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Flashovers and Strikes to Transmission Lines
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This famous picture is of a shielding failure (the lightning
stroke bypasses the shield wire and terminates on a phase
conductor). The line is built to 765-kV construction, but
operated at 345 kV, so it has a very high insulation capability.
No flashover is observed. This confirms an aspect of the
electrogeometric models showing that shielding failures should
be small magnitude events. The lightning stroke was small
enough that the large insulation level was able to withstand
the voltage surge.
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Wide angle view: |
Zoomed in view: |
View of the structure: |
The Hit
This lightning flash hit the shield
wire of a 115-kV, double circuit transmission line. All three
phases of each circuit flashed over, and of interest, not all
of the flashovers occurred on the same tower. These faults required
the circuit breakers of both circuits to open to clear the fault.
This circuit had poor lightning performance because the line
had poor grounding (75-150 ohms at each tower) and a low insulation
level (BIL=500kV) for a line of this voltage. "The Hit"
was captured as part of the NMPC/Champion
Power Quality Project.
By digitally overlaying a reference image of the towers and
wires, it is easier to see where each phase flashed over and
that the lightning hit the shield wire at the midpoint between
two towers.
Note that streamers are visible on many insulators -- these
streamers did not make it across the insulator before the
other phases flashed over. When the other phases flashed over,
the voltage collapsed which prevented a full flashover on
these insulators.
Each camera system has two cameras pointing in opposite directions
along the transmission line. The camera pointing in the opposite
direction also captured streamers across two insulators:
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Far View: |
Digital Enhancement |
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Shield Wire Hit
This picture was captured as part of the NMPC/Champion
Power Quality Project.
Lightning hit the shield wire with no flashovers on either circuit.
This picture provided evidence that the arresters which were
installed on one of the 115-kV circuits are helping to eliminate
lightning-caused flashovers.
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Multiple Flashovers
This picture was captured as part of the NMPC/Champion
Power Quality Project.
In this event, lightning caused flashovers on the 115-kV circuit,
where three of the six phases flashed over. This lightning flash
probably hit just next to the camera system and out of the field
of view. Induced flashovers also occurred on the 23-kV circuit
running parallel to the 115-kV line.
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Western View: |
Eastern View: |
| This picture was captured as part of the NMPC/Champion
Power Quality Project.
In this event, lightning caused flashovers on the 115-kV
circuit, where four of the six phases flashed over. This lightning
flash contained only one stroke, so the camera system was
not fast enough to capture the lightning channel. A very significant
finding with this picture is the fact that a flashover occurred
about 2 miles from the location of the lightning strike point.
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View Showing Flashovers Separated by 2 Miles: |
This lightning/fault event also caused damage to insulators: |
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This is a lightning flash to a 69-kV circuit that flashed
over. This area of line is protected by an arrester (intermediate
or station-class) placed on the top phase approximately every
6 poles. This protection scheme may not always be effective
because of the wide spacing between arresters.
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