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American Power Distribution Practice - Is a multi-grounded primary more desirable than a single-grou

B

Beachcomber

Jan 1, 1970
0
First off, let me say that I am no expert in this subject, but I would
like to hear the latest current thinking of the professional
electrical community as to what the current thinking is on this and
if any 20007 NEC code changes can be expected as a result.

Detailed background information on each case is available at the
following links:

Argument in favor of multi-point primary neutral grounding:

http://www.neiengineering.com/pdfs/paper10JN.pdf

Argument in favor of single-point primary neutral grounding:

http://www.mikeholt.com/documents/strayvoltage/pdf/MultiGroundedNeutralFinal5-3-03.pdf

As far as I can determine, the current multi-point primary grounding
system in the US...

1. is favored by most utilities
2. has less expensive capital costs (fewer conductors - insulators -
uses single bushing transformers vs. double bushing, etc.)
3. Perceived as safer to lineman (assured neutral grounding at
multiple points)
4. Easier on transformers (less intense surges and easier to connect
lightning arrestors to).
5. Works better for isolated distant distribution transformers (as
typically found on US farms)

On the downside...the multi-point neutral primary grounding system...

1. Can produce undesirable stray voltages (more properly - stray
currents) under the right set of circumstances. Stray currents may be
harmful to livestock and humans.

2. Can cause shocks in swimming pools and electric showers.

What is the current thinking on this subject? I understand that
Europe bans the multi-point neutral grounded systems, but Europe has
fewer isolated transformers serving distant farmhouses.

Beachcomber



2. Can lead to shocks in swiming pools and electric showers
 
S

SQLit

Jan 1, 1970
0
Beachcomber said:
First off, let me say that I am no expert in this subject, but I would
like to hear the latest current thinking of the professional
electrical community as to what the current thinking is on this and
if any 20007 NEC code changes can be expected as a result.

Detailed background information on each case is available at the
following links:

Argument in favor of multi-point primary neutral grounding:

http://www.neiengineering.com/pdfs/paper10JN.pdf

Argument in favor of single-point primary neutral grounding:

http://www.mikeholt.com/documents/strayvoltage/pdf/MultiGroundedNeutralFinal5-3-03.pdf

As far as I can determine, the current multi-point primary grounding
system in the US...

1. is favored by most utilities
2. has less expensive capital costs (fewer conductors - insulators -
uses single bushing transformers vs. double bushing, etc.)
3. Perceived as safer to lineman (assured neutral grounding at
multiple points)

I have not worked on distribution in a few years. I do not remember ANY
medium voltage system ( less than 69kv) that has a neutral. 3 hots and a
ground but not a neutral.
 
C

Charles Perry

Jan 1, 1970
0
SQLit said:
I have not worked on distribution in a few years. I do not remember ANY
medium voltage system ( less than 69kv) that has a neutral. 3 hots and a
ground but not a neutral.

??
The system you see hanging on most three phase poles in the US had three
phase conductors and a neutral (grounded conductor). Each piece of medium
voltage equipment, along with many poles (often every third one) in areas
without a lot of medium voltage equipment, will have a ground (grounding
conductor).

As for Mike Holts support of a 5 wire system, he has gone overboard with his
stray voltage tirades. He often equates stray voltage (very low voltages
that are annoying but do not kill) with unintended energized metal objects
(which can and do kill). One has NOTHING to do with the other. An
unintended energized metal object is energized by a power source (such as a
street light circuit) and has the capability of killing someone who comes in
contact, such as the woman walking her dog in New York City recently. Stray
voltage, on the other hand, is usually on the order of a few volts and can
cause an unsettling shock, but not a damaging one.

I have a lot of respect for Mike's knowledge of the code and the reasons for
things in the code, but on this issue he has missed the boat completely.

Charles Perry P.E.
 
C

Charles Perry

Jan 1, 1970
0
Beachcomber said:
First off, let me say that I am no expert in this subject, but I would
like to hear the latest current thinking of the professional
electrical community as to what the current thinking is on this and
if any 20007 NEC code changes can be expected as a result.

The NEC does not govern medium voltage distribution construction of electric
utilities. So any change would be irrelevent.

Charles Perry P.E.
 
C

Charles Perry

Jan 1, 1970
0
Bill Shymanski said:
Well, there's more and more stuff in the NEC every code cycle - who
knows what will be
included by 20007?

Bill

Still wouldn't matter. The NEC could include any requirement they wanted
and it wouldn't matter. Electric Utilities are held to the NESC, not the
NEC. Two completely different codes.

Charles Perry P.E.
 
B

Beachcomber

Jan 1, 1970
0
Still wouldn't matter. The NEC could include any requirement they wanted
and it wouldn't matter. Electric Utilities are held to the NESC, not the
NEC. Two completely different codes.

Charles Perry P.E.
One of the reasons I posted these two articles is that, in my
research, I found it fascinating that there could be so much strong
emotions amongst professional engineers in the arguements for and
against ungrounded vs. grounded distribution systems.

Apparently, in the US at least, the split also goes along with the two
regulatory bodies NEC and NESC, that you describe and more roughly,
splits the interests of utilities vs. the safety and well-being of
homeowners and farmers.

