ultra-high-speed relaying for transmission lines · how much faster? • present-day relays...
TRANSCRIPT
Copyright © SEL 2015
Ultra-High-Speed Relaying for Transmission Lines
Focus for Today
• Benefits of faster line protection
• Limitations of present-day phasor-based protection
• Principles of time-domain protection
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
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
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
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
Speed of Present-Day Relays
• Phasors represent steady state
• Determining steady state takes time
Speed of Present-Day Relays
• Phasors represent steady state
• Determining steady state takes time
• Shorter windows are faster but less accurate
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)
Why Only Now?
• Better technology♦ High-speed ADC
♦ Processing power
♦ High-bandwidth communications
• TWFL experience and new ideas
• Advanced simulation tools
• Simplicity
Introducing the SEL-T400L
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
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
Traveling Wave Current DifferentialExternal Faults
TW that entered at one terminal…• Leaves at other
terminal
• After line propagation time
• With opposite polarity
Traveling Wave Current DifferentialInternal Faults
Internal fault launches two TWs that…• Are of the same
polarity
• Arrive with time difference, P ≤
Traveling Wave Current DifferentialCorner Case
The principle holds true• TW that entered S
leaves R after
• TW that entered Rleaves S after
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
Differential Equation ProtectionIncremental Quantities
Fault
Prefault
And the network simplifies…
Subtract…
0
eS vF
RS LSS
mR mL F
i
v
Differential Equation ProtectionIncremental Quantities
Fault
Prefault
“Source”
And the network simplifies…
eS vF
RS LSS
mR mL F
i
v
Subtract…
Incremental QuantitiesExample
Vol
tage
–0.5 0 0.5 1–50
0
50
Cur
rent
Time, cycles
Incremental QuantitiesExample
1 kHz500 Hz300 Hz
Differential Equation ProtectionIncremental Quantities
Introduce replica current
Even simpler equations…
RS
LS
SmR mL F
vF
i
v
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
Directional Element
R L
SF
i
vRR
LR
R
Directional Element
Directional Element
The principle is solid despite transients left in the operating signal. No need for excessive filtering!
300 Hz LPF 500 Hz LPF
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
Distance Element
Want to reach up to m0…
Voltage change at the fault:
Therefore, trip if:
SmR mL F
vF
i
v
Distance Element
Fault at 25% of the reach
300 Hz LPF
500 Hz LPF
Trip
Distance Element
m0 = 0.2 – 0.4
Fault at 50% of the line (300 Hz LPF)
m0 = 0.6 – 0.9
Distance ElementSimilar to Zone 1
21 (Z1) TD21Controlled reach
Directionality
Direct tripping
Setting in length units
Independence from SIR
RF impact
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
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
Conclusions
• Modern power systems need faster protection
• We have technology for fast line protection
• Time-domain principles are easy to use