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On 1/16/19 3:42 PM, hooverrl@xxxxxxxxxxxxxx wrote:
Date: Tue, 15 Jan 2019 21:08:46 -0500
From: William Fox <wm9fox@xxxxxxxxx>
Subject: [TCML] TC Max Spark Length & Output Voltage
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My experience working with high voltage Marx generators (DC uni-potential
only devices) showed 100 kV/ft was a good clearance distance for a rod gap
or capacitor case to mounting frame. This indicated that a sparkover could
occur ~125 kV/ft. Therefore, an 8-ft gap would not likely exceed 1 million
volts through air. Experience saw a surface flashover of a 13-ft insulator
with ribbed convolutions (skirts or petticoats), at 2.1 million volts (slow
switching surge) where the flash occurred over the entire insulator string.
At 2.05 million volts, we only saw streamers protruding from the end
electrodes. Since that was negative polarity at the power end, when
reversing the polarity to positive saw a significant drop in flashover
voltage (down to 1.8 million volts) due to clear sparkover, where the higher
voltage flashover more closely followed the contours of the insulator.
10kV/inch is a similar guideline.. but it starts to breakdown [sic]
around 200-300 kV...
For long sparks, it's about field uniformity, and streamer/leader length
- just like lightning, and whether you can keep the channel hot.
That's why the "clearance guidelines" for EHV transmission lines deviate
from a "feet/kilovolt" kind of thing.