DAR Lecture

8/10/2019 DAR Lecture

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Auto-Reclose onDistribution Networks


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Auto-Reclose on Distribution Networks MStockton 2012 - P 2 ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subjectto change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particularpurpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

Agenda

1st topic Why Perform Auto-Reclose ? Page 3

2nd topic Where can we apply Auto-Reclose ? Page 7

3rd topic Terminology, Sequences & Settings Page 15

4th topic Check Synchronism Page 46

5th topic Conclusion Page 56


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Why Perform Auto-Reclose ?

Auto-Reclose is the automatic closure

of a Circuit Breaker without theintervention of a person

It is a Control Technique

IEC61850 (parts -5 and 7-4) bothinclude autoreclose as a ProtectionRelated function, with a logical nodename of RREC

ANSI / IEEE C37.2 reference 79

IEC 60617 symbol:

What is Auto-Reclose

O I

PTOC

RREC

PTOC Fault

RREC

PTOC Fault

RREC

Pre-Fault

Trip

Reclose

Trip

Close


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Continuity of Supply Restoration is Automatic, therefore quicker Shorter duration of Power Outages

Fewer Customer Minutes Lost

Reduced Asset Damage

Autoreclose permits use of faster, non-discriminative protection Some overtripping is deemed acceptable

Less chance of faults evolving to more damaging scenarios

Lower pre-heating of CB contacts May reduce maintenance requirements ?

What are the Benefits ?


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Reduction in Operating Costs (OPEX) Reduced requirement for substation visits Reduction in damage of asset Increase in capital costs (CAPEX)

Higher price of switchgear capable of autoreclose duty Additional control relay (Autoreclose & Check Sync)

Improve System Stability Not traditionally considered at Distribution voltages

Traditionally the distribution network was/is radial in design

With modern networks (Embedded generation) a definiteconsideration

Part of the SMART Grid

What are the Benefits ?


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Agenda







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Where Can We Apply Auto-Reclose ?

Type and relative quantities of Fault

Type of Plant

Circuit Breaker Capabilities

HUMAN SAFETY

On some areas of distribution networks, human safety will be theoverriding decision even when autoreclose seems applicable

Consider overhead line feeders in sparsely populated areas

What Dictates Application ?


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Permanent Faults

Require human intervention to resolve

Successive re-energisations of the system will extend the damage

Self Clearing Faults

No permanent damage to the power system

When cleared, the power system can be safely re-energised Further classification:

Transient: Cleared by immediate isolation of the fault when the CB is

opened

Semi-Permanent: Cleared after a short time of isolation of the fault,

when the cause of the fault has been burnt or blown away

Fault Types


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Transformers Most faults are PERMANENT and require investigation &

rectification

Machines (motors & generators)

Most faults on machines are PERMANENT and requireinvestigation & rectification

Underground Cables

Most faults are considered as PERMANENT, require investigation& rectification

Pecking faults may be self healing initially but consequential

weakening of the insulation requires intervention

Fault Types related to Plant Items


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Overhead Lines Can have all fault types:

Permanent: Broken Conductors or Insulators

Transient: Insulator flashovers due to switching or lightning transient

overvoltages, conductor clashing (due to high winds or ice shedding)

Semi-Permanent: Phases bridged by animals or vegetation

Relative incidence depends upon the voltage level as this dictatesthe spacing between conductors

Typical figures are 80-85% transient, 5 to 10% semi-permanent and10% permanent

Statistically, 70-90% of all faults are -E faults at EHV



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Auto-Reclose on Distribution Networks MStockton 2012 - P 11

ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subjectto change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particularpurpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.


Auto-Reclose is generally applied to Overhead Lines only Auto-Reclose on Mesh Busbar arrangements although controlling

other CBs, only provides auto-reclose for line faults

Auto-Reclose is generally not applied to Underground Cables,Transformers or Machines

May be required for auto-reclose action on Mesh Busbararrangements

May be required for auto-reclose action on embedded generation

incomer circuits to restore connection to utility network (afternetwork faults)



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In order for the system to be safe, it is considered that the CB must always becapable of achieving the open state safely ie tripping and breaking fault current

Circuit Breakers are required to declare an operating or duty cycle by ANSI/IEEEand IEC standards, typically of the form

O t CO t CO , where

t is the minimum time between initial tripping before reclosure can be attempted t is the minimum time between subsequent tripping and reclosure events

