Fundamentals of bus bar protection
Download
1 / 92

Fundamentals of Bus Bar Protection - PowerPoint PPT Presentation


  • 5959 Views
  • Uploaded on

Fundamentals of Bus Bar Protection. GE Multilin. Outline. Bus arrangements Bus components Bus protection techniques CT Saturation Application Considerations: High impedance bus differential relaying Low impedance bus differential relaying Special topics.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Fundamentals of Bus Bar Protection' - connie


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Fundamentals of bus bar protection l.jpg

Fundamentals ofBus Bar Protection

GE Multilin


Outline l.jpg
Outline

  • Bus arrangements

  • Bus components

  • Bus protection techniques

  • CT Saturation

  • Application Considerations:

    • High impedance bus differential relaying

    • Low impedance bus differential relaying

    • Special topics


Single bus single breaker l.jpg
Single bus - single breaker

  • Distribution and lower transmission voltage levels

  • No operating flexibility

  • Fault on the bus trips all circuit breakers


Slide4 l.jpg

Multiple bus sections - single breaker with bus tie

  • Distribution and lower transmission voltage levels

  • Limited operating flexibility


Slide5 l.jpg

Double bus - single breaker with bus tie

  • Transmission and distribution voltage levels

  • Breaker maintenance without circuit removal

  • Fault on a bus disconnects only the circuits being connected to that bus


Slide6 l.jpg

Main and transfer buses

  • Increased operating flexibility

  • A bus fault requires tripping all breakers

  • Transfer bus for breaker maintenance


Slide7 l.jpg

Double bus – single breaker w/ transfer bus

  • Very high operating flexibility

  • Transfer bus for breaker maintenance


Slide8 l.jpg

Double bus - double breaker

  • High operating flexibility

  • Line protection covers bus section between two CTs

  • Fault on a bus does not disturb the power to circuits


Slide9 l.jpg

Breaker-and-a-half bus

  • Used on higher voltage levels

  • More operating flexibility

  • Requires more breakers

  • Middle bus sections covered by line or other equipment protection


Slide10 l.jpg

Ring bus

  • Higher voltage levels

  • High operating flexibility with minimum breakers

  • Separate bus protection not required at line positions


Slide11 l.jpg

SF6, EHV & HV - Synchropuff

Low Voltage circuit breakers

Bus components

breakers



Slide13 l.jpg

Oil insulated current transformer (35kV up to 800kV)

Gas (SF6) insulated current transformer

Bushing type (medium voltage switchgear)

CurrentTransformers


Protection requirements l.jpg
Protection Requirements

  • High bus fault currents due to large number of circuits connected:

    • CT saturation often becomes a problem as CTs may not be sufficiently rated for worst fault condition case

    • large dynamic forces associated with bus faults require fast clearing times in order to reduce equipment damage

  • False trip by bus protection may create serious problems:

    • service interruption to a large number of circuits (distribution and sub-transmission voltage levels)

    • system-wide stability problems (transmission voltage levels)

  • With both dependability and security important, preference is always given to security


Bus protection techniques l.jpg
Bus Protection Techniques

  • Interlocking schemes

  • Overcurrent (“unrestrained” or “unbiased”) differential

  • Overcurrent percent (“restrained” or “biased”) differential

  • Linear couplers

  • High-impedance bus differential schemes

  • Low-impedance bus differential schemes


Interlocking schemes l.jpg

Blocking scheme typically used

Short coordination time required

Care must be taken with possible saturation of feeder CTs

Blocking signal could be sent over communications ports (peer-to-peer)

This technique is limited to simple one-incomer distribution buses

Interlocking Schemes


Overcurrent unrestrained differential l.jpg

Differential signal formed by summation of all currents feeding the bus

CT ratio matching may be required

On external faults, saturated CTs yield spurious differential current

Time delay used to cope with CT saturation

Instantaneous differential OC function useful on integrated microprocessor-based relays

Overcurrent (unrestrained) Differential


Slide18 l.jpg

0 V feeding the bus

40 V

10 V

10 V

0 V

20 V

If = 8000 A

2000 A

2000 A

0 A

4000 A

Linear Couplers

ZC = 2  – 20  - typical coil impedance

(5V per 1000Amps => 0.005 @ 60Hz )

59

External

Fault


Linear couplers l.jpg

If = 8000 A feeding the bus

40 V

0 V

10 V

10 V

0 V

20 V

0 A

2000 A

2000 A

0 A

4000 A

Linear Couplers

Esec= Iprim*Xm - secondary voltage on relay terminals

IR= Iprim*Xm /(ZR+ZC) – minimum operating current

where,

Iprim – primary current in each circuit

Xm – liner coupler mutual reactance (5V per 1000Amps => 0.005 @ 60Hz )

ZR – relay tap impedance

ZC – sum of all linear coupler self impedances

Internal Bus

Fault

59


Linear couplers20 l.jpg

Fast, secure and proven feeding the bus

Require dedicated air gap CTs, which may not be used for any other protection

Cannot be easily applied to reconfigurable buses

The scheme uses a simple voltage detector – it does not provide benefits of a microprocessor-based relay (e.g. oscillography, breaker failure protection, other functions)

Linear Couplers


High impedance differential l.jpg
High Impedance Differential feeding the bus

  • Operating signal created by connecting all CT secondaries in parallel

    • CTs must all have the same ratio

    • Must have dedicated CTs

  • Overvoltage element operates on voltage developed across resistor connected in secondary circuit

    • Requires varistors or AC shorting relays to limit energy during faults

  • Accuracy dependent on secondary circuit resistance

    • Usually requires larger CT cables to reduce errors  higher cost

  • Cannot easily be applied to reconfigurable buses and offers no advanced functionality


Percent differential l.jpg

Percent characteristic used to cope with CT saturation and other errors

Restraining signal can be formed in a number of ways

No dedicated CTs needed

Used for protection of re-configurable buses possible

Percent Differential


Low impedance percent differential l.jpg
Low Impedance Percent Differential other errors

  • Individual currents sampled by protection and summated digitally

    • CT ratio matching done internally (no auxiliary CTs)

    • Dedicated CTs not necessary

  • Additional algorithms improve security of percent differential characteristic during CT saturation

  • Dynamic bus replica allows application to reconfigurable buses

    • Done digitally with logic to add/remove current inputs from differential computation

    • Switching of CT secondary circuits not required

  • Low secondary burdens

  • Additional functionality available

    • Digital oscillography and monitoring of each circuit connected to bus zone

    • Time-stamped event recording

    • Breaker failure protection


Digital differential algorithm goals l.jpg
Digital Differential Algorithm Goals other errors

  • Improve the main differential algorithm operation

    • Better filtering

    • Faster response

    • Better restraint techniques

    • Switching transient blocking

  • Provide dynamic bus replica for reconfigurable bus bars

  • Dependably detect CT saturation in a fast and reliable manner, especially for external faults

  • Implement additional security to the main differential algorithm to prevent incorrect operation

    • External faults with CT saturation

    • CT secondary circuit trouble (e.g. short circuits)


Low impedance differential distributed l.jpg
Low Impedance Differential (Distributed) other errors

  • Data Acquisition Units (DAUs) installed in bays

  • Central Processing Unit (CPU) processes all data from DAUs

  • Communications between DAUs and CPU over fiber using proprietary protocol

  • Sampling synchronisation between DAUs is required

  • Perceived less reliable (more hardware needed)

  • Difficult to apply in retrofit applications


Low impedance differential centralized l.jpg
Low Impedance Differential (Centralized) other errors

  • All currents applied to a single central processor

  • No communications, external sampling synchronisation necessary

  • Perceived more reliable (less hardware needed)

  • Well suited to both new and retrofit applications.


Ct saturation l.jpg
CT Saturation other errors


Ct saturation concepts l.jpg
CT Saturation Concepts other errors

  • CT saturation depends on a number of factors

    • Physical CT characteristics (size, rating, winding resistance, saturation voltage)

    • Connected CT secondary burden (wires + relays)

    • Primary current magnitude, DC offset (system X/R)

    • Residual flux in CT core

  • Actual CT secondary currents may not behave in the same manner as the ratio (scaled primary) current during faults

  • End result is spurious differential current appearing in the summation of the secondary currents which may cause differential elements to operate if additional security is not applied


Ct saturation29 l.jpg
CT Saturation other errors

No DC Offset

  • Waveform remains fairly symmetrical

With DC Offset

  • Waveform starts off being asymmetrical, then symmetrical in steady state


External fault ideal cts l.jpg
External Fault & Ideal CTs other errors

  • Fault starts at t0

  • Steady-state fault conditions occur at t1

t1

t0

  • Ideal CTs have no saturation or mismatch errors thus produce no differential current


External fault actual cts l.jpg
External Fault & Actual CTs other errors

  • Fault starts at t0

  • Steady-state fault conditions occur at t1

t1

t0

Actual CTs do introduce errors, producing some differential current (without CT saturation)


External fault with ct saturation l.jpg
External Fault with CT Saturation other errors

t2

  • Fault starts at t0, CT begins to saturate at t1

  • CT fully saturated at t2

t1

t0

  • CT saturation causes increasing differential current that may enter the differential element operate region.


Some methods of securing bus differential l.jpg
Some Methods of Securing Bus Differential other errors

  • Block the bus differential for a period of time (intentional delay)

    • Increases security as bus zone will not trip when CT saturation is present

    • Prevents high-speed clearance for internal faults with CT saturation or evolving faults

  • Change settings of the percent differential characteristic (usually Slope 2)

    • Improves security of differential element by increasing the amount of spurious differential current needed to incorrectly trip

    • Difficult to explicitly develop settings (Is 60% slope enough? Should it be 75%?)

  • Apply directional (phase comparison) supervision

    • Improves security by requiring all currents flow into the bus zone before asserting the differential element

    • Easy to implement and test

    • Stable even under severe CT saturation during external faults



High impedance voltage operated relay external fault l.jpg
High Impedance Voltage-operated Relay other errorsExternal Fault

  • 59 element set above max possible voltage developed across relay during external fault causing worst case CT saturation

  • For internal faults, extremely high voltages (well above 59 element pickup) will develop across relay


High impedance voltage operated relay ratio matching with multi ratio cts l.jpg
High Impedance Voltage Operated Relay other errorsRatio matching with Multi-ratio CTs

  • Application of high impedance differential relays with CTs of different ratios but ratio matching taps is possible, but could lead to voltage magnification.

  • Voltage developed across full winding of tapped CT does not exceed CT rating, terminal blocks, etc.


High impedance voltage operated relay ratio matching with multi ratio cts37 l.jpg
High Impedance Voltage Operated Relay other errorsRatio matching with Multi-ratio CTs

  • Use of auxiliary CTs to obtain correct ratio matching is also possible, but these CTs must be able to deliver enough voltage necessary to produce relay operation for internal faults.


Electromechanical high impedance bus differential relays l.jpg
Electromechanical High Impedance Bus Differential Relays other errors

  • Single phase relays

  • High-speed

  • High impedance voltage sensing

  • High seismic IOC unit


Slide39 l.jpg

other errorsP -based High-Impedance Bus Differential Protection Relays

Operating time: 20 – 30ms @ I > 1.5xPKP


Slide40 l.jpg

High Impedance Module for Digital Relays other errors

RST = 2000 - stabilizing resistor to limit the current through the relay, and force it to the lower impedance CT windings.

MOV – Metal Oxide Varistor to limit the voltage to

1900 Volts

86 – latching contact preventing the resistors from overheating after the fault is detected


Slide41 l.jpg

High-Impedance Module other errors+ Overcurrent Relay


Slide42 l.jpg

Fast, secure and proven other errors

Requires dedicated CTs, preferably with the same CT ratio and using full tap

Can be applied to small buses

Depending on bus internal and external fault currents, high impedance bus diff may not provide adequate settings for both sensitivity and security

Cannot be easily applied to reconfigurable buses

Require voltage limiting varistor capable of absorbing significant energy

May require auxiliary CTs

Do not provide full benefits of microprocessor-based relay system (e.g. metering, monitoring, oscillography, etc.)

High Impedance Bus Protection - Summary



P based low impedance relays l.jpg
other errorsP-based Low-Impedance Relays

  • No need for dedicated CTs

  • Internal CT ratio mismatch compensation

  • Advanced algorithms supplement percent differential protection function making the relay very secure

  • Dynamic bus replica (bus image) principle is used in protection of reconfigurable bus bars, eliminating the need for switching physically secondary current circuits

  • Integrated Breaker Failure (BF) function can provide optimal tripping strategy depending on the actual configuration of a bus bar


Slide45 l.jpg

Small Bus Applications other errors

2-8 Circuit Applications

  • Up to 24 Current Inputs

  • 4 Zones

    • Zone 1 = Phase A

    • Zone 2 = Phase B

    • Zone 3 = Phase C

    • Zone 4 = Not used

  • Different CT Ratio Capability for Each Circuit

  • Largest CT Primary is Base in Relay


Slide46 l.jpg

CB 11 other errors

CB 12

Medium to Large Bus Applications

9-12 Circuit Applications

  • Relay 1 - 24 Current Inputs

  • 4 Zones

    • Zone 1 = Phase A (12 currents)

    • Zone 2 = Phase B (12 currents)

    • Zone 3 = Not used

    • Zone 4 = Not used

  • Relay 2 - 24 Current Inputs

  • 4 Zones

    • Zone 1 = Not used

    • Zone 2 = Not used

    • Zone 3 = Phase C (12 currents)

    • Zone 4 = Not used

  • Different CT Ratio Capability for Each Circuit

  • Largest CT Primary is Base in Relay


Large bus applications l.jpg
Large Bus Applications other errors

87B phase A

87B phase B

87B phase C

Logic relay

(switch status,

optional BF)


Large bus applications for buses with up to 24 circuits l.jpg
Large Bus Applications other errorsFor buses with up to 24 circuits


Summing external currents not recommended for low z 87b relays l.jpg
Summing External Currents other errorsNot Recommended for Low-Z 87B relays

  • Relay becomes combination of restrained and unrestrained elements

  • In order to parallel CTs:

    • CT performance must be closely matched

      • Any errors will appear as differential currents

    • Associated feeders must be radial

      • No backfeeds possible

    • Pickup setting must be raised to accommodate any errors


Definitions of restraint signals l.jpg
Definitions of Restraint Signals other errors

“sum of”

“scaled sum of”

“geometrical average”

“maximum of”


Sum of vs max of restraint methods l.jpg

“Sum Of” Approach other errors

More restraint on external faults; less sensitive for internal faults

“Scaled-Sum Of” approach takes into account number of connected circuits and may increase sensitivity

Breakpoint settings for the percent differential characteristic more difficult to set

“Max Of” Approach

Less restraint on external faults; more sensitive for internal faults

Breakpoint settings for the percent differential characteristic easier to set

Better handles situation where one CT may saturate completely (99% slope settings possible)

“Sum Of” vs. “Max Of” Restraint Methods



Bus differential adaptive logic diagram l.jpg

DIF other errorsL

AND

OR

DIR

OR

87B BIASED OP

AND

SAT

DIFH

Bus Differential Adaptive Logic Diagram


Phase comparison principle l.jpg

Secondary Current of Faulted Circuit other errors(Severe CT Saturation)

Phase Comparison Principle

  • Internal Faults: All fault (“large”) currents are approximately in phase.

  • External Faults: One fault (“large”) current will be out of phase

  • No Voltages are required or needed



Ct saturation56 l.jpg
CT Saturation other errors

  • Fault starts at t0, CT begins to saturate at t1

  • CT fully saturated at t2

t2

t1

t0


Ct saturation detector state machine l.jpg

NORMAL other errors

SAT := 0

The differential

saturation

current below the

condition

first slope for

certain period of

time

EXTERNAL

FAULT

SAT := 1

The differential-

The differential

restraining trajectory

characteristic

out of the differential

entered

characteristic for

certain period of time

EXTERNAL

FAULT & CT

SATURATION

SAT := 1

CT Saturation Detector State Machine


Ct saturation detector operating principles l.jpg
CT Saturation Detector Operating Principles other errors

  • The 87B SAT flag WILL NOT be set during internal faults, regardless of whether or not any of the CTs saturate.

  • The 87B SAT flag WILL be set during external faults, regardless of whether or not any of the CTs saturate.

  • By design, the 87B SAT flag WILL force the relay to use the additional 87B DIR phase comparison for Region 2

The Saturation Detector WILL NOT Block the Operation of the Differential Element – it will only Force 2-out-of-2 Operation


Ct saturation detector examples l.jpg
CT Saturation Detector - Examples other errors

  • The oscillography records on the next two slides were captured from a B30 relay under test on a real-time digital power system simulator

  • First slide shows an external fault with deep CT saturation (~1.5 msec of good CT performance)

    • SAT saturation detector flag asserts prior to BIASED PKP bus differential pickup

    • DIR directional flag does not assert (one current flows out of zone), so even though bus differential picks up, no trip results

  • Second slide shows an internal fault with mild CT saturation

    • BIASED PKP and BIASED OP both assert before DIR asserts

    • CT saturation does not block bus differential

  • More examples available (COMTRADE files) upon request


Ct saturation example external fault l.jpg

200 other errors

150

~1 ms

100

50

current, A

0

-50

-100

-150

-200

0.06

0.07

0.08

0.09

0.1

0.11

0.12

time, sec

Despite heavy CT

saturation the

external fault current

is seen in the

opposite direction

CT Saturation Example – External Fault



Applying low impedance differential relays for busbar protection l.jpg
Applying Low-Impedance Differential Relays for Busbar Protection

Basic Topics

  • Configure physical CT Inputs

  • Configure Bus Zone and Dynamic Bus Replica

  • Calculating Bus Differential Element settings

    Advanced Topics

  • Isolator switch monitoring for reconfigurable buses

  • Differential Zone CT Trouble

  • Integrated Breaker Failure protection


Configuring ct inputs l.jpg
Configuring CT Inputs Protection

  • For each connected CT circuit enter Primary rating and select Secondary rating.

  • Each 3-phase bank of CT inputs must be assigned to a Signal Source that is used to define the Bus Zone and Dynamic Bus Replica

  • Some relays define 1 p.u. as the maximum primary current of all of the CTs connected in the given Bus Zone


Per unit current definition example l.jpg
Per-Unit Current Definition - Example Protection

  • For Zone 1, 1 p.u. = 3200 AP

  • For Zone 2, 1 p.u. = 5000 AP


Configuration of bus zone l.jpg
Configuration of Bus Zone Protection

  • Dynamic Bus Replica associates a status signal with each current in the Bus Differential Zone

  • Status signal can be any logic operand

    • Status signals can be developed in programmable logic to provide additional checks or security as required

    • Status signal can be set to ‘ON’ if current is always in the bus zone or ‘OFF’ if current is never in the bus zone

  • CT connections/polarities for a particular bus zone must be properly configured in the relay, via either hardwire or software


Configuring the bus differential zone l.jpg
Configuring the Bus Differential Zone Protection

Bus Zone settings defines the boundaries of the Differential Protection and CT Trouble Monitoring.

  • Configure the physical CT Inputs

    • CT Primary and Secondary values

    • Both 5 A and 1 A inputs are supported by the UR hardware

    • Ratio compensation done automatically for CT ratio differences up to 32:1

  • Configure AC Signal Sources

  • Configure Bus Zone with Dynamic Bus Replica


Dual percent differential characteristic l.jpg

High Breakpoint Protection

Low Breakpoint

Dual Percent Differential Characteristic

High Set (Unrestrained)

High Slope

Low Slope

Min Pickup


Calculating bus differential settings l.jpg
Calculating Bus Differential Settings Protection

  • The following Bus Zone Differential element parameters need to be set:

    • Differential Pickup

    • Restraint Low Slope

    • Restraint Low Break Point

    • Restraint High Breakpoint

    • Restraint High Slope

    • Differential High Set (if needed)

  • All settings entered in per unit (maximum CT primary in the zone)

  • Slope settings entered in percent

  • Low Slope, High Slope and High Breakpoint settings are used by the CT Saturation Detector and define the Region 1 Area (2-out-of-2 operation with Directional)


Calculating bus differential settings minimum pickup l.jpg
Calculating Bus Differential Settings – ProtectionMinimum Pickup

  • Defines the minimum differential current required for operation of the Bus Zone Differential element

  • Must be set above maximum leakage current not zoned off in the bus differential zone

  • May also be set above maximum load conditions for added security in case of CT trouble, but better alternatives exist


Calculating bus differential settings low slope l.jpg
Calculating Bus Differential Settings – ProtectionLow Slope

  • Defines the percent bias for the restraint currents from IREST=0 to IREST=Low Breakpoint

  • Setting determines the sensitivity of the differential element for low-current internal faults

  • Must be set above maximum error introduced by the CTs in their normal linear operating mode

  • Range: 15% to 100% in 1%. increments


Calculating bus differential settings low breakpoint l.jpg
Calculating Bus Differential Settings – ProtectionLow Breakpoint

  • Defines the upper limit to restraint currents that will be biased according to the Low Slope setting

  • Should be set to be above the maximum load but not more than the maximum current where the CTs still operate linearly (including residual flux)

  • Assumption is that the CTs will be operating linearly (no significant saturation effects up to 80% residual flux) up to the Low Breakpoint setting


Calculating bus differential settings high breakpoint l.jpg
Calculating Bus Differential Settings – ProtectionHigh Breakpoint

  • Defines the minimum restraint currents that will be biased according to the High Slope setting

  • Should be set to be below the minimum current where the weakest CT will saturate with no residual flux

  • Assumption is that the CTs will be operating linearly (no significant saturation effects up to 80% residual flux) up to the Low Breakpoint setting


Calculating bus differential settings high slope l.jpg
Calculating Bus Differential Settings – ProtectionHigh Slope

  • Defines the percent bias for the restraint currents IRESTHigh Breakpoint

  • Setting determines the stability of the differential element for high current external faults

  • Traditionally, should be set high enough to accommodate the spurious differential current resulting from saturation of the CTs during heavy external faults

  • Setting can be relaxed in favour of sensitivity and speed as the relay detects CT saturation and applies the directional principle to prevent maloperation

  • Range: 50% to 100% in 1%. increments


Calculating unrestrained bus differential settings l.jpg
Calculating Unrestrained Bus Differential Settings Protection

  • Defines the minimum differential current for unrestrained operation

  • Should be set to be above the maximum differential current under worst case CT saturation

  • Range: 2.00 to 99.99 p.u. in 0.01 p.u. increments

  • Can be effectively disabled by setting to 99.99 p.u.


Dual percent differential characteristic75 l.jpg

High Breakpoint Protection

Low Breakpoint

Dual Percent Differential Characteristic

High Set (Unrestrained)

High Slope

Low Slope

Min Pickup


Reconfigurable buses l.jpg
Reconfigurable Buses Protection

Protecting re-configurable buses


Reconfigurable buses77 l.jpg
Reconfigurable Buses Protection

Protecting re-configurable buses


Reconfigurable buses78 l.jpg
Reconfigurable Buses Protection

Protecting re-configurable buses


Reconfigurable buses79 l.jpg
Reconfigurable Buses Protection

Protecting re-configurable buses


Isolators l.jpg
Isolators Protection

  • Reliable “Isolator Closed” signals are needed for the Dynamic Bus Replica

  • In simple applications, a single normally closed contact may be sufficient

  • For maximum safety:

    • Both N.O. and N.C. contacts should be used

    • Isolator Alarm should be established and non-valid combinations (open-open, closed-closed) should be sorted out

    • Switching operations should be inhibited until bus image is recognized with 100% accuracy

    • Optionally block 87B operation from Isolator Alarm

  • Each isolator position signal decides:

    • Whether or not the associated current is to be included in the differential calculations

