Fault Calc's on existing gear when utility company change transformer

[petersonra]

I am not sure you have any recourse with the POCO.

You might want to check with the switch gear manufacturer and see if they can give you some help. I have been told that at least some of them have done some testing with CL fuses that might be of some help.

I have also heard that there are some retrofit kits available for at least some switch gear to improve the rating of the bracing.

 

[nicknorth]

Assuming PSE is Puget Sound Electric and in the U.S.:

http://www.utc.wa.gov/consumers/Pages/ConsumerComplaints.aspx

Thanks I looked up that link and it gave me all the information I need to file a complaint. I'm not sure I want to file a complaint because we have to work with the POCO all the time and it would seem it could make things even tougher then they already are. I don't understand why it's always so difficult to deal with them and they always push any issue off to someone else. Do you know or have you ever filed a complaint through the UTC? I could see it being some dog and pony show where I get forced to spend a lot of time into this matter and then nothing changes as far the issues I have to deal with.

I got another response from their engineering dept. which is why off and I don't know why these don't use the actual specs of the wire size and distance because they have this information and also I have given it to them. The gear is feed with parallel 750MCM AL that is 15' runs. When you have parallel sets or more then one run you just take the distance of one conductor, is that correct? Does anyone know what "C" & "f" & "M" values stand for?

Phase-Phase Voltage (V) 208
Transformer Rating (VA) 500,000
Transformer Full Load (A) 1,388
Transformer Impedance (%) 2.30
Transformer Multiplier 43.48
Short Circuit Current at Transformer's Secondary Bus (A) 60,344
Transforemer R/X 0.20
Conductor (kcmil) 500
Conductor Length (ft) 100
Conductor Resistance (Ohm/1000ft) 0.04
Conductor Reactance (Ohm/1000ft)
"C" Value 21,391
"f" Vaule 2.35
"M" Value (Multiplier) 0.30
Short Circuit Current at Gear (A) 18,018

So here's what I'm coming up with using there same excel spreadsheet:
Phase-Phase Voltage (V) 208
Transformer Rating (VA) 500,000
Transformer Full Load (A) 1,388
Transformer Impedance (%) 2.30
Transformer Multiplier 43.48
Short Circuit Current at Transformer's Secondary Bus (A) 60,344
Transforemer R/X 0.20
Conductor (kcmil) 750 ------------------------This doesn't change anything
Conductor Length (ft) 18
Conductor Resistance (Ohm/1000ft) 0.03 -------This figure doesn't change any values either
Conductor Reactance (Ohm/1000ft) ------------This was left blank
"C" Value 21,391 ---------------------------------------\
"f" Vaule 0.42 --------------------------------------------> I'm not sure what these numbers are related to can someone help me?
"M" Value (Multiplier) 0.70 ------------------------------/
Short Circuit Current at Gear (A) 42,411 --- The gear is rated at 42k

Thanks for all the help

 

[nicknorth]

I do have the Excel spreadsheet to do these calc's, but it will not let me attach an Excel file type as a attachment. If anyone has a way to get this posted please let me know so everyone can get a better understand and also this would be helpful for anyone else that needs to do fault current calc.

 

[nicknorth]

I am not sure you have any recourse with the POCO.
You might want to check with the switch gear manufacturer and see if they can give you some help. I have been told that at least some of them have done some testing with CL fuses that might be of some help.
I have also heard that there are some retrofit kits available for at least some switch gear to improve the rating of the bracing.

This gear is past the point of trying to repair or upgrade as it is at the end of its life and honestly should be replaced, but this is $200,000 job and the building owners already spent $110,000 replacing service gear in the same complex on a different building. I know that they do want to do this but it boils down to money. Why do you say you are not sure that I have any recourse with POCO? Is that because you are like me and everytime you have to deal with them its always very difficult and they always pass the buck to someone else and then if you need a service upgrade they want to charge you up the a** for something that ends up taking a Linemen crew a few hours and a couple hundred dollars in materials. I know there's a lot more that goes into it then just that but that's why we pay for this service and they have a lot of fees in power cost to cover tons of other items. It's not like we have a choice of using another power company. It seems corrupt how utility companies run their operations.

 

[templdl]

This gear is past the point of trying to repair or upgrade as it is at the end of its life and honestly should be replaced, but this is $200,000 job and the building owners already spent $110,000 replacing service gear in the same complex on a different building. I know that they do want to do this but it boils down to money. Why do you say you are not sure that I have any recourse with POCO? Is that because you are like me and everytime you have to deal with them its always very difficult and they always pass the buck to someone else and then if you need a service upgrade they want to charge you up the a** for something that ends up taking a Linemen crew a few hours and a couple hundred dollars in materials. I know there's a lot more that goes into it then just that but that's why we pay for this service and they have a lot of fees in power cost to cover tons of other items. It's not like we have a choice of using another power company. It seems corrupt how utility companies run their operations.

Did you get a system coordination study done by a PE who is qualified in doing such a study and submit a report to the building owners and let them make the decision? Am I correct to conclude that no such study has been done and that this far there have been are assumptions and opinions but no studies as were done by someone who is qualified to do so.