My concern is with the reinforcement and codification of bad policy.
For example, as one of the papers pointed out, NEC standards for RV
vehicles were apparently just plain wrong in the 1950's when the
neutral was allowed to served as ground and people were electrocuted
just by touching the metal frame of their RV and standing on damp
ground.

Apparently there were similar problems extended to marinas, which have
their own unique problems with grounding issues. It took years of
study before the regulations "made it right" with a safer insulation
and a fully grounded system. In the meantime, how many unnecessary
electrocution deaths occured to swimmers in all those early years when
inferior and lax regulations were in place?

Beachcomber
 
C

Charles Perry

Jan 1, 1970
0
Beachcomber said:
One of the reasons I posted these two articles is that, in my
research, I found it fascinating that there could be so much strong
emotions amongst professional engineers in the arguements for and
against ungrounded vs. grounded distribution systems.

Apparently, in the US at least, the split also goes along with the two
regulatory bodies NEC and NESC, that you describe and more roughly,
splits the interests of utilities vs. the safety and well-being of
homeowners and farmers.

My concern is with the reinforcement and codification of bad policy.
For example, as one of the papers pointed out, NEC standards for RV
vehicles were apparently just plain wrong in the 1950's when the
neutral was allowed to served as ground and people were electrocuted
just by touching the metal frame of their RV and standing on damp
ground.

Apparently there were similar problems extended to marinas, which have
their own unique problems with grounding issues. It took years of
study before the regulations "made it right" with a safer insulation
and a fully grounded system. In the meantime, how many unnecessary
electrocution deaths occured to swimmers in all those early years when
inferior and lax regulations were in place?

Beachcomber

The problem with your arguement is that the current system, as applied to
medium voltage distribution lines in the US, is NOT killing people. Some
stray voltage problems exist, but they are usually localized problems.
These stray voltages are not killing people. They do scare people but they
don't kill them.

In many of the stray voltage cases we have studied, the high levels of 3rd
harmonic current in the neutral have been a major contributor. These
currents are created by electronic loads and since they are triplens, they
add, rather than cancel, in the neutral. I propose that the US adopt a
European style regulation for all, and I mean ALL, electronic equipment
requiring power factor corrected power supplies. Fewer harmonics, better
power factor, everyone wins.

Charles Perry P.E.
 
B

Beachcomber

Jan 1, 1970
0
The problem with your arguement is that the current system, as applied to
medium voltage distribution lines in the US, is NOT killing people. Some
stray voltage problems exist, but they are usually localized problems.
These stray voltages are not killing people. They do scare people but they
don't kill them.

In many of the stray voltage cases we have studied, the high levels of 3rd
harmonic current in the neutral have been a major contributor. These
currents are created by electronic loads and since they are triplens, they
add, rather than cancel, in the neutral. I propose that the US adopt a
European style regulation for all, and I mean ALL, electronic equipment
requiring power factor corrected power supplies. Fewer harmonics, better
power factor, everyone wins.

Charles Perry P.E.
Thanks for the reply. Just to clarify, I'm not advocating either
point of view. I'm just interested in hearing from the experts in the
industry, like yourself, as to what the current state of this debate
is.

I will say this though, yes the stray voltages, where they exist, are
not killing people, but apparently there are serious consequences to
dairy farms, in particular, with the cows becoming sick, not producing
milk, etc. I'm not sure that all of these problems are solved, but it
does seem to be a good thing that utilities now pay attention to the
problem when it comes up, instead of issuing a summary dismissal as a
"customer wiring problem".

I don't think there is any best solution or design to an electrical
system. I think the systems evolved with the culture and the unique
characteristics of the region.

Here in the US, the formulative agency seemed to be the REA (Rural
Electrification Administration) that decided during the depths of the
depression that the new distribution system would be a grounded
system, single-phase to most residential users, and a 240/120 split
phase Edison 3-wire connection at the service entrance.

I'm sure they did this with the cost savings in mind (it does seem to
be the most economical system in terms of using the least amount of
copper wire). But that is logical as it was the depression, after
all.

I like to think that the appointed reps who issue changes to the
electrical codes should be open to new ideas and not just say "well
that's the way we've been doing it for fifty years... why do we need
to change it"?

Beachcomber
 
C

Charles Perry

Jan 1, 1970
0
I do not say this to be quarrelsome but I am troubled by your assertion
that the stray current problem is only a nuisance. Stray currents are
causing losses in the dairy industry and many dairy farmers are unaware
that their production is affected.
I will agree that the stray voltage is more a problem for dairy farmers. We
have done several projects for dairy farms, utilities in dairy areas, and
even state commissions.

We did have to clean up several ground faults caused by the older method
of connecting separate structures.

This is the telling part. I most, but not all, cases poor wiring is the
culpret. The worst part is that your farm might be wired perfect but if
your neighbor has bad wiring, you might experience stray voltage problems.
These problems can be very hard, and expensive, to track down. I would say
"you would be surprised at some of the wiring we see" but since you have
seen it, you wouldn't be. Perhaps disgusted would be a more accurate term.
I am always amazed at what passes as acceptable wiring at some facilities.

I can't see the entire electrical industry rebuilding all of the
distribution lines for the dairy farmers. Those problems are best addressed
individually.

Charles Perry P.E.
 
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