM FOR UNNATURAL CONDITIONS VIZ. - OVERLOAD SUPERVISION - BROKEN CONDUCTER  - LOSS OF VOLTAGE

•

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.

General Line Protection

12- Fault locator 

General Line Protection FAULT LOCATOR P

IFA

DA

× R 

F

UA

UA = IA × P ZL +

P

IA ×pZL

2

IFA × R F DA

P - p × k 1 + k 2 - k 3 × R F = 0

I

R F

General Line Protection FAULT LOCATOR Fault Locator Measuring Principle

L F

∼

ZA

A

pZL

IF

IA

( I - p )ZL B ZB IB

∼ UA=IA X P ZL + IFA X R F

 R F

DA

pZL

ZA

( 1- p ) ZL

∼ +

ZB

(I-P) ZL +ZB DA = ZA+ZL +ZB

General Line Protection FAULT LOCATOR For Double Circuit Lines. UA = IA . pZL +

IFA . R F + IOP . ZOM DA

 2 p - p k 1 + k 2 - k 3 R F = 0

DA = WHERE

(1-p) ( Z1A + Z1L + Z1B )  2 Z1A + ZIL + 2Z1B

UA K 1 = IA Z1L+ IFA  ( K 2 = IA Z1L

Z1B Z1L+ ZADD + 1 Z1A + Z1B ) + 1 Z1L+ ZADD

,

K 2 =

UA IA Z1L (

Z1B Z1L+ ZADD + 1 )

General Line Protection

13- Stub protection

General Line Protection Stub protection function Bus A

+

>Z

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

Bus B

I  STUB >

25ms

&

trip

General Line Protection

14- Earth fault protection

General Line Protection Earth fault current in solidly grounded system

Reverse operation

0.6x3I0D

φ=65 3I0D

Upol

Forward operation

-3U0

3I0 X cos(65-φ)=3I0D

φ = the characteristic angle of zero sequence source impedance

3I0 >

General Line Protection EARTH FAULT CURRENT IN SOLIDLY GROUNDED SYSTEM. • 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.

General Line Protection

15- Auto reclosing

General Line Protection 1.0 1.0 GENERAL 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

General Line Protection 1.1 1.1 Recommendations Recommendationsfor forprovisions provisionsof ofauto-reclosing 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.

General Line Protection 2.0 2.0 SETTING SETTINGCRITERIA CRITERIA 2.1 2.1 Dead DeadTime Time

• Auto- reclosing requires a dead time which exceeds the de-ionising time • Time required for the de-ionising of the fault path depends on:- arcing time, fault duration, wind conditions, circuit voltage, capacitive coupling to adjacent conductors, etc. • Single phase dead time of 1.0 sec is recommended for both 400kV and 220kV system.

General Line Protection 2.2 2.2 Reclaim ReclaimTime Time

• The time during which a new start of the auto-reclosing equipment is   blocked. • If reclosing shot has been carried out and the line is energized and a new fault occurs before the reclaim time has elapsed, the auto-reclosing equipment is blocked and a signal for definite tripping of the breaker is   obtained. • After the reclaim time has elapsed, the auto-reclosing equipment returns to the starting position and a new reclosing sequence can occur. • The reclaim time must not be set to such a low value that the intended operating cycle of the breaker is exceeded, when two faults incidents occur close together.

General Line Protection • If the breaker is closed manually, the auto reclosing equipment is blocked and cannot start again until the reclaim time has elapsed. • For the breaker to be used for auto-reclosing, it is essential that it has the operating mechanism and breaking capacity necessary for  it to be able to perform the auto-reclosing sequences required.

General Line Protection 2.3 2.3 Circuit CircuitBreaker BreakerRequirement Requirement

• According to IEC Publication 56.2, a breaker must be capable of  withstanding the following operating cycle with full rated breaking   current: O + 0.3 s + CO + 3 min + CO • The recommended operating cycle at 400kV and 220kV is as per the IEC standard. • Reclaim time of 25 sec is recommended.