Line Arresters. 2012

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Line Arrester Applications

International Conference cum Tutorial on HV SA Technology & ApplicationsNew Delhi, 26th November, 2012Bengt Johnnerfelt

26th November 2012


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Why Line Arresters?

Lightning has been reported as the

main cause of non-scheduled

outages on overhead sub-transmission and transmission lines

United States: 57%

Brazil: 50 70% Japan: 70 80%

Denmark: 57%

Colombia: 47 69%

Lightning is the most frequent cause

of transmission outage and service

interruption in the United States,accounting for about 30% of all

power outages, and resulting in

economic losses approaching $1billion annually http://www.epri.com
http://www.epri.com/http://www.epri.com/


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Flashover due to Lightning on Transmission Lines

Lightning may cause flashover of line insulators in three different ways:

1.Strikes to shield wires or towers

2.Direct strikes to the phase conductors

Shielding failure

Unshielded lines

3.Flashovers due to induced voltages

Rarely exceeding 300kV

Limited to distribution andsub-transmission lines

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Shielded lines Back Flashover

Current is typically shared between several towers and arresters

Current travels from the tower to the phase conductor.


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Shielded lines Back Flashover Criteria

VISi(t) Transient voltage on the insulators strings (kV)

Vcrossarmi(t) Transient voltage on the cross arms (kV)

Vinduced(t) Induced voltages (kV)VPFi Power frequency voltage (kV)

( ) ( ) ( )[ ]iii PFinducedicrossarmIS

VtVtVtV

( ) ( )tVtVithstinsulatorwISi .

Flashover when:

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Shielded Lines - Shielding FailureUnshielded Lines

Shielding failure low current amplitudesUnshielded lines nearly all strikes leadto flashovers.

Current travels from phase conductor tothe tower.

( ) ( )tVtVithstinsulatorwISi .


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Parameters Effecting Risk of Lightning Flashovers

Ground flash density; Transient tower footing resistance and transient response of the

tower;

Lightning current amplitude; The electromagnetic coupling among shield wires and phase

conductors;

The effect of the adjacent towers and their footing resistances;

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Lightning strike: two traveling waves of= Z (Example: = 350 20 kA = 3.5 MV)



Probability of Lightning Currents CIGRE Data

( )

+

=6.2

311

1

I

IIPd



Shielded Lines Effect of Grounding System

Transmission line lightning performance depends strongly on the

transient grounding system response.


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Procedures to Improve the Transmission LinesLightning Performance

Increase the line insulation;

Improvement in the grounding system;

Shield wire application on unshielded lines or improvement of the

shielding angle for shielded lines;

Line Arrester (LA)

Externally Gapped Line Arresters - EGLA

Non-Gapped Line Arresters - NGLA (TLA)

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Purpose of the Installed LA

Protection againstfast front (lightning)overvoltages only.

Protection against allovervoltages including

slow front (switching) andfast front (lightning)overvoltages.

or5000 s T1 20 s

T1/T2 = 250/2500 s

20 s T1 0.1 s

T1/T2 = 1.2/50 s

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Line Arrester Applications

Protecting line insulators from flashovers - reduced systeminterruption caused by lightning, improving system reliability;

Protecting line insulators from flashovers substitute for shield wires

Control switching surges along the lines substitutes for reclosing

resistors;

Extended substation protection - lowering/better protection of the BIL

levels in substations;

Upgrading system voltages with existing line insulation compact

insulation lines;

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History of Line Arresters

Distribution line arresters

First installation of distribution line arresters in 1975 (Japan, 33 kV)

Today several tens of millions of distribution line arresters assumedlyin service

Transmission line arresters

First installation of transmission line arresters around 1980 (Japan,66 kV, 77 kV and 138 kV)

Today huge quantities of transmission line arresters in service


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Line Arrester Designs

There are two basic designs;1. NGLA, non gapped line arresters, often called TLA (transmission line

arresters):

Can take higher energies & switching. Can be used on unshielded lines;

Can be used instead of reclosing resistors;

Need disconnector to facilitate fast reclosing;

After disconnector operation possible swaying of the ground lead must be

considered;

2. EGLA, externally gapped line arresters:

Shorter (& lighter) than NGLA. No COV or creepage requirements;

Fast reclosing possible without disconnector;

Difficult to find overloaded/failed EGLA in the field;

Cannot handle switching surges or TOV, only used on shielded lines;

Coordination of the spark gap;

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NGLA basic configuration for 245 kV system


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Typical EGLA Design IEC 60099-8

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Installation of EGLA & NGLA

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EGLANGLA


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Important Factors for Electrical Selection of LA forLI protection on Shielded LinesArrester rating;

Higher than corresponding stationarresters - Avoid switching & TOVstresses.

