fundamentals related to distance relays

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Apparatus Maintenance and Power Management for Energy Delivery

Introduction to Distance Protection Jay Gosalia Vice President of Marketing Doble Engineering Company

Objective of Relay Protection ¾ Protect persons and equipment in the surrounding of the power system ¾ Protect apparatus in the power system ¾ 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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Electrical Fault in Power System ¾ Transmission lines ¾ Busbar ¾ Transformer/ Generator 12%

85% 12% 03%

3%

85%

Transmission lines

Busbar

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TFR/Gen

Fault Statistics ¾ ¾ ¾ ¾

Single phase to earth Two phases to earth Phase to phase faults Three phase faults 10%

5%

80% 10% 5% 5%

5%

80% Ph-G Flt

Ph-Ph-G Flt

Ph-Ph Flt

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3 Ph Flt

Fault Type in Transmission Line ¾ Transient faults

Common on transmission lines, approximately 80-85% Lightnings are the most common reason Caused by birds, falling trees, forest growth, Swinging lines, High velocity winds etc. • Disappear after a short dead interval

¾ Persistent faults Caused by a broken conductor fallen down Tree falling on a line • Must be located and repaired before normal service

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Protection Types ¾ Unit Protection ¾ Non-Unit protection

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Protection Types ¾ Unit Protection Differential protection • Transformer differential protection Bus differential protection • Generator differential protection • Line differential protection Pilot protection • Transfer trip schemes • Under/over reaching pilot protection with distance protection

¾ Non-Unit protection Over Current protection • Time over current or instantaneous protection 3 Zones of distance protection Knowledge Is Power

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Unit Protection TFR

Protection Unitprotection protectionprovides providesthe theprotection protectionififthe the Unit faultisisinside insidethe theZone Zoneof ofprotection protection fault doesnot notprovide providethe theprotection protectionififthe thefault fault ItItdoes outsidethe theZone Zoneof ofprotection protection isisoutside Knowledge Is Power

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Non-Unit Protection B

A

C

Time

Zone 3

Zone 2 Zone 1 Distance

Zone11provides providesthe theinstantaneous instantaneousprotection protection Zone forthe theline lineAB AB for Zone22and andZone Zone33are arethe theback backup upprotection protection Zone Knowledge Is Power

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D

Non-Unit Protection ¾It’s a Non Unit Protection but can be modified to Unit Protection when combined with signaling channel

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Application Application Examples Examples

Design Design

Basicsof of Basics Distance Distance Protection Protection

Distance Protection

Theoryof of Theory operation operation Knowledge Is Power

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Distance Protection: Principle

¾ Protection works on impedance seen by the protection ¾ Impedance is directly proportional to distance so it’s a distance protection ¾ Requires inputs for voltage and current Using CTs and PTs ¾ Current is an operating force and voltage is a restraining force Normal load condition restraining force is higher then the operating force Knowledge Is Power

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Distance Protection: Principle Voltage

Current

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Fault condition B

A

C

¾ Normal condition Normal voltage & load current 69 Volts and 1 A load current

¾ Fault condition Depressed voltage & high current 20 Volts & 10 A fault current Knowledge Is Power

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D

Fault condition A

B

C

¾ Quick isolation of the faulted section Reduces damage caused by the fault Less stress on the electrical apparatus Maintains the flow of electricity to healthy section

¾ Quick and fast detection of the fault condition Fast operation of the distance protection Knowledge Is Power

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D


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Distance Protection: Ph-Ph Fault

The measured impedance is equal to the Positive & Negative sequence impedance up to the fault location Knowledge Is Power

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Distance Protection: 3 Ph Faults

The measured impedance is equal to the Positive Sequence impedance up to the fault location Knowledge Is Power

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Distance Protection: Ph-G Faults

The measured impedance is equal to the Positive, Negative & Zero Sequence impedance up to the fault location Knowledge Is Power

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Distance Protection: Ph-G Faults

¾The current is Phase current + the Residual current ¾Residual current = Iph * (Z0-Z1) / 3Z1, ¾ KN = Zero Sequence compensation factor. ¾The factor KN is a transmission line constant ¾Identical throughout the whole line length. ¾ Total loop impedance = (1+KN) Z1 Knowledge Is Power

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Distance Protection: Principle B

A

Reactance : X

C

D

Z

RF

Resistance : R Knowledge Is Power

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Distance Protection: Principle I

Z

IZ

+

V

IX

Angle Comparator >= 900

IZ V-IZ

Angle = 900 V IR Knowledge Is Power

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Output

Distance Protection: Principle I

Z

IZ

+

V

IX


IZ V-IZ

V IR Knowledge Is Power

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Output


Angle between the two cords drawn from the diameter Of a circle is always 90 degrees. Knowledge Is Power

