0810 Power Swing Relaying in the Texas Panhandle - An Out-Of-Step Odyssey FINAL 03312015

7/24/2019 0810 Power Swing Relaying in the Texas Panhandle - An Out-Of-Step Odyssey FINAL 03312015

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Power Swing Relaying

in the Texas Panhandle

An Out

-

Of

-

Step Odyssey

Presented by Kevin W. Jones, P.E.

Principal System Protection Engineer

68th Annual Conference for Protective Relay Engineers

March 31, 2015


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Outline

History of the Southwestern Public ServiceCompany (SPS) System

Brief Review of Power Swing Basics

Early SPS Power Swing Philosophy Modern SPS Power Swing Philosophy

Early Philosophy in the Modern World

Conclusions


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SPS System History

Company history began as anelectric franchise in 1904 inRoswell, NM

By the early 1930s, SPS had

expanded throughout the TexasPanhandle and Texas SouthPlains

The southeast New Mexicoregion was electrically isolatedfrom the Texas region until1946

Electrically

Isolated


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SPS System History

In the Fall of 1946, SPS placedits first 115 kV line in servicefrom Carlsbad, New Mexico toDenver City, Texas

This line stretched 109 milesand completed theinterconnection of all the SPSservice territory

UFO crash in June, 1947 nearRoswell???

109 Mile 115 kV

Transmission

Line


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SPS System History

The electrical system continuedto grow through the 1950s andearly 1960s

The SPS system remained

isolated from the rest of theEastern grid


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SPS System History

In May 1963, the 115 kV linefrom Guymon, Oklahoma toLiberal, Kansas wassynchronized and closed tyingSPS to the Eastern Interconnect

for the first time

Too weak to be left closedpermanently


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SPS System History

In 1964, a major outage foreverchanged SPSs approach to system-wide protection

A large Amarillo generating unit

tripped while another unit was off-line for maintenance

The northsouth tie lines tripped,resulting in a Texas North blackout


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SPS System History

Out-of-step tripping was allowed toforce islanding at strategic locationsto create three load/generation

islands PSB was installed on all looped

transmission lines

Under frequency relaying wasinstalled throughout the system at

three steps

About 10% of system load was to beshed at each UF step

Texas

North

New

Mexico

Texas

South

1964 Lessons Learned


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SPS System History

In May 1972, SPS connected to theEastern Interconnect via a new 230kV line from Amarillo, Texas to Elk

City, Oklahoma From 1983 to 1985, 11 tie line

power swing trips occurred,resulting in islanding with theEastern Interconnect and UF loadshed

Five events were caused by theloss of a single 350 MW generationunit

Growing Pains


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SPS System History

By 1985, the first 345 kV line wasbuilt from Abernathy, Texas toOklaunion, Texas

This new line strengthened the SPS

connection to the EasternInterconnect, allowing the 115 kVties to be operated closed

This stronger system stabilized theSPS system, and no power swingtrips occurred again until an event in1996 and another event in 2008


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SPS System History

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In 1996, A 230 kV bus fault resultedin the loss of about 1000 MW ofgeneration and the loss of nineinternal 230 kV transmission lines

All the Eastern Interconnect andTexas North to Texas South tie linestripped

All levels of UFLS tripped

75% (~2000 MW) of system load waslost by UFLS and tie line trips

This is the largest system outage tothe SPS system

Stronger System, Test #1


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SPS System History

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Stronger System, Test #2 In 2008, a loss of 800 MW of

generation caused EasternInterconnect tie line trips

The tie line trips resulted in a decayof system frequency, resulting inlevel 1 UFLS tripping (59.3 Hz)

Around 650 MW of load was shed(about 15% of system load)


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SPS System History

Today, the SPS connection to theEastern Interconnect has beenfurther strengthened by the addition

of three 345 kV lines

SPSs islanding scheme has beentested and proven to preventsystem-wide blackouts

The increased strengthening of the

SPS system has resulted in lessfrequent islanding events

Strongest System


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Power Swing Basics

What is a power swing?

Power Swing: a variation in three

phase power flow which occurs

when the generator rotor anglesare advancing or retarding relative

to each other in response to

changes in load magnitude and

direction, line switching, loss of

generation, faults, and other

system disturbances [1].


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Power Swing Basics

What causes power swings?

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Faults

o Generators accelerate until fault clears

Loss of Loado Generators accelerate Pm > Pe

Loss of Generation

o Generators decelerate Pm < Pe

Switching (line, capacitor, inductor, etc.)o Changes in power flow affect generator

output


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Power Swing Basics

Stable power swing (generator)

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Rotor Angle

(degrees)

Time (seconds)

Angle damps out with time

0

120

System Angle < 120 degrees


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Power Swing Basics

Un-stable power swing (generator)

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Time (seconds)

0

180

Rotor Angle

(degrees)

120

Angle continues to

increase with time

System Angle > 120 degrees

Pole Slip


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Power Swing Basics

Effects of power swings

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Relays can trip undesirably for stable power swings if not

set properly

Generators can be damaged after they slip a pole during

unstable power swings Breakers can be damaged if they try to open during

unstable power swings if the system angle is near 180

degrees


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Power Swing Basics

Power Swing Studies in the R-X Impedance Plane

Data required to perform a power swing study

o Line impedance (ZL)

o Sending end source impedance (ZS)

o Receiving end source impedance (ZR)o Parallel transfer impedance (ZTR)

o System maximum slip rate (Hz or degrees/second)

ZS ZR

ZTR

ZL


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Power Swing Basics

Line Impedance

Sending end source

impedance

Receiving end

source impedance

System Impedance

in the R X Plane

Total system source

impedance

Equal emf power

swing trajectory

Equal emf stabilityboundary


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Power Swing Basics

System Impedance

in the R X Plane

ES

ER

ES > ER

ES = 1.0 p.u.

ER = 0.7 p.u.

ES / ER = 1.43

ES < ERES = 0.7 p.u.

ER

= 1.0 p.u.

ES / ER = 0.7

ES = ER

ES / ER = 1.0


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Power Swing Basics

Slip Rate Calculation:

Inner angle Ai

Outer angle Ao

=( ) ()

360

()

=(120 90) 60()

360

2.0()

= 2.5


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Power Swing Basics

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PSB timer starts

here when outer

blinder is entered

PSB timer expires

before inner blinder is

reached blocking Z1

and Z2

Swing ends and new

steady state operatingpoint is achieved

Steady state load

operating point

pre-swing

PSB Example:


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Power Swing Basics

OST Example:

OST timer starts

here when outer

blinder is entered

OST timer expires

before inner blinder is

reached

Breaker trips as the

system angle is getting

smaller

Steady state load

operating point

pre-swing

OST armed to trip on-the-way-out when inner blinder is

entered (can also trip here)

Systems slip-a-pole where

the system angle is 180

degrees

TOWO occurs whenswing leaves inner

blinder


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Early SPS Power Swing Philosophy

Power Swing Tools of the Early Years

Prior to 1962, graph paper, slide rules and DCcalculating boards were used

Stability studies were run off-site on AC networkanalyzers

In 1962, SPS used an IBM 1620 computer to run loadflow, short circuit and stability studies


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Early PSB (Mho) Relay Settings Philosophy

Only block tripping of 3-phase elements on zone 1and zone 2 relays

Set PSB mho concentric about zone 2 The PSB timer was fixed at 3 to 4 cycles, depending

on manufacturer


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The first PSB philosophy seta buffer zone of half zone 2around zone 2

As zone 2 grew, the gapbetween the relays grewproportionally

This philosophy allowed forhigher slip rates, but less line

loadability This philosophy remained

until about the mid 1990s(~40 years)


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The next philosophy set theoffset mho a fixed 2-ohmssecondary separation from

zone 2

With this philosophy, as thezone 2 grew, the gap betweenzone 2 and the PSB relaydecreased

This philosophy allowed forbetter line loadability, butlower slip rates


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Early OST Relay Settings Philosophy

Identify lines to be tripped to form balancedload/generation islands

One end of line was typically tripped to keep tappedload energized or to keep the line energized for VARsupport

OST Philosophy in a nutshell:

Set Per I.M.


