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.

Stand-alone Line Protection • 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.

Rem

ote

Term

inal

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.

• 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.

Why Communications Aided Relaying?

• A means of providing fast clearing for 100% of the zone of protection.

• Requires a communications channel. – 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.

What is Pilot Relaying?

Current Differential

• 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

• 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

B ZL

• 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

• 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.

BA F

Tripping Relay

Carrier Start Relay

X/0

AND

Carrier Start Relay

Tripping Relay

Trip

0/Y

Carrier Start

Directional Comparison UnBlocking

• 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

• 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.

A

B ZL

Permissive Over-Reach

• 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.

A

B ZL

Direct Transfer Trip • 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

Line TuningUnit

Transmitter/Receiver

Relay

CircuitBreaker

Netw

ork B

us

Jeff Brown October 2014

A Field Engineer’s Perspective Best Practices

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

Speed – FIDVR – Critical Carriers – Tighter Systems

Security – Fewer Misops – Slower trip times – More Reliable

APPLICATION ENGINEER

COMPLIANCE ENGINEER

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. Mediums and Possible Errors 2. Schemes and Common Flaws 3. The Future 4. 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 • DCUB vs POTT • DCB • POTT (Fiber) • Current Diff (Fiber)

• Utilities get these confused? – DCUB

• Power Line Carrier – POTT

• Fiber • Tone • Microwave

POTT vs. DCUB

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 = 159.8 kHz RX = 160.0 kHz

TX = 160.2 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

• 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)

• 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

Feature Highlights

Common Configuration

• 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.

Application Highlights

Questions?