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!