Substation Insulator Flashover Point
Substation Insulator Flashover Point
(OP)
In a situation such as a 115kV substation the post insulators are approximately 38 inches high. Now the dielectric breakdown in air is approximately 10kV per inch or for 115kV about 11.5". So the insulators are approximatly 3 times larger than the dielectric breakdown distance.
My questions:
1. Would or is it possible for a flashover to occur over the entire insulator which would result in an arc length of 38 inches?
2. Or would the flashover only occur when the distance was 11.5 inches meaning the insulator had failed in some way?
My questions:
1. Would or is it possible for a flashover to occur over the entire insulator which would result in an arc length of 38 inches?
2. Or would the flashover only occur when the distance was 11.5 inches meaning the insulator had failed in some way?






RE: Substation Insulator Flashover Point
The 10% BD probability is when the applied voltage equals to BIL, i.e. roughly 450H (H height in meters, BIL in kV).
at 50% BD probability, the applied voltage is called CFO (Critical Flash Over),
The relationship between BIL & CFO depends on statistical analysis of BD curve.
RE: Substation Insulator Flashover Point
If a substation is located in a northern climate near a busy highway where in the winter the spreading of salt on roadways is employed, under just the right [or is it wrong?] meteorological conditions, such as during a night-time fall of wet snow, the entire switchyard can start to light up and sizzle like something out of a Frankenstein movie; it can be quite awe-inspiring to behold...although you might not want to be looking when one of those arcs finally becomes a full-blown flashover that takes out an entire bus by relay protection; the sound and fury of the flashover itself combined with the operation of a half-dozen air-blast circuit breakers interrupting fault current can be quite unnerving.
At locations like this, idle insulators are deliberately placed on wooden skids at strategic spots in the switchyard, and over the course of the winter periodic measurements are taken so that prophylactic 'power washing' [spraying of insulators with clean demineralized water] can be undertaken as needed to avoid getting into this pickle in the first place...unless the good Lord looks upon us with undeserved favour and sends a heavy rain along with a driving wind - - and there've been times that that's exactly what we've yearned for!
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
RE: Substation Insulator Flashover Point
1990's saw the development of RTV (room temperature vulcanizing) silicone coatings (mainly from Canada) which made a quantum jump in pollution performance. Refer CIGRE Reports 442,478.
observations from crshears is quite interesting, something unknown to me. a tropical man. One interesting feature seen in India-only certain areas the seashore salt deposit on porcelain is causing problem while other areas it is not an issue at all.