Wye to wye questions

[tortuga]

The forum wont let me upload a file larger than a 146KB.
I put it here: http://www.think-electric.com/continuingEd/wye-wye2.pdf

 

[hhsting]

The the ground lug in the HV compartment. I am beginning to think that this WOULD BE an SDS, if you call that concentric conductor an EGC and not a neutral. When the definition of SDS and wye wye come together, things get kinda screwy and into semantics. So I am leaning towards: HV switchboard N-G bond, 3 phases plus EGC (concentrics used as EGC per 250.190(C)(2)) to transformer, then make N-G bond for SDS in transformer, then to LV switchboard probably with separate N-G depending on your reading of that exception in 250.30(A).

Ground lug in HV compartment maybe be tank ground since another additional groung lug is in LV compartment. Also the LV compartment has additional neutral ground pad with ground strap. Do you still place concentric neutral ground lug HV compartment?

 

[electrofelon]

I am beginning to think that this WOULD BE an SDS, if you call that concentric conductor an EGC and not a neutral.

I am going to rescind that statement. I was thinking "like conductor to like conductor" but that is not a requirement for an SDS. The LV neutral is connected to the HV phase conductors through the factory XO/HO connection and the HV windings.:dunce:

 

[electrofelon]

The forum wont let me upload a file larger than a 146KB.
I put it here: http://www.think-electric.com/continuingEd/wye-wye2.pdf

Thanks for the drawings. I believe A and B to both be acceptable. There are a few things I like about B better. One is that the path back to the source for a 600V fault is shorter and less convoluted. Also the 600V neutral to ground potential should be a bit lower during normal operation.

 

[hhsting]

The forum wont let me upload a file larger than a 146KB.
I put it here: http://www.think-electric.com/continuingEd/wye-wye2.pdf

What in the world? Can you please re draw? Please see post # 116 xfmr second page and please show the terminals HV compartment H1, H2, H3, ground pad and on LV side X1, X2, X3, H0/X0, ground neutral strap and ground pad and how concentric neutral lands. More realistic wiring and how are ground pads connected HV and LV etc

 

[electrofelon]

What in the world? Can you please re draw? Their is only one huge pad not two different. Second please see post # 116 xfmr second page and please show the terminals HV compartment H1, H2, H3, ground pad and on LV side X1, X2, X3, H0/X0, ground neutral strap and ground pad and how concentric neutral lands. More realistic wiring and how are ground pads connected HV and LV etc

WHAT???? Why dont YOU post the complete drawing as has been asked multiple times. THAT is the only thing that matters here. We are not here to design your system. :rant:

 

[hhsting]

WHAT???? Why dont YOU post the complete drawing as has been asked multiple times. THAT is the only thing that matters here. We are not here to design your system. :rant:

Once I get revised drawings from the engineer/designer I will. I dont want post and repost. I apologize to you and tortgua. What I meant was the attachments does not depict real situation it has two gnd pads, what you stated in post #123, terminals etc etc but I guess the drawing would not be specific either.

 

[hhsting]

I am going to rescind that statement. I was thinking "like conductor to like conductor" but that is not a requirement for an SDS. The LV neutral is connected to the HV phase conductors through the factory XO/HO connection and the HV windings.:dunce:

And you still think concentric neutral HV is connected to ground pad HV compartment? If not then where?

 

[hhsting]

Thanks for the drawings. I believe A and B to both be acceptable. There are a few things I like about B better. One is that the path back to the source for a 600V fault is shorter and less convoluted. Also the 600V neutral to ground potential should be a bit lower during normal operation.

Option A three questions:

1. can you bring concentric neutrals from HV compartment to LV compartment?

2. Can you tie neutral directly together like that?

3. Dont you have to ground the neutral? Would their be more harmonics?

Option B question:

1. If its not SDS then how come their system bonding jumper i.e. neutrl to ground bond secondary 600V xfmr?

 

[tortuga]

Option A three questions:

1. can you bring concentric neutrals from HV compartment to LV compartment?

