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An insulator flashoverAn insulator flashover
that leads to a systemthat leads to a system
ground fault that inground fault that inturn causesturn causes
The BackflashThe Backflash
Possible conductor damagePossible conductor damage
momentary ormomentary orlong term outageslong term outages
possibly insulator damagepossibly insulator damage
breaker agingbreaker aging
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It can only occur on aIt can only occur on a
shielded line orshielded line or
where the top phasewhere the top phase
acts like a shieldacts like a shield
It can be eliminatedIt can be eliminated
It is usually causedIt is usually caused
by lightningby lightning
The BackflashThe Backflash
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This is how it happensThis is how it happens
on a typical shieldedon a typical shielded
69kV or 115kV69kV or 115kVtransmission line.transmission line.
Normal Voltage
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In most cases, the CriticalIn most cases, the Critical
Flashover Voltage of theFlashover Voltage of the
insulators is not reached,insulators is not reached,so everything returns toso everything returns to
normal after the stroke.normal after the stroke.
Note, the
duration ofthe impulse is
many times
shorter than
the power
frequency
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If conditions are notIf conditions are not
optimum, a backflash andoptimum, a backflash and
ground fault will occurground fault will occur
Note, the
powerfrequency
voltage is
now reduced
to near zero
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The follow currentThe follow currentcontinues until a breaker orcontinues until a breaker or
other device interrupts theother device interrupts the
event.event.
Breaker clear the
circuit
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System
voltagereturns to
normal
After the event isAfter the event is
interrupted, the systeminterrupted, the system
returns to normal.returns to normal.
But only after a momentaryBut only after a momentary
outage for an untoldoutage for an untold
number of customers.number of customers.
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The Backflash fromThe Backflash from
beginning to end withbeginning to end with
all its harmful effectsall its harmful effects
The BackflashThe Backflash
Possible conductor damagePossible conductor damage
momentary ormomentary orlong term outageslong term outages
possibly insulator damagepossibly insulator damage
breaker agingbreaker aging