No need for very low protection levelsas BIL of line insulators is high.

Arrester class;Lower than station arresters.Typically IEC class 2 will work up to245kV systems.

How many and in which phases;Study needed in most cases.LA needed in a few towers on bothsides with normal footing resistanceafter LA installed in towers with highfooting resistance

Desired outage rate

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Electrical Spark Gap Selection for EGLA

Coordination of sparkover and flashover voltageSound arrester

lightning impulse sparkover voltage

must be lower than insulator's LIflashover voltage

switching impulse sparkover voltagemust be higher than insulator's SI

flashover voltage

Failed arrester

switching impulse sparkovervoltage must be higher thaninsulator's SI flashover voltage

Insulator

f/o voltage

EGLA

s/o voltage

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Special Pollution Consideration for EGLA

Performance under pollution conditions:

Follow current that partly flows on thepolluted arrester housing must be

safely interrupted special, verycomplicated test in 60099-8

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Arrester class;

Will see higher energies;

System study needed;

Selected based on the study

result for the desired outage rate;

Lower tower footing resistance not

necessarily good as this may lead

to that all current will be taken bytwo arresters only;

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Important Factors for Electrical Selection ofNGLA on Unshielded Lines


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Selection of LA System Studies

Several commercial programs available.

Basic Information Required for Modelling TLA for transmission lines:

System voltage

Basic configuration of the line & BIL of line insulators

Tower type, phase-to-earth and phase-to-phase distances, shielded

or unshielded line, phase conductors and shield wire sags, span

length between towers, conductors diameters, etc. Short-circuit currents and temporary overvoltages conditions

Ground Flash Density of the region crossed by the line

Grounding system Existing station arresters electrical data

Suggested LA data


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Installation Issues for Mechanical Selection of NGLA

Disconnector installation;Weakest point of installation.Make room for swinging of the line.Consider lead lengths swaying afterarrester overloading.

Check that operation times fits actualfault clearing times.

Arrester classification;Check short-circuit capability. Is theLA allowed to fall down afteroverloading?

Check mechanical data like vibration.

Installation methods;Hot installation or not.Make sure that the arrester have pivotpoints so that it can move without too

much stresses.

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Installation Issues for Mechanical Selection of EGLA

Gap installation;Most critical point of installation.Need fixture/model to ensure properelectrode distance.

Make sure that the gap electrodesalways keep the same distance evenduring high winds and/or vibrations.

Different BIL/sparkover voltage for

some towers?Arrester classification;

Check short-circuit capability. Is partsof the EGLA allowed to fall down after

overloading?Check mechanical data like vibration.

Installation methods;Hot installation or not.

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LA Special Considerations after Overload &Short-Circuit

Recommended requirementsexceeding those applicable to stationarresters:

Mechanical integrity should be maintained

after failure - Public access; Any open flames should not occur orself

extinguish in a very short time Risk ofcausing fires;


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LA Special Considerations Regarding EnergyHandling Capability

The only definition in IEC 60099-4: line discharge class not appropriate

Based on long duration current impulses of

Td = 2000, 2400, 2800, 3200 s


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IEC 60099-4, Ed. 2.2, Annex N:Test procedure to determine

the lightning impulse dischargecapability

IEC 60099-8, 8.6: Lightningdischarge capability test

Typical test current,voltage and energy

LA Special testing for Lightning Impulse DischargeCapability (1)

current(A),

voltage(V),energy(J)

time

Test applies to line arresters for system voltages exceeding 52 kV

A sinusoidal impulse of200 microseconds time duration consideredas a suitable compromise to cover all kind of realistic stress (shielded

and unshielded lines, multiple strikes)


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Required impulse current amplitudes for injecting the same energy intoan MO resistor as by one line discharge equivalent to LD classes 2 to 4.

