Welcome
Username or Email:

Password:


Missing Code




[ ]
[ ]
Online
  • Guests: 38
  • Members: 0
  • Newest Member: omjtest
  • Most ever online: 396
    Guests: 396, Members: 0 on 12 Jan : 12:51
Members Birthdays:
One birthday today, congrats!
GrantX (34)


Next birthdays
03/30 Adam Horden (39)
03/30 Mr.Warwickshire (23)
03/31 Swedish Coiler (41)
Contact
If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.


Special Thanks To:
  • Aaron Holmes
  • Aaron Wheeler
  • Adam Horden
  • Alan Scrimgeour
  • Andre
  • Andrew Haynes
  • Anonymous000
  • asabase
  • Austin Weil
  • barney
  • Barry
  • Bert Hickman
  • Bill Kukowski
  • Blitzorn
  • Brandon Paradelas
  • Bruce Bowling
  • BubeeMike
  • Byong Park
  • Cesiumsponge
  • Chris F.
  • Chris Hooper
  • Corey Worthington
  • Derek Woodroffe
  • Dalus
  • Dan Strother
  • Daniel Davis
  • Daniel Uhrenholt
  • datasheetarchive
  • Dave Billington
  • Dave Marshall
  • David F.
  • Dennis Rogers
  • drelectrix
  • Dr. John Gudenas
  • Dr. Spark
  • E.TexasTesla
  • eastvoltresearch
  • Eirik Taylor
  • Erik Dyakov
  • Erlend^SE
  • Finn Hammer
  • Firebug24k
  • GalliumMan
  • Gary Peterson
  • George Slade
  • GhostNull
  • Gordon Mcknight
  • Graham Armitage
  • Grant
  • GreySoul
  • Henry H
  • IamSmooth
  • In memory of Leo Powning
  • Jacob Cash
  • James Howells
  • James Pawson
  • Jeff Greenfield
  • Jeff Thomas
  • Jesse Frost
  • Jim Mitchell
  • jlr134
  • Joe Mastroianni
  • John Forcina
  • John Oberg
  • John Willcutt
  • Jon Newcomb
  • klugesmith
  • Leslie Wright
  • Lutz Hoffman
  • Mads Barnkob
  • Martin King
  • Mats Karlsson
  • Matt Gibson
  • Matthew Guidry
  • mbd
  • Michael D'Angelo
  • Mikkel
  • mileswaldron
  • mister_rf
  • Neil Foster
  • Nick de Smith
  • Nick Soroka
  • nicklenorp
  • Nik
  • Norman Stanley
  • Patrick Coleman
  • Paul Brodie
  • Paul Jordan
  • Paul Montgomery
  • Ped
  • Peter Krogen
  • Peter Terren
  • PhilGood
  • Richard Feldman
  • Robert Bush
  • Royce Bailey
  • Scott Fusare
  • Scott Newman
  • smiffy
  • Stella
  • Steven Busic
  • Steve Conner
  • Steve Jones
  • Steve Ward
  • Sulaiman
  • Thomas Coyle
  • Thomas A. Wallace
  • Thomas W
  • Timo
  • Torch
  • Ulf Jonsson
  • vasil
  • Vaxian
  • vladi mazzilli
  • wastehl
  • Weston
  • William Kim
  • William N.
  • William Stehl
  • Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Forums
4hv.org :: Forums :: High Voltage
« Previous topic | Next topic »   

11kV termination earthing through core balance CT

1 2 
Move Thread LAN_403
beniroli
Thu Apr 06 2017, 08:29AM Print
beniroli Registered Member #61276 Joined: Mon Nov 07 2016, 08:44AM
Location:
Posts: 6
Hi All, first post and fairly new to the HV department in my company.....on a recent 11kV installation, an experienced HV jointer terminated the 3 single AWA cables. I am concerned that he insisted on running separate earth conductors up through the core balance CT and back down through it, even though the armour is made off on an insulated plate, and the copper screen is also made off below the CT.

I will try to attach a simple diagram pdf of how each core is connected, missing out the final heat shrink layer for clarity.

my concern is that a) it is conducive to partial discharge, earth conductors being irregularities around unscreened cable and no copper screen on cable going through CT, and b) the earth conductors didn't need to go through the CT at all. my understanding is that returning the earth back through the CT is only necessary if the cable screen goes through, i.e. to generate the earth fault current imbalance into the CT.

any thoughts, opinions, advice welcome.

Thank you.
]hvearth.pdf[/file]
1491467335 61276 FT0 Hvearth2
Back to top
Dr. Slack
Thu Apr 06 2017, 11:52AM
Dr. Slack Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Those loops of earth conductor only happen to be in the CT physically. Electrically, as they go up and then down again, they are not in any way electromagnetically coupled to the CT.

The insulation on those conductors is deemed to be sufficient to insulate them. The sharp edges on the CT core would probably look like sharper irregularities then the nice rounded earth conductors, so if the conductors can cope with the core, I'm sure they can cope with the earth conductors.

I think those loops of earth conductor are pushed through the CT for somewhere convenient to put them, as the guy has left them so long they'd get untidy if draped around somewhere else. Which suggests that the installation hygiene is not fully thought through.
Back to top
beniroli
Thu Apr 06 2017, 12:20PM
beniroli Registered Member #61276 Joined: Mon Nov 07 2016, 08:44AM
Location:
Posts: 6
Posted: Thu Apr 06 2017, 12:52PM

Firstly thanks for the response, i'll try to answer each bit separately.