2. Can you tie neutral directly together like that?

3. Dont you have to ground the neutral? Would their be more harmonics?

1. Yes
2. Yes
3. Yes I suspect while option A is NEC compliant it would not be good engineering.

Option B question:

1. If its not SDS then how come their system bonding jumper i.e. neutrl to ground bond secondary 600V xfmr?

I think option B is the best, the MGN code exception allows it.

Hope that solves it. The wye-wye is a fascinating beast indeed.

 

[tortuga]

The ground resistance of MGN is often less than 1 ohm.

^^^ Even more reason for option B

 

[electrofelon]

3. Dont you have to ground the neutral?

Yes and it is, just not immediately. Follow the concentric conductor back to the service disconnect and there it meets the GEC

I think option B is the best, the MGN code exception allows it.

While I also think B is the best, I do see the MGN situation to be a little murky when you have an autotransformer/non SDS involved and the voltage changes to LV. MGN only applies to MV. So you are into a game of where you ground the neutral and where that point of demarcation is. It should be on the MV side/MV compartment I guess to avoid neutral current that is returning to the LV windings hitting that ground connection first. Probably nitpicky but IMO that is what the code says.

One final note, 250.142(B) was thrown out (by me I think) as the section prohibiting a N-G bond on the LV side. I am not sure that applies since that appears to be for providing a fault clearing path, i.e. grounding a range or dryer with the neutral, not just earthing the neutral. I think 250.24(A)(5) is a better reference.

 

[hhsting]

Yes and it is, just not immediately. Follow the concentric conductor back to the service disconnect and there it meets the GEC




While I also think B is the best, I do see the MGN situation to be a little murky when you have an autotransformer/non SDS involved and the voltage changes to LV. MGN only applies to MV. So you are into a game of where you ground the neutral and where that point of demarcation is. It should be on the MV side/MV compartment I guess to avoid neutral current that is returning to the LV windings hitting that ground connection first. Probably nitpicky but IMO that is what the code says.

One final note, 250.142(B) was thrown out (by me I think) as the section prohibiting a N-G bond on the LV side. I am not sure that applies since that appears to be for providing a fault clearing path, i.e. grounding a range or dryer with the neutral, not just earthing the neutral. I think 250.24(A)(5) is a better reference.

electrofelon my buddy always helpful thanksfor that code reference load side N to G bond.

Option B: lets say you ground neutral MV not N to G bond on MV side but then on LV you have to create equipment grounding conductor. Guess how thats accomplish N to G bond. So how can option B be code compliant? Can someone here point this out to people of NEC how could one get option B to be code compliant?

 

[electrofelon]

electrofelon my buddy always helpful thanksfor that code reference load side N to G bond.

Option B: lets say you ground neutral MV not N to G bond on MV side but then on LV you have to create equipment grounding conductor. Guess how thats accomplish N to G bond. So how can option B be code compliant? Can someone here point this out to people of NEC how could one get option B to be code compliant?

I do not understand the question, sorry.

 

[hhsting]

I do not understand the question, sorry.

Option B: xfmr is not SDS 600V side one needs EGC. How else you would get and EGC but to have N to G bond again secondary side at xfmr? Even if you do N to G at primary side compartment of xfmr it would not be 250.24(A)(5) compliant?

 

[electrofelon]

Option B: xfmr is not SDS 600V side one needs EGC. How else you would get and EGC but to have N to G bond again secondary side at xfmr? Even if you do N to G at primary side compartment of xfmr it would not be 250.24(A)(5) compliant?

I addressed exactly this point in post #132

 

[Hv&Lv]

I really can’t believe this thread is still going...

 

[electrofelon]

I really can’t believe this thread is still going...

Yeah me neither. The only reason I don't give up is like Tortuga I find it quite interesting.

 

[hhsting]

Yeah me neither. The only reason I don't give up is like Tortuga I find it quite interesting.

Interesting? This thing is a mess a headache and their should be some sort of exception in code to comply with option B. I still am not able to see my post #135 question in your post #132.

 

[electrofelon]

Interesting? This thing is a mess a headache and their should be some sort of exception in code to comply with option B. I still am not able to see my post #135 question in your post #132.

Part X of 250 is for over 1kv and allows grounding the neutral. That takes precedence over the general requirements such as 250.24(A)(5). So you can ground the neutral as long as you do it on the MV side, so start your EGC on the MV side.