System Protection and Control
Seminar
Desirable Protection
• We want to detect a fault within 100% of
the zone of protection.
• We want to avoid interrupting non-faulted
zones of protection.
• We want to clear a fault as quickly as
possible.
– Limit damage to equipment.
– Limit the impact to external customers.
• It is desirable to have
instantaneous clearing over
100% of the line, but that is not
attainable without a
communications channel.
• Due to uncertainty of modeling,
the stand-alone instantaneous
elements can only be set for
up to 90% of the line
“comfortably”.
• The remaining 10 to 15% will
have delayed clearing to
coordinate with remote
terminals.
Remote Terminal
Stand-alone Line Protection
Stand-alone Overcurrent Protection
• Similar to impedance relays,
overcurrent relays with a
graduated operating curve may
be applied.
• An instantaneous element may
be set similar to the zone
distance elements based on
fault magnitudes.
• The final protection is delayed
based on curve stacking.
Why Communications
Aided Relaying?
• Stand-alone protective scheme sensitivity (tap
range) is limited for low impedance (short) lines.
• Stand-alone schemes cannot offer
instantaneous clearing over 100% of the line.
• There may be a need for fast fault clearing over
100% of the zone of protection.
• System stability requires fast clearing of out-of zone equipment.
What is Pilot Relaying?
• A means of providing fast clearing for 100% of
the zone of protection.
• Requires a communications channel.
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–
–
–
–
Power Line Carrier
Leased Phone Circuit
Microwave / Spread Spectrum Radio
Fiber Optic
Pilot Wire / Twisted Pair
• It is an added expense addition to stand-alone
relaying systems.
Current Differential
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HCB, LCB, CPD, SPD, REL-356, DLS2000, L90, 311L, LFCB, RFL9300, etc.
Local sequence filter converts terminal currents to a single ac signal that is sent
to the remote terminal.
Logic at each terminal compares local ac signal to received ac signal by magnitude.
Signals cancel for external faults and double up for internal faults.
Simple relays revert to sensitive non-directional overcurrent protection for loss of
channel.
Advantage: Simplicity and Fast.
Does not need comparator signal to trip.
Disadvantage: Requires a continuous channel to avoid an incorrect trip.
Does not allow for tapped loads without additional terminals.
Phase Comparison
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SKBU, REL-352, REL-350, P547, SLD-21, SLD-41, etc.
Local current level detectors are required to start comparison process.
Local sequence filter converts terminal currents to a square wave signal that is sent to the remote
terminal.
Logic at each terminal compares local square wave to received square wave by phase shift.
Signals form a continuous wave for external faults and is disrupted for internal faults.
Relays revert to sensitive non-directional overcurrent protection for loss of channel.
Advantage: Simple and (really) Fast.
Can be applied to power line carrier.
Can accept tapped loads within limits.
Disadvantage: It will trip incorrectly if no remote signal is received.
Low-side faults on tapped loads may cause a misoperation.
Phase shift of the pilot signals can lead to misoperation from “holes” in the signal.
Directional Comparison Overview
A
ZL
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•
•
•
B
System consists of:
– a single zone phase distance relay looking into the protected line.
– a single zone phase distance relay looking in reverse from the
protected line.
– a non-directional ground overcurrent relay
– a directional ground relay looking into the protected line.
The reverse phase relay is set greater than the over-reach of the
remote forward looking relay.
The non-directional ground relay is set as low as possible without
nuisance keying from neutral imbalance.
The directional ground relay (either overcurrent or impedance based) is
set with the same pickup setting as the stand-alone directional ground
(or for impedance based the same as a zone 2 element).
Directional Comparison Blocking
Tripping Relay
B
A
F
Carrier Start Relay
Tripping Relay
X/0
AND
Carrier Start Relay
Trip
0/Y
Carrier Start
•
•
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KDAR KD/KA/KR (KR, TC, TC-10, TC10B); CEY/CEB (CS26; CS27); most micro-processor
relays; etc.
Local non-directional current fault detectors are required to start carrier.
Local directional relays either:
Continue to key the carrier transmitter for faults in the reverse direction.
Stop transmitter keying for faults in the forward direction.
Advantage: Does not require carrier signal to trip.
Allows tapped loads.
Reliable tripping.
Disadvantage: Not secure. It will over trip if the remote terminal fails to send blocking carrier.
Requires random channel testing to verify working order of channel.
Directional Comparison UnBlocking
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KDAR KD/KA/KR, SKDU(A2B1A) (TCF, TCF-10, TCF-10B); CEY/CEB, SLYP/SLYCN(Type 50,
60, 70s); microprocessor relays; etc.
Carrier guard signal is sent continuously to determine channel health.
Local directional relays either:
Continue to key carrier guard for faults in the reverse direction.
Shift carrier signal to trip frequency for faults in the forward direction.
Advantage: Reasonably secure, relative to Directional Carrier Blocking logic.
Allows tapped loads.
Channel is continuously monitored by guard signal.
Disadvantage: Can over trip during trip permission window.
Uses more frequency spectrum.
Continuous radio transmission contributes to radio frequency interference.
Permissive Under-Reach
A
ZL
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B
KD, SKD, GCY, GCX, CEY, SLY, SLYP; any microprocessor relay; etc.
Can be On/Off or Frequency Shift Keying.
Local terminal trips if the forward directional sensing element is picked up or direct
transfer trip is received from the remote end.
Local terminal sends direct transfer trip to the remote end for faults within the forward
zone of protection.
Advantage: Reasonably secure.
Allows tapped loads.
Does not require channel to trip locally for in zone forward fault.
Disadvantage: Can trip by direct trip signal, accidentally.
(Needs fault detector to reduce this exposure).
Needs a secure channel to have 100% coverage.
Permissive Over-Reach
A
ZL
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•
•
•
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•
B
KD, SKD, GCY, GCX, CEY, SLY, SLYP; any microprocessor relay; etc.
Can be On/Off or Frequency Shift Keying.
Local terminal trips if the forward directional sensing element is picked up
and direct transfer trip is received from the remote end.
Local terminal sends direct transfer trip to the remote end for faults within
the forward zone of protection.
Advantage: Secure.
Allows tapped loads.
Disadvantage: Must have a secure and reliable channel.
Can not trip without remote trip permission.
Direct Transfer Trip
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Can be On/Off or Frequency
Shift Keying.
Local terminal trips if direct
transfer trip signal is received
from the remote end.
Local terminal sends direct
transfer trip to the remote end by
local logic (Breaker Failure, AOM
remote breaker, etc.).
Advantage:
– Fast.
– Allows tapped loads.
– May be more economical than
adding additional breakers.
•
Disadvantage:
– Single channel applications are
not secure.
– Requires a second
transmitter/receiver to improve
security and reliability.
Power Line Coupling
Network
Bus
Circuit
Breaker
Line Tuning
Unit
Transmitter/
Receiver
Relay
A Field Engineer’s Perspective
Best Practices
Jeff Brown
October 2014
Two Things to remember about
Pilot Systems!
Pilot Systems give you the capability to have
instantaneous tripping for 100% of the line.
Pilot Systems are a balance between
Speed vs. Security
Speed vs Security
Reliability
APPLICATION
ENGINEER
Speed
– FIDVR
– Critical Carriers
– Tighter Systems
COMPLIANCE
ENGINEER
Security
– Fewer Misops
– Slower trip times
– More Reliable
DCUB Guard Holes
6 msec
10 msec
6 msec
7 msec
DCB Misop
Reliability
• Timers in Radio
• Timers in Relay
DCUB
Unblock Security Timer = 20 ms
DCB
Block Extend = ???
SERC Requirements
Best Practices
1.
2.
3.
4.
Mediums and Possible Errors
Schemes and Common Flaws
The Future
Open the Floor to Questions
1. Mediums
Power Line Carrier
COAX CABLE
Fiber
• Dirty connectors
• Tie Wraps
• Rodents
• Expensive
But it is …..
• Secure
Tone
•
•
•
•
•
Radio Vendors
Bell Companies
Parts, Hybrids
Expensive
Only available for a
few more years
2. Schemes
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•
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DCUB vs POTT
DCB
POTT (Fiber)
Current Diff (Fiber)
POTT vs. DCUB
• Utilities get these confused?
– DCUB
• Power Line Carrier
– POTT
• Fiber
• Tone
• Microwave
Timers
• DCUB Timers
– Two places
• Radio
or
• Relay
Timers
DCUB
OPTION #1
Radio – set up for DCUB
Relay – set up for POTT
OPTION #2
Radio – set up for POTT
Relay – set up for DCUB
How is this a problem
• Timers in both the relay and radio creates a
conflicting race
• Timers missing from both relay and radio
• If both ends of the lines don’t do it the same
– Tie Lines
– Mismatching generations
DCB
• Not as many timers!
• Requires Automation
• Local Tx’s vs Remote Tx’s
TX = 160 kHz
TX = 160 kHz
Back in the Day
• Radios required Crystals for the frequency
• New radios no Crystals
• Solution is……
TX = 160.2 kHz
RX = 160.0 kHz
TX = 159.8 kHz
RX = 160.0 kHz
Fiber Scheme 1 - POTT
• Protocols
• Baud Rates
• Dirty Fiber
• Lost Packets
Fiber Scheme 2 – Line Current Differential
Line Current Diff
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•
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Keying DCUB or DCB does no tripping
LCD is not forgiving
Transfer Bus
Test Switches that isolate currents
Training
Back to the Future
PCM-5350
Power Communications Monitor
Advanced Monitoring For Analog Channels
(Power Line Carrier or Audio Tone Channels)
Feature Highlights
• 5 Channel Frequency Selective Monitoring
• Record Events on Changes in Frequency, Level,
Reflected Power & Noise.
• Trend Reflected Power, Level & Noise.
• Real Time View – Remote Access at any time via
Ethernet or RS-232/485
• Event Driven or Real Time Spectral Analysis of the
Communication Path
• SOE with 32,000 Event Capacity
Common Configuration
Application Highlights
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Maintenance Checks with NO Outage required.
Extend Maintenance Cycles with constant monitoring.
Spectral Analysis synchronization with DFR’s or Relay’s
Assist with Mis-operation evaluation and diagnosis
– Out of band noise Detection Alarms
– Verify trip frequency, levels and reflected power during event
– Review In Band Spectral Analysis during trip/fault occurrence for
noise intrusion
• Monitor Adjacent Line Frequencies for Line Trap Failure
• Accurate Reflected Power Measurements.
Questions?