System Protection in Rurla Transmission lines

7/29/2019 System Protection in Rurla Transmission lines

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Dr Campbell BoothUniversity of Strathclyde

Review of ConventionalDistribution System Protection

EES-UETP Course title

University of ManchesterMarch 2011


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Distribution System Protection: Overview

Typical distribution network architectures

Protection basics and requirements (review)

Brief review of protection philosophies and

schemes: Unit/non-unit

Differential/distance/overcurrent

Reclosers/Sectionalisers/Fuses

Summary of operation and

setting of distribution protection

Practical considerations

University of Strathclyde, 2011http://www.flickr.com/photos/10223809@N02/847602455/


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Gers and HolmesProtection of Electricity Distribution Networks,IEE Power & Energy Series 47

Transmission& DistributionArchitecture

University of Strathclyde, 2011


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ProtectionZones

Gers and Holmes

Protection of Electricity Distribution Networks,IEE Power & Energy Series 47


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Electrical Arc

Pressure Waves

Copper Vapor:

Solid to VaporExpands by67,000 times

Molten Metal

Intense Light

Hot Air-Rapid Expansion

20,000 C

Shrapnel

Sound Waves



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Faults on power systems

Faults on power systems

(Usually) characterised by large fault currents

Fault current level usually drops with distanceaway from source due to impedance oflines/transformers in the network

Large voltage depression around the point of

fault (load impedances shorted)



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SourceLoad

(High Z)Load

(High Z)

Line(Low Z)

Line

(Low Z)

Line(Low Z)

Line(Low Z)

Typical section of power system one line diagram

Power System Protection - How?

Load(High Z)



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SourceLoad

(High Z)Load

(High Z)

Line(Low Z)

Line(Low Z)

Line(Low Z)

Line(Low Z)


v v v v

V V V


Load(High Z)



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SourceLoad

(High Z)Load

(High Z)

Line(Low Z)

Line(Low Z)

Line(Low Z)

Line(Low Z)


v v v v

V V V

Fault 1


Load(High Z)



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SourceLoad

(High Z)Load

(High Z)Load

(High Z)

Line(Low Z)

Line(Low Z)

Line(Low Z)

Line(Low Z)


v v v v

V V V

Fault 1




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SourceLoad

(High Z)Load

(High Z)Load

(High Z)

Line(Low Z)

Line(Low Z)

Line(Low Z)

Line(Low Z)


v v v v

V V V

Current much higher than load currentVoltage at fault = 0

Fault 1

Voltagehere?

Voltagehere?




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Measurement of current (and often voltage)at many locations:

Fault current flow usually lessens in magnitude as

fault distance from source increases Voltage at a measurement point usually increases

as fault distance from measurement pointincreases




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SourceLoad

(High Z)Load

(High Z)Load

(High Z)

Line(Low Z)

Line(Low Z)

Line(Low Z)

Line(Low Z)


v v v v

V V V


Fault 1

Voltageand current measured

here?


P



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Source

Line(Low Z)

Line(Low Z)

Line(Low Z)

Line(Low Z)


v v v v

Current much higher than load current

(but not as high as fault at position 1)Voltage at fault = 0

Fault 2



here?

P

V V

Much reduced

current due to

line voltage

depression



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Factors affecting fault severity

Magnitude of fault current How much and what nature of generation is

on the system

How close generation is to fault position impedance to fault

Power system configuration

Nature of fault

Earthing arrangements (only applicable forparticular types of fault)

Duration of fault



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Protection System Requirements (1)

The protection systems must:

rapidly and automatically disconnect the

faulty item(s) of plant or section of thepower network;

minimise the disconnection of healthy

plant, thus ensuring maximum security ofsupply to consumers.



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The degree to which any protectionsystem satisfies the aforementioned

requirements can be described by fourinter-related parameters -

discrimination, sensitivity, operating

time and stability.



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Discrimination is the degree of ability of theprotection system to select whether or not to

operate for a given measured system state. Sensitivityis a measure of the ability of the

protection system to identify the presence of a

fault or other undesirable condition, eventhough that condition may be only slightlydifferent from an apparently healthy condition.



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Operating time is the total time taken fromthe onset of the fault to the protection relay

sending a trip signal to the circuit breaker(s). Stability is a measure of the ability of the

protection system to remain inoperative

under certain fault conditions, because thefault is of such a nature that some otherprotection system is intended to effecttripping.



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Protection Philosophies

Two major protection philosophies unit schemes should only detect and

react to primary system faults within thezone of protection, while remaining

inoperative for external faults;

non-unit schemes do not independentlyprotect one clearly defined part (or zone)

of the system - adjacent non-unitprotection schemes on an interconnectedpower system have an element ofoverlap with respect to their respective

zones of protection. University of Strathclyde, 2011


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Unit Protection Schemes

Measurements/comparisons of

quantities

React only to faults inside protectedzone

Employs communications - expensive

Remain stable for external faults No backup for neighbouring system



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Unit Protection: Normal Conditions

Communications

I1 I2

Irelay1= Irelay2Relay 1 Relay 2



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Unit Protection: Internal Fault

Communications

I1 I2

Irelay1 Irelay2Relay 1 Relay 2



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Unit Protection: Internal Fault



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Unit Protection: External Fault

Communications

I1 I2

Irelay1= Irelay2Relay 1 Relay 2



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Unit Protection Schemes

Examples:

Current differential protection

Phase comparison protection

Balanced voltage protection

Fault-generated noise protection

Distance protection with zone 1 inter-tripping



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Non-Unit Protection Schemes

Do not independently protect one clearlydefined part (or zone) of the system

Non-unit protection schemes overlap withrespect to their zones of protection -provides backup

Settings are important to ensure

discrimination and stability Communications sometimes used to

enhance operation



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Sub 2Sub 1

I

Decreasing Fault Current

I

Fault 1

Fault 1t

Fault 2tFault 2t

Fault 2

Relay 1 Relay 2

Non-Unit Protection



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Non-Unit Protection Schemes

Examples:

Overcurrent schemes

Measure current

Distance/impedance measuring schemes

Measure voltage and current



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Non-unit set to operatewith a time delay in this

region

Unit/non-unit

protection

Main transformerunit Protection

sub1

sub2

Back-upnon-unit protection

t

I

Fault 2

Fault 3

Fault 1



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SourceLoad

(High Z)Load

(High Z)Load

(High Z)

Line(Low Z)

Line(Low Z)

Line(Low Z)

Line(Low Z)

v v v v

V V V


Fault 1

Assuming all line Zs are equalVoltage at P = 0.5VsourceFault current = X

Voltagehere?

Distance Protection

P



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Source

Line(Low Z)

Line(Low Z)

Line(Low Z)

Line(Low Z)

v v v v

Current much higher than load current

(but not as high as fault at position 1)Voltage at fault = 0

Fault 2


here?

P

Assuming all line Zs are equalVoltage at P = 0.75VsourceFault current = 0.5X

Distance Protection



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Distance Protection

Measures voltage and current Faults further away from measurement point

V relatively high

I relatively low Faults nearer to measurement point

V relatively low

I relatively high



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Distance Protection

System is set to operate for certain ratios of V, I

Can react with different time delays (e.g. as fast aspossible for close faults, slower (backup) for furtheraway faults

www.protectionrelaytest.com

O P i
http://www.protectionrelaytest.com/http://www.protectionrelaytest.com/


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Overcurrent Protection

Inverse characteristic

Used as main protection

in distribution networks,backup in transmission

networks

Provides different time of operation

depending on level of fault current University of Strathclyde, 2011


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Timesetting

Restrainingspring

Disc

Plugsetting

Core

(carriesflux)

Relay

contacts

Shadingrings

(introducephase shift)

Contactmaker

Induction Disc Relay


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Coil withmultiple tapping

points(results in more

or less flux forsame input current).

Tapping useddictated

by plug setting.

Induction Disc Relay

View from Rear


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Overcurrent Protection - Operation

BA

t

I

t


I

Fault 1

Fault 1tF1

Fault 2tF2

Fault 2tF2

Fault 2

Relay 1 Relay 2

Source



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Effect on curve positionof modifying

Time Multiplier Setting

Effect on curve positionof modifyingPlug Setting

Overcurrent Protection - Operation



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Relays Standard Types



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http://www.youtube.com/watch?v=kU6NSh7hr7Q

Video that describes magnetic fields, induced eddy currents andforces:

http://www.youtube.com/watch?v=TgzkA3fo-D8&feature=relate

Video showing induction disc relay operation (1:25), marginaloperation, or creep just before 2 minutes:

Induction disc relay operation

http://www.youtube.com/watch?v=kU6NSh7hr7Qhttp://www.youtube.com/watch?v=TgzkA3fo-D8&feature=relatedhttp://www.youtube.com/watch?v=TgzkA3fo-D8&feature=relatedhttp://www.youtube.com/watch?v=TgzkA3fo-D8&feature=relatedhttp://www.youtube.com/watch?v=TgzkA3fo-D8&feature=relatedhttp://www.youtube.com/watch?v=kU6NSh7hr7Q


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Alternative methods exist

One method:

Start at furthest downstream relay Progress upstream

Each relay is set with the objective of providing

backup to next downstream relay with a time delay Important to ensure that upstream relays will not

begin to operate before downstream relays for any

current

Setting of overcurrent relays



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BA C

Source(Grid)

Load Load Load

I1 I2 I3 I4

IL1 IL2 IL3

I1=I2+IL1

Normal Operation


O


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BA


C

Source(Grid)

Load Load Load

Operate (quickly)Operate

(after a delay)Dont operate

Operation During Fault


S i /G di f O R l


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Summary of procedure for each relay Calculate (or get from previous study) fault current, CT

ratio, relay rating, desired grading margin

Calculate plug setting (PS) must result in operating

current threshold greater than (130%?) of max loadcurrent check current discrimination withdownstream relay(s)

Get characteristic operating time (for TSM=1) for fault

current Use (or calculate) desired operating time to calculate

required TSM Desired operating time is known for furthest downstream relay, or is

downstream relays operating time for a fault at the downstream

location+grading margin)

Setting/Grading of Overcurrent Relays


Overcurrent Protection Practical


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Overcurrent Protection PracticalConsiderations

Maximum/minimum fault levels

Motor starting

Embedded generation Meshed networks

Instantaneous/delayed operation



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Use of directional relaysto provide correct protectionoperation on parallel feeders

From NPAG: - chapter 9www.deadsmall/2VA

http://www.deadsmall/2VAhttp://www.deadsmall/2VA


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Use of overcurrentrelays

for protection of ringmains

From NPAG: - chapter 9www.deadsmall/2VA


Gradingexample with
http://www.deadsmall/2VAhttp://www.deadsmall/2VA


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example withinstantaneous

& inverserelays (1A)

From ArevaNPAG

3000A125%125%

125%

PS(%)


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Protection of Distribution Networks

132/33kV Distance, differential (some), overcurrent

11kV/415V Overcurrent, reclosers, sectionalisers, fuses, RCDs

Remember, majority of faults transient fuses shouldonly operate if fault is permanent

Typically, faults are isolated very quickly by reclosers,multiple reclose attempts are attempted, and if fault is

permanent and downstream of fuses, fuses ultimatelymelt while system is in reclosed state

Reclose is then successful

If permanent fault between recloser and fuse, then

recloser will lock-out after pre-defined number of attempts


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Protection of distribution networks

Distribution network protection is

based on overcurrent protection

reclosers, sectionalisers and and

fuses

In rural distribution networks,>80% of faults are temporary and

auto reclose schemes are

adopted.

CBT1-11

CBT1-33

CBT2-11

CBT2-33B33kV

B11kV

SpurA1

SpurA2

SpurA3

SpurA4

SpurA5

SpurA6

SpurA7

SpurA8

SpurB1

SpurB2

SpurB3

SpurB4

SpurB5

R-A R-B

PMAR-A

PMAR-B

Feeder

A

Feeder

B

SpurA9

SpurA10

SpurA1



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Transient fault

Recloser willsuccessfully reclose

Permanent fault

Recloser will reclosemultiple times (withvariable delays beforere-opening) and fuse

will melt before maxreclosures attempted

Sectionalisers/smartlinks may be used to

save fuses

Gers and HolmesProtection of

Electricity

DistributionNetworks,IEE Power &Energy Series 47

P i f Di ib i N k


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Gers and HolmesProtection of Electricity

Distribution Networks,

IEE Power & Energy Series 47

P i f Di ib i N k


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BA C

Load


PMAR Sectionaliser

Fuse

IDMT

PMAR

Sectionaliser

Fuse

IDMT StartOpen

Count 1

1 shot

ResetOpen

Count 1

1 shot

ResetClose

Count 1

2 shots

StartOpen

Count 2

2 shots

ResetOpen

Count 2

2 shots

ResetClose

Count 2

melt

ResetClose

Reset

melted

tFault inception

120

P i f Di ib i N k


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BA C

Load


PMAR Sectionaliser

Fuse

IDMT

PMAR

Sectionaliser

Fuse

IDMT StartOpen

Count 1

ResetOpen

Count 1

ResetClose

Count 1

ResetClose

Reset

tFault inception

10

Distribution System Protection: Summary


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Distribution System Protection: Summary

Typical distribution network architectures

Protection basics and requirements (review)

Brief review of protection philosophies and

schemes: Unit/non-unit Differential/distance/overcurrent

Reclosers/Sectionalisers/Fuses

Summary of operation andsetting of distribution protection

Practical considerations

Documents

System Protection in Rurla Transmission lines