[Boatanchors] Storm Damage to Electronics

[rbethman]

The 240V is NOT a two phase!

The rest of your comment is correct.

This can also stem from a very poor ground.  Look at the distribution 
system.  In a heavily populated area.  You'll see three pole mounted 
transformers.  EACH is ONE of the three phase distribution.  For that 
matter, a less densely populated area will have a single pole mounted 
transformer every pole.  Look carefully, and you'll see that each one is 
fed from a different phase.

This is to keep the entire Three Phase system fairly balanced.

Each single phase transformer transforms ONE phase down from the 
4160/2400VAC, (Note the sqrt of three figured in.) down to a SINGLE 
phase 240VAC with a center tap of the winding that becomes the neutral.

Yes, when the neutral is broken, things get wild.  This also occurs when 
the ground is broken.  The poles in areas of VERY good soil conductivity 
can run ground by pole butt grounding.  However, places like coral 
islands with changing tides, REQUIRE a continuous ground from pole to pole.

Otherwise, the same effect is seen when the tide changes.

Been there, done that.  Eniwetok Atoll 1977.  The engineers designed the 
system solely on butt grounds.  Bad news!  We spent one day stringing a 
fourth overhead ground over a 40 acre rock of coral.

The issue went away.  The neutrals were ALWAYS connected.

The neutral on a single phase transformer is NOT connected to ground.  
The transformer "can" is grounded.  That way if the insulation and oil 
breakdown, the fused disconnect on the pole blows, NOT a surge to the 
residence.

Bob - N0DGN

On 11/4/2011 7:22 PM, J. Forster wrote:
> When the neutral failed, the sides of the flat two-phase were unbalanced.
>
> Instead of it being 120-0-120; the voltages were divided unequally, such
> as 210-0-30.
>
> The line-to-line stayed the same, but the line-to-neutral went way up on
> one side, way down on the other.
>
> The overvoltage blew stuff.
>
> -John
>
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