Fundamentals and Improvements for Directional Relaysfor Directional Relays

K l Zi d D id C t llKarl Zimmerman and David CostelloSchweitzer Engineering Laboratories, Inc.

Copyright © SEL 2010

www.selinc.com

Outline

Di ti l El t F d t l• Directional Element Fundamentals

• How and Why Directional Elements Have yEvolved

• Directional Element Performance During• Directional Element Performance During Loss-of-Potential Condition

Directional Elements

• Determine fault direction (normally not used to detect load or power flow)

• Supervise overcurrent and distance• Supervise overcurrent and distance elements for phase and ground faults

• Form ground quadrilateral elements

• Evolve with time and experienceEvolve with time and experience

Basic Directional Element Principle

Angle Between Polarizing and Operating Q tit D t i RQuantity Determines Response

T i lTypical Electromechanical DesignDesign

Quadrature Polarization

• A-Phase Relay Uses

• A-Phase current

VAB lt• VAB voltage

• Max torque when IA leads VBC by 450Max torque when IA leads VBC by 45

• Limit to Sensitivity of 2.3VA

• 1% rated voltage and 2A

• Special Applications Challenge Design

Directional Element Design Quantities

Element Polarizing Operating

Phase VBC, VCA, VAB IA, IB, IC

V Z (with V memory) I I IV1, Z1 (with V1 memory) IA, IB, IC

V2, Z2 IA, IB, ICGround V0, Z0 3*I0

V2, Z2 3*I02, 2 0

IN 3*I0

Negative-Sequence Quantities

• Capable of providing a larger signal –V t l l ti i ll f ll ZV2 at relay location is small for small Z2S(strong) and large for large Z2S (weak)

• Immune to Z0 mutual coupling

• Less affected by VT neutral shift

• Applicable with only 2 VTs• Applicable with only 2 VTs

• Easy to implement with numerical relaysy p y

Early (1980s) MicroprocessorMicroprocessor

Design Uses Torque Product

T32Q > 0.1VA

( )2 2 2 2T32Q V • I • cos V I MTA⎡ ⎤= ∠− − ∠ +∠⎣ ⎦

Generating Testing QuantitiesN ti S E tiNegative-Sequence Equations

223 A B CV V a V aV= + +

223 A B CI I a I aI= + +

where 1 120a = ∠ °2and 1 240a = ∠ °

V2 & I2 for Forward A Ph t G d F ltA-Phase-to-Ground Fault

V

V

VCa2VBaVC

VA

VA3V2VB

IA

3V2

3I2A

Current and Voltage Phasors Negative-Sequence Phasors

Negative-Sequence Voltage D l d F Th Ph V ltDeveloped From Three-Phase Voltage

Inputs

VVC

a2VBaVC

VA

VB VA3V2

Negative-Sequence Voltage D l d F Si l PhDeveloped From Single-Phase

Voltage Input

VBB

VA 3V2VC

Negative-Sequence Current D l d F Si l PhDeveloped From Single-Phase

Current Input

IA 3I2

Symmetrical Components for Si l Li t G d F ltSingle-Line-to-Ground Fault

1993 Innovation N ti S

R2

Negative-Sequence Impedance for L2

R2

Systems With Small V2 2

L2Z Angle+ϕ

2 2

R2S2

F2

( )2 2Re V • 1 Z1ANG•I ∗⎡ ⎤∠⎣ ⎦

S2

( )2 22measured 2

2

ZI

⎣ ⎦=

Testing the Negative-Sequence I d Di ti l El tImpedance Directional Element

R b if Z2 ( F R) i iti• Remember, if Z2n (n = F or R) is positive, this indicates a reverse fault

♦ Set current phase angle for a reverse fault

• If Z2n is negative, this indicates a forwardfaultfault

♦ Set current phase angle for a forward fault

Testing the Negative-Sequence Impedance Directional ElementImpedance Directional Element

Z2R and Z2F Are Positive

3I2 = 50QRA

3I2 = 3V2 / Z2R32QR

B

3I2 = 3V2 / Z2F

BC

3V2

MTA32QF MTA32QFMTL

Limits to Sensitivity Comparison

Impedance Based 32Q vs ElectromechanicalImpedance-Based 32Q vs. Electromechanical

Z2 Element Improves S iti it C d tSensitivity Compared to

Electromechanical Designs

F

Z2 Element Correctly Detects 500 Ω F lt 525 kV Li500 Ω Fault on 525 kV Line

Impedance-Based Element Requires Th h ld Z2F d Z2RThresholds Z2F and Z2R

Engineer-Calculated Thresholds M H EMay Have Errors

Design Evolves (AUTO)A t ti S tti Si lif C l l tiAutomatic Settings Simplify Calculations

• Z = 0 5 • Z• ZF2 = 0.5 • ZL1

• ZR2 = ZF2 + 0.1• 3I2 > 0.5 A (forward)• 3I2 > 0 25 A (reverse)3I2 > 0.25 A (reverse)• I2 / I1 > 0.1 blocks for three-phase faults• Automatically switch from Z2 to Z0 to I0

