[Lowfer] Here's a good one!

[Bill Ashlock]

John,

Thanks for the input on the danger of electrical shock. The friction in the 
movement of the oil certainly explains the cause of the static build-up. 
Probably the magnitude of the charge depends to a large degree on what type 
of oil is filtered. I'll be doing some safety reporting on our setup come 
Monday morning.

Bill A


    I see that Laurence has posted a good article on this subject.  And I 
can
confirm that this is indeed a very common problem!

Occasionally, the 32kV DC supplies in our TV transmitters will blow up a
string of diodes and MOVs in the rectifier stacks, which are in the oil tank
with the 3-phase transformer.  This leaves soot in the oil, which must
sometimes be filtered to maintain its dielectric properties.  We have to
ground everything in the tank to everything else, to an absolute
fare-thee-well, during the filtering operation...and that, in turn, to
whatever ground the pump is connected to.  The friction of the oil flowing
out of the tank, through the pump/filter gear, and back into the tank,
otherwise causes massive buildup of charge on any metal components that are
isolated from each other.

A couple decades ago, one of my (former) co-workers received a serious shock
after merely pouring oil into such a supply on a cold, dry day--a shock
which may have contributed to his fatal heart attack several hours later.  I
would regard this risk as worthy of careful management.

John

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