Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > sci.electronics.design > #610773 > unrolled thread

HVDC line grounding system question

Back to article view | Back to sci.electronics.design

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  HVDC line grounding system question moroney@world.std.spaamtrap.com (Michael Moroney) - 2021-01-04 16:09 +0000
    Re: HVDC line grounding system question Joe Gwinn <joegwinn@comcast.net> - 2021-01-04 14:14 -0500
    Re: HVDC line grounding system question legg <legg@nospam.magma.ca> - 2021-01-04 15:01 -0500
    Re: HVDC line grounding system question upsidedown@downunder.com - 2021-01-05 08:13 +0200
      Re: HVDC line grounding system question Cydrome Leader <presence@MUNGEpanix.com> - 2021-01-05 21:38 +0000
        Re: HVDC line grounding system question legg <legg@nospam.magma.ca> - 2021-01-05 18:15 -0500
    Re: HVDC line grounding system question moroney@world.std.spaamtrap.com (Michael Moroney) - 2021-01-06 06:59 +0000

#610773 — HVDC line grounding system question

I posted this to alt.engineering.electrical and it was suggested I post
this here since this group is more active than alt.engineering.electrical
and with knowledgeable people.

(somewhat edited)

There is a long HVDC power line from northern Quebec Canada to Ayer, 
Massachusetts USA. It operates at either +/- 375 kV or +/- 450 kV
depending on source.  As I understand it, it is grounded at exactly one
point, near Saint-Claude, Quebec. You can see it on this Google
satellite view: https://goo.gl/maps/bnsYcbv9Q3ewmkG49  where the power 
line ROW runs diagonally on the right side, and the actual grounding
point is the weird circular shape at the upper left.  Additionally,
multiple conductors (6) run from the ROW to the circle.  The street
view at https://goo.gl/maps/K94ZceiRfUL2ePaU7 near the grounding poing 
shows the huge towers as well as 4 conductors, two at the top of the 
towers and two others on wooden poles.  They are on rather substantial 
insulators.

I don't think the lines on top of the towers are lightning arrestors. They 
are insulated from the towers while lightning lines aren't. In addition, 
near the south end of this line (near Ayer, Mass.), this line has an 
insulated conductor as well as a pair of (uninsulated) lightning arrestor 
lines.  https://goo.gl/maps/LGNiEYMcC7rrtjMQA

> the other two on the wooden poles seem to
>carry too high a potential to being ground wires. they probably could be
>a MV feed for a nearby town.

They are not a feed for a town.

I followed these lines to the circular ground point using Google Satellite 
View zoomed in.  It showed enough detail to see the towers/poles (and 
their shadows) and the lines themselves. They are two of the 6 conductors 
which go there. Two others are the two conductors on top of the pylons. It 
appears the other two are also the two conductors on top of the pylons but 
from the ones continuing past the point where the lines go to the circle.

See: https://goo.gl/maps/UQTnoFfkAh9hP6zu8, the actual HVDC line goes from
top right to the bottom, and 6 individual lines go to the weird circular
area to the top left.

Does anyone know any details for this rather odd setup? Why multiple 
grounding conductors, and any details of the circular structure? Do the 
grounding conductors sometimes carry current during normal operation, 
perhaps with the line at half power with one side of the HVDC conductors 
out of service and the grounding line carries the return current? Meaning 
it's more like the neutral wire in home electrical wiring, carrying 
current and connected to the actual ground at only one point?