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Distance Protection I

Z

IZ

+

V

IX


Output

IZ V-IZ

Internalfault fault Internal Angle>=90 >=9000 Angle


SM


Distance Protection I

Z

IZ

+

V

IX


Output

IZ V-IZ

Externalfault fault External Angle<<90 9000 Angle


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Distance Protection : Design IX

¾ Set a replica impedance

IZR Vpol - IZR

Replica of line impedance Magnitude and angle : ZR Called reach of the Relay

Vpol

¾ Convert current I in to vector IZR ¾ Derive voltage of the system : V

IR

Reference voltage V , Polarizing Voltage : Vpol

¾ Calculate voltage vector Vpol - IZR ¾ Measure the angle between Vpol and Vpol – IZR ¾ Output if the angle is 900 or greater ¾ This produces “MHO” Characteristic Knowledge Is Power

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Distance Protection : Ph-G Fault ¾ For A-G fault IZR is IA*ZR Vpol is VA Vpol – IZR is VA – IAZR

¾ When polarizing voltage = Fault voltage Self polarized Relay For B-G fault • Polarized voltage = Fault voltage = VB

¾ Earlier designs were self polarized distance relays Knowledge Is Power

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Self Polarized Protection ¾ Limitations What happens if the fault is at the terminal of the breaker? • Fault voltage is 0 • Polarized voltage is 0 • No reference voltage Vpol to compare with V-IZ • Self polarized distance protection no good for 0 voltage phase to ground fault

¾ Solution Use memory voltage instead of faulted phase voltage Knowledge Is Power

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Memory Polarized Protection I V

Z

IZ

+

Output Angle Comparator >= 900

Memory

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Memory Polarized Protection I V

Z

IZ

+

Output Angle Comparator >= 900

Memory

¾ What memory voltage does to the “MHO” characteristic?

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Memory Polarization E

G

E

B

Load Current

A

Zs

21 Pre-Fault voltage at the protection before the fault is E (neglecting load current drop in Zs)

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Memory Polarization

A

G

Zs

VF E

B

Fault Current IF

21

Pre-Fault voltage at the protection before the fault is E (neglecting load current drop in Zs) Just after the fault the E = VF + IFZs Knowledge Is Power

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Memory Polarization IX

IZR V-IZ

Angle>>90 9000 Angle VF IR Vpol = V pre fault IZs

E = VF + IFZs Knowledge Is Power

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Mho Ch. : Memory Polarization IX

IZR V-IZ

VF IR Vpol = V pre fault IZs

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Memory Polarization Effect IX

IZR Morefault faultresistance resistance More Coveragedue dueto to Coverage memoryPolarization Polarization memory

V-IZ

VF IR

IZs

Vpol = V pre fault

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Memory Polarization: Summary ¾ Provides reference voltage (Vpol) under all phase and ground faults ¾ Expand the self polarized characteristic to cover more fault resistance No overreaching at reach point Circle with a diameter = Source impedance + Reach impedance • Higher the source impedance (weak source) larger the diameter means more fault resistance coverage

¾ Numerical protections uses memory, self, healthy phase voltages for polarizations and or different combinations of the same Partially or fully cross polarized protections are very common now a days Knowledge Is Power

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Cross Polarization ¾ It is very common to use healthy phase voltage for phase to ground fault Provides polarizing voltage for a zero voltage fault For A-G fault: Polarizing voltage is -(VB+VC) • Called Cross polarizing • Same effect as Memory Polarization VC

-(VB+VC) VA

VB Knowledge Is Power

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Memory Polarization : Questions How protection works when there is a 3 phase zero voltage faults? How the protection works when there is a permanent 3 phase zero voltage faults during reclosing? Looks like that protection can trip for a reverse faults. True?

IX

IZR

IR IZs

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Distance Protection: Architecture

I V

ZR

IZ

+

Output Timer = 0.25 Cycles

Memory

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Distance Protection: Architecture I

ZR

IZ

V

Memory

+ Phase Shift - 900

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Phase Detector V-IZ in phase Or lag Vpol

Output


IZ

ZR

+

V

Phase Shift - 900

Memory

ZR V-IZ

Vpol Zs

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Output


IZ

ZR

+

V


Phase Shift - 900

Memory

ZR

ZR V-IZ

V-IZ

Vpol Zs

Vpol Zs

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Output

Review Question - 1 ZR V-IZ

Vpol Zs

Howprotection protectionworks worksfor foraa33phase phasezero zerovoltage voltagefaults? faults? How Typicallythe theprotection protectionmemorizes memorizes16-20 16-20cycles cyclesof ofpre prefault fault Typically voltageswhich whichisisused usedwhen whenthere thereisisZero ZeroVoltage VoltageFault. Fault. voltages Knowledge Is Power

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Review Question - 2 B

A

G

Zs

21 Howthe theprotection protectionworks worksfor foraapermanent permanent33phase phasezero zero How voltagefaults faultsduring duringclosing closingof ofthe thebreaker? breaker? voltage thegrounding groundingchains chainswere wereleft lefton onthe thebreaker breaker&&breaker breakerisis IfIfthe closed,protection protectionhas hasno novoltage voltageininthe thememory memoryas aswell wellas as closed, thefault faultvoltage voltageisiszero. zero.Protection Protectionsees seesonly onlyfault faultcurrent. current. the SwitchOn OnTo ToFault Fault--SOTF SOTFfeature featureisisemployed employedwhich whichtrips trips Switch thebreaker breakerififprotection protectionsees seesthe thecurrent currentbut butno novoltage voltage the followingbreaker breakerclose. close. following Knowledge Is Power

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Review Question - 3 ZR V-IZ

Vpol Zs

Lookslike likethat thatprotection protectioncan cantrip tripfor foraareverse reversefaults. faults. Looks True? True? Characteristicisistrue trueonly onlyfor forforward forwardfaults faultsfor forreverse reverse Characteristic faultprotection protectionwill willnot notoperate operate fault Knowledge Is Power

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Memory Polarization : Facts G

A

B Zs

ZL

ZR

21

V-IZ

Characteristic is circle whose diameter is Zs - ZR For faults behind the protection ZS = Zs + ZR So characteristic should be a circle whose diameter is Zs - ZR Substitute the value for Zs Characteristic should be circle with a diameter equal to Zs

Vpol Zs

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Memory Polarization : Facts G

A

B Zs

ZL

Zs

21 Characteristic is circle whose diameter is Zs - ZR For faults behind the protection ZS = Zs + ZR So characteristic should be a circle whose diameter is Zs - ZR Substitute the value for Zs Characteristic should be circle with a diameter equal to Zs

ZR

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Memory Polarization : Conclusion G

A

B Zs

ZL

Zs

21

ZR

Memorypolarized polarizedMHO MHO Memory characteristicisisvery very characteristic secureand andnot notprone proneto to secure operatefor forreverse reversefaults faults operate

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Fault Res.: Memory Vs. Self Polarized A

G

B

Zs

Zs

ZL

RF 21

ZR

ZR

Zs

Zs Knowledge Is Power

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Fault Res.: Strong Vs. Weak Source A

G

B

Zs

Zs

ZL

RF 21

ZR

ZR

Zs Zs

Strong Source

Weak Source Knowledge Is Power

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Fault Res.: Short Vs. Long Line G

Zs

Zs

ZL

RF 21

ZR

ZR

Zs Strong Source/Short line Knowledge Is Power

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Zs Weak Source/long line

Fault Resistance Coverage ¾ Strong source & short line reduces fault resistance coverage Use quadrilateral characteristic to improve fault resistance coverage

¾ Weak Source & long line increases fault resistance coverage ¾ Memory polarized protection is more secure under all fault conditions ¾ Self polarized protection does not provide good fault resistance coverage ¾ Memory polarization increases fault resistance coverage compare to self polarized protection ¾ Healthy phase polarization provides the same effect as memory polarized protection Knowledge Is Power

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Quadrilateral Characteristics X

ZL

ZR Reach Load Blinder

Load Area Dir

KR

R

Fourcomparators comparatorsare areused usedto todetect detectfault faultconditions conditions Four allfour fourcomparators comparatorsproduces producesoutput, output,protection protectiontrips trips IfIfall Quadcharacteristic characteristicprovide providegood goodfault faultresistance resistancecoverage coverage Quad Knowledge Is Power

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Quadrilateral Characteristics X

ZL

ZR Reach Load Blinder

Dir

KR

How directional directional line line works? works? How Knowledge Is Power

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R

Directional line : Int. Fault IX IZ = Signal B

If A lags B By 00 – 1800

VF

Ope rate IR Dir line

VF <-900 = Signal A Knowledge Is Power

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True

Directional line : Ext. Fault IX IZ = Signal B


VF <-900 = Signal A

IR

VF

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True

Reach line : Ext. Fault IX

VF - IZ = Signal A


IZ VF

I*Kr = Signal B

IR

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Reach line : Int. Fault IX VF - IZ = Signal A


IZ VF I*Kr = Signal B

IR

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Reach line IX

VF - IZ = Signal A


IZ VF

I*Kr = Signal B

IR

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Load Blinder: Internal Fault IX


VF - IZ = Signal B

IZ VF

VF-IKR=Signal A

KR Setting for the load blinder I*KR

IR

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Load Blinder: External Fault Operate

IX

VF - IZ = Signal B


IZ VF-IKR=Signal A VF

IR

I*Kr

KR Setting for the load blinder

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Quadrilateral Characteristic : Facts ¾ Quad characteristic is better for short line and/or strong source as it provides better fault resistance coverage ¾ Very good for ground fault protection Fault resistance can be high • Tower footing resistance, Tree touching the line etc.

¾ Reactance and resistance reach can be set independent of each other for optimum fault coverage Knowledge Is Power

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Ph-G Faults: High Resistance Fault

¾High Resistance Faults •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 Knowledge Is Power

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Quad Characteristic : Reactance Line Reactance line is not a straight line parallel to R axis. Top line has a tilt of 30 The tilt enables protection to not operate for an external fault If the tilt is not there then protection can operate for an external fault due to effect of load on the line How? Knowledge Is Power

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Effect of Load : Quad Ch. X G

Y

Zs

Zs

ZL

Vx <00

21

Iy

Ix

Ix+Iy <-Ө

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VY <-300

G

Impedance Seen at Protection X G

Zs

Vx <00

21

G

Zs

ZL

Iy

Ix

VY <-300

Ix+Iy <-Ө

Ix

(Ix+Iy)*R Iy

Ix + Iy

(Ix)*ZL

Tiltof ofthe thereactance reactanceline line Tilt Preventstripping trippingfor forthe the Prevents Externalfaults faults External Knowledge Is Power

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Effect of Load : Quad Ch. X G

Y

Zs

Zs

ZL

Vx <00

Iy

Ix

21

Ix+Iy <+Ө

Iy

Ix + Iy

Ix

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VY <+300

G

Impedance Seen at Protection X G

Zs

Zs

ZL

Vx <00

21

Iy

Ix

G

VY <-300

Ix+Iy <-Ө (Ix+Iy)*R

Tiltof ofthe thereactance reactanceline line Tilt Preventsoperation operationfor forthe the Prevents Internalfaults faults Internal

(Ix)*ZL

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Quad Characteristics : Ext. Fault

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Quad Characteristics : Int. Fault

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Quad Characteristics : Int. Fault

Bypolarizing polarizingthe thetop topline linewith with–Ve –Veor orZero Zero By sequencecurrent, current,ititwill willadapt adaptto toload loadCondition Condition sequence

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MHO Characteristics : Zone 3 ¾ Zone 3 provides the back up protection in case Zone 1 and Zone 2 fails to operate ¾ Zone 3 is typically time delayed zone ¾ It is used in blocking scheme to determine direction of the fault ¾ Zone 3 is mostly offset characteristic that it includes the Origin in the characteristic means it can trip for a reverse fault ¾ To avoid load encroachment due to large setting of Zone 3 it’s shape can lens Knowledge Is Power

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Zones of Protection Zone 3 : Offset MHO

Load profile

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OFFSET MHO IZ V-IZ ForwardReach Reach ZZ==Forward Z’==Reverse ReverseReach Reach Z’

V-IZ’

-IZ’ Knowledge Is Power

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OFFSET MHO IZ

ForwardReach Reach ZZ==Forward Z’==Reverse ReverseReach Reach Z’

Load profile

-IZ’

TwoComparators Comparatorsare arephase phaseshifted shiftedby bysame same angle angleininopposite oppositedirection direction Two Knowledge Is Power

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OFFSET MHO IZ

ForwardReach Reach ZZ==Forward Z’==Reverse ReverseReach Reach Z’

Load profile

-IZ’

Majoraxis axisto tominor minoraxis axisratio ratioisisequal equalto totan tan(180 (180--Ө)/2 Ө)/2 Major Knowledge Is Power Eachcomparator comparator isshifted shiftedby by anangle angleӨӨ Each is an Apparatus Maintenance and Power Management SM

for Energy Delivery

MHO or Quad : Pros and Cons ¾ Simple Simpleand anddirectional directional ¾ ¾ Lees Leessensitive sensitiveto to ¾ powerswings swings power

Reachdoes doesnot notextend extend Reach asfar faralong alongR-Axis R-Axis as

¾ Good Goodfault faultresistance resistance ¾ coverageas aschar. char.can can coverage beset setalong alongRR-Axis Axis be Goodfor forshort shortline lineand and Good strongsource source strong

¾ Sensitive Sensitiveto topower power ¾ Limited Limitedfault faultresistance resistance ¾ ¾ swing coveragefor forshort short swing coverage Characteristicextends extendson on lines Characteristic lines R-Axis R-Axis

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fundamentals related to distance relays

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