transmission line protection

Fundamentals of Distance Protection

GE Multilin

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April 7, 2023

Outline• Transmission line 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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April 7, 2023

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 their limits.

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April 7, 2023

Transmission Lines

Classification of line length depends on: Source-to-line Impedance Ratio (SIR),

and Nominal voltage

Length considerations: Short Lines: SIR > 4 Medium Lines: 0.5 < SIR < 4 Long Lines: SIR < 0.5

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April 7, 2023

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 overcurrent• Inverse time overcurrent• Current Differential

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April 7, 2023

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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April 7, 2023

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)

IntendedREACH point

Z

F1

I*Z

V=I*ZF

I*Z - V

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April 7, 2023


For external faults:> IZ – V and V approximately

out of phase (mho)> IZ – V and IZ approximately

out of phase (reactance)

RELAY (V,I)

IntendedREACH point

Z I*Z

V=I*ZF

I*Z - V

F2

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April 7, 2023


RELAY

IntendedREACH point

Z

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April 7, 2023

Source Impedance Ratio, Accuracy & Speed

LineSystem

Relay

Voltage at the relay:SIRf

fVV

PULOC

PULOCNR

][

][

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 7, 2023

Source Impedance Ratio, Accuracy & Speed

Line

SystemRelay

Voltage at the relay:SIRf

fVV

PULOC

PULOCNR

][

][

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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April 7, 2023

Challenges in relay design>Transients:

– High frequency– DC offset in currents– CVT transients in voltages

CVT output

0 1 2 3 4

steady-stateoutput

power cycles

-30

-20

-10

0

10

20

30

volt

ag

e,

V

C1

C22

3 5

6

1

4

7

High Voltage Line

Seco

ndar

y Vo

ltage

Out

put

8

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April 7, 2023

Challenges in relay design>Transients:

– High frequency– DC offset in currents– CVT transients in voltages

C1

C22

3 5

6

1

4

7

High Voltage Line

Seco

ndar

y Vo

ltage

Out

put

8

CVToutput

0 1 2 3 4

steady-stateoutput

-60

-40

-20

0

20

40

power cyclesvolt

ag

e,

V

60

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April 7, 2023

Challenges in relay design

-0.5 0 0.5 1 1.5-100

-80

-60

-40

-20

0

20

40

60

80

100

Volta

ge [V

]

-0.5 0 0.5 1 1.5-3

-2

-1

0

1

2

3

4

5

Curr

ent [

A]

vA vB vC

iA

iB, iC

-0.5 0 0.5 1 1.5-100

-50

0

50

100

Reacta

nce c

om

para

tor

[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 current depends on instant in the cycle at which fault occurred• Rate of decay of dc offset depends on system X/R

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Zone 1 and CVT Transients

Capacitive Voltage Transformers (CVTs) create certain problems 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 for a 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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April 7, 2023

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 is actually 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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April 7, 2023

-10 -5 0 5 10-5

0

5

10

15R

eact

ance

[ohm

]

Resistance [ohm]

18

22

26

30

3442

44 Actual FaultLocation

LineImpedance

Trajectory(msec)

dynamic mhozone extendedfor high SIRs

-10 -5 0 5 10-5

0

5

10

15R

eact

ance

[ohm

]

Resistance [ohm]

18

22

26

30

3442

44 Actual FaultLocation

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 delayto obtain stability

Impedance locus may pass below the origin of the Z-plane - this would call for a time delayto obtain stability

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>apply delay (fixed or adaptable)>reduce the reach>adaptive techniques and better filtering

algorithms

CVT Transient Overreach Solutions

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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 – Adaptive Solution

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The outer zone 1:The outer zone 1:

> is fixed at the actual reach> applies certain security delay to cope with CVT

transients

DelayedTrip

InstantaneousTrip

R

XThe inner zone 1:The inner zone 1:

> has its reach dynamically controlled by the voltage magnitude

> is instantaneous

CVT Transients – Adaptive Solution

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Desirable Distance Relay AttributesFilters:

>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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April 7, 2023


20ms

15ms

25ms 30ms

35ms

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SLG faults LL faults

3P faults

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April 7, 2023

0 5 10 15 20 25 300

10

20

30

40

50

60

70

80

90

100

Max

imum

Rac

h [%

]

SIR

0 5 10 15 20 25 300

10

20

30

40

50

60

70

80

90

100

Max

imum

Rac

h [%

]

SIR

Actual maximum reach curvesActual 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 will accommodate larger amount of arc resistance

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Traditional

Directional angle lowered and “slammed”

Directional angle “slammed”

Both MHO and directional angles “slammed” (lens)

Mho Characteristics

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April 7, 2023

Typical load characteristic impedance

+R

Operate

area

No Operate area

+XL

+ = LOOKING INTO LINE normally considered forward

Load Trajectory

Rea

ch

Load Swings

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April 7, 2023

Load swingLoad swing

“Lenticular” Characterist

ic

Load Swings

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Load Encroachment Characteristic

The load encroachment element responds to The load encroachment element responds to positive sequence voltage and current and can positive sequence voltage and current and can

be used to block phase distance and phase be used to block phase distance and phase overcurrent elements.overcurrent elements.

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April 7, 2023

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)

XL

R Resultant impedance outside of the mho operating region

Quadrilateral Characteristics

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April 7, 2023

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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April 7, 2023

Distance Element PolarizationThe 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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April 7, 2023

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 fault

Dynamic MHO characteristic for a forward fault

Impedance During Close-up FaultsImpedance During Close-up Faults

Static MHO characteristic (memory not established or expired)

ZL

ZS

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April 7, 2023

Memory Polarization

Memory Polarization…Improved Resistive Coverage

Dynamic MHO characteristic for a forward fault

Static MHO characteristic (memory not established or expired)

jX

R

ZL

ZS

RL

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April 7, 2023

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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April 7, 2023

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 to give more coverage for high resistance faults

>Directional discrimination based on the ground quantities is fast:

– Accurate angular relations between the zero and negative sequence quantities establish very quickly because:

During faults zero and negative-sequence currents and voltages build up from very low values (practically from zero)

The pre-fault values do not bias the developing fault components in any direction

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April 7, 2023

Distance Schemes

Pilot Aided Schemes

No Communication between Distance

Relays

Communication between Distance

relays

Non-Pilot Aided Schemes

(Step Distance)

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April 7, 2023

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 remote terminal– Reaches beyond Z2, load encroachment a consideration

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April 7, 2023

BU

S BU

S

Z1Z1

Z1Z1

LocalLocal

RemotRemotee

Step Distance Schemes

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April 7, 2023

BU

S BU

S

Z1Z1

Z1Z1

End End ZoneZone

End End ZoneZone

LocalLocal

RemotRemotee


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April 7, 2023

BU

S

Z1Z1

Z1Z1BreakeBreaker r TrippeTrippedd

BU

S

BreakeBreaker r ClosedClosed

LocalLocal

RemotRemotee


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April 7, 2023

BU

S

Z1Z1

Z1Z1B

US

Z2 (time Z2 (time delayed)delayed)

RemotRemotee

LocalLocal



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April 7, 2023

BU

S

Z1Z1

BU

S


Step Distance SchemesZ3 (remote Z3 (remote

backup)backup) …

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April 7, 2023

Step Distance Protection

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April 7, 2023

Local Relay – Z2Local Relay – Z2

Zone 2 PKPZone 2 PKP

Local RelayLocal Relay Remote RelayRemote Relay

Remote Relay – Z4Remote Relay – Z4


Over LapOver Lap

Distance Relay Coordination

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April 7, 2023

BU

SBU

S

Communication Communication ChannelChannel

Local Local RelayRelay

Remote Remote RelayRelay

Need For Pilot Aided Schemes

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April 7, 2023

Pilot Communications Channels• Distance-based pilot schemes traditionally utilize simple on/off communications between relays, but can also utilize peer-to-peer communications and GOOSE messaging over digital channels• Typical communications media include:

– Pilot-wire (50Hz, 60Hz, AT)– Power line carrier– Microwave– Radio– Optic fiber (directly connected or multiplexed

channels)

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April 7, 2023

Distance-based Pilot Protection

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April 7, 2023

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

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April 7, 2023

Direct Underreaching Transfer Trip (DUTT)• Requires only underreaching (RU) functions which overlap in reach (Zone 1).•Applied with FSK channel

– GUARD frequency transmitted during normal conditions

– TRIP frequency when one RU function operates• Scheme does not provide tripping for faults beyond RU reach if remote breaker is open or channel is inoperative.• Dual pilot channels improve security

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April 7, 2023

Bus

Line

Bus

Zone 1

Zone 1

DUTT Scheme

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April 7, 2023

Permissive Underreaching Transfer Trip (PUTT)

• Requires both under (RU) and overreaching (RO) functions • Identical to DUTT, with pilot tripping signal supervised by RO (Zone 2)

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April 7, 2023

Bus

Line

Bus

Zone 1

Zone 2

Zone 2

Zone 1

To protect end ofline

& Local Trip Zone 2

Rx PKP

OR Zone 1

PUTT Scheme

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April 7, 2023

Permissive Overreaching Transfer Trip (POTT)• Requires overreaching (RO) functions (Zone 2).• Applied with FSK channel:

– GUARD frequency sent in stand-by– TRIP frequency when one RO function

operates• No trip for external faults if pilot channel is inoperative• Time-delayed tripping can be provided

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April 7, 2023

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

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April 7, 2023

POTT Scheme

POTT – Permissive Over-reaching POTT – Permissive Over-reaching Transfer TripTransfer Trip

BU

S BU

S

End End ZoneZone


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April 7, 2023

Local Local RelayRelay

Remote Remote RelayRelay

Remote Remote Relay Relay FWD IFWD IGNDGND

Ground Dir OC FwdGround Dir OC Fwd

OROR


ZONE 2 PKPZONE 2 PKP

Local Local Relay FWD Relay FWD I IGNDGND

Ground Dir OC Ground Dir OC FwdFwd

OROR

TRIPTRIP


POTT TX

ZONE 2 ZONE 2 PKPPKP

POTT RX

CommunicatCommunication Channelion Channel

POTT Scheme

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April 7, 2023

POTT TX 4

POTT TX 3

POTT TX 2

POTT TX 1 A to GA to G

B to GB to G

C to GC to G

Multi PhaseMulti Phase


POTT RX 4

POTT RX 3

POTT RX 2

POTT RX 1

Com

munications

Channel(s)

POTT Scheme

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April 7, 2023


POTT TX ZONE 2 ORZONE 2 OR

GND DIR OC FWDGND DIR OC FWD


TRIPTRIP

GND DIR OC REVGND DIR OC REVGND DIR OC REVGND DIR OC REV POTT RX

Start Start TimerTimerTimer Timer ExpireExpire

GND DIR OC FWDGND DIR OC FWD

POTT SchemeCurrent reversal example

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April 7, 2023

Local RelayLocal Relay

OpenOpen

Remote RelayRemote Relay

Remote FWD Remote FWD IIGNDGND

POTT TX

Remote – Z2Remote – Z2


POTT RX

OPENOPEN

POTT TX


POTT RX

TRIPTRIP

POTT SchemeEcho example

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April 7, 2023

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

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April 7, 2023

Bus

Line

Bus

Zone 1

Zone 2

Zone 2

Zone 1 Zone 4

LocalRemoteWeak

system

Hybrid POTT

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April 7, 2023

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 blocking function(s) operate

– Receipt of signal from remote end blocks tripping relays

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

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April 7, 2023

Bus

Line

Bus

Zone 1

Zone 2

Zone 2

Zone 1

LocalRemote

DCB Scheme

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April 7, 2023

BU

S

BU

S

End ZoneEnd Zone

Communication ChannelCommunication Channel

Directional Comparison Blocking (DCB)

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April 7, 2023

Directional Comparison Blocking (DCB)Internal Faults




TRIP Timer TRIP Timer StartStart

FWD IFWD IGNDGND

GND DIR OC FwdGND DIR OC Fwd

ORORDir Block RXNONO

TRIPTRIP

ExpiredExpired

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April 7, 2023




REV IREV IGNDGND

GND DIR OC RevGND DIR OC Rev

OROR

DIR BLOCK TX



Dir Block RX


FWD IFWD IGNDGND

GND DIR OC FwdGND DIR OC Fwd

OROR

TRIP Timer TRIP Timer StartStart No TRIPNo TRIP

Directional Comparison Blocking (DCB)External Faults

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April 7, 2023

Directional Comparison Unblocking (DCUB)• Applied to Permissive Overreaching (POR) schemes to overcome the possibility of carrier signal attenuation or loss as a result of the fault• Unblocking provided in the receiver when signal is lost:

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

– Unblocking logic produces short-duration TRIP signal (150-300 ms). If RO function not picked up, channel lockout occurs until GUARD signal returns

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April 7, 2023

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

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April 7, 2023

BU

S

BU

S

End ZoneEnd Zone

Communication ChannelCommunication Channel

Directional Comparison Unblocking (DCUB)

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April 7, 2023

Directional Comparison Unblocking (DCUB)Normal conditions


GUARD1 TXGUARD1 RX


GUARD2 TX GUARD2 RXNO Loss of GuardNO Loss of Guard

FSK CarrierFSK Carrier FSK CarrierFSK Carrier

NO PermissionNO Permission

NO Loss of GuardNO Loss of Guard

NO PermissionNO Permission

Load CurrentLoad Current

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April 7, 2023

Directional Comparison Unblocking (DCUB)Normal conditions, channel failure


GUARD1 TXGUARD1 RX


GUARD2 TX GUARD2 RX


Loss of GuardLoss of Guard

Block Timer StartedBlock Timer Started


Block Timer StartedBlock Timer Started

Load CurrentLoad Current

NO RX

NO RX

Block DCUB Block DCUB until Guard OKuntil Guard OK

ExpiredExpired

Block DCUB Block DCUB until Guard OKuntil Guard OK

ExpiredExpired

Loss of ChannelLoss of Channel

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April 7, 2023

Directional Comparison Unblocking (DCUB)Internal fault, healthy channel

Local RelayLocal Relay Remote RelayRemote RelayGUARD1 TXGUARD1 RX


GUARD2 TX GUARD2 RX



PermissionPermission

TRIP1 TX



TRIP1 RX

TRIP2 TX

TRIPTRIP



TRIP Z1TRIP Z1

TRIP2 RX

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April 7, 2023

Directional Comparison Unblocking (DCUB)Internal fault, channel failure

Local RelayLocal Relay Remote RelayRemote RelayGUARD1 TXGUARD1 RX


GUARD2 TX GUARD2 RX


TRIP1 TX



NO RX

TRIP2 TX

TRIPTRIP



TRIP Z1TRIP Z1

NO RX


Loss of ChannelLoss of Channel

Loss of GuardLoss of GuardBlock Timer StartedBlock Timer StartedDuration Timer StartedDuration Timer StartedExpiredExpired

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April 7, 2023

Redundancy Considerations

• Redundant protection systems increase dependability of the system:Multiple sets of protection using same protection

principle and multiple pilot channels overcome individual element failure, or

Multiple sets of protection using different protection principles and multiple channels protects against failure of one 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, trip coil circuits, etc. also need to be considered.

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April 7, 2023

BU

S

BU

S

End ZoneEnd Zone

Communication Channel 1Communication Channel 1

Communication Channel 2Communication Channel 2

Loss of Channel 2Loss of Channel 2

AND Channels:AND Channels:

POTT Less ReliablePOTT Less Reliable

DCB Less SecureDCB Less Secure

OR Channels:OR Channels:

POTT More ReliablePOTT More Reliable

DCB More SecureDCB More Secure

More Channel SecurityMore Channel Security More Channel DependabilityMore Channel Dependability

Redundant Communications

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April 7, 2023

Redundant Pilot Schemes

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April 7, 2023

• Integrated functions:weak infeedecholine pick-up (SOTF)

• Basic protection elements used to key the communication:distance elementsfast and sensitive ground (zero and

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

Pilot Relay Desirable Attributes

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April 7, 2023

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 (HYB

POTT)Blocking scheme (DCB)Unblocking scheme (DCUB)

Pilot Relay Desirable Attributes

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April 7, 2023

Security for dual-breaker terminals• Breaker-and-a-half and ring bus terminals are common 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 line relays.

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April 7, 2023

Security for dual-breaker terminals

Accurate CTs preserve the reverse current direction under weak remote infeed

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April 7, 2023

Security for dual-breaker terminals

Saturation of CT1 may invert the line current as measured from externally summated CTs

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April 7, 2023

Security for dual-breaker terminals • Direct measurement of

currents from both circuit breakers allows the 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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April 7, 2023

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 each

breaker 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 forward direction. Block is then lifted to permit tripping.

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April 7, 2023

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 any reclosing attempt.

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April 7, 2023

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 an interconnected system.

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April 7, 2023

Out-of-Step RelayingOut-of-step blocking relays

– Operate in conjunction with mho tripping relays to prevent a terminal from tripping during severe system 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 pole slip.– Initiate tripping of breakers that separate system in

order to balance load with available generation on any isolated part of the system.

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April 7, 2023

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 element is ready to trip

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April 7, 2023

Power Swing BlockingApplications:>Establish a blocking signal for stable power swings

(Power Swing Blocking)>Establish a tripping signal for unstable power swings

(Out-of-Step Tripping) Responds to:>Positive-sequence voltage and current

97 /GE /

April 7, 2023

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

98 /GE /

April 7, 2023


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

99 /GE /

April 7, 2023

Series-compensated linesSeries Capacitor with MOV

100 /GE /

April 7, 2023


101 /GE /

April 7, 2023

Series-compensated linesDynamic Reach Control

102 /GE /

April 7, 2023

Series-compensated linesDynamic Reach Control for External Faults

103 /GE /

April 7, 2023

Series-compensated linesDynamic Reach Control for External Faults

104 /GE /

April 7, 2023

Series-compensated linesDynamic Reach Control for Internal Faults

105 /GE /

April 7, 2023

Distance Protection Looking Through 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

106 /GE /

April 7, 2023

Transformer Group Compensation

Depending on location of VTs and CTs, distance relays Depending on location of VTs and CTs, distance relays need to compensate for the phase shift and magnitude need to compensate for the phase shift and magnitude

change caused by the power transformerchange caused by the power transformer

107 /GE /

April 7, 2023

Setting Rules

• Transformer positive sequence impedance must be included in reach setting only if transformer lies between VTs and intended reach point• Currents require compensation only if transformer located between CTs and intended reach point• Voltages require compensation only if transformer located between VTs and intended reach point• Compensation set based on transformer connection & vector group as seen from CTs/VTs toward reach point

108 /GE /

April 7, 2023

>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 distance

applications with power transformers

Distance Relay Desirable Attributes

109 /GE /

April 7, 2023

>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


110 /GE /

April 7, 2023

>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


111 /GE /

April 7, 2023

transmission line protection

Documents

directional

directional

reaching transfer

sequence directional

voltageshigh

trip z1fsk

source impedance

secondary