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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
Communications
Zone 1Zone 2
Blocking Zone / Zone 3Differential Zone
Relay 2Relay 1
Scheme and Media Must Match
Zone 2Trip Permission
Received
Transmit Permission
TripANDPOTT Logic
DCB Logic
AND
AND
Zone 3 (Reverse)Transmit Block
TripZone 2
Block Received
PU
DO
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
KeyKey ReceiveReceive
Key to Receive:
0.375 cycles
Digital input over multiplexed fiber with low-speed
data cardKeyKey
ReceiveReceive
Digital Is Faster Than Contact
1.5 cycles
0.375cycles
Contact Digital
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
Receivedblock justin time
Receivedblock justin time
Receivedblocktoo late
Receivedblocktoo 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 10thGood Test of Current Differential Over Radio
Licensed Radio Current Differential Test Was a Big Success
Nofailures
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!Thank You!