230 s current amplitudes will be in the range of15 kA 30 kA

LA Special testing for Lightning Impulse DischargeCapability (2)


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Testing of LA

NGLA EGLA

52 kV > 52 kV

IEC 60099-4no special

requirements

IEC 60099-4special requirements on

energy testing mechanical testing

IEC 60099-8

Selection:IEC 60099-5, Ed. 2.0 (to be published 2013)Cigr TB 440 (2010)Software tools (commercially available)

Testing:

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LA Applied on Sections of a Line, in One or TwoPhases

Individual towers with higher footing resistance protected with TLA: Installing one TLA on an individual tower reduces the probability of

flashover, installed on the bottom phase. If a second TLA is installedthe reduction in probability is minimal.

- Installation of additional TLAs on adjacent towers reduces the probability offlashover.

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gesprobability

58 59 60 61 62 65 66 70 72 76

"Cambuci - Sto Antnio Pdua" 69 kV TL

Current configuration 1 TLA per structure 2 TLA per structure


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Installation along Sections of Towers with HighFooting Resistance

Typical examples are: River, lake, gorge crossings

Mountain crossings

Important considerations; System study

LA should also be installed in 3-6 towers at each side with normal footing

resistance Otherwise flashovers are pushed to these towers instead

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tages

probability

58 59 60 61 62 65 66 70 72 76

"Cambuci - Sto Antnio Pdua" 69 kV TL

Current configuration 1 TLA per structure 2 TLA per strucuture


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LA Protection against Double Line TrippingSimultaneously

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NGLA in all three phase on one circuit

reduces also the risk for flashover onthe other circuit.


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Installation of NGLA - Field Experience

Norway 300 kV Brazil 145 kV


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Installations of NGLA - Field Experience

Brazil 36 kV


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Installations of NGLA - Field Experience

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24 kV - Peru

145 kV - Italy


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Brazil 145 kV

TLA were installed on anew structure built inthe tower to allow TLA

installation on hot line.This procedure has ashorter installation timecompared with the usual

procedure used to installTLA on hot line.


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Peru 145 kV


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Field Performance after LA Installation

Field experience of the Brazilian utilities Analysis and evaluation of the Brazilians overhead line lightning

performance (average number of outages per 100 km & year) before

and after transmission line arresters installation have shown a goodeffectiveness with average indexes for the improvement higher than

70% for overhead lines from 36 kV to 145 kV.

Average improvement of approximately 70% for 36 kV lines. Average improvement of approximately 79% for 72.5 kV lines.

Average improvement of approximately 76% for 145 kV lines.

There is not yet a reliable information for 245 kV lines. These indexes can be higher for overhead lines protected with

line arresters in all three phases.


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Extended Station Protection (1)

Back flashover at 600 m from the substation with one surge arrester

installed


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Extended Station Protection (2)

Back flashover at 600 m from the substation with two surge arresters

installed


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Extended Station Protection

Back flashover at 300 m from the substation with a set of TLA

installed on the structure closest to the substation with one surge

arresters installed


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Extended Station Protection

Simulao_3.pl4: v:5SIMULAO_1.pl4: v:5SIMULAO_2.pl4: v:5

0.0 1.5 3.0 4.5 6.0 7.5 9.0[us]0

100

200

300

400

500

600

[kV]

Back flashover at 600 m from thesubstation with one surge arrester

installedBack flashover at600 m from thesubstation with twosurge arrestersinstalled

Back flashover at 300 m fromthe substation with a set of TLA installed on the structure

closest to the substation

C ll d S i hi i h NGLA


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Controlled Switching with NGLA

800 kV USA 800 kV Russia

Only few sets of NGLA needed at 50% of line length or at 1/3 and 2/3for longer lines.Not sensitive to harmonics in the voltage.Works well in combination with controlled switching.

Rated voltage - same as station arresters Arrester class - one class lower than station arresters

C t Li ith t Shi ld Wi


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Compact Lines without Shield Wires

Unshielded compact line 420 kV

Source: Different Transmission Line Arrester Applications, Installations,and Designs MSA / ABB CIGR tutorial Rio de Janeiro 2005


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Thank You For Your Attention!

Documents

Line Arresters. 2012