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
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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
Disadvantages• Will not operate for faults beyond the underreach zone if
– Remote terminal is open– Communications channel is inoperative
• 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
Disadvantages• Will not operate for faults beyond the underreach zone if
– Remote terminal is open– Communications channel is inoperative
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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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