Not all current breaking devices are intended for auto-reclose application

The times t and t will affect the settings for the auto-reclose relay and hence

define whether auto-reclose can be effective

Circuit Breaker Capability


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Conventional OHL Application

Protection relay & auto-reclose relayoperate for OHL faults only Control of single CB only

Embedded Generation Application

Protection relay used to disconnectgeneration for network faults eginterconnection (G59) protection

Auto-reclose used to re-connectdistributed generation automaticallywhen network recovers

Mesh Corner Application

OHL protection relay triggers threeauto-reclose relays, including relay onLV side of transformer circuit

Auto-reclose relays operate to restoresupply for transient faults

Permanent (and transformer) faultscause auto-isolation prior to auto-reclose

Examples of Auto-Reclose Applications

PTOC

RREC

Simple OHL Application

G59

RREC

Public

Network

Public

Network

Embedded

Generation

OHL Circuit

Transformer Circuit

RREC

RRECRREC

PDIS


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Agenda







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Terminology, Sequences & Settings

Successful Auto-Reclose for Transient Fault

PTOC Fault

RREC

Trip

Close

Time (non-linear)

Fault

Inception Trip

Contacts

Separate

End of

Sequence

Operating Time OperatedProtection Relay

Circuit Breaker

Opening

Time

Auto-Reclose Relay

Closing

Pulse

Closing

Time

Closing

Pulse

Contacts

Fully Closed

CB Reclaim Time

Reclaim Time

Auto-Reclose in Progress (ARIP)

Arc

Extinguished

Arcing

Time

CB Operating Time

Fault Clearance Time

Dead Time

Protection

Reset

Contacts

Fully Open

Reset Time

Dead Time

Contacts

Make

Recovery Time

Disturbance Time

System


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Unsuccessful Auto-Reclose for Permanent Fault

PTOC Fault

RREC

Trip

Close

Time (non-linear)

Fault

Inception Trip

Contacts

Separate

End of

Sequence

Operating Time OperatedProtection Relay

Circuit Breaker

Opening

Time

Auto-Reclose Relay

Closing

Pulse

Closing

Time

Closing

Pulse

Contacts

Fully Closed

CB Reclaim Time


Arc

Extinguished

Arcing

Time

CB Operating Time


Dead Time

Protection

Reset

Contacts

Fully Open

Reset Time

Dead Time

Contacts

Make

onto

Fault

Recovery Time

System

Disturbance Time

Contacts

Separate

Operating Time Operated

Opening

Time

Arc

Extinguished

Arcing

Time

CB Operating Time

Protection

Reset

Contacts

Fully Open

Reset Time

Re-Trip

Auto-RecloseLockout

Reclaim Time



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For system stability, the System Disturbance Time should beminimised Fast (instantaneous) Protection Short Dead Times

High Speed Auto-Reclose (HSAR): Fault initiation to CB Closure is less than 1 second

Low Speed or Delayed Auto-Reclose (DAR): Fault initiation to CB Closure is greater than 1 second (but often

10s of seconds) Generally only applicable on highly interconnected systems (where

system synchronism is maintained) or on single sourced, radialsystems

Speed


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Fast Protection is preferred to minimise system disturbance

At higher voltages, fast, discriminating protection is normal Eg Line Differential, Phase Comparison, Directional Comparison,

Distance (Z1 or Aided Schemes)

At lower voltages, fast, discriminating protection may not beavailable but auto-reclose allows: Fast, non-discriminating (overreaching) protection for the initial

trip cycle

Eg Instantaneous OC/EF, Distance (Z1 Extension)

Slower, discriminating protection for the final trip

Eg IDMT Overcurrent/Earth Fault

Protection


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Fast (Non-discriminating) Z1X trip causes

initial trip to cover 100% of line length fromboth ends

Some possibility of tripping for adjacentlines

After reclosure, the Z1X element is inhibited, sothat discriminating distance protection is used

Advantage transient faults are cleared quickly

Example of Auto-Reclose Application (Distance Z1 Extension)Z3

Z3

Z2

Z2

Z1X

Z1X Z1

Z1

1

t3Z3

Trip

&

Z1 1

Z2

Z1X

A/R

t2Z2

Z1

Z1X

A/R

Trip 1

t3 Z3

Trip

&

Z11

Z2

Z1X

A/R

t2 Z2

Z1

Z1X

A/R

Trip


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Sequence diagrams showed two Dead Times System Dead Time

Time when arc goes out, to when CB contacts touch Relay Dead Time

Typically from protection reset to start of close pulse

For stability, the System Dead time must be minimised

System Dead Time needs to consider:

Load Type

Protection Reset Time

Fault De-ionisation Time

Circuit Breaker Capabilities

Dead Time


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Predominantly Motors

Induction machines will typically ride through 0.5s supply interruptions

Synchronous machines will lose synchronism quickly, typically in less than0.3s

Generally allow for 3-10s dead times (to allow UV isolation of machines)

Street Lighting For safety (traffic, theft, violence) outages should be minimised, typically

1-2 seconds

Domestic

Traditionally, could be long (measured in minutes)

Modern systems impose penalties due to outages, therefore minimised(according to local legislation)

Dead Time & Load Type


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Embedded Generation Generally treated as a negative load Similar to motor considerations

Minimum dead time to allow safe disconnection of generation

Can be set much longer (minutes) to allow for system to stabiliseprior to reconnection

Future systems cannot follow this approach

Embedded generation will be required to stay on-line and ride

through system faults as much as possible Reconnection will need to occur as quickly as safely possible

Dead Time & Load Type


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Usually the Auto-Reclose Dead time only starts when the

protection trip resets Check scheme some simple schemes start the Dead Time earlier!

Protection should fully reset during dead time

Ensures that a fully discriminative trip can occur on reclosure

Technology considerations

Electromechanical (Induction Disc) relays had long resets(seconds)

Static relays designed with Instantaneous Reset (


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Must allow for the ionised air at the fault point to disperse Ionised air constitutes a conduction path

De-ionisation time depends upon:

System Voltage Type of Fault

Current Weather Conditions


Difficult to establish an exact time

Approximate formula is (10.5+KV/34.5) cycles

For 66kV: 250ms (@50Hz); 210ms (@60Hz)

For 132kV: 290ms (@50Hz); 240ms (@60Hz)

Usually considered on HV systems only distribution systems have CBoperating time criteria that are more onerous

Dead Time & Fault De-ionisation


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In order for the system to be safe, it is considered that the CB must always becapable of achieving the open state safely ie tripping and breaking faultcurrent

Circuit Breakers are required to declare an operating or duty cycle by

ANSI/IEEE and IEC standards, typically of the form O t CO t CO , where

t is the minimum time between initial tripping before reclosure can be

attempted

t is the minimum time between subsequent tripping and reclosure events

t defines the CB mechanism reset

t may be more significant (if longer) for multi-shot schemes

Dead Time & CB Capability


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Mechanism Reset + Closing Time imposes a minimum systemdead time

Significant for HSAR to satisfy stability requirements

Most CBs have a trip free mechanism

Tripping is the priority and can interrupt the closing stroke After tripping the trip free mechanism must be reset before

attempting closure



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Time (non-linear)

Fault

Inception Trip

Contacts

Separate

Circuit Breaker

Opening

Time

Closing

Pulse

Closing

Time

Contacts

Fully Closed

Arc

Extinguished

Arcing

Time

CB Operating Time


Contacts

Fully Open

Dead Time

Contacts

Make

Recovery Time

Disturbance Time

System

4012020107020T2 (msec)

70110300550280240Minimum Dead Time (msec)

60806535048160Closing Time (msec)

10302352002380T1 (msec)

5070456053100Operating Time (msec)

204035303860Opening Time (msec)

SF6380kV

SF6132kV

Air380kV

Oil132kV

Vacuum15kV

Oil11kV

T1 T2


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Needs to be of sufficient duration to release the closingmechanism eg spring

Usually a fixed pulse duration to ensure mechanism is fullyoperated

Can be terminated by the CB auxiliary contact

Anti-pumping is required to prevent repetitive open/close inquick succession when both trip & close circuits are active

Trip circuit is given priority !

Closing Pulse


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The Auto-Reclose device should not reset before the Protectionhas had time to operate, to ensure that permanent and semi-permanent faults are seen as part of the same Auto-Reclosesequence

Set Reclaim Time > Maximum Protection Operating Time

Set shorter reclaim time and inhibit its timing if a fault is detectedby use of a protection start signal

Reclaim Timer settings need to consider:

Supply Continuity

Fault Incidence/Past Experience Switchgear Capability & Maintenance requirements

Reclaim Time


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Supply Continuity Setting a long reclaim time risks that separate fault events will be

seen as the same fault and cause inadvertent lockout of the auto-reclose cycle

Setting a short reclaim time imposes a risk that a permanent faultisnt detected

The appropriate setting is largely dictated by knowledge of pastnetwork events

Reclaim Time


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Advantages

Correctly identifies thepermanent fault condition &trips to lockout on thediscriminative (IDMT) trip

Minimises CB duty

Disadvantages

Incorrectly identifies twosuccessive independent

transient faults as a permanentfault condition

Leads to unwanted lockout &unplanned outages

Example of Long Reclaim Time Settings

PIOC & PTOC Permanent

FaultRREC

Trip

Close

PIOC & PTOC F1

RREC

Trip

Trip

Close

F2

Time (non-linear)

Fault

Inception

PIOC

Trip

CB Contacts

Make onto Fault

Arc

Extinguished

Arc

Extinguished

PTOC

Trip &

Lockout

Reclaim Time >30s

Maximum PTOC

Time =30s

Time (non-linear)

Fault F1Inception PIOC

Trip CB Contacts

Make

Arc

Extinguished

Arc

Extinguished

PTOC

Trip &

Lockout

Reclaim Time >30s

Maximum PTOC

Time =30s

Fault F2Inception


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Advantages

Correctly identifies thepermanent fault condition &trips to lockout on thediscriminative (IDMT) trip

Correctly identifies twosuccessive independenttransient faults & recloses foreach

Disadvantages

Increased switchgear duty,

especially in areas of frequentlightning

May require remote Auto-Reclose Control

Example of Short Reclaim Time Settings

PIOC & PTOC Permanent

FaultRREC

Trip

Close

PIOC & PTOC F1

RREC

Trip

Trip

Close

F2

Time (non-linear)

Fault

Inception

PIOC

Trip

CB Contacts

Make onto Fault

Arc

Extinguished

Arc

Extinguished

PTOC

Trip &

Lockout

Reclaim Time Setting = 10s

Maximum PTOC

Time =30s

Time (non-linear)

Fault F1Inception PIOC

Trip CB Contacts

Make

Arc

Extinguished

Arc

Extinguished

PIOC

Trip

Reclaim Time = 10s

Fault F2Inception

PTOC

Start

Reclaim Time Extended by Start signaloperation to allow Trip & Lockout

CB Contacts

Make

Reclaim Time = 10s


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In order for the system to be safe, it is considered that the CB must always becapable of achieving the open state safely ie tripping and breaking faultcurrent

Circuit Breakers are required to declare an operating or duty cycle byANSI/IEEE and IEC standards, typically of the form

O t CO t CO , where t is the minimum time between initial tripping before reclosure can beattempted

t is the minimum time between subsequent tripping and reclosure events

t effectively imposes a minimum reclaim time as this is the taken to re-

energise the breaker (spring winding, establish air pressure, etc) Usually a contact is made available to the auto-reclose device to indicate

when the CB is ready for operation (Springs Charged) Used to inhibit reclosure until safe

Reclaim Time & CB Capability


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Theoretically, the Reclaim Time can be set


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In auto-reclose, every attempted reclosure of the CB is termed aShot

Single shot schemes predominate at higher voltage levels

Increased risk of plant damage for multiple shots

Increased system disturbance and risk of stability issues

Increased plant maintenance requirements

At lower voltages (distribution), multi-shot schemes can be

considered Use very dependent upon knowledge of faults on the network

Number of Shots


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Successful Auto-Reclose for Semi-Permanent Fault

PTOC Fault

RREC

Trip

Close

Time (non-linear)

Fault

Inception Trip

Contacts

Separate

End of

Sequence

Op. Time OperatedProtection Relay

Circuit Breaker

Opening

Time

Auto-Reclose Relay

Closing

Pulse

Closing

Time

Closing

Pulse

Contacts

Fully Closed


Arc

Extinguished

Arcing

Time

CB Operating Time


Dead Time 1

Protection

Reset

Contacts

Fully Open

Reset

Dead Time

Contacts

Make

onto

Fault

Recovery Time

System

Disturbance Time

Contacts

Separate

Operated

Opening

Time

Arc

Extinguished

Arcing

Time

CB Operating Time

Protection

Reset

Contacts

Fully Open

Reset

Re-Trip

Reclaim Time


Op. Time

Closing

Pulse

Closing

Time

Closing

Pulse

Contacts

Fully Closed

Dead Time 2

Dead Time

Contacts

Make

Reclaim Time


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Typical experience from areas of frequent thunderstorms 83.25% are successful 1st Shot reclosures Additional 10.05% are successful for 2nd Shot reclosures

(Dead Time 15-45s)

Additional 1.42% are successful for 3rd

Shot reclosures(Dead Time 120s)

This suggest that 1 or 2 shot schemes are the most successfulwith limited benefit from further attempts

Almost imposes minimal additional duty on switchgear

Number of Shots


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Benefits of Multi-Shot Auto-Reclose Improved Supply Continuity Helps prevent lockout during thunderstorms Systems with relatively high levels of semi-permanent faults

First shot may be unsuccessful

Second shot allows for the bridging material (vegetation or animal) to

burn itself clear and give successful re-closure

Helps on systems with fused spurs

Promotes fuse operation for low fault levels Saves fuses for some transient faults

Number of Shots


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For Permanent Faults with low IF

Fuse may not blow before PTOC

If fault reapplied during auto-reclose, the fuse will be pre-heated and may eventually blowbefore the PTOC element

Maintains supply to most

customers

For Transient Faults

PIOC element may operatebefore fuse

Maintains supply to allcustomers after a briefinterruption (No need to replacefuse)

Example of Multi-shot schemes with Fused Tees

PIOC & PTOC

Permanent

Fault (Low IF)

RREC

Trip

Close

PIOC & PTOC

Transient

Fault (Low IF)

RREC

Trip

Close


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If auto-reclosure is unsuccessful the auto-reclose device willlockout and prevent further reclose attempts. Other causesinclude: Failure of the CB to open & clear the fault when protection has

operated

Lack of CB energy within an acceptable time period

Lack of synchronism when attempting reclosure Too many CB operations (maintenance) Too many CB operations in a defined period (Excessive Fault

Frequency)

Operation of protection that doesnt initiate auto-reclose (BARinput)

Eg Busbar protection, VT Buchholz, etc

Lockout


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Once Lockout is attained, reset mechanisms include: Manual reset (either locally or via telecontrol) After Manual CB closure (either local or via telecontrol) usually

with a time delay and/or detection of healthy load state for a

period Automatically timed reset after lockout occurrence

In all cases, the condition(s) causing lockout needs to have beenresolved

Reset from Lockout


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On LV networks, it is impossible to have switching stations at all requiredlocations

Fused spurs are used

Pole Mounted Reclosers (PMR) are used

Upstream auto-reclose relays should discriminate with the installed PMRs

Co-ordinate the reclose cycles

Carefully select the auto-reclose sequences on both PMRs and switching stationsto ensure that the PMRs lockout for downstream faults.

Utilise sequence co-ordination

This ensures that the upstream auto-reclose device monitors but doesnt trip for

downstream events which are controlled by the PMRs

Upstream protection and auto-reclose only trips when PMR sequences have

completed but without the need for additional reclose attempts

Sequence Co-ordination


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Most schemes will have simple Auto-Reclose In/Out selection If remote selection, is possible then care should be taken

Any local selection should override the remote selection

Eg if a local user switches DAR out of service for testing purposes, to remainsafe it is necessary to ensure that the DAR can not be switched back intoservice remotely

With Auto-Reclose switched out of service, non-discriminating protectionshould be blocked

Eg Instantaneous elements, Distance Z1X

If Live Line working is permitted Auto-Reclose should be switched out of service Auto-Reclose mode selection by telecontrol should be disabled All instantaneous (including non-discriminating) elements should be

enabled

Auto-Reclose Mode Selection


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Agenda







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Check Synchronism

Check Sync refers to the check of voltages either side of a CB that is to bereclosed, either manually or during an auto-reclose cycle. It monitors

Angle Difference the difference in phase angle between the voltages

Slip Frequency the difference in frequency between the voltages Voltage Magnitude the absolute value of the voltage Voltage Difference the difference in magnitude between the voltages

Combinations of these measurements are used to ascertain if it is safe to close theCB

Check synchronism is usually measured on a single phase

A Check Synchronism device only checks the status it doesnt issue control pulses

to bring systems into synchronism Synchronising controls are issued from a Auto-Synchroniser, or manually