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OST Relays:

Concentric mho


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OST Relays:

Dual blinder

Inner blinders set between arc

impedance region and 120 degrees

(120 150 degrees typically)

Arc Impedance

Region

Outer blinders set to

accommodate a

3.33 Hz slip rate

=(144.5 84.0) 60()

360

3.0()

= 3.36


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OST Relays:

Lens

Outer tomato set at70 degrees

Middle circle set at

108 degrees

Inner lens set at

151 degrees

Reach set beyond

system impedance


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Modern SPS Power Swing Philosophy

Power Swing Tools of the Modern Years

Short circuit programmacro to plot reducedsystem impedance and

theoretical swingtrajectories


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Out-of-step analysisspreadsheet


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Out-of-step COMTRADE filecalculator using MathCAD

COMTRADE file play-backthrough relay using test set


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Modern PSB Relay Settings Philosophy

PSB Major Considerations

NERC PRC-023 load limit

o Outer blinder must not encroach upon load region

Worst case system slip rate (Hz)

o Typically 2-5 Hz for stable swings

Worst case expected arc impedance

o Inner blinder must not be set too close to arc

impedance region if used to supervise Z1 or Z2tripping


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Set outer PSB blinders

just inside the NERC

PRC-023 limit


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Set inner PSB blinders

just outside zone 2

phase mho circle


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Set top inner blinder a

percentage BEYOND

the apparent impedance

for a L-L fault at the

remote bus

Why???




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Fault at end of the line could fall

between inner and outer top

blinders, allowing the OOS block

timer to expire before the Z2

timer, thus delaying the Z2 trip

until the negative sequence

unblock timer times out!

This would be considered a slow

trip mis-operation.




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Set top outer blinder to 0.1 ohms

secondary higher than top inner

blinder

Set bottom blinders to mirror top

blinders (current philosophy)




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PSB spreadsheet final graph



Set OOS block time delay to

achieve a slip rate of at least 2.5

Hz (current philosophy)

Set higher than minimum distanceelement operating time based

upon SIR (see relay instruction

manuals)


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Modern OST Relay Settings Philosophy OST Major Considerations

NERC PRC-023 load limit

Worst case system slip rate (Hz)

o Typically 2-10+ Hz for un-stable swings

Worst case expected arc impedance

Slow evolving faults

o OST time delay should be > 1.5 cycles!!!


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Modern OST Relay Settings Philosophy

OST Settings

Outer blinder settings are set the same as PSB blinders

Inner blinder set between arc impedance zone and 120

degree system angle

Top and bottom blinders should be set to account for areasonable worst case weak system

Set for minimum slip rate of 3 Hz (current philosophy)


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Final actual in-service settings


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Final actual in-service settings

Arc Impedance

Region

Inner Blinder

Supervision of

Z1 and Z2Required!

=

(147.6 93.0) 60()

360

2.0()

= 4.55

Supervise Breaker Tripping

with Outer Blinder


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NERC PRC-026


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SPS still has over 100 Electromechanical PSB relays inservice

NERC PRC-023 will be effective for 100-200 kV lineswithin the next couple of years

Some of these relays will have to be evaluated toensure they comply with PRC-023


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50% of zone 2 buffer philosophy check:

NERC PRC-023

Load Region

NERC Region

Violation!!!

=(98 50) 60()

360

4.0()

= 2.0

23-mile 115 kV line


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50% of zone 2 buffer philosophy check:

=

(114 59) 60()

360

4.0()

= 2.29

Pull Z2 back to

125% of line

impedance

=(114 59) 60()

3603.0()

=3.06

23-mile 115 kV line


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2-ohm secondary separation philosophy check:

= (121 69) 60()360

3.0()

= 2.89

Different 23-mile115 kV line

Good!!!


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2-ohm secondary separation philosophy check:

= (105 79) 60()360

3.0()

= 1.44

Same line, impedancedoubled, ignore load limit

NOT Good!!!


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Conclusions

Conclusions

SPSs external and internal islanding strategy has beenproven to avoid total system blackouts

Technological advancements in analysis tools have

improved confidence in power swing settings Technological advancements in power swing relaying

have added much needed flexibility to allow relays to beset to achieve desired slip rates

NERC Reliability Standards PRC-023 and PRC-026 will

require re-evaluation of power swing philosophies


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Conclusions

Moving Forward

SPS will have to re-evaluate its existing islanding schemevalidity with SPP performing Balancing Authorityfunctions

SPS will continue to refine and test power swing settingsusing simulations and COMTRADE play-back

IEEE PSRC Working Group D29 will create a tutorial onsettings conventional blinder power swing settings in asimulated environment

The Odyssey Continues


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Questions???


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References

[1] IEEE Power System Relaying Committee WG D6, Power Swing and Out -of-Step Considerations on Transmission Lines, July2005. Available: http://www.pes-psrc.org.

0810 Power Swing Relaying in the Texas Panhandle - An Out-Of-Step Odyssey FINAL 03312015

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