    • Whether or not the associated breaker is to be tripped



Switch status logic and dyanamic bus replica l.jpg

Isolator Open ProtectionAuxiliary Contact

Isolator Closed Auxiliary Contact

Isolator Position

Alarm

Block Switching

Off

On

CLOSED

No

No

Off

Off

LAST VALID

After time delay until acknowledged

Until Isolator Position is valid

On

On

CLOSED

On

Off

OPEN

No

No

Switch Status Logic and Dyanamic Bus Replica

  • NOTE: Isolator monitoring function may be a built-in feature or user-programmable in low impedance bus differential digital relays


Differential zone ct trouble l.jpg
Differential Zone CT Trouble Protection

  • Each Bus Differential Zone may a dedicated CT Trouble Monitor

  • Definite time delay overcurrent element operating on the zone differential current, based on the configured Dynamic Bus Replica

  • Three strategies to deal with CT problems:

    • Trip the bus zone as the problem with a CT will likely evolve into a bus fault anyway

    • Do not trip the bus, raise an alarm and try to correct the problem manually

    • Switch to setting group with 87B minimum pickup setting above the maximum load current.


Differential zone ct trouble84 l.jpg
Differential Zone CT Trouble Protection

  • Strategies 2 and 3 can be accomplished by:

    • Using undervoltage supervision to ride through the period from the beginning of the problem with a CT until declaring a CT trouble condition

    • Using an external check zone to supervise the 87B function

    • Using CT Trouble to prevent the Bus Differential tripping (2)

    • Using setting groups to increase the pickup value for the 87B function (3)


Differential zone ct trouble strategy 2 example l.jpg

Undervoltage condition Protection

87B operates

CT OK

Differential Zone CT Trouble – Strategy #2 Example

  • CT Trouble operand is used to rise an alarm

  • The 87B trip is inhibited after CT Trouble element operates

  • The relay may misoperate if an external fault occurs after CT trouble but before the CT trouble condition is declared (double-contingency)


Example architecture for large busbars l.jpg

Dual (redundant) fiber with 3msec delivery time between neighbouring IEDs. Up to 8 relays in the ring

Phase A AC signals and trip contacts

Phase B AC signals and trip contacts

Phase C AC signals and trip contacts

Digital Inputs for isolator monitoring and BF

Example Architecture for Large Busbars


Example architecture dynamic bus replica and isolator position l.jpg

Isolator Position neighbouring IEDs. Up to 8 relays in the ring

Isolator Position

Phase A AC signals wired here, bus replica configured here

Phase B AC signals wired here, bus replica configured here

Phase C AC signals wired here, bus replica configured here

Isolator Position

Isolator Position

Auxuliary switches wired here; Isolator Monitoring function configured here

Example Architecture – Dynamic Bus Replica and Isolator Position


Example architecture bf initiation current supervision l.jpg

BF Initiate & Current Supv. neighbouring IEDs. Up to 8 relays in the ring

BF Initiate & Current Supv.

Phase A AC signals wired here, current status monitored here

Phase B AC signals wired here, current status monitored here

Phase C AC signals wired here, current status monitored here

BF Initiate & Current Supv.

BF Initiate & Current Supv.

Breaker Failure elements configured here

Example Architecture – BF Initiation & Current Supervision


Example architecture breaker failure tripping l.jpg

Trip neighbouring IEDs. Up to 8 relays in the ring

Trip

Trip

Trip

Breaker Fail Op

Breaker Fail Op

Phase A AC signals wired here, current status monitored here

Phase B AC signals wired here, current status monitored here

Phase C AC signals wired here, current status monitored here

Breaker Fail Op

Breaker Fail Op

Example Architecture – Breaker Failure Tripping

Breaker Fail Op command generated here and send to trip appropriate breakers


Ieee 37 234 l.jpg
IEEE 37.234 neighbouring IEDs. Up to 8 relays in the ring

  • “Guide for Protective Relay Applications to Power System Buses” is currently being revised by the K14 Working Group of the IEEE Power System Relaying Committee.


Slide91 l.jpg

Questions? neighbouring IEDs. Up to 8 relays in the ring


Slide92 l.jpg

Thanks for the time neighbouring IEDs. Up to 8 relays in the ring


ad