Terminology

h k h i


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Check Synchronism

Line Voltage is the voltage measured on the protected circuit Measured from a circuit VT

Bus Voltage is the voltage measured behind the protected circuit

Measured from a busbar VT, or from a suitable circuit VT via a

voltage selection scheme

Generally we consider the Bus Voltage as the reference with the

Line Voltage rotating relative to it

Terminology

Ch k S h i


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Check Synchronism

Dead Voltage is when the measurementindicates a de-energised state

Live Voltage is when the measurementindicates an energised state

Voltages between the Dead and Livevoltage bands are undefined

For In Sync or System Splitmeasurement both voltages must be Live

In Synchronism is when the voltages areless than X apart

System Split is when the voltages are

180 apart On System Split detection the

criteria for permitting closure maychange

Terminology

NominalVolts

Live Volts

Dead Volts

VBUS

VLINE

0

180

In Sync

Region

System

Split

Region

Ch k S h i


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Check Synchronism

To permit CB closure during an auto-reclose cycle it will often be necessary toconfirm that the voltages either side of the breaker are suitable

The Check Synchronism device performs this task. Suitable states for closureare one or more of the following:

In Sync - when both voltages are Live and within X apart Dead Line Charging when the Bus voltage is live and the Line voltage

is dead Dead Bus Charging when the Line voltage is live and the Bus voltage

is dead

When the Line and Bus voltages are both dead (less common) For the In Sync condition, the dead time may be shortened or even ignored

Check Synchronism & Auto-Reclose

Ch k S h i


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Check Synchronism

IEC61850 (parts -5 and 7-4) both include

Check Synchronising as a Protection Related

function, with a logical node name of RSYN

End X attempts to reclose first after 5 seconds,

to charge the dead line

If reclose is successful, End Y will

immediately reclose assuming an In

Sync condition is measured If reclose is unsuccessful, End Y will

reclose after a further 10s, to charge the

dead line

End X is the permitted to reclose

assuming an In Sync condition is

measured Typical Dead Line Charge settings are in the

range of 5s to 60s

Revertive Dead Line Charging

PIOC & PTOC

RREC

Trip

Close

PIOC & PTOC

RREC

Trip

Close

RSYNRSYN

End X End Y

Dead Line Charge

Time = 5s

Dead Line Charge

Time = 15s

Check Synchronism


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Check Synchronism

With the voltage in the In Sync region,contact closure of the breaker can occur with

some phase angle difference

Some Check Synchronism elements have aPredictive Closure facility

Monitors the frequency of rotation ofthe vectors

With knowledge of the CB closingtime, it predicts when to issue theclosing pulse such that contact closureoccurs when the phase angledifference is virtually 0

This places less stress on the CB andthe system but may delay the overalltime to closure

Predictive Closure

NominalVolts

Live Volts

Dead Volts

VBUS

VLINE

0

180

In Sync

Region

System

Split

Region

Predictive Closure

Region. Close pulse

issued to promote

closure at top dead

centre

Check Synchronism


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Check Synchronism

At some point, two vectors rotating at different frequencies will have little orno phase angle

Some customers perceive a risk that the check synchronism could be defeatedat Manual Closure by maintaining the close command and waiting for the insynchronism signal . Risk is overcome by:-

Use of Slip Frequency measurement & blocking, and/or

Use of Guard Relays

An additional perceived risk, is that the output contacts of the check syncrelay could be damaged and hence give erroneous in synchronism signals

Risk overcome by use of additional logic that prevents the output being

used if it is present before the request to close

With modern numeric relays and Programmable Scheme Logic, thesefacilities can all be mimicked and the risk negated

Concerns with Check Synchronism

Check Synchronism


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Check Synchronism

Concerns of Damaged Check Synch Relay

Check Synchronism


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Check Synchronism

Implementation in Modern Numeric Relay

Agenda


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Agenda






Auto-Reclose on Distribution Networks


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Auto Reclose on Distribution Networks

Traditionally this has been limited to Delayed Auto-Reclose withlittle or no concern for synchronism check or stability

Modern networks are pushing for more efficient use of thenetwork, with fewer and shorter supply interruptions

Increase requirement for Check Synchronism

Use of faster protection, shorter dead times and reclaim times

Scheme settings are largely dependent upon network faulthistory

CB Capability and understanding has a large impact on possibleauto-reclose scheme selection & settings

Conclusions


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