[toc] | [next] | [standalone]

#610784

On Mon, 4 Jan 2021 16:09:12 +0000 (UTC),
moroney@world.std.spaamtrap.com (Michael Moroney) wrote:

>I posted this to alt.engineering.electrical and it was suggested I post
>this here since this group is more active than alt.engineering.electrical
>and with knowledgeable people.
>
>(somewhat edited)
>
>There is a long HVDC power line from northern Quebec Canada to Ayer, 
>Massachusetts USA. It operates at either +/- 375 kV or +/- 450 kV
>depending on source.  As I understand it, it is grounded at exactly one
>point, near Saint-Claude, Quebec. You can see it on this Google
>satellite view: https://goo.gl/maps/bnsYcbv9Q3ewmkG49  where the power 
>line ROW runs diagonally on the right side, and the actual grounding
>point is the weird circular shape at the upper left.  Additionally,
>multiple conductors (6) run from the ROW to the circle.  The street
>view at https://goo.gl/maps/K94ZceiRfUL2ePaU7 near the grounding poing 
>shows the huge towers as well as 4 conductors, two at the top of the 
>towers and two others on wooden poles.  They are on rather substantial 
>insulators.
>
>I don't think the lines on top of the towers are lightning arrestors. They 
>are insulated from the towers while lightning lines aren't. In addition, 
>near the south end of this line (near Ayer, Mass.), this line has an 
>insulated conductor as well as a pair of (uninsulated) lightning arrestor 
>lines.  https://goo.gl/maps/LGNiEYMcC7rrtjMQA
>
>> the other two on the wooden poles seem to
>>carry too high a potential to being ground wires. they probably could be
>>a MV feed for a nearby town.
>
>They are not a feed for a town.
>
>I followed these lines to the circular ground point using Google Satellite 
>View zoomed in.  It showed enough detail to see the towers/poles (and 
>their shadows) and the lines themselves. They are two of the 6 conductors 
>which go there. Two others are the two conductors on top of the pylons. It 
>appears the other two are also the two conductors on top of the pylons but 
>from the ones continuing past the point where the lines go to the circle.
>
>See: https://goo.gl/maps/UQTnoFfkAh9hP6zu8, the actual HVDC line goes from
>top right to the bottom, and 6 individual lines go to the weird circular
>area to the top left.
>
>Does anyone know any details for this rather odd setup? Why multiple 
>grounding conductors, and any details of the circular structure? Do the 
>grounding conductors sometimes carry current during normal operation, 
>perhaps with the line at half power with one side of the HVDC conductors 
>out of service and the grounding line carries the return current? Meaning 
>it's more like the neutral wire in home electrical wiring, carrying 
>current and connected to the actual ground at only one point?

To me, that circular feature looks like a radial array of buried
ground rods, covering sufficient area to be an adequate earth terminal
for such a high power DC power line.  I see four radials, but there
may be more.  The ring may also be a buried ground rod.

Joe Gwinn

[toc] | [prev] | [next] | [standalone]

#610791

On Mon, 4 Jan 2021 16:09:12 +0000 (UTC),
moroney@world.std.spaamtrap.com (Michael Moroney) wrote:

>I posted this to alt.engineering.electrical and it was suggested I post
>this here since this group is more active than alt.engineering.electrical
>and with knowledgeable people.
>
>(somewhat edited)
>
>There is a long HVDC power line from northern Quebec Canada to Ayer, 
>Massachusetts USA. It operates at either +/- 375 kV or +/- 450 kV
>depending on source.  As I understand it, it is grounded at exactly one
>point, near Saint-Claude, Quebec. You can see it on this Google
>satellite view: https://goo.gl/maps/bnsYcbv9Q3ewmkG49  where the power 
>line ROW runs diagonally on the right side, and the actual grounding
>point is the weird circular shape at the upper left.  Additionally,
>multiple conductors (6) run from the ROW to the circle.  The street
>view at https://goo.gl/maps/K94ZceiRfUL2ePaU7 near the grounding poing 
>shows the huge towers as well as 4 conductors, two at the top of the 
>towers and two others on wooden poles.  They are on rather substantial 
>insulators.
>
>I don't think the lines on top of the towers are lightning arrestors. They 
>are insulated from the towers while lightning lines aren't. In addition, 
>near the south end of this line (near Ayer, Mass.), this line has an 
>insulated conductor as well as a pair of (uninsulated) lightning arrestor 
>lines.  https://goo.gl/maps/LGNiEYMcC7rrtjMQA
>
>> the other two on the wooden poles seem to
>>carry too high a potential to being ground wires. they probably could be
>>a MV feed for a nearby town.
>
>They are not a feed for a town.
>
>I followed these lines to the circular ground point using Google Satellite 
>View zoomed in.  It showed enough detail to see the towers/poles (and 
>their shadows) and the lines themselves. They are two of the 6 conductors 
>which go there. Two others are the two conductors on top of the pylons. It 
>appears the other two are also the two conductors on top of the pylons but 
>from the ones continuing past the point where the lines go to the circle.
>
>See: https://goo.gl/maps/UQTnoFfkAh9hP6zu8, the actual HVDC line goes from
>top right to the bottom, and 6 individual lines go to the weird circular
>area to the top left.
>
>Does anyone know any details for this rather odd setup? Why multiple 
>grounding conductors, and any details of the circular structure? Do the 
>grounding conductors sometimes carry current during normal operation, 
>perhaps with the line at half power with one side of the HVDC conductors 
>out of service and the grounding line carries the return current? Meaning 
>it's more like the neutral wire in home electrical wiring, carrying 
>current and connected to the actual ground at only one point?

