ultra-high-speed relaying for transmission lines · how much faster? • present-day relays...
TRANSCRIPT
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Copyright © SEL 2015
Ultra-High-Speed Relaying for Transmission Lines
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Focus for Today
• Benefits of faster line protection
• Limitations of present-day phasor-based protection
• Principles of time-domain protection
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Already Pretty Fast – Why Faster?
• Higher power transfers(investment dollars saved)
• Reduced equipment wear (generators and transformers)
• Improved safety
• Reduced property damage
• Improved power quality
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How Much Faster?
• Present-day relays♦ Based on phasors
♦ Operate in 0.5–1.5 cycles
• Present-day breakers operate in 2 cycles
• Ultra-high-speed fault clearing♦ Consistent relay operating times
♦ 2 ms (TW) to 4 ms (differential equations)
♦ Subcycle times from future dc breakers
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Phasor-Based Protection Makes Sense
• Power systems were traditionally designed and modeled for steady-state operation at system frequency
• “Forcing functions” are at system frequency
• Instrument transformers are rated at system frequency
• CCVTs are band-pass devices
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Speed of Present-Day Relays
• Phasors represent steady state
• Determining steady state takes time
This is what we know if we trip in 0.5 cycles
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Speed of Present-Day Relays
• Phasors represent steady state
• Determining steady state takes time
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Speed of Present-Day Relays
• Phasors represent steady state
• Determining steady state takes time
• Shorter windows are faster but less accurate
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1970s and 1980s Designs
• Based on incremental quantities
• Not true TW protection
• Underperformed on security
• No manufacturer follow-through
ASEA RALDA (1976)
BBC LR-91 (1985)
GEC LFDC (1988)
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Why Only Now?
• Better technology♦ High-speed ADC
♦ Processing power
♦ High-bandwidth communications
• TWFL experience and new ideas
• Advanced simulation tools
• Simplicity
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Introducing the SEL-T400L
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SEL-T400L Key Functionality
• Subcycle protection♦ TD21 4 ms for 50% of line
♦ TD32 2 ms + channel time
♦ TW87 1–2 ms + channel time
• Fast MIRRORED BITS® and I/O
• TW fault locator – two-ended and single-ended methods
• 1 Msps DFR and analytics
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Phasor and Time-Domain PrinciplesSimilarities and Differences
Algorithm Phasor-Based Differential Equations Traveling Waves
Spectrum 50 / 60 Hz 1 kHz 100 kHz
Filtering
Sampling 16–32 s/c 8 kHz 1 MHz
Line theory
Operating time ~ 1 cycle A few milliseconds 1 ms
Requirements for CTs and PTs Low Moderate High
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Traveling Wave Current DifferentialExternal Faults
TW that entered at one terminal…• Leaves at other
terminal
• After line propagation time
• With opposite polarity
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Traveling Wave Current DifferentialInternal Faults
Internal fault launches two TWs that…• Are of the same
polarity
• Arrive with time difference, P ≤
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Traveling Wave Current DifferentialCorner Case
The principle holds true• TW that entered S
leaves R after
• TW that entered Rleaves S after
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TW87 Differential Element
• Operates in 1–2 ms
• Uses current TWs♦ No need for high-fidelity voltage
♦ Will work with CCVTs and CTs
• Communications-based (100 Mbps)
• Not affected by series capacitors
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Differential Equation ProtectionIncremental Quantities
Fault
Prefault
And the network simplifies…
Subtract…
0
eS vF
RS LSS
mR mL F
i
v
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Differential Equation ProtectionIncremental Quantities
Fault
Prefault
“Source”
And the network simplifies…
eS vF
RS LSS
mR mL F
i
v
Subtract…
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Incremental QuantitiesExample
Vol
tage
–0.5 0 0.5 1–50
0
50
Cur
rent
Time, cycles
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Incremental QuantitiesExample
1 kHz500 Hz300 Hz
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Differential Equation ProtectionIncremental Quantities
Introduce replica current
Even simpler equations…
RS
LS
SmR mL F
vF
i
v
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Directional ElementFirst 1 ms of Fault
–60 –40 –20 0 20 40 60–60
–40
–20
0
20
40
60
500 Hz300 Hz
–15 –10 –5 0
0
0.4
0.8
1.2
1.6
500 Hz300 Hz
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Directional Element
R L
SF
i
vRR
LR
R
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Directional Element
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Directional Element
The principle is solid despite transients left in the operating signal. No need for excessive filtering!
300 Hz LPF 500 Hz LPF
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Directional Element
–60 –40 –20 0 20 40 60–60
–40
–20
0
20
40
60
500 Hz300 Hz
Reverse fault
Forward faultReplica current makes the element stay picked up
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Distance Element
Want to reach up to m0…
Voltage change at the fault:
Therefore, trip if:
SmR mL F
vF
i
v
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Distance Element
Fault at 25% of the reach
300 Hz LPF
500 Hz LPF
Trip
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Distance Element
m0 = 0.2 – 0.4
Fault at 50% of the line (300 Hz LPF)
m0 = 0.6 – 0.9
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Distance ElementSimilar to Zone 1
21 (Z1) TD21Controlled reach
Directionality
Direct tripping
Setting in length units
Independence from SIR
RF impact
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Differential Equation 32/21 Elements
• Operate in 2–4 ms
• Use incremental quantities ♦ No need for high-fidelity voltage
♦ Will work with CCVTs and CTs
• Work with any channel
• Not affected by series capacitors
• Inherently secure for LOP
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SEL-T400L SettingsNo Short-Circuit Studies Required
• CT, PT ratios, Vnom (nameplate data)
• Line Z1 and Z0 (known for every line)
• Line propagation time (line energization test)
• TD21 reach (user preference)
• Basic channel configuration parameters
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Conclusions
• Modern power systems need faster protection
• We have technology for fast line protection
• Time-domain principles are easy to use