EE 256 Notes 4 - Line Protection
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Transcript of EE 256 Notes 4 - Line Protection
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Prof. Rowaldo R. del MundoDepartment of Electrical & Electronics Engineering
University of the Philippines
EE 256 - POWER SYSTEM PROTECTION
Line ProtectionLine Protection
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University of the Philippines
Department of Electrical & Electronics Engineering2
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
TRANSMISSION AND DISTRIBUTIONLINE PROTECTION
4.1 Overcurrent Protection andCoordination
4.2 Distance Relaying
4.3 Pilot Relaying
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University of the Philippines
Department of Electrical & Electronics Engineering3
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
GENERAL PROCEDURE ON COORDINATION OF OVERCURRENT PROTECTION
1. Gather data required for coordination.
a. Updated Single Line Diagram of the system
- show the type & ratings of protective devices (CB, recloser, relay, fuse, CT, PT and other related information)
b. Line currents that goes through the protective devices (normal, max. and emergency)
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University of the Philippines
Department of Electrical & Electronics Engineering4
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
c. Short circuit currents (min. & max.)
- all types of faults (symm.& asymm)
d. Time-current characteristic curves of protective device.
2. Select current & voltage reference to be used in the log-log paper & scale all quantities to this reference (base)
a. Log-log paper has 4.5 decades
b. Current scale must show lowest normal current & max. short circuit current
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University of the Philippines
Department of Electrical & Electronics Engineering5
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
c. Voltage scale: use one reference voltage (voltage of distribution)
*refer the current values to the chosen reference voltage
3. Plot current characteristics of equipment to be protected (inrush, starting, damage curves & points)
4. Plot the TCCs of devices being coordinated
-select settings or ratings based on principles of coordination
5. Draw the line diagram of the portion that you are coordinating & label the devices
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University of the Philippines
Department of Electrical & Electronics Engineering6
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
Overcurrent Protection andCoordination
Overcurrent protection is directed primarily to the clearance of faults. The settings are usually adopted to obtain some measure of overload protection.
Coordination is the selection of ratings, settings and characteristics of overcurrent protective devices to ensure that the minimum unfaulted load is interrupted when protective devices isolate a fault or overload.
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University of the Philippines
Department of Electrical & Electronics Engineering7
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
Overcurrent Protection andCoordination
WHEN DO YOU CONDUCT COORDINATION?
New electrical system is being designed
Significant loads are added to the system
Existing equipment are replaced with higher rated equipment
Available short circuit current is increased
A fault on the periphery of the system shuts down a major portion of the system
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University of the Philippines
Department of Electrical & Electronics Engineering8
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
Overcurrent Protection andCoordination
DATA REQUIREMENTS
Single line diagram
Impedances
Short circuit currents
Starting and Inrush currents
Peak/Full load currents
Decrement curves of generators
Time-current characteristics (TCC) curves
Performance curves of CTs
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University of the Philippines
Department of Electrical & Electronics Engineering9
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
Overcurrent Protection andCoordination
COORDINATION PROCEDURE
Update and/or develop the single line diagram
Calculate fault currents (maximum and minimum)
Determine protection requirements of various elements of the system (motors, transformers, generators, feeders, etc.)
Prepare load analysis (maximum load and characteristics of load)
Obtain TCC of protective devices
Select proper scale (voltage and current) using a log-log paper
Select rating or setting which provide coordination margin
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University of the Philippines
Department of Electrical & Electronics Engineering10
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
Overcurrent Protection andCoordination
COORDINATION MARGIN
The time interval between the operation of two adjacent relays depends on the following factors:
circuit breaker interrupting time
Overshoot time of the relay
Errors
Final margin
Recommended Time: 0.3 0.5 seconds
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University of the Philippines
Department of Electrical & Electronics Engineering11
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
Overcurrent Protection andCoordination
A B C D E
MAX 7850AMIN 3920A
120A 170A 80A 50A
R4 R3 R2 R1
4500A2860A
2690A2003A
1395A1182A
500/5 400/5 200/5 100/5
Determine settings of R1 to R4 using the following relay data:
Normal Inverse Curve (see manufacturers TCC) Current Tap Setting: 0.5 2.5 x In (multiples of 0.5) Time Multiplier: 0.05 1.0 (multiples of 0.05) Instantaneous: 2.5 20 x In (multiples of 0.5)
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University of the Philippines
Department of Electrical & Electronics Engineering12
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering13
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering14
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering15
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
Distance Relaying
Distance relaying provides discriminating zones of protection, provided that fault distance is a simple function of impedance
Distance Relay Types
Impedance Relay
Reactance Relay
Mho Relay
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University of the Philippines
Department of Electrical & Electronics Engineering16
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
Distance Relaying
ZONES OF PROTECTION
Zone 1 (instantaneous zone)
- Choose relay ohmic setting of 80% of the protected line impedance (to provide an ample margin against over-reach)
Zone 2
- 100% of the protected line
- Plus 50% of the next shortest line (to deal with possible under-reach)
Zone 3
- 100% of the protected line
- Plus 100% of longest second line
- Plus 25% of longest third line (to provide back-up)
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University of the Philippines
Department of Electrical & Electronics Engineering17
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
Distance Relaying
Transmission LinesZ1 = 2.5 + j5Zo = 7.5 + j20.5
Radial FeedersZ1 = 3.5 + j7Zo = 10.5 +j28.7
34.5 kV
34.5 kV
500 MVA fault @ 115 kV
R
Determine the settings of the distance relay using:
a. Impedance relayb. 45 Mho relay
36kV/ 120V
400/5Assignment:Compute minimum voltage at relay for a fault at Zone 1 reach
a. Phase faultb. Ground fault
Transformers50MVA, 115/34.5kVZ = 10%
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University of the Philippines
Department of Electrical & Electronics Engineering18
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
Pilot Relaying
Pilot Relaying is an adaptation of the principles of differential relaying that avoids the use of control cable between terminals for fast clearing of faults of transmission lines
Communication Channels
Power Line Carrier (PLC)
Microwave
Fiber Optics
Pilot Wire
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University of the Philippines
Department of Electrical & Electronics Engineering19
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
Pilot Relaying
Directional Comparison
Blocking Scheme
Unblocking Scheme
Tripping Scheme
Underreaching Transfer Trip
Overreaching Transfer Trip
Phase Comparison
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University of the Philippines
Department of Electrical & Electronics Engineering20
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering21
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering22
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering23
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering24
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering25
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering26
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering27
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering28
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering29
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering30
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering31
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering32
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering33
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering34
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
Lateral Tap Fusing
Fuse must clear a Bolted SLGF in 3
seconds; or
Bolted SLGF = 6 X Fuse rating; or
Fuse must clear a SLGF with a 30-
ohm fault resistance in 5 seconds
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University of the Philippines
Department of Electrical & Electronics Engineering35
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
Expulsion Fuse Expulsion Fuse Coordination
Downstream Fuse (referred to as the Protecting Fuse)
should operate before the Upstream Fuse (the
Protected Fuse)
Total Clearing Time of the Protecting Fuse should be less
than the Damage Time of the Protected Fuse [Note: Damage Time is 75% of the Minimum Melting Time]
Fuse-Fuse Coordination Table provides maximum fault currents that the protecting and protected fuse are
coordinated
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University of the Philippines
Department of Electrical & Electronics Engineering36
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
Backup Current Limiting Fuse Coordination
CLF protecting Expulsion Fuse
Select a Backup CLF that have a maximum melting I2t below the
maximum clearing I2t of the expulsion element (Matched-Melt
Coordination Principle)
Check the TCC The expulsion link should always clear fault
currents in the low current operating region, especially below the
minimum interrupting current of the CLF
Estimating maximum melting I2t of expulsion links Take the
minimum calculated from the minimum melting TCC at 0.0125
sec. and multiply by 1.2 for Tin or 1.1 for Silver links
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University of the Philippines
Department of Electrical & Electronics Engineering37
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering38
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
Recloser Expulsion Fuse Coordination
Adjust Fast Curve (A) of the recloser
For one fast operation: A curve time x 1.25
For two fast operation with a reclosing time greater or equal to 1 sec.: A curve time x
1.25
For two fast operation with a reclosing time
from 25 to 30 cycles: A curve time x 1.8
Smallest fuse must coordinate with the fast operation (A
curve) of the recloser.
Largest fuse must coordinate with the delayed operation (B
or C curve) of the recloser. Choose C curve if largest fuse
cannot coordinate with B curve
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University of the Philippines
Department of Electrical & Electronics Engineering39
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
Recloser Recloser Coordination
Hydraulically-controlled Reclosers (Cooper)
Series-Coil Operated: Need more than 12 cycles
Solenoid Closing: Need 8 cycles separation
Coordinating Instantaneous Elements
Find a setting where the instantaneous relay will not operate for faults downstream of the
second protective device. The upstream relay will not operate if its pickup is above the
available fault current at the location of the downstream element. The instantaneous pickup
on the element must be higher than its time-overcurrent pickup.
[Note: This rules out hydraulic reclosers which have the same pickup for the fast (A) curve &
delayed curves (A&B)]
Use a time delay on the upstream instantaneous element. Choose enough time delay (6 to
10 cycles), to allow downstream device to clear before the station device operates.
Sequence Coordination If the device senses current above some minimum trip setting and
the current does not last long enough to trip based on the devices fast curve, the device
advances its control-sequence counter as if the unit had operated on its fast curve. So when
the downstream device moves to its delayed curve, the upstream device with sequence
coordination also is operating on its delayed curve.
Station device detects and counts faults (but does not open) for a fault cleared by a
downstream protection on the fast trip
If the fault current occurs again (usually because the fault is permanent), the station device
switches to the time-overcurrent element because it counted the first as an operation.
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University of the Philippines
Department of Electrical & Electronics Engineering40
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
Station Relay and Recloser Settings
Phase Time-Overcurrent (TOC) Relay
Pickup at 2X the normal designed peak load on the circuit
Pickup < 75% of the bolted LTLF
Ground Time-Overcurrent (TOC) Relay
Pickup at 0.75X the normal designed peak load on the
circuit
Pickup < 75% of the SLGF current at the end of the line or
the next protective device
Must coordinate with the largest lateral fuse
Instantaneous Phase and Ground Relays
2X the TOC relay pickup
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University of the Philippines
Department of Electrical & Electronics Engineering41
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
Sequence Coordination
Even with coordinated Fast Curves, nuisance momentary interruptions occur for faults cleared by downstream recloser
Sequence:
R2 operates on its A curve. (R1 will not operate)
After a delay, R2 recloses. The fault is still there, so R2 operates on its delayed B curve
R1 operates too on its a curve which operates before R2s curve
After R1 recloses, R2 should then clear the fault on its B curve, which should operate before R1s B curve
The fault is still cleared properly, but customers upstream of R2 have extra momentary interruptions
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University of the Philippines
Department of Electrical & Electronics Engineering42
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering43
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering44
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering45
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering46
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering47
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering48
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering49
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering50
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering51
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering52
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering53
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering54
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering55
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering56
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering57
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering58
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering59
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering60
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering61
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering62
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering63
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering64
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering65
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering66
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering67
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo
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University of the Philippines
Department of Electrical & Electronics Engineering68
EE 256 Power System ProtectionProf. Rowaldo R. del Mundo