Ultra-High-Speed Relaying for Transmission Lines

Transcription

1 Ultra-High-Speed Relaying for Transmission Lines Copyright SEL 2015

2 Focus for Today Benefits of faster line protection Limitations of present-day phasor-based protection Principles of time-domain protection

3 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

4 How Much Faster? Present-day relays Based on phasors Operate in 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

5 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

6 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

7 Speed of Present-Day Relays Phasors represent steady state Determining steady state takes time

8 Speed of Present-Day Relays Phasors represent steady state Determining steady state takes time Shorter windows are faster but less accurate

9 1970s and 1980s Designs Based on incremental quantities Not true TW protection Underperformed on security ASEA RALDA (1976) No manufacturer follow-through BBC LR-91 (1985) GEC LFDC (1988)

10 Why Only Now? Better technology High-speed ADC Processing power High-bandwidth communications TWFL experience and new ideas Advanced simulation tools Simplicity

11 Introducing the SEL-T400L

12 SEL-T400L Key Functionality Subcycle protection TD21 TD32 TW87 4 ms for 50% of line 2 ms + channel time 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

13 Phasor and Time-Domain Principles Similarities and Differences Algorithm Phasor-Based Differential Equations Traveling Waves Spectrum 50 / 60 Hz 1 khz 100 khz Filtering Sampling 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

14 Traveling Wave Current Differential External Faults TW that entered at one terminal Leaves at other terminal After line propagation time With opposite polarity

15 Traveling Wave Current Differential Internal Faults Internal fault launches two TWs that Are of the same polarity Arrive with time difference, P

16 Traveling Wave Current Differential Corner Case The principle holds true TW that entered S leaves R after TW that entered R leaves S after

17 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

18 Differential Equation Protection Incremental Quantities R S L S S mr ml F i Fault e S v v F Prefault Subtract 0 And the network simplifies

19 Differential Equation Protection Incremental Quantities R S L S S mr ml F i Fault e S v v F Prefault Subtract Source And the network simplifies

20 Incremental Quantities Example Voltage 50 Current Time, cycles

21 Incremental Quantities Example 1 khz 500 Hz 300 Hz

22 Differential Equation Protection Incremental Quantities i S mr ml F R S L S v v F Introduce replica current Even simpler equations

23 Directional Element First 1 ms of Fault Hz 300 Hz Hz 300 Hz

24 Directional Element F S i R R L v R R L R

25 Directional Element

26 Directional Element 300 Hz LPF 500 Hz LPF The principle is solid despite transients left in the operating signal. No need for excessive filtering!

27 Directional Element Hz 300 Hz Replica current makes the element stay picked up Forward fault Reverse fault

28 Distance Element i S mr ml F Want to reach up to m 0 v v F Voltage change at the fault: Therefore, trip if:

29 Distance Element Fault at 25% of the reach 500 Hz LPF Trip 300 Hz LPF

30 Distance Element Fault at 50% of the line (300 Hz LPF) m 0 = m 0 =

31 Distance Element Similar to Zone 1 21 (Z1) TD21 Controlled reach Directionality Direct tripping Setting in length units Independence from SIR R F impact

32 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

33 SEL-T400L Settings No 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

34 Conclusions Modern power systems need faster protection We have technology for fast line protection Time-domain principles are easy to use