2 4-4 communication sanders a reliable power-line carrier-based relay system
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7/29/2019 2 4-4 Communication Sanders a Reliable Power-Line Carrier-Based Relay System
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A Reliable Power-Line Carrier-basedRelay System
Avoiding Mistakes That Cause PLC Systems toMisoperate or Fail to Operate
Miriam P Sanders, PE(Quanta Technology, LLC)
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Page 2
Outline
Review the PLC Channel. What is reliability?
Review systems utilizing PLC channels.
Designing the PLC system for better reliability.
Installing the PLC system for better reliability.
Maintaining the PLC System for better reliability.
After Final Checkouts.
Summary and resources.
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Page 3
The PLC Channel
Coupling CapacitorVoltage
Transformer (ccvt)
DrainCoil
LineTuner
Coaxial Cable
Line Trap
Station A Bus
Fault2 1
ProtectiveRelay
System
T
R
H
Control
House
Switchyard
Received Signal Level
Signal to Noise Ratio
Signal:
30 to 500 kHz1 to 100 Watts(7 to 70 V rms)
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Page 4
Reliability
Dependability Security
Trip when it should Not trip when it shouldn’t
Transmission Line Protection PLC based systemstend towards the Dependability side
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Page 5
Transmission Line Protection
Directional Comparison Systems.
Compares fault current direction to make trip/no trip decision.
Phase Comparison Systems.
Compares the fault current phase angle to make trip/no trip decision.
Blocking Systems.
Blocks for external faults, no signal required for internal fault.
Permissive Systems.
Provides “permission” to trip.
Unblock Logic – provides a short window of permission on LOC.
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Page 6
Directional Comparison Blocking (DCB)
21S at Sub B keys the channel to send a block signal toSub A to prevent tripping because 21P is armed to trip
X
0AND TRIP
21P
BLOCK
CoordinationTimer
Stop Channel if
initiated locally
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Page 7
Directional Comparison Unblocking (DCUB)
21P at either end keys the channel to send a trip signal to otherend to give permission to trip and local 21P is armed to trip
X0AND TRIP
21P
TRIP RECEIVED
Coincidence Timer
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Page 8
Unblock Logic
Loss of GuardAND
Low Level results in Unblock window
0N
UnblockTimer
CLKCL
Q
VCC
O PR
Q
N=0 to 5001 ms increments0=Disabled
TRIP
Received
GBT
Low Level=0
Guard
Unblock Trip
TRIP
Output
Drop out of guard
starts timer
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Page 9
Equipment Protection – Direct Transfer Trip
Breaker Failure.
Transformer Protection.
Reactor Protection.
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Page 10
Designing a PLC System
How many line protection channels are needed? What types of line protection channels are
desired? This can be on-off, FSK or acombination of both.
Is DTT required?
If DTT is required, a single or a dual channelsystem?
Is coupling redundancy required? This will bedictated by the criticality of the circuit usually.
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Page 11
Single DCB system
Single Frequency orWideband Tuner
LT
Line Trap
LineRelay
CCVT
1200 or 600 Hz BW
PLCON-OFF
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Page 12
DCB and DTT
RCVR
XMTR
FSK DTT300 Hz BW
R Hybrid
X Hybrid
Line Trap
Single Frequency or
Wideband Tuner
LT
LineRelay
BreakerFailure
System
CCVT
ON-OFF
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Page 13
DCB and DTT w/Skewed Hybrid
RCVR
XMTR
FSK DTT300 Hz BW
R Hybrid
OUTPUT
Line Trap
Single Frequency or
Wideband Tuner
LT
LineRelay
BreakerFailure
System
CCVT
ON-OFF
S Hybrid
XMTRport
Rcvr port
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Page 14
DCUB with DTT
RCVR
XMTR
RCVR
XMTR
FSK DTT300 Hz BW
FSK DCUB600 Hz BW
R Hybrid
Breaker
Failure
System
Line Traps
CCVTs
S Hybrid
XMTRport
Rcvr port
LT
LineRelay
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Page 15
DCUB with Dual DTT
RCVR
XMTR
RHybrid
RCVR
XMTR
RCVR
XMTR
DCUB600 Hz BW
RHybrid
SHybrid
Line Trap
Single Frequencyor Wideband
Tuner
LT
CCVT
XMTRport
RCVRport
FSK DTT300 Hz BW
FSK DTT300 Hz BW
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Page 16
Coupling Options
Single Phase to Ground Coupling. Dual Phase Coupling.
Three Phase (Mode 1) Coupling.
Economics.
Redundancy.
Reliability.
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Page 17
Dual Phase Coupling
ON-OFF
FSK DTT
RHybrid
XMTR port
RCVR port
S HybridOUTPUT
Line Trap
Single Frequencyor WidebandTuners
LineRelay
BreakerFailureSystem
CCVT
BalanceXFMR
LT
LT
RCVR
XMTR
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Page 18
Coupling Redundancy (?)
LTSTR
LTSTR
Not as much isolationfor the transmitters as
phase-to-phasecoupling
These 2transmitters see
only about a 5 to10 dB isolation atmost.
