1. Copyright © SEL 2008 Updated Transmission Line Protection Communications Roy Moxley, Ken Fodero, and Héctor J. Altuve Schweitzer Engineering Laboratories, Inc.

2. Critical Clearing Times Never Seem to Increase Because Generation Is Remote From Loads

3. Reduce the Times You Control

4. Communications-Assisted Protection

5. Scheme and Media Must Match POTT Logic DCB Logic

6. Can We Transmit Through a Fault? Signal attenuation problems Arc noise interference Common mode failures Photo courtesy of Niagara Mohawk, a National Grid Company

7. Power Line Carrier Strengths  Protection owned  Single function  High signal-to-noise ratio Weaknesses  Must transmit through fault  Only transmits single bit

8. Optical Fiber Strengths  Unaffected by arcs or ground potential rise  Wide bandwidth Weaknesses – shared resource

9. Spread-Spectrum Radio Strengths  Low cost  No licensing required Weaknesses  Line of sight required  Interference possible

10. Licensed Radio Strengths  Exclusive ownership of frequency  Independent of line path Weaknesses  License required  Line of sight required

11. Let’s Look at Relay Reports POTT  Multiplexed fiber  Digital communication  Contact inputs  Spread-spectrum radio DCB – power line carrier Line current differential – licensed radio

12. Contact input over multiplexed fiber with DTT card Key to Receive: 1.5 cycles Key Receive

13. Key to Receive: 0.375 cycles Digital input over multiplexed fiber with low-speed data card Key Receive

14. Digital Is Faster Than Contact 1.5 cycles 0.375 cycles ContactDigital Contact  Contact time  Input time  Debounce time Digital  Integral error checking  Direct input to logic

15. POTT Over Spread-Spectrum Radio CFE Mexico Experience Transmission time: < 0.5 cycles Correct trips: 12 of 12 Correct nontrips: 27 of 27

16. DCB Time Coordination Is Critical 2.0 ms between block and unintended operation Received block just in time Received block too late

17. Get a Clock!! Hours spent correlating event reports Settings need to be coordinated with accuracy Troubleshooting improved after questionable operation

18. FAQ: Can We Put Line Current Differential Over Radio? Requires 56/64 Kbps channel Needs to be secure and reliable ISM Band

19. Tested Radio System Licensed 900 MHz radios Interleaving removed – much faster, no errors Nonrecommended semiparabolic antenna worked great Radio and relay from different manufacturers

20. Choose Correct Antenna for Application 3 miles

21. Snowfall on June 10th Good Test of Current Differential Over Radio

22. Licensed Radio Current Differential Test Was a Big Success No failures No lost packets 2 ms transmission

23. Conclusions

24. Fiber Is Great for Most Applications Cost and availability is a drawback Digital data is faster than contacts

25. Spread Spectrum Is Proven Subcycle transmission times Reliable and secure performance Reasonable cost and installation

26. Licensed Radio Is Reliable and Fast for Line Current Differential License attainment is not difficult if frequency is available Transmission is fast (2 ms) Protection is secure and reliable with care

27. Considerations Ensure communication is appropriate to scheme and vice versa Test and monitor communications Verify performance with clocks

28. Thank You!