Don Borowski/SEL
12/11/2007 08:29 To
AM "Brian O'Connell"
<[email protected]>
cc
Subject
Re: stray voltage ???(Document
link: Don Borowski)
I too was under the same impression about using the pole transformer to
isolate the high voltage distribution system from the low voltage side (240
VAC center tapped, yielding 120-0-120 / 240 VAC, in the US).
However, in standard practice, this is NOT the case. Take the simple case
of several farms or residences being fed from one high-voltage phase, each
with its own transformer. In this case, there are two wires on the high
voltage side. One wire is grounded (periodically, by a grounding wire
running down the pole to a ground rod) and one wire is "hot" at the
distribution voltage. When a transformer is installed to create a service
drop, the center tap (neutral) of the transformer secondary is tied to the
ground wire on the high voltage primary side (and also tied to a ground
rod).
The "stray" voltage problem is inherent in the system, as the current
running on the high voltage side can cause substantial voltage drops along
the length of the ground wire. This then shows up as voltages along the
ground. The voltage gradient can be especially high near ground rods. If I
am not mistaken, barns often have their own breaker panel and local ground
rod, thus setting up a high voltage gradient in the immediate vicinity of
the animals.
I have heard of this problem, and it makes me wonder if it is time to
re-think the system of tying together on the primary and secondary side,
especially for farms. There may be safety concerns, but they could be
addressed using modern electronics.
Don Borowski
Schweitzer Engineering Labs
Pullman, WA, USA
"Brian O'Connell"
<oconnellb@tamura
corp.com> To
Sent by: <[email protected]>
[email protected] cc
Subject
12/11/2007 07:59 stray voltage ???
AM
Good People,
The Wisconsin Supreme Court thinks that 'stray' voltage from the power
grid is causing livestock problems. Note these links to this issue.
http://www.thonline.com/store/view.cfm?id=JiZNUz7AxXXkdICgz3Dz3D
http://www.strayvoltage.org/stories/index.php3?Story=20010812_researchers.
inc
My (probably stupid) questions:
1. As most ground-loop current problems are caused when neutral is
grounded at multiple points, why is the power utility blamed for an
end-user wiring error ?
2. The result of 'stray' voltage would seem to be excessive ground-wire
current. Why is a protection device not interrupting this fault current ?
3. The multiple instances of power distribution transformers should
isolate, and therefore interrupt current leakage paths, because the
customer's (secondary-side) neutral is grounded at a single point for each
customer. So the only excessive (continuous) fault current should result
>from the customer stringing extra grounds to the distribution
transformer's case. So what is the leakage path and why is a sufficient
potential developed that can cause this continuous fault current ?
luck,
Brian
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