 

[nicknorth]

Did you get a system coordination study done by a PE who is qualified in doing such a study and submit a report to the building owners and let them make the decision? Am I correct to conclude that no such study has been done and that this far there have been are assumptions and opinions but no studies as were done by someone who is qualified to do so.

I do believe they did have some studies done, but I do not know if it was before the POCO replaced their transformer. They might only of got load studies done, but maybe there was more done that I'm not aware of. I will look into this and see what I can find.

 

[kwired]

I do have the Excel spreadsheet to do these calc's, but it will not let me attach an Excel file type as a attachment. If anyone has a way to get this posted please let me know so everyone can get a better understand and also this would be helpful for anyone else that needs to do fault current calc.

Export the results to a pdf file and attach it. Or better yet export to a jpg file then it can be displayed in the post.

 

[kwired]

Thanks I looked up that link and it gave me all the information I need to file a complaint. I'm not sure I want to file a complaint because we have to work with the POCO all the time and it would seem it could make things even tougher then they already are. I don't understand why it's always so difficult to deal with them and they always push any issue off to someone else. Do you know or have you ever filed a complaint through the UTC? I could see it being some dog and pony show where I get forced to spend a lot of time into this matter and then nothing changes as far the issues I have to deal with.

I got another response from their engineering dept. which is why off and I don't know why these don't use the actual specs of the wire size and distance because they have this information and also I have given it to them. The gear is feed with parallel 750MCM AL that is 15' runs. When you have parallel sets or more then one run you just take the distance of one conductor, is that correct? Does anyone know what "C" & "f" & "M" values stand for?

Phase-Phase Voltage (V) 208
Transformer Rating (VA) 500,000
Transformer Full Load (A) 1,388
Transformer Impedance (%) 2.30
Transformer Multiplier 43.48
Short Circuit Current at Transformer's Secondary Bus (A) 60,344
Transforemer R/X 0.20
Conductor (kcmil) 500
Conductor Length (ft) 100
Conductor Resistance (Ohm/1000ft) 0.04
Conductor Reactance (Ohm/1000ft)
"C" Value 21,391
"f" Vaule 2.35
"M" Value (Multiplier) 0.30
Short Circuit Current at Gear (A) 18,018

So here's what I'm coming up with using there same excel spreadsheet:
Phase-Phase Voltage (V) 208
Transformer Rating (VA) 500,000
Transformer Full Load (A) 1,388
Transformer Impedance (%) 2.30
Transformer Multiplier 43.48
Short Circuit Current at Transformer's Secondary Bus (A) 60,344
Transforemer R/X 0.20
Conductor (kcmil) 750 ------------------------This doesn't change anything
Conductor Length (ft) 18
Conductor Resistance (Ohm/1000ft) 0.03 -------This figure doesn't change any values either
Conductor Reactance (Ohm/1000ft) ------------This was left blank
"C" Value 21,391 ---------------------------------------\
"f" Vaule 0.42 --------------------------------------------> I'm not sure what these numbers are related to can someone help me?
"M" Value (Multiplier) 0.70 ------------------------------/
Short Circuit Current at Gear (A) 42,411 --- The gear is rated at 42k

Thanks for all the help

C is a constant that changes depending on conductor size, type, and whether it is in magnetic or non magnetic conduit. If doing these calculations yourself you need to find data that contains these constants, not sure off the top of my head where to locate them - seems like wire and cable companies have such tables, or maybe overcurrent device manufacturers.

F factor - can't remember exactly what the "F" means, but here is a formula for determining F factor for a 3 phase situation:

F= (1.732 x length x fault current at beginning of run) / (number of conductors in parallel x C (mentioned above) x line to line voltage)

M is a multiplier that is determined by the following formula:

M= 1/(1+F)

multiply M by available fault current on supply side of conductors and your result is available fault current at the load end of the conductors.

You don't really need to know what they mean all that much when using the spreadsheet as the spread sheet figures them all for you based on what you input in other fields.



Don't have the time now but I can enter data you have in quoted post above and export to jpg and post it maybe tonight unless someone beats me to it. The spreadsheet I would be using is same one that is on Mike Holt's free stuff page.

 

[don_resqcapt19]

I think this Bussmann publication has the "C" and "F" factor information.

 

[kwired]

Thanks I looked up that link and it gave me all the information I need to file a complaint. I'm not sure I want to file a complaint because we have to work with the POCO all the time and it would seem it could make things even tougher then they already are. I don't understand why it's always so difficult to deal with them and they always push any issue off to someone else. Do you know or have you ever filed a complaint through the UTC? I could see it being some dog and pony show where I get forced to spend a lot of time into this matter and then nothing changes as far the issues I have to deal with.

I got another response from their engineering dept. which is why off and I don't know why these don't use the actual specs of the wire size and distance because they have this information and also I have given it to them. The gear is feed with parallel 750MCM AL that is 15' runs. When you have parallel sets or more then one run you just take the distance of one conductor, is that correct? Does anyone know what "C" & "f" & "M" values stand for?

Phