06_curso_Fundamentals of Distance Protection

8/10/2019 06_curso_Fundamentals of Distance Protection

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Fundamentals of DistanceProtection

GE Multilin


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November-1-14

Outline

Transmission lin

e introduction

What is distance protection?

Non-pilot and pilot schemes

Redundancy considerations Security for dual-breaker terminals

Out-of-step relaying

Single-pole tripping Series-compensated lines


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Transmission Lines

Classification of line length depends on:

Source-to-line Impedance Ratio (SIR),

and Nominal voltage

Length considerations:

Short Lines: SIR > 4Medium Lines: 0.5 < SIR < 4

Long Lines: SIR < 0.5


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Typical Protection SchemesShort Lines

Current differential

Phase comparison

Permissive Overreach Transfer Trip (POTT)Directional Comparison Blocking (DCB)


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Typical Protection SchemesMedium Lines

Phase comparison

Directional Comparison Blocking (DCB)

Permissive Underreach Transfer Trip (PUTT)

Permissive Overreach Transfer Trip (POTT)

Unblocking

Step Distance

Step or coordinated overcurrentInverse time overcurrent

Current Differential


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Typical Protection SchemesLong Lines

Phase comparison

Directional Comparison Blocking (DCB)

Permissive Underreach Transfer Trip (PUTT)

Permissive Overreach Transfer Trip (POTT)

Unblocking

Step Distance

Step or coordinated overcurrent

Current Differential


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For internal faults:> IZV and Vapproximately

in phase (mho)

> IZVand IZapproximately in phase(reactance)

RELAY (V,I)

Intended

REACH point

Z

F1

I*Z

V=I*ZF

I*Z - V


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For external faults:> IZVand Vapproximately

out of phase (mho)

> IZVand IZapproximately out of phase(reactance)

RELAY (V,I)

Intended

REACH point

Z I*Z

V=I*ZF

I*Z - V

F2


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RELAY

Intended

REACH point

Z


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Source Impedance Ratio,Accuracy & Speed

LineSystem

Relay

Voltage at the relay:SIRf

fVV

PULOC

PULOC

NR

][

][

Consider SIR = 0.1

Fault location Voltage

(%)

Voltage change

(%)

75% 88.24 2.76

90% 90.00 0.91

100% 90.91 N/A

110% 91.67 0.76


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Source Impedance Ratio,Accuracy & Speed

Lin

e

System

Relay

Voltage at the relay:SIRf

fVV

PULOC

PULOC

NR

][

][

Consider SIR = 30

Fault location Voltage

(%)

Voltage change

(%)

75% 2.4390 0.7868

90% 2.9126 0.3132

100% 3.2258 N/A

110% 3.5370 0.3112


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Challenges in relay design

> Transients:

High frequency

DC offset in currents

CVT transients involtages

CVT output

0 1 2 3 4

steady-stateoutput

power cycles

-30

-20

-10

0

10

20

30

voltage,

V

C1

C2

2

3 5

6

1

4

7

High Voltage Line

Secondar

yVoltage

Output

8


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> Transients:

High frequency

DC offset in currents

CVT transients involtages

C1

C2

2

3 5

6

1

4

7

High Voltage Line

Secondar

yVoltage

Output

8

CVToutput

0 1 2 3 4

steady-stateoutput

-60

-40

-20

0

20

40

power cycles

voltage,

V

60


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-0.5 0 0.5 1 1.5-100

-80

-60

-40

-20

0

20

40

60

80

100

Voltage[V]

-0.5 0 0.5 1 1.5-3

-2

-1

0

1

2

3

4

5

Current

[A]

vA

vB vC

iA

iB, i

C

-0.5 0 0.5 1 1.5-100

-50

0

50

100

Reacta

ncecomparator[V]

power cycles

SPOL

SOP

Sorry Future (unknown)

> In-phase = internal

fault

> Out-of-phase =external fault


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Transient Overreach

Fault current generally contains dc offset in

addition to ac power frequency component

Ratio of dc to ac component of currentdepends on instant in the cycle at which fault

occurred

Rate of decay of dc offset depends onsystem X/R


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Zone 1 and CVT Transients

Capacitive Voltage Transformers (CVTs) create certainproblems for fast distance relays applied to systems with

high Source Impedance Ratios (SIRs):

> CVT-induced transient voltage components may

assume large magnitudes (up to 30-40%) and last fora comparatively long time (up to about 2 cycles)

> 60Hz voltage for faults at the relay reach point may be

as low as 3% for a SIR of 30

> the signal may be buried under noise


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CVT transients can cause distance relays to overreach.Generally, transient overreach may be caused by:

> overestimation of the current (the magnitude of the

current as measured is larger than its actual value,

and consequently, the fault appears closer than it isactually located),

> underestimation of the voltage (the magnitude of the

voltage as measured is lower than its actual value)

> combination of the above

Zone 1 and CVT Transients


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Distance Element Fundamentals

XL

XC

R

Z1 End Zone


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-10 -5 0 5 10-5

0

5

10

15

Reactance[ohm]

Resistance [ohm]

18

22

26

30

3442 44 Actual Fault

Location

LineImpedance

Trajectory(msec)

dynamic mhozone extendedfor high SIRs

Impedance locus may pass

below the origin of the Z-plane -

this would call for a time delay

to obtain stability


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> apply delay (fixed or adaptable)> reduce the reach

> adaptive techniques and better filtering

algorithms

CVT Transient OverreachSolutions


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> Optimize signal filtering:

currents - max 3% error due to the dc component

voltages - max 0.6% error due to CVT transients

>Adaptive double-reach approach

filtering alone ensures maximum transient

overreach at the level of 1% (for SIRs up to 5) and

20% (for SIRs up to 30)

to reduce the transient overreach even further an

adaptive double-reach zone 1 has been

implemented

CVT TransientsAdaptiveSolution


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The outer zone 1:

> is fixed at the actual reach

> applies certain security delay to cope with CVT transients

Delayed

Trip

Instantaneous

Trip

R

XThe inner zone 1:

> has its reach dynamically

controlled by the voltage

magnitude

> is instantaneous

CVT TransientsAdaptiveSolution


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Desirable Distance RelayAttributesFilters:

> Prefiltering of currents to remove dc decaying transients

Limit maximum transient overshoot (below 2%)

> Prefiltering of voltages to remove low frequency transients

caused by CVTs Limit transient overreach to less than 5% for an SIR of

30

>Accurate and fast frequency tracking algorithm

>Adaptive reach control for faults at reach points


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Distance Relay Operating Times


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Distance Relay Operating Times

20ms

15ms

25ms 30ms

35ms


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Maximum Torque Angle

Angle at which mho element has maximum

reach

Characteristics with smaller MTA willaccommodate larger amount of arc resistance


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Traditional

Directional

angle lowered

and slammed

Directional angle

slammed

Both MHO anddirectional angles

slammed (lens)

Mho Characteristics


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Typical load characteristic

impedance

+R

Operate

area

No Operate area

+XL

+ = LOOKING INTO LINE

normally considered

forward

Load

Trajectory

Load Swings


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Load swing

LenticularCharacteristic

Load Swings


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Load Encroachment Characteristic

The load encroachment element responds to positive

sequence voltage and current and can be used to

block phase distance and phase overcurrent

elements.


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Blinders

Blinders limit the operation of distance relays

(quad or mho) to a narrow region that parallels

and encompasses the protected line

Applied to long transmission lines, where

mho settings are large enough to pick up on

maximum load or minor system swings


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Quadrilateral Characteristics


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Ground Resistance

(Conductor falls on ground)

R Resultant impedance outside of

the mho operating region

Quadrilateral Characteristics


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Mho Quadrilateral

Better coverage for

ground faults due

to resistance added

to return path

Lenticular

Used for phase elements

with long heavily loaded

lines heavily loaded

Standard for phase

elements

JX

R

Distance Characteristics -Summary


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Distance Element Polarization

The following polarization quantities are commonly

used in distance relays for determining directionality:

Self-polarized

Memory voltage

Positive sequence voltage

Quadrature voltage

Leading phase voltage


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Memory Polarization

> Positive-sequence memorized voltage is used for

polarizing:

Mho comparator (dynamic, expanding Mho)

Negative-sequence directional comparator (Ground

Distance Mho and Quad)

Zero-sequence directional comparator (Ground

Distance MHO and QUAD)

Directional comparator (Phase Distance MHO and

QUAD)

> Memory duration is a common distance settings (all zones,

phase and ground, MHO and QUAD)


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Memory PolarizationjX

R

Dynamic MHO characteristic for a reverse faul

Dynamic MHO characteristic for a forward fa

Impedance During Close-up Faults

Static MHO characteristic (memory not established or

expired)

ZL

ZS


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Memory Polarization

Memory PolarizationImproved ResistiveCovera e

Dynamic MHO characteristic for a forward faul

Static MHO characteristic (memory not established or

expired)

jX

R

ZL

ZS

RL


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Choice of Polarization

In order to provide flexibility modern distance

relays offer a choice with respect to

polarization of ground overcurrent direction

functions:

Voltage polarization

Current polarization

Dual polarization


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Ground Directional Elements> Pilot-aided schemes using ground mho distance relays

have inherently limited fault resistance coverage> Ground directional over current protection using either

negative or zero sequence can be a useful supplement togive more coverage for high resistance faults

> Directional discrimination based on the ground quantities is

fast:

Accurate angular relations between the zero andnegative sequence quantities establish very quicklybecause:

During faults zero and negative-sequencecurrents and voltages build up from very lowvalues (practically from zero)

The pre-fault values do not bias the developing

fault components in any direction

S


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Distance Schemes

Pilot Aided

Schemes

No Communicationbetween Distance

Relays

Communicationbetween Distance

relays

Non-Pilot Aided

Schemes

(Step Distance)


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Step Distance SchemesZone 1:

Trips with no intentional time delay Underreaches to avoid unnecessary operation for faults

beyond remote terminal

Typical reach setting range 80-90% of ZL

Zone 2: Set to protect remainder of line

Overreaches into adjacent line/equipment

Minimum reach setting 120% of ZL

Typically time delayed by 15-30 cyclesZone 3:

Remote backup for relay/station failures at remoteterminal

Reaches beyond Z2, load encroachment a consideration


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Z1

Z1

Local

Remote

Step Distance Schemes


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Z1

Z1

Breaker

Tripped

Breaker

Closed

Local

Remote



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Z1

Z1

Z2 (time delayed)

Remote

Local


Z2 (time delayed)


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Z1

Z2 (time delayed)


Z3 (remote backup)


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Step Distance Protection


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Local Relay

Z2

Zone 2 PKP

Local Relay Remote Relay

Remote Relay

Z4

Zone 4 PKP

Over Lap

Distance Relay Coordination


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Communication

Channel

Local

Relay

Remote Relay

Need For Pilot Aided Schemes


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Pilot Communications Channels

Distance-based pilot schemes traditionally utilizesimple on/off communications between relays, butcan also utilize peer-to-peer communications andGOOSE messaging over digital channels

Typical communications media include: Pilot-wire (50Hz, 60Hz, AT)

Power line carrier

Microwave

Radio

Optic fiber (directly connected or multiplexedchannels)


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Distance-based Pilot Protection

Pil t Aid d Di t B d S h


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Pilot-Aided Distance-Based Schemes

DUTTDirect Under-reaching Transfer Trip

PUTTPermissive Under-reaching Transfer

Trip

POTTPermissive Over-reaching Transfer Trip

Hybrid POTTHybrid Permissive Over-

reaching Transfer Trip

DCBDirectional Comparison Blocking

Scheme

DCUBDirectional Comparison Unblocking

Scheme

Di t U d hi T f T i


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Direct Underreaching Transfer Trip(DUTT)

Requires only underreaching (RU) functions whichoverlap in reach (Zone 1).

Applied with FSK channel

GUARD frequency transmitted during normalconditions

TRIP frequency when one RU function operates

Scheme does not provide tripping for faults beyond

RU reach if remote breaker is open or channel isinoperative.

Dual pilot channels improve security

DUTT S h


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Bus

Line

Bus

Zone 1

Zone 1

DUTT Scheme

P i i U d hi


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Permissive UnderreachingTransfer Trip (PUTT)

Requires both under (RU) and overreaching

(RO) functions

Identical to DUTT, with pilot tripping signal

supervised by RO (Zone 2)

PUTT S h


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Bus

Line

Bus

Zone 1

Zone 2

Zone 2

Zone 1

To protect end ofline

& Local TripZone 2

Rx PKP

ORZone 1

PUTT Scheme

P i i O hi T f


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Permissive Overreaching TransferTrip (POTT)

Requires overreaching (RO) functions (Zone2).

Applied with FSK channel:

GUARD frequency sent in stand-by

TRIP frequency when one RO functionoperates

No trip for external faults if pilot channel isinoperative

Time-delayed tripping can be provided

POTT S h


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Bus

Line

Bus

Zone 1

Zone 2

TripLine

Breakers

OR

t

Rx

Tx

AND

(Z1)

(Z1)

o

Zone 1

Zone 2

Zone 2

Zone 1

POTT Scheme

POTT Scheme


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POTT Scheme

POTTPermissive Over-reaching Transfer

TripEnd

Zone

CommunicationChannel

POTT Scheme


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Remote

Relay FWD

IGND

Ground Dir OC Fwd

OR

Local RelayZ2

ZONE 2 PKP

Local Relay

FWD IGND

Ground Dir OC Fwd

OR

TRIP

Remote RelayZ2

POTT TX

ZONE 2 PKP

POTT RX

Communicatio

n Channel

POTT Scheme

POTT Scheme


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POTT TX 4

POTT TX 3

POTT TX 2

POTT TX 1 A to G

B to G

C to G

Multi Phase


POTT RX 4

POTT RX 3

POTT RX 2

POTT RX 1

Com

munications

C

hannel(s)

POTT Scheme

POTT Scheme


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POTT TX ZONE 2 OR

GND DIR OC FWD

CommunicationChannel

TRIP

GND DIR OC REVGND DIR OC REV POTT RX

StartTimerTimerExpire

GND DIR OC FWD

POTT SchemeCurrent reversal example

POTT Scheme


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Local Relay

Open

Remote Relay

Remote FWD

IGND

POTT TX

Remote

Z2

Communication

Channel

POTT RX

OPEN

POTT TX

Communication

Channel

POTT RX

TRIP

POTT SchemeEcho example

Hybrid POTT


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Hybrid POTT

Intended for three-terminal lines and weak

infeed conditions

Echo feature adds security during weak

infeed conditions

Reverse-looking distance and oc elements

used to identify external faults

Hybrid POTT


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Bus

Line

Bus

Zone 1

Zone 2

Zone 2

Zone 1 Zone 4

LocalRemote

Weak

system

Hybrid POTT

Directional Comparison Blocking


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Directional Comparison Blocking(DCB)

Requires overreaching (RO) tripping and blocking(B) functions

ON/OFF pilot channel typically used (i.e., PLC)

Transmitter is keyed to ON state when blockingfunction(s) operate

Receipt of signal from remote end blockstripping relays

Tripping function set with Zone 2 reach or greaterBlocking functions include Zone 3 reverse and low-set ground overcurrent elements

DCB Scheme


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Bus

Line

Bus

Zone 1

Zone 2

Zone 2

Zone 1

LocalRemote

DCB Scheme



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End Zone

Communication Channel


(DCB)



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(DCB)Internal Faults


Local Relay

Z2

Zone 2 PKP

TRIP Timer

Start

FWD IGND

GND DIR OC Fwd

ORDir Block RXNO

TRIP

Expired



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Remote Relay

Z4

Zone 4 PKP

REV IGND

GND DIR OC Rev

OR

DIR BLOCK TX

Local Relay

Z2

Zone 2 PKP

Dir Block RX

Communication

Channel

FWD IGND

GND DIR OC Fwd

OR

TRIP Timer

Start No TRIP


(DCB)External Faults

Directional Comparison


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Directional ComparisonUnblocking (DCUB)

Applied to Permissive Overreaching (POR)schemes to overcome the possibility of carrier signalattenuation or loss as a result of the fault

Unblocking provided in the receiver when signal islost:

If signal is lost due to fault, at least onepermissive RO functions will be picked up

Unblocking logic produces short-duration TRIPsignal (150-300 ms). If RO function not pickedup, channel lockout occurs until GUARD signalreturns

DCUB Scheme


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Bus

Line

Bus

TripLine

Breakers

Tx1(Un-Block)

Forward

Forward

Tx2(Block)

Forward

Rx2

Rx1

to

AND to

AND

AND

AND

Lockout

(Block)

(Un-Block)

DCUB Scheme

Directional Comparison Unblocking


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End Zone

Communication Channel


(DCUB)



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(DCUB)Normal conditions

Local Relay Remote RelayGUARD1 TXGUARD1 RX

Communication

Channel

GUARD2 TX GUARD2 RXNO Loss of Guard

FSK Carrier FSK Carrier

NO Permission

NO Loss of Guard

NO Permission

Load Current



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(DCUB)Normal conditions, channel failure


Communication

Channel

GUARD2 TX GUARD2 RX


Loss of Guard

Block Timer Started

Loss of Guard

Block Timer Started

Load Current

NO RX

NO RX

Block DCUB

until Guard OK

Expired

Block DCUB

until Guard OK

Expired

Loss of Channel



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(DCUB)Internal fault, healthy channel


Communication

Channel

GUARD2 TX GUARD2 RX


Loss of Guard

Permission

TRIP1 TX

Local RelayZ2

Zone 2 PKP

TRIP1 RX

TRIP2 TX

TRIP

Remote RelayZ2

ZONE 2 PKP

TRIP Z1

TRIP2 RX



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(DCUB)Internal fault, channel failure


Communication

Channel

GUARD2 TX GUARD2 RX


TRIP1 TX

Local RelayZ2

Zone 2 PKP

NO RX

TRIP2 TX

TRIP

Remote RelayZ2

ZONE 2 PKP

TRIP Z1

NO RX

Loss of Guard

Loss of Channel

Loss of Guard

Block Timer Started

Duration Timer StartedExpired

Redundancy Considerations


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Redundancy Considerations

Redundant protection systems increase dependability of thesystem:Multiple sets of protection using same protection principle

and multiple pilot channels overcome individual elementfailure, or

Multiple sets of protection using different protectionprinciplesand multiple channels protects against failure ofone of the protection methods.

Security can be improved using voting schemes (i.e., 2-out-of-3), potentially at expense of dependability.

Redundancy of instrument transformers, battery systems, tripcoil circuits, etc. also need to be considered.

Redundant Communications


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End Zone

Communication Channel 1

Communication Channel 2

Loss of Channel 2

AND Channels:

POTT Less Reliable

DCB Less Secure

OR Channels:

POTT More Reliable

DCB More Secure

More Channel Security More Channel Dependability

Redundant Communications

Redundant Pilot Schemes


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Redundant Pilot Schemes

Pilot Relay Desirable Attributes


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Integrated functions:

weak infeedecho

line pick-up (SOTF)

Basic protection elements used to key thecommunication:

distance elements

fast and sensitive ground (zero and negative

sequence) directional IOCs with current,voltage, and/or dual polarization




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Pre-programmed distance-based pilot schemes:

Direct Under-reaching Transfer Trip (DUTT)

Permissive Under-reaching Transfer Trip (PUTT)

Permissive Overreaching Transfer Trip (POTT)

Hybrid Permissive Overreaching Transfer Trip (HYBPOTT)

Blocking scheme (DCB)

Unblocking scheme (DCUB)


Security for dual-breaker terminals


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Security for dual breaker terminals

Breaker-and-a-half and ring bus terminals arecommon designs for transmission lines.

Standard practice has been to:

sum currents from each circuit breaker

externally by paralleling the CTs use external sum as the line current for

protective relays

For some close-in external fault events, poor CT

performance may lead to improper operation of linerelays.



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Accurate CTs preserve thereverse current direction

under weak remote infeed



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Saturation of CT1 may

invert the line current as

measured from externally

summated CTs



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Direct measurement of currents

from both circuit breakers allowsthe use of supervisory logic to

prevent distance and directional

overcurrent elements from

operating incorrectly due to CT

errors during reverse faults.

Additional benefits of direct

measurement of currents:

independent BF protection

for each circuit breakerindependent autoreclosing

for each breaker



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Security for dual breaker terminalsSupervisory logic should:

not affect speed or sensitivity of protection elements correctly allow tripping during evolving external-to-

internal fault conditions

determine direction of current flow through eachbreaker independently:

Both currents in FWD directioninternal fault

One current FWD, one current REV external fault

allow tripping during all forward/internal faults

block tripping during all reverse/external faults

initially block tripping during evolving external-to-internal faults until second fault appears in forwarddirection. Block is then lifted to permit tripping.

Single-pole Tripping


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Single pole Tripping

Distance relay must correctly identify a SLG

fault and trip only the circuit breaker pole for

the faulted phase.

Autoreclosing and breaker failure functions

must be initiated correctly on the fault event

Security must be maintained on the healthy

phases during the open pole condition and anyreclosing attempt.

Out-of-Step Condition


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Out of Step Condition

For certain operating conditions, a severe

system disturbance can cause system

instability and result in loss of synchronism

between different generating units on aninterconnected system.

Out-of-Step Relaying


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Out of Step Relaying

Out-of-step blocking relays

Operate in conjunction with mho tripping relaysto prevent a terminal from tripping during severesystem swings & out-of-step conditions.

Prevent system from separating in an

indiscriminate manner.

Out-of-step tripping relays

Operate independently of other devices to

detect out-of-step condition during the first poleslip.

Initiate tripping of breakers that separate systemin order to balance load with available

generation on any isolated part of the system.

Out-of-Step Tripping


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Out of Step TrippingThe locus must stay

for some time

between the outer

and middle

characteristics

Must move and stay

between the middle

and inner

characteristics

When the inner

characteristic is

entered the elementis ready to trip

Power Swing Blocking


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Power Swing Blocking

Applications:

> Establish a blocking signal for stable power swings (PowerSwing Blocking)

> Establish a tripping signal for unstable power swings (Out-

of-Step Tripping)

Responds to:> Positive-sequence voltage and current

Series-compensated lines


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Series compensated lines

EXs SC XL Infinte

Bus

Benefits of series capacitors:

Reduction of overall XLof long linesImprovement of stability margins

Ability to adjust line load levels

Loss reduction

Reduction of voltage drop during severe disturbances

Normally economical for line lengths > 200 miles



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p

EXs SC XL Infinte

Bus

SCs create unfavorable conditions for protective relays and

fault locators:Overreaching of distance elements

Failure of distance element to pick up on low-current faults

Phase selection problems in single-pole tripping

applications

Large fault location errors



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pSeries Capacitor with MOV



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p



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pDynamic Reach Control



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pDynamic Reach Control for External Faults



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pDynamic Reach Control for External Faults



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pDynamic Reach Control for Internal Faults

Distance Protection Looking


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gThrough a Transformer

Phase distance elements can be set to see beyond

any 3-phase power transformer

CTs & VTs may be located independently on

different sides of the transformerGiven distance zone is defined by VT location (not

CTs)

Reach setting is in sec, and must take into

account location & ratios of VTs, CTs and voltage

ratio of the involved power transformer

Transformer Group Compensation


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p p

Depending on locat ion o f VTs and CTs, distance relays need to

compensate for the phase shi f t and magni tude change caused by the

power transformer

Setting Rules


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g

Transformer positive sequence impedance must beincluded in reach setting only if transformer liesbetween VTs and intended reach point

Currents require compensation only if transformer

located between CTs and intended reach pointVoltages require compensation only if transformerlocated between VTs and intended reach point

Compensation set based on transformer connection

& vector group as seen from CTs/VTs toward reachpoint

Distance Relay Desirable


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> Multiple reversible distance zones

> Individual per-zone, per-element characteristic: Dynamic voltage memory polarization

Various characteristics, including mho, quad,lenticular

> Individual per-zone, per-element current supervision(FD)

> Multi-input phase comparator:

additional ground directional supervision

dynamic reactance supervision

> Transient overreach filtering/control

> Phase shift & magnitude compensation for distanceapplications with power transformers

yAttributes



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> For improved flexibility, it is desirable to have the following

parameters settable on a per zone basis: Zero-sequence compensation

Mutual zero-sequence compensation

Maximum torque angle

Blinders

Directional angle

Comparator limit angles (for lenticular characteristic)

Overcurrent supervision

yAttributes



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>Additional functions

Overcurrent elements (phase, neutral, ground,directional, negative sequence, etc.)

Breaker failure

Automatic reclosing (single & three-pole)

Sync check Under/over voltage elements

> Special functions

Power swing detection

Load encroachment Pilot schemes

Attributes


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Documents

06_curso_Fundamentals of Distance Protection