"Those loops of earth conductor only happen to be in the CT physically. Electrically, as they go up and then down again, they are not in any way electromagnetically coupled to the CT"

- why do you say they aren't elecomagnetically coupled? because they cancel themselves out?

"The insulation on those conductors is deemed to be sufficient to insulate them. The sharp edges on the CT core would probably look like sharper irregularities then the nice rounded earth conductors, so if the conductors can cope with the core, I'm sure they can cope with the earth conductors."

- I agree about the sharp edges of the CT core, but the screen which is on the cable is deliberate and uniform for this reason I believe. so crossing the unscreened 11kV conductor with earth potential (either CT core OR earth cable) seems unwise.

"I think those loops of earth conductor are pushed through the CT for somewhere convenient to put them, as the guy has left them so long they'd get untidy if draped around somewhere else. Which suggests that the installation hygiene is not fully thought through"

- I know for a fact that these earth conductors were installed in this way on purpose with the thinking that the earth HAD to run up and back through the CBCT for it to work. THIS is what I think is a misunderstanding of how the earth fault detection works.
Back to top
Dr. Slack
Thu Apr 06 2017, 03:41PM
Dr. Slack Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
The red/blue/yellow conductors are looped once each through the CT core, they couple one turn each.

The green/yellow striped earth conductors *appear* (correct me if I'm wrong) to go up through the hole (+1 turn) then back down through the same hole again (-1 turn) for a grand total of zero turns each through the CT. Therefore there is no magnetic, that is transformer, coupling. It looks like if you pulled down on a loop of earth conductor, the loop could be pulled out of the CT. That is, the conductor does not loop the core. As far as the CT is concerned, those earth conductors do not exist.
Back to top
beniroli
Thu Apr 06 2017, 03:49PM
beniroli Registered Member #61276 Joined: Mon Nov 07 2016, 08:44AM
Location:
Posts: 6
Exactly right. so the earth conductors (green/yellow) can, and should have, been routed straight to the earth bar, NOT through the CT.

as I understand, the only reason to return the earth conductor back through the CT is if the screen is still on the cable as it runs through the CT. i.e. it has to return through to "generate" earth fault current in the event of one.
Back to top
Dr. Slack
Thu Apr 06 2017, 06:36PM
Dr. Slack Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
They were not 'routed' through the CT, the loops were pushed into the space pf the CT.

The CT detects imbalance between the 3 phases, measures the neutral current if you will. Fault current phase to ground may, or may not, generate a neutral current, depending whether the neutral is floating or connected to ground. Current in those earth tails will be irrelevant to any fault currents that flow from the pashes to ground.
Back to top
Uspring
Fri Apr 07 2017, 11:00AM
Uspring Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
Location:
Posts: 711
Dr. Slack wrote:
Those loops of earth conductor only happen to be in the CT physically. Electrically, as they go up and then down again, they are not in any way electromagnetically coupled to the CT.
I'm wondering about this. First think of loop of wire which encloses the toroid. Obviously this loop is coupled to the CT, since toroidal transformers are made this way. Say you put an AC current through the CT than this implies, that there would be (rotational) electric fields where the loop wire is.
Now think of a loop not enclosing the toroid. Wouldn't that also see the electric field, i.e. be coupled? The field path integrals might cancel, but why?

Put in other words: An AC driven toroidal winding would create an electric field outside the winding but no magnetic one. That could be caught by a loop outside the winding. Maybe you are right, but you got me puzzling.
Back to top
Dr. Slack
Fri Apr 07 2017, 04:28PM
Dr. Slack Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
There's electrostatic coupling, but that's not what we call transformer coupling. Perhaps I should have specified 'magnetically' rather than 'electromagnetically' at first.

I'm not sure what you mean by a loop 'enclosing' the toroid. Transformer coupling only occur when a conductor 'links' the core, topologically. That's why I said get hold of the earth loop, and try to pull it down. It turns out that being magnetically linked with the core is the same as passing through the core once in such a fashion that it's not possible to pull the loop of conductor out of the core.

A convenient way to see whether a conductor is linked magnetically to the core is to see whether the conductor encloses (that word again) the flux that's in the core.
Back to top
klugesmith
Fri Apr 07 2017, 06:20PM
klugesmith Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714
>> A convenient way to see whether a conductor is linked magnetically to the core is to see
whether the conductor encloses the flux that's in the core.


Sometimes a conductor is locally rather straight, and/or the current return path is not obvious.
Then it may be conceptually simpler to see
whether the core (closed flux path) encloses the current that's in the conductor.


1491588950 2099 FT179454 Linked Rings
from Link2
Back to top
radiotech
Sat Apr 08 2017, 07:35AM
radiotech Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
From what I see the CT is for a ground fault device. The routing of the ground leads is to prevent a sharp bend
at the bottom.

Not seen, but of interest, is how the single cables enter the (presumed) steel enclosure .

Are the individual cables secured with a non ferrous connector? Cables of ampacity in the hundreds
will heat iron ring surrounds to an extent to , melt or compromise the cable insulation.

I am not an inspector, but have installed cables to boxes, low and high voltage. An inspector
might grumble the box is too small to cramp the CT like that




Back to top
1 2 

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob

Go to:

Powered by e107 Forum System
 
Legal Information
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.