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TRANSMISSION LINE TRANSMISSION LINE
PROTECTIONPROTECTION
TRANSMISSION LINE TRANSMISSION LINE
PROTECTIONPROTECTION
April 8, 2023 1Protection Courses
April 8, 2023 2Protection Courses
TUTORIAL SCOPE
1. FUNDAMENTALS
2. CHARACTERISTICS
3. POLARIZATION
4. ZONES SETTING CRITERIA
5. MHO VS QUADRILATERAL
6. SWITCH ON TO FAULT
7. POWER SWING BLOCKING/TRIPPING
April 8, 2023 3Protection Courses
TUTORIAL SCOPE
8. LOAD ENCROACHMENT
9. LOSS OF POTENTIAL
10. UNIT PROTECTION
11. PERMISSIVE UNDER REACH
12. PERMISSIVE OVER REACH
13. CARRIER BLOCKING
14. CURRENT REVERSAL
15. ZONE 1 EXTENSION
April 8, 2023 4Protection Courses
TUTORIAL SCOPE
16. WEAK IN-FEED
17. SERIES COMPENSATION
18. MUTUAL COMPENSATION
19. AUTO RECLOSER
20. STUB PROTECTION
21. CCVT TRANSIENT
22. DIRECTIONAL EARTH FAULT
April 8, 2023 5Protection Courses
MHO CHARACTERISTICS
MHO
April 8, 2023 6Protection Courses
MHO CHARACTERISTICS
April 8, 2023 7Protection Courses
QUADRILATERAL CHARACTERISTICS
Quadrilateral
April 8, 2023 8Protection Courses
OFFSET MHO CHARACTERISTICS
April 8, 2023 9Protection Courses
April 8, 2023 10Protection Courses
POLARIZATION METHODS
SELF POLARIZATION
Terminal faults will not cover
CROSS POLARIZATION
Use other healthy phase voltages
Terminal three phase fault will not
cover
MEMORY POLARIZATION
Covers all type of faults
April 8, 2023 11Protection Courses
VR
VB
VY
VRB
VBY
VYR
POLARIZATION METHODS
April 8, 2023 12Protection Courses
S/Stn 1 S/Stn 2 S/Stn 3
Time
Zone 3R
Zone 3R
Zone 3R
Zone 2
Zone 2Zone 3R
Zone 2
Relay A
Relay B
Relay C
Relay D
Zone 3F
Zone 2Zone 3
Zone 1
Zone 1
Zone 1
Zone 1
ZONES SETTING CRITERIA
April 8, 2023 13Protection Courses
A B C
X
R
Zone 1
Zone 3Zone 2
ZONES SETTING CRITERIA
Zone 4
April 8, 2023 14Protection Courses
SWITCH ON TO FAULT
SWITCH ON TO FAULT. Failure to remove Earth Clamps after CB Maintenance Practically Zero Impedance in fault path. Fault Point is at the Origin - Boundary condition for Zones 1 & 2 For a 3-Phase fault, cross-polarising will have no effect
SOTF Fault Point
April 8, 2023 15Protection Courses
AC SOTF - Used where VT is on LINE SIDE of the CBIF Current and Voltage have been Dead for 10 SecsAND the Current Rises ABOVE 30% of NominalAND Voltage remains BELOW 20% of NominalTHENRemove the Time Delay from Zone 3ANDAllow tripping on Overcurrent onlyFOR200ms
DC SOTF - Used where VT is on BUSBAR SIDE of the CBWhen Circuit Breaker Manual Close Handle is OperatedRemove the Time Delay from Zone 3FOR 400ms(Longer delay allows for CB Closing time)
SOTF ALGORITHMS
April 8, 2023 16Protection Courses
Power Swing Outer boundary
Power Swing Inner boundary
Transittime
Power swing locusZone 1
Zone 2
Zone 3
If the System Impedance Remains in the Power SwingDetection Zone for longer than the PSD Transit Time (Nominally 50 ms)POWER SWING ALARMwill Operate
POWER SWING DETECTION & BLOCKING
April 8, 2023 17Protection Courses
POWER SWING DETECTION & BLOCKING
April 8, 2023 18Protection Courses
LOAD ENCROACHMENT
April 8, 2023 19Protection Courses
LOSS OF POTENTIAL
April 8, 2023 20Protection Courses
Zone 2Carrier Aided Trip
S/Stn 1 S/Stn 2
Time
Zone 1 (No Operation)
Distance
Distance
Zone 1
Relay B
Relay C
Relay A Signalling Channel
Zone 2Time Delayed Trip
Operation of Zone 1 sends signal to remote end
Instantaneous trip if Zone 1 Operation Zone 2 + Signal from Remote end
ALLOWS INSTANTANEOUS TRIPPING OVER 100% OF THE LINE LENGTH
Zone 2
SIGNALLING CHANNEL REQUIRED BETWEEN ENDS
PERMISSIVE UNDER REACH
April 8, 2023 21Protection Courses
Zone 2Carrier Aided Trip
S/Stn 1 S/Stn 2
Time
Zone 1 (No Operation)
Distance
Distance
Relay B
Relay C
Relay A Signalling Channel
Zone 2Time Delayed Trip
Instantaneous Operation of Zone 2 sends signal to remote end
Instantaneous trip if Zone 1 Operation Zone 2 + Signal from Remote end
Zone 2
Zone 2 InstantaneousZone 1
SIGNALLING CHANNEL REQUIRED BETWEEN ENDS
ALLOWS INSTANTANEOUS TRIPPING OVER 100% OF THE LINE LENGTH
PERMISSIVE OVER REACH
April 8, 2023 22Protection Courses
Zone 2Carrier Aided Trip