There are two 'earths'. The main earth electrode for power
transmission is located some KM away from the generating station, or
main receiving terminal, to reduce local corrosion in equipment.
The grounding point is constructed within treated coke packing, which 
has a defined impedance and low decomposition characteristics. 

The station earth is connected to the neutral point of converters at
substations, as part of local overvoltage surge protection.

The 'insulated' wires you see above the transmission line are actually
surge arrested, not insulated, and provide a distributed surge
protection to the system.

RL

[toc] | [prev] | [next] | [standalone]

#610811

On Mon, 4 Jan 2021 16:09:12 +0000 (UTC),
moroney@world.std.spaamtrap.com (Michael Moroney) wrote:

>
>There is a long HVDC power line from northern Quebec Canada to Ayer, 
>Massachusetts USA. It operates at either +/- 375 kV or +/- 450 kV
>depending on source.  As I understand it, it is grounded at exactly one
>point, near Saint-Claude, Quebec. You can see it on this Google
>satellite view: https://goo.gl/maps/bnsYcbv9Q3ewmkG49  where the power 
>line ROW runs diagonally on the right side, and the actual grounding
>point is the weird circular shape at the upper left.  Additionally,
>multiple conductors (6) run from the ROW to the circle.  The street
>view at https://goo.gl/maps/K94ZceiRfUL2ePaU7 near the grounding poing 
>shows the huge towers as well as 4 conductors, two at the top of the 
>towers and two others on wooden poles.  They are on rather substantial 
>insulators.

Old unipolar SCR based under sea HVDC systems have grounding
electrodes at each shore and only one conductor runs from coast to
coast. Those SCR based systems also require a line potential reversal
if energy is to be transferred in the opposite direction.

Newer IGBT based systems are usually bipolar and two conductors are
required. What is the point to ground the midpoint except electric
safety ? In these systems one conductor is always positive and the
other negative, regardless in which direction energy is transferred.

[toc] | [prev] | [next] | [standalone]

#610850

upsidedown@downunder.com wrote:
> On Mon, 4 Jan 2021 16:09:12 +0000 (UTC),
> moroney@world.std.spaamtrap.com (Michael Moroney) wrote:
> 
>>
>>There is a long HVDC power line from northern Quebec Canada to Ayer, 
>>Massachusetts USA. It operates at either +/- 375 kV or +/- 450 kV
>>depending on source.  As I understand it, it is grounded at exactly one
>>point, near Saint-Claude, Quebec. You can see it on this Google
>>satellite view: https://goo.gl/maps/bnsYcbv9Q3ewmkG49  where the power 
>>line ROW runs diagonally on the right side, and the actual grounding
>>point is the weird circular shape at the upper left.  Additionally,
>>multiple conductors (6) run from the ROW to the circle.  The street
>>view at https://goo.gl/maps/K94ZceiRfUL2ePaU7 near the grounding poing 
>>shows the huge towers as well as 4 conductors, two at the top of the 
>>towers and two others on wooden poles.  They are on rather substantial 
>>insulators.
> 
> Old unipolar SCR based under sea HVDC systems have grounding
> electrodes at each shore and only one conductor runs from coast to
> coast. Those SCR based systems also require a line potential reversal
> if energy is to be transferred in the opposite direction.
> 
> Newer IGBT based systems are usually bipolar and two conductors are
> required. What is the point to ground the midpoint except electric
> safety ? In these systems one conductor is always positive and the
> other negative, regardless in which direction energy is transferred.