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Page 19
Better Coupling Redundancy
1st PrimaryRelay System
LT
LT
BalanceCombiner
RCVR
XMTR
RCVR
XMTR
FSK DCUB600 Hz BW
FSK DCUB600 Hz BW
LineRelay
LineRelay
2nd PrimaryRelay System
CCVT
CCVT
S
S
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Page 20
DTT Security
Narrowband Channels provide 3 dB improvementof S/N.
Pre-trip delays add to security.
The longer the delay, more security.
Dual Channels.
Both channels required to trip (AND).
Add some dependability back in with revert tosingle channel on loss of one.
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Page 21
Revert To Single Channel DTT Scheme
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Page 22
DTT Security
Narrowband Channels provide 3 dB improvementof S/N.
Pre-trip delays add to security.
The longer the delay, more security.
Dual Channels.
Both channels required to trip (AND).
Add some dependability back in with revert tosingle channel on loss of one.
Unblock Window disabled.
New technology has provided flexibility.
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Page 23
FSK Security
1200
120
0
N0
Trip
Guard
Low Level = 0
Noise = 1
HF=1
LF=1
All timers in ms
Trip
Guard
Pre-Trip TImer
N=0 to 30Guard before Trip
Timer
Trip After Guard
Window Timer
Trip
Guard
GBT
Channel Requirements:Guard Before TripTrip After GuardPre-Trip Timer
+ Security
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Page 24
0
N
N
0
N=0 to 1001 ms increments
UnblockTimer
CLK
CL
Q
VCC
O PR
Q
N=0 to 5001 ms increments
0=Disabled
Unblock Delay
TRIP
Received
GBT
Low Level=0
Guard
Unblock Trip
TRIPOutput
Drop out of guard
starts timer
DCUB Dependability and Security
For this system to trip, the relay must first see a forward faultAND
receive the trip frequency
X0AND TRIP
21P
TRIP RECEIVED
Coincidence Timer
+ Security + Dependable
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Page 25
Words of Caution
Use the PLC channel’s logic for Unblock.Well proven logic since mid-1960’s.
More accurate.
Source of the information.
More timely and accurate information.
Demarcation for operational analysis.
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Page 26
Increasing Security in DCB
Automatic Checkback systems. Verifies channel under non-fault conditions.
May not undercover “carrier holes”.
Carrier Hole Filling logic adds security, at theexpense of dependability.
Be careful.
Review all logic.
Tripping for cross over faults.
Need more security – go with a DCUB.
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Page 27
DCB Keying Logic
Carrier STOP must have priority.
Removing Start does not equal Stop.
NC reduces contact bounce.
NC monitors integrity of start circuit.
AND
Turn on
transmitter(send block signal)
NOT STARTSTOP
(+) (+)
OR
STARTSTOP
(+) (+)
AND
Turn ontransmitter
(send block signal)
(a) Key transmitter with opening ofnormally closed contact
(b) Key transmitter with closing ofnormally open contact
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Page 28
Installation/Commissioning
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Page 29
Installation/Commissioning
Receivers After transmitters, line tuners and hybrids.
15 dB margin typical.
= level received – 15 dB signal loss.
Margin for weather and signal degradation.
Icing will result in no signal
Setting it absolute minimum level will allow noise to
operate it.
FSK systems usually boost another 10 dB to ride thrufaults.
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Page 30
Installation/Commissioning
Proper Grounding:Chassis Grounding.
Braided cable or heavy conductor.
Direct Connection to ground bar (no daisy-chains).
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Page 31
Coax/Triax Grounding
Coax Grounding:
Outer Shield ground in house, not at tuner.
Triax Grounding:
Inner shield ground in house.
Outer shield ground in house and at tuner.
Coupling CapacitorVoltage
Transformer (ccvt)
DrainCoil
Line
Tuner
Coaxial Cable
Line Trap
Station A Bus
Fault2 1
Protective
RelaySystem
T
R
H
ControlHouse
Switchyard
S
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Page 32
Knife Switch
Braided Shield
CenterConductor
Coax to LineTuner
Coax to PLCEquipment
M i
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Page 33
Maintenance
Monitored vs. Interval Testing Revisit practices, particularly when upgrading
systems
Reduce manual testing by including moremonitoring
Margin Levels
Reflected Power trends
Automated Testing where possible
ON OFF Ch l M i
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Page 34
ON-OFF Channel Maintenance
Automatic Checkback Testing
Alarms if the system becomes non-functional
Can revert to step-distance if so desired
Does not normally run during internal or externalfaults
Integral systems may not verify interface to relay
Interval determined by utility practice
C i H l
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Page 35
Carrier Holes
Transients on transmission line can:Cause flash-over of equipment
Coax/Triax Cable
Lead-in cables
GAPS
Pi t
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Page 36
Picture
GAPS
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Page 37
GAPS
Air Gaps
Gas Tube
Other limiting device
Coordinate GAPS
FSK Ch l M i t
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Page 38
FSK Channel Maintenance
Self Monitored Channel Not self-monitored equipment
Will the transmitter shift?
Will the receiver see the shift?
DTT or DCUB systems could fail to trip
B f l k th d
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Page 39
Before you lock the door
Check all knife switches In house
In tuner
On ccvt
Check all selector switches
85CO
Pilot Selection
S mmar
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Page 40
Summary
Understanding the PLC Channel Pros and Cons
Flexibility
New Technologies
Questions
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Questions
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