Z2 Element U li blUnreliable

When –+

–+

Z Z Z(1 m)Zm • ZGenerator Offline

ZS1 ZT1 ZR1(1 – m)ZL1m • ZL1

ZS2 ZT2 ZR2(1 – m)ZL2m • ZL2 ( )

ZS0 ZT0 ZR0(1 – m)ZL0m • ZL0

3RF

Offline Generator Creates Isolated Z S SZero-Sequence Source

IAIB

ICV

B V

C

67N 3OUT A1 *

VA

VD

igita

lsD

Automatic Switch From Z2 to Z0D t t F lt (ORDER)Detects Fault (ORDER)

)IA

IB

IC

A V

B V

C (k

V)s

VAD

igita

ls

Transformer Energization Challenges A t ti S ttiAutomatic Settings

Forward “Fault” Declared With Low V2

R2

F2

F22measured

Changing Forward Setting Threshold (Z ) C t N O t R i(ZF2) Creates No-Operate Region R2

F2

F2 2measured

Application Witho t Lines 50N50P

Utility Line A

Utility Line B

C

Without Lines Challenges

50N50P

ED

FAutomatic Settings

H

G50/51P

F

gRES

87T

TransI

TransJ 00

67P

RES

51N

LK

67P

IndustrialBus 2

IndustrialBus 1

N QPO

M

LOADR

LOADS

LOADU

LOADT

Non-Line Application Settings

• Set ZF2 = –0.3 Ω and ZR2 = +0.3 ΩF2 R2

• Use directional power element to detect reverse power flowreverse power flow

• Use V1 memory polarized phaseUse V1 memory polarized phase overcurrent with load encroachment for high-side, three-phase faultshigh side, three phase faults

• Use Z2 polarized 3I2 overcurrent for unbalanced faults

Fault on Parallel Line Challenges A t ti S it hiAutomatic Switching

Small I2 During Fault Prompts Ch t Z El tChange to Z0 Element

Very Little I2, But Enough I0 to C O tiCause Operation

Channel Magnitude AngleChannel Magnitude AngleIA(A) 442.1 253.2IB(A) 507 6 99 1IB(A) 507.6 99.1IC(A) 597.1 4.3IG(A) 407 5 17 7IG(A) 407.5 17.7

VA(kV) 207.7 240.1VB(kV) 202 9 120 2VB(kV) 202.9 120.2VC(kV) 207.2 0.0

I0 135 6 17 6I0 135.6 17.6I2 37.3 275.0

New Automatic Settings (AUTO2) I S itImprove Security

R2R2

F2

F2F2

Creates no-operate region when V2 and Z2 are near 0

New Automatic Settings R d tiRecommendations

• Use original AUTO method for strong• Use original AUTO method for strong source (Z2 < 0.5 Ω secondary)

• Use AUTO2 for Z2 > 0.5 Ω secondary

S l t l ti l t• Select only negative-sequence element with no automatic switching unless system changes dictatechanges dictate

Directional Element Performance D i LOP C ditiDuring LOP Condition

Directional Element Responses From 1980 1993 1996 D i1980s, 1993, 1996 Designs

1 VA 1 VB 1 VC 1 V0Mag 1 I0Mag

-250

25 .0 sec

_ _ _ _ g _ g

2_V2Mag 2_I2Mag 3_V1Mag 3_I1Mag 3_I0Mag

-25

01020

20

01020

255075

1 LOP *1_21P 12_LOP *2_ZBC 4 23_LOP

025

1_LOP

21.60 21.61 21.62 21.63 21.64 21.65 21.66 21.67 21.68Event Time (Sec) 23:27:21.595666

Avoiding Single Points of Failure

• Apply NERC standard for redundancy• Apply NERC standard for redundancy requirement

• Use two redundant systems

• Alert SCADA and make directional elementAlert SCADA and make directional element decision during LOP

Z1LOP Performs Correctly D i LOP C diti BDuring LOP Condition Because

V1 Angle Is Stable

⎡ ⎤( ) ( )

( )1 1

1measured 2

Re V • I • Z1ANGZ

∗⎡ ⎤⎣ ⎦=

( )1measured 21I

Forward Midline CG Fault With A Ph F BlWith A-Phase Fuse Blown

Forward Midline AG Fault With A Ph F BlWith A-Phase Fuse Blown

Reverse Midline AG Fault With A Ph F BlWith A-Phase Fuse Blown

Conclusions

• Directional element designs evolve

• Electromechanical and early microprocessor-based relays were lessmicroprocessor-based relays were less sensitive and could not easily respond to changeschanges

• Newer designs are more sensitive and flexible, but sensitivity must be studied

Conclusions

• Non-line and transformer applications differ from line applications and must be evaluated

• Automatic settings are helpful but can be misapplied if not clearly understoodbe misapplied if not clearly understood

Conclusions

• New guidelines use the local positive-sequence source impedance

• A new positive-sequence impedance• A new positive-sequence impedance directional element can be employed during LOP conditions (provides some protectionLOP conditions (provides some protection to address the need for redundancy in protection systems)protection systems)

Questions?

d @ lidaveco@selinc.com