CALCULATION OF THE FLASHOVER RATE DUE TO LIGHTNING WITH THE

EMTP TOOLBOX LIPS

Arnaud GUERRIER 30 / 04 / 09

Context■ For the French overhead lines

Faults due to lightning = 65% of all types of flashover

■ Flashover rate due to lightning depends on : Grounding resistance of towers Presence of shield wire Tower geometry Length of span Relief of the area

■ Last important flashover : 3 november 2008 on Néoules –Réaltor 400 kV double circuit line 3-phase tripping occuring simultaneously on both circuits=> load shedding of 1450 MW

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Description of LIPS

■ EMTP Toolbox■ Development by EDF, HydroQuébec, RTE■ Calculation of the flashover rate due to lightning function

of the grounding resistance tower■ Possible studies :

Evaluation of the flashover rate of an existing line Optimization of the number of line surge arresters to install on a

line Impact of grounding improvement or installation of sky wires on

the flashover rate

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Description of LIPS

■ Modelling of the overhead line Position of conductors and possible shield wires (same tower

used for each span) Length of span Phase equiped with Line Surge Arrester

■ Calculation of the flashover rate due to lightning with ground flash density : number of lightning stroke per year per km²

■ 2 types of flashover : Shield failure flashover Back flashover

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Description of LIPS

■ Shield failure flashover :lightning strike on conductors Overvoltage higher than

the lightning withstand voltage of the insulatorstrings

Arcing between the spark gap

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■ Back flashover : lightning strike on towers or shield wires A part of the lightning

current goes into the grounding electrode

=> Overvoltage of the tower

Arcing if the overvoltage higher than the lightning withstand of the line

du

i(t); di(t)/dt

Example of study (1/3)

■ Objective : Limit the rate of three-phase tripping

occurring on both circuits of a 400 kV double-circuit line

Optimize the number of line surge arresters to install

■ Current rate calculated with LIPS ■ Modelling of the line

2 shield wires 6 spans of 500 m

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Example of study (2/3) : modelling

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Start a Flashover Rates study

Analyse Flashover Rates study results

Lightning current sourcefound in the LIPS libraryThere must be only one per design

BFORSFFOR

View results

Lightning1

6kA, 70us

6 spans, line length is 3 km

bfor1c1phAc1phBc1phCc2phAc2phBc2phC

sw1sw2

c1phAc1phBc1phCc2phAc2phBc2phC

sw1sw2

+

AC1

400kVRMSLL /_300

FD +12345678

FD +12345678

LINE DATAmodel in: adapt50km_rv.pun

adapt50km.lin

cc

b

b

a

a

Example of study (3/3) : results

■ Number of 3-phase double circuit flashover function of grounding resistance

■ Installation of line surge arresters necessary for grounding resistance of tower higher than 30 ohms.

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Impact of Line Surge Arresters on double circuit line

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1 circuit without LSA

Flashover rate on circuit 1 with LSA on phase 1A and 1C

Flashover rate on circuit 2 with LSA on phase 1A and 1C

Flashover rate of the line function of grounding resistance tower

Conclusion

■ Calculation of the flashover rate due to lightning with LIPS

■ Measurement : grounding resistance tower■ For a flashover rate given => optimization of the number

of towers to treat and reducing the costs

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Thank you for your attention

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