Page 4 of 8 FirstFirst ... 23456 ... LastLast
Results 31 to 40 of 71

Thread: Faults with Transformers

  1. #31
    Join Date
    Dec 2012
    Location
    Placerville, CA, USA
    Posts
    19,537
    In regard to fault current reduction, a transformer provides it incidentally, at the expense of energy waste to resistive and core losses which you pay for both when the transformer is loaded and when it is unloaded.
    A series reactor set, OTOH, consumes less power than the equivalent transformer when the load is on and no power at all when the load is off.
    Initial cost is not the only cost factor to consider.
    Quote Originally Posted by mbrooke View Post
    ...
    ...
    In regards to fault reduction, why wouldn't a trafo be used? Is cost what you have in mind?
    Sent from my XT1585 using Tapatalk

  2. #32
    Join Date
    Jan 2016
    Location
    Earth
    Posts
    6,049
    Quote Originally Posted by mbrooke View Post
    I have yet to see a Y-Y 600 volt and under transformer. Sure you could custom make one (MGM does it https://www.mgmtransformer.com/ ), but an off the shelf delta wye will do. Saves on N wire as well. So even if fault current was purely a concern and the supply was wye, the trafo would still be delta wye.
    that is because they don't use them
    kind of defeats the purpose

    the reason they use delta in plant/industrial settings are 2 fold
    serves only 3 ph loads
    can operate on a gf
    not to save a wire

    a wye-wye can be unstable under certain conditions
    most have a sec tertiary delta winding

  3. #33
    Join Date
    Jan 2016
    Location
    Earth
    Posts
    6,049
    Quote Originally Posted by GoldDigger View Post
    In regard to fault current reduction, a transformer provides it incidentally, at the expense of energy waste to resistive and core losses which you pay for both when the transformer is loaded and when it is unloaded.
    A series reactor set, OTOH, consumes less power than the equivalent transformer when the load is on and no power at all when the load is off.
    Initial cost is not the only cost factor to consider.

    Sent from my XT1585 using Tapatalk

  4. #34
    Join Date
    Jan 2011
    Location
    United States
    Posts
    7,855
    Quote Originally Posted by Ingenieur View Post
    those reactors are shunt, not series
    different function

    Nope, series in the example I'm thinking of. To limit fault current down to 10k amps when all the trafos are paralleled together. I know that for a fact.
    Last edited by mbrooke; 07-13-18 at 03:50 AM.
    I'm in over my head...

  5. #35
    Join Date
    Jan 2011
    Location
    United States
    Posts
    7,855
    Quote Originally Posted by GoldDigger View Post
    In regard to fault current reduction, a transformer provides it incidentally, at the expense of energy waste to resistive and core losses which you pay for both when the transformer is loaded and when it is unloaded.
    A series reactor set, OTOH, consumes less power than the equivalent transformer when the load is on and no power at all when the load is off.
    Initial cost is not the only cost factor to consider.

    Sent from my XT1585 using Tapatalk
    I know
    I'm in over my head...

  6. #36
    Join Date
    Jan 2011
    Location
    United States
    Posts
    7,855
    Quote Originally Posted by Ingenieur View Post
    that is because they don't use them
    kind of defeats the purpose
    You just said:


    http://forums.mikeholt.com/showthrea...65#post1928465

    not fault limitation
    if it already were y they would insert a y:y iso xfmr to reduce i fault

    If the supply was wye, the trafo wouldn't automatically be a wye primary. Almost all 600 volt dry types are delta wye or delta delta. All off the the shelf 480:480/277Y isolation are delta wye. No engineer, if seeking isolation, is going to order a none standard unit just because the 480 volt service is solidly grounded. You keep implying that if the trafo was for isolation, it would have been Y:Y and not delta wye. Not the case, nothing about isolation stops a delta wye.



    the reason they use delta in plant/industrial settings are 2 fold
    serves only 3 ph loads
    can operate on a gf
    I'm not talking about ungrounded systems. I'm talking about a delta primary and wye secondary trafo.

    not to save a wire

    What I was referring to was this:

    Delta wye isolation would require 3 wires + ground primary feed.

    Wye wye isolation would require 4 wires + ground primary feed.

    So you do save a wire by having a delta primary isolation transformer.


    a wye-wye can be unstable under certain conditions
    most have a sec tertiary delta winding
    Very true, thank you, which is why that isolation was delta wye and not wye wye.
    I'm in over my head...

