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Communication Aided Tripping

Common Methods, Schemes and

Considerations

Presented by: Matt Horvath, P.E. March 13, 2017

• Background• Purpose• Methods and Mediums• Schemes• Considerations

Application: 69 kV to 500 kV AC Transmission Lines

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Content Summary

Content area• First Level

» Second Level– Third Level

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Content titleTraditional Step Distance Protection

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• Developed in 1910’s• Instantaneous Zone 1 coverage

~ 60% of line• Remaining ~ 40% of line cleared

in Zone 2 time

Relay 1

Relay 1

Remote Bus

Zone 1

Zone 2

X

Remote Bus

X



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Content titleFaster Fault Clearing Required

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• I2t damage too high• System stability jeopardized• Line is too electrically short to

allow zone 1 reach setting• Sequential tripping cases



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Content titleSequential Tripping

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May not be possible for one terminal to detect faults:

• Fault Types• Fault location• Week source terminal• Three terminal lines• Strong Infeed• Generally not acceptable



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Content titleGoals For Comm-Aided Tripping

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If Both Terminals Can Communicate:1. Speed2. Coverage3. Primary 4. Simultaneous 5. Any Fault Type

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COMM Aided Tripping Schemes

Current Based (Communications Centered)Directional Comparison (Communications Assisted/Aided)



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Content titleDirect Underreaching Transfer Trip

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Basic Logic for DUTT Scheme



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Content titleDUTT Scheme Continued

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Advantages• High speed operation for any line fault location• Will not over-trip for remote line faults

Disadvantages• Will not operate for faults beyond the underreach zone if

– Remote terminal is open– Communications channel is inoperative

• DUTT signal is converted to trip without any local supervision



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Content titlePermissive Underreaching Transfer Trip

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Basic Logic for PUTT Scheme



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Content titlePUTT Scheme Continued

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Advantages• Same as DUTT, but added security provided by

overreaching elements at receiving terminal



• Requires under and overreaching elements



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Content titleZone Acceleration

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Basic Logic for Zone Acceleration (Extension) Scheme



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Content titleZone Acceleration Scheme Continued

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Advantages• Same as DUTT but with increased security for faults

beyond the standard underreach elements





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Content titlePermissive Overreaching Transfer Trip

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Basic Logic for POTT Scheme



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Content titlePOTT Scheme Continued

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Advantages• Security – Inherently well supervised, requires

– Local fault detection by overreaching zone– Permissive signal received from remote end

Disadvantages• Dependability – Will not operate for internal faults when:

– Remote terminal is open– Communication channel is inoperative



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Content titleDirectional Comparison Blocking

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Basic Logic of DCB Scheme



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Content titleDCB Scheme Continued

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Advantages• Dependability – Will continue to operate regardless of:

– Open terminal– Communication channel failure

Disadvantages• Security

– Over-tripping concern– No supervision during COMM channel failure

• Slight time delay



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Content titleDirectional Comparison Unblocking

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Content titleDCUB Scheme Continued

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Advantages• Essentially same security as the POTT scheme• May have dependability similar to that of the DCB scheme

Disadvantages• Requires additional & continuous Guard signal

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Important Considerations

• Current Reversal• Breaker Open Keying• Echo Key Logic• Week Infeed



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Content titleCurrent Reversal

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• Initial faulted state on parallel line:

Zone 2A

Key



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Content titleCurrent Reversal Continued

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• First breaker on faulted line opens:

Zone 2B

Key



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Content titlePreventing Current Reversal Missoperation

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• Reverse ‘Blocking’ zone• Dropout Timer

– Maintains a block for Zone 2 permissive tripping until it expires• Criteria for dropout timer

– Breaker C Opening Time + Zone 2 Reset Time + Channel Reset Delay

• Effective for both POTT and DCUB schemes• Typical dropout timer delay ~ 4 – 8 cycles



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Content titleOpen Breaker Conditions

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Problem

Solutions• Continuous open-breaker keying• Permissive-trip echo-keying Logic

Key



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Content titleWeek Infeed Logic

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Results:• Terminal A: Trips by Time-Delayed Backup• Terminal B: Possible Sequential TripSolution in Relay B:• Supervise with Phase-to-Phase and/or Zero Sequence Overvoltage

Element• Trip Logic: Supervision AND Permissive Key

Strong Source Terminal

Weak Source TerminalKey A

Key B

Zone 2A Zone 2B



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Content titleEcho Keying

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Problems• Open Terminal• Weak Infeed

Strong Source Terminal

Weak Source TerminalKey A

Echo Key B

Zone 2A Zone 2B

Echo Supervision• Duration Time Delay• Pickup Time Delay• Block Time Delay

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Communication Methods and Mediums

• On-OFF• Frequency Shift • Pulse-Code• Phase-shift Keying• Various Digital

Telecommunications• Operating Speed & Security



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Content titlePilot Wires (Copper)

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• Developed in 1930’s• Telephone Wire• Twisted Pair• 50Hz, 60Hz or DC



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Content titleAudio Frequency Tones

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• Leased or utility owned telecom lines• Common frequency

range: 1 kHz to 3 kHz• Line route flexibility• Channel availability



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Content titlePower-Line Carrier

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• Developed in 1930’s• Superimposed on transmission lines• Line tuner & Coupling capacitor• Line/Wave Traps• Off/On or Frequency Shift



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Content titleMicrowave

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• Developed in 1940’s• 1 GHz to 300 GHz• Point‐to‐Point



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Content titleDigital Channels

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• Dedicated Fiber • Multiplexed Fiber Systems

• SONET, T1• Digital Microwave, Radio link, or Telecom Line

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Conclusion

Comm-Aided Tripping Achieves:

1. Speed2. Coverage3. Primary 4. Simultaneous 5. Any Fault Type

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References

Industry Standards• IEEE C37.113-2015 – “Guide for Protective Relay Applications to Transmission

Lines”• IEEE C37.93-2004 – “Guide for Power System Protective Relay Applications of

Audio Tones Over Voice Grade Channels”

Other Useful References• Blackburn, Lewis J. and Domin, Thomas J. – “Protective Relaying Principles and

Applications” Reference Text, Third Edition, 2007• Schweitzer, Edmund O. and Kumm, John J. – “Statistical Comparison and

Evaluation of Pilot Protection Schemes”, Whitepaper, 23rd WPRC 1996

Questions?

Thank You

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