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

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

Reduce the Times You Control

Communications-Assisted Protection

Scheme and Media Must Match POTT Logic DCB Logic

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Choose Correct Antenna for Application 3 miles

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

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

Conclusions

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

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

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

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

Thank You!