  7. #37
    Join Date
    Jan 2016
    Location
    Earth
    Posts
    6,049
    Quote Originally Posted by mbrooke View Post
    Nope, series in the example I'm thinking of. To limit fault current down to 10k amps when all the trafos are paralleled together. I know that for a fact.
    that is rare
    usually shunt for compensation and voltage regulation

  8. #38
    Join Date
    Jan 2016
    Location
    Earth
    Posts
    6,049
    Quote Originally Posted by mbrooke View Post
    You just said:


    http://forums.mikeholt.com/showthrea...65#post1928465

    If the supply was wye, the trafo wouldn't automatically be a wye primary. Almost all 600 volt dry types are delta wye or delta delta. All off the the shelf 480:480/277Y isolation are delta wye. No engineer, if seeking isolation, is going to order a none standard unit just because the 480 volt service is solidly grounded. You keep implying that if the trafo was for isolation, it would have been Y:Y and not delta wye. Not the case, nothing about isolation stops a delta wye.

    I'm not talking about ungrounded systems. I'm talking about a delta primary and wye secondary trafo.

    What I was referring to was this:

    Delta wye isolation would require 3 wires + ground primary feed.

    Wye wye isolation would require 4 wires + ground primary feed.

    So you do save a wire by having a delta primary isolation transformer.

    Very true, thank you, which is why that isolation was delta wye and not wye wye.
    it was an absurd example to show the absudity of stating that the use of a delta-wye 480:480 is for fault reduction or for sl fault clearing...ridiculous lol
    it is to derive a neut for 1 ph loads

    saving 'the wire' or what we call the neut is not why they use delta in a plant
    it's operational continuity
    btw, delta is ungrounded in inductrial settings ( may be corner grounded but you need 'the wire')
    Last edited by Ingenieur; 07-13-18 at 06:22 PM.

  9. #39
    Join Date
    Jan 2011
    Location
    United States
    Posts
    7,855
    Quote Originally Posted by Ingenieur View Post
    that is rare
    usually shunt for compensation and voltage regulation
    Depends on the POCO. Generally it is avoided, not found in some territories, but for some a countable amount of substations have feeder reactors.


    But you are right, shunt reactors are also encountered and needed, often for underground cables to cancel out excessive capacitive current.




    Quote Originally Posted by Ingenieur View Post
    it was an absurd example to show the absudity of stating that the use of a delta-wye 480:480 is for fault reduction or for sl fault clearing...ridiculous lol
    it is to derive a neut for 1 ph loads
    Most of the time thats what it was used for. However, again, if I wanted to reduce fault current nothing stops me from going to 480:480/277.



    saving 'the wire' or what we call the neut is not why they use delta in a plant
    it's operational continuity
    btw, delta is ungrounded in inductrial settings ( may be corner grounded but you need 'the wire')
    Again, not what I had in mind. I was thinking only of the feed to a D-Y vs Y-Y and nothing else.

    But since we are on the subject, yes ungrounded delta is for service continuity provided you are only taking bolted ground faults into account. I say solid, because an arcing or intermittent fault will cause many more problems then if you just solidly grounded the system. Which is why high resistance grounding is used today where service continuity is required (outside of isolated power systems in health care of course).
    I'm in over my head...

  10. #40
    Join Date
    Jan 2016
    Location
    Earth
    Posts
    6,049
    Quote Originally Posted by mbrooke View Post
    Most of the time thats what it was used for. However, again, if I wanted to reduce fault current nothing stops me from going to 480:480/277.
    Again, not what I had in mind. I was thinking only of the feed to a D-Y vs Y-Y and nothing else.

    But since we are on the subject, yes ungrounded delta is for service continuity provided you are only taking bolted ground faults into account. I say solid, because an arcing or intermittent fault will cause many more problems then if you just solidly grounded the system. Which is why high resistance grounding is used today where service continuity is required (outside of isolated power systems in health care of course).
    good enginerring?
    it's poor design

    nrg is used for several reason
    it lowers frame potential
    clears ground faults

    but ungrounded delta with gf protection is just as common
    maybe more so

    the only industry that uses ngr as a standard is mining
    and by law, not by choice
    it can cause issues and you must ground to sqrt3 x ph-ph v

    arcing faults severity is not a function of delta or wye

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •