DC-GFP/2 protection [RE-wrenches]

[Rob Wills]

Todd - an ungrounded system with no high voltage bleed can charge up with
static electricity and perhaps start insulation breakdown.  I was in
Antarctica in the 70s and during a blizzard, we could draw 3" sparks from a
piece of wire (antenna) out in the (100+mph) wind.

We have proposed resistive bleed plus TVS type surge protection to UL as
meeting the requirements of 690-41, but they have not come back with a
response at this point.

Rob Wills
VP Engineering
Advanced Energy

-----Original Message-----
From: Todd Cory, Mt. Shasta Energy Services
[mailto:toddcory at finestplanet.com]
Sent: Friday, August 23, 2002 6:38 PM
To: RE-wrenches at topica.com
Subject: Re: DC-GFP/2 protection [RE-wrenches]


Bill Brooks wrote:

> Another one of the issues with an ungrounded system is that it still must
> have a method to reference it to ground potential. You can't have a module
> operating at 5000 Volts sitting next to a module frame at ground
potential.
> It will flashover and cause a big mess as well as potentially energize the
> array frames if the ground gets loose. Somehow you must limit the
> differential from an electrical insulation point of view.

Bill, I am not sure I understand the statement above. Why do ungrounded
systems
need to be referenced to ground? If it is ungrounded the 5 kV you mention
above
will be with respect to *ONLY* the other conductor. It will NOT "flash over"
to
any other thing just because it is metal or grounded. That is the beauty not
having any conductors grounded. The potential only is between the 2
conductors.

With an ungrounded system, the only way you could get a shock is if you
touch
both conductors at the same time, or if (like is foolishly done in this
country)
one conductor is grounded. Then when you are standing on the earth you are
in
contact with one conductor. This seems much less safe than a system that is
totally floated and thusly insulated from people (who usually stand on the
earth).

I have heard our wonderfully "safe" grounded conductor system was
implemented to
sell more wire and the labor to install it... and has nothing to do with
"safety".

Todd

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