S/Stn 1 S/Stn 2
Time
Zone 1 (No Operation)
Distance
Distance
Zone 1
Relay B
Relay C
Relay A Signalling Channel
Zone 4 - Blocking
Operation of Zone 4 sends blocking signal to remote end Instantaneous trip if
Zone 1 Operation Zone 2 + No blocking Signal from Remote end
WITHIN the Permissive Trip Time
Zone 2
SIGNALLING CHANNEL REQUIRED BETWEEN ENDS
ALLOWS INSTANTANEOUS TRIPPING OVER 100% OF THE LINE LENGTH
BLOCKING SCHEME
April 8, 2023 23Protection Courses
Zone 2Carrier Aided Trip
S/Stn 1 S/Stn 2
Time
Zone 1 (No Operation)
Distance
Distance
Zone 1
Relay B
Relay C
Relay A Signalling Channel
Zone 4 - Blocking (No Operation)
Operation of Zone 4 sends blocking signal to remote end Instantaneous trip if
Zone 1 Operation Zone 2 + NO BLOCKING SIGNAL from Remote End
WITHIN the Permissive Trip Time
Zone 2
SIGNALLING CHANNEL REQUIRED BETWEEN ENDS
ALLOWS INSTANTANEOUS TRIPPING OVER 100% OF THE LINE LENGTH
BLOCKING SCHEME
24Protection Courses
CURRENT REVERSAL
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April 8, 2023 25Protection Courses
CURRENT REVERSAL
April 8, 2023 26Protection Courses
CURRENT REVERSAL
April 8, 2023 27Protection Courses
RelayA
RelayB
RelayC
S/Stn 1 S/Stn 2
RelayC
S/Stn 3
Time
Gives improved fault clearancetime for fault @ this position
Will trip CB @ 'A' forfault @ this position
No Signalling used between ends Used with Auto-Recloser only Results in More Breaker Operations
Zone 2 Zone 3F
Distance
Distance
Trip
Reclose
Zone 1 Ext
Zone 1
ZONE 1 EXTENSION SCHEME
April 8, 2023 28Protection Courses
WEAK IN FEED LOGIC
April 8, 2023 29Protection Courses
SERIES COMPENSATION
• Used to increase load capacity
• Improve power system stability
• Improve load division on parallel paths
• Reduce transmission losses
April 8, 2023 30Protection Courses
SERIES COMPENSATION
• Voltage reversal
April 8, 2023 31Protection Courses
• COUPLING BETWEEN LONG LINES CAN HAVE A SIGNIFICANT EFFECT ON DISTANCE PROTECTION MEASUREMENT
• ONLY AFFECTS ZERO SEQUENCE COMPONENT (PPS AND NPS COMPONENTS ARE BALANCED AND THEREFORE SUM TO ZERO)
• IF RELAY NOT COMPENSATED FOR EARTH RETURN AND MUTUAL EFFECTS Z1 WILL BE OVER-ESTIMATED AND THE RELAY WILL UNDER-REACH
Ia
Z M OFault
Ib
Double Circuit Line
MUTUAL COMPENSATION 1
April 8, 2023 32Protection Courses
• When one of the lines is out of service and earthed at both ends
• Energise a Status Input SWITCH TO ALTERNATE SETTINGS group
• ALTERNATE SETTING GROUP uses
– Increased Earth Fault Compensation Factor to take account of the Zero Sequence Mutual Coupling due to the parallel line
MUTUAL COMPENSATION 2
April 8, 2023 33Protection Courses
CCVT TRANSIENT
April 8, 2023 34Protection Courses
CCVT TRANSIENT
Distance element may over reach CCVT Trans. Reduce the fundamental component of the fault voltage results in decrease in the calculated impedance High capacitance reduced transient effect Passive Ferro-resonance reduced transient effect
April 8, 2023 35Protection Courses
CCVT TRANSIENT
April 8, 2023 36Protection Courses
DIRECTIONAL EARTH FAULT 1
• Unrestricted Characteristic
– Operates for any fault current above setting in selected direction
• Detects high impedance earth faults
– Operate quantity - residual current
– Polarising quantity - residual voltage
X
R
Line Angle
April 8, 2023 37Protection Courses
DUAL DIRECTIONAL EARTH FAULT
• TWO Unrestricted Characteristics
• Common Line Angle Setting
• Different Operating Current Settings
• Forward DEF
– Operates on Current above FWD setting in FORWARD direction
• Reverse DEF
– Operates on Current above REV setting in REVERSE direction
X
R
Line Angle
Forward DEF
Reverse DEF
April 8, 2023 38Protection Courses
• Discrimination using DTL or IDMTL Time Grading (DEF Direct Trip)
• OR
• High Speed operation using a Signalling Channel (DEF POR)
Operation of both DEF elements allows instantaneous tripping
• If no Signalling Channel is available
• OR
• Signalling Channel fails
• RELAY CAN OPERATE AS BACK-UP TIME GRADED OVER CURRENT
DIRECTIONAL EARTH FAULT 2
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