Any idea what the resistance of the sea and earth are as measured for this 
applications?

What might the ground currents be into the coke pile?

[toc] | [prev] | [next] | [standalone]

#610854

On Tue, 5 Jan 2021 21:38:09 +0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:

>upsidedown@downunder.com wrote:
>> On Mon, 4 Jan 2021 16:09:12 +0000 (UTC),
>> moroney@world.std.spaamtrap.com (Michael Moroney) wrote:
>> 
>>>
>>>There is a long HVDC power line from northern Quebec Canada to Ayer, 
>>>Massachusetts USA. It operates at either +/- 375 kV or +/- 450 kV
>>>depending on source.  As I understand it, it is grounded at exactly one
>>>point, near Saint-Claude, Quebec. You can see it on this Google
>>>satellite view: https://goo.gl/maps/bnsYcbv9Q3ewmkG49  where the power 
>>>line ROW runs diagonally on the right side, and the actual grounding
>>>point is the weird circular shape at the upper left.  Additionally,
>>>multiple conductors (6) run from the ROW to the circle.  The street
>>>view at https://goo.gl/maps/K94ZceiRfUL2ePaU7 near the grounding poing 
>>>shows the huge towers as well as 4 conductors, two at the top of the 
>>>towers and two others on wooden poles.  They are on rather substantial 
>>>insulators.
>> 
>> Old unipolar SCR based under sea HVDC systems have grounding
>> electrodes at each shore and only one conductor runs from coast to
>> coast. Those SCR based systems also require a line potential reversal
>> if energy is to be transferred in the opposite direction.
>> 
>> Newer IGBT based systems are usually bipolar and two conductors are
>> required. What is the point to ground the midpoint except electric
>> safety ? In these systems one conductor is always positive and the
>> other negative, regardless in which direction energy is transferred.
>
>Any idea what the resistance of the sea and earth are as measured for this 
>applications?
>
>What might the ground currents be into the coke pile?

I+ + I- .

Des Cantons / Windsor circuit ~770A under worst 
case single line fault. Normally <70A, when first in service.

https://en.wikipedia.org/wiki/Quebec_%E2%80%93_New_England_Transmission

https://www.cigre.cl/wp-content/uploads/2017/02/Brochure-Cigre-FRancia-HVDC-Electrones-675.pdf

I don't know where the plans to triple this went, but not necessarily 
on the same lines.

RL

[toc] | [prev] | [next] | [standalone]

#610858

A few things I have learned since posting this:

The grounding area is spread out to decrease the "step charge" voltage 
(voltage between two points on the ground) below a certain level. I saw a 
diagram for a circular grounding system (unsure if it was the same one I 
mentioned) and there were multiple cables leading to the grounding circle, 
to different points evenly spaced along the circle, to ensure the current 
is dissipated evenly.  Important when an irresistable force is pushing 
hundreds or even thousands of amperes into the ground.

A big issue is electrolytic corrosion where metal can be eaten away by
the current. Not as much of an issue with grounded monopolar system
(connect the ground to the negative terminal) but is for bipolar system
where the ground can be either the positive or negative terminal when
operating in monopolar mode. Apparently they can be run this way for days
under a fault situation.  Probably the reason for the coke (carbon) 
mentioned.  p.s. look at the car battery terminals of an older car and
notice the positive terminal is more corroded.

The ground should be somewhat away from human activity since currents can
affect underground water pipes, oil pipelines etc.

[toc] | [prev] | [standalone]

Back to top | Article view | sci.electronics.design

csiph-web