88665474 transmission line protection

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Fundamentals of DistanceProtection

GE Multilin



2 /GE /

April-9-12

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



3 /GE /

April-9-12

Transmission Lines

A Vital Part of the Power System: • Provide path to transfer power between generation and load

• Operate at voltage levels from 69kV to 765kV

• Deregulated markets, economic, environmental requirements

have pushed utilities to operate transmission lines close to theirlimits.



4 /GE /

April-9-12

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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April-9-12

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


• Directional Comparison Blocking (DCB)

• Permissive Underreach Transfer Trip (PUTT)

• Permissive Overreach Transfer Trip (POTT)

• Unblocking

• Step Distance

• Step or coordinated overcurrent• Inverse time overcurrent

• Current Differential



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April-9-12

Typical Protection SchemesLong Lines


• 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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What is distance protection?

For internal faults:> IZ – V and V approximately

in phase (mho)

> IZ – V and IZ approximately in phase(reactance)

RELAY (V,I)

Intended

REACH point

Z

F1

I*Z

V=I*ZF

I*Z - V



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April-9-12


For external faults:> IZ – V and V approximately

out of phase (mho)

> IZ – V and IZ approximately 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:SIR f

f V V

PU LOC

PU LOC

N R

][

][

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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April-9-12

Source Impedance Ratio,Accuracy & Speed

Lin

e

System

Relay

Voltage at the relay:SIR f

f V V

PU LOC

PU LOC

N R

][

][

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-state output

power cycles

-30

-20

-10

0

10

20

30

v o l t a g e ,

V

C1

C2

2

3 5

6

1

4

7

High Voltage Line

S e c o n d a r

y V o l t a g e

O u t p u t

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

S e c o n d a r

y V o l t a g e

O u t p u t

8

CVToutput

0 1 2 3 4

steady-state output

-60

-40

-20

0

20

40

power cycles

v o l t a g e ,

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

V o l t a g e [ V ]

-0.5 0 0.5 1 1.5-3

-2

-1

0

1

2

3

4

5

C u r r e n t

[ A ]

v A

vB v

C

i A

iB, i

C

-0.5 0 0.5 1 1.5 -100

-50

0

50

100

R e a c t a

n c e c o m p a r a t o r [ V ]

power cycles

S POL

S OP

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



Distance Element Fundamentals

XL

XC

R

Z1 End Zone



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-10 -5 0 5 10-5

0

5

10

15

R e a c t a n c e [ o h m ]

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 Transients – AdaptiveSolution



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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 Transients – AdaptiveSolution



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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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20ms

15ms

25ms 30ms

35ms



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SLG faults LL faults

3P faults



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0 5 10 15 20 25 300

10

20

30

40

50

60

70

80

90

100

M a x i m u m R

a c h [ % ]

SIR

Actual maximum reach curves

Relay 1

Relay 3

Relay 2

Relay 4



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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

“Lenticular”Characteristic

Load Swings



33 /

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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 Polarization jX

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 Polarization…Improved 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 Schemes• Zone 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 cycles• Zone 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

End

Zone

End

Zone

Local

Remote




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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

DUTT – Direct Under-reaching Transfer Trip

PUTT – Permissive Under-reaching Transfer

Trip

POTT – Permissive Over-reaching Transfer Trip

Hybrid POTT – Hybrid Permissive Over-

reaching Transfer Trip

DCB – Directional Comparison Blocking

Scheme

DCUB – Directional 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 of line

& Local TripZone 2

Rx PKP

OR Zone 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

POTT – Permissive Over-reaching Transfer

TripEnd

Zone

CommunicationChannel

POTT Scheme



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Remote

Relay FWD

IGND

Ground Dir OC Fwd

OR

Local Relay – Z2

ZONE 2 PKP

Local Relay

FWD IGND

Ground Dir OC Fwd

OR

TRIP

Remote Relay – Z2

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

C om

m uni c a t i on s

C

h a nn e l ( s )

POTT Scheme

POTT Scheme



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POTT TX ZONE 2 OR

GND DIR OC FWD

CommunicationChannel

TRIP

GND DIR OC REV GND DIR OC REV POTT RX

StartTimer TimerExpire

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 greater• Blocking 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 Relay GUARD1 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 Relay – Z2

Zone 2 PKP

TRIP1 RX

TRIP2 TX

TRIP

Remote Relay – Z2

ZONE 2 PKP

TRIP Z1

TRIP2 RX



Redundancy Considerations



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Redundancy Considerations

• Redundant protection systems increase dependability of the

system:Multiple sets of protection using same protection principle

and multiple pilot channels overcome individual elementfailure, or

Multiple sets of protection using different protection principles and 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 breaker independent 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 direction internal 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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April-9-12

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 XL of long lines• Improvement 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 transformer• Given 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 point• Voltages 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

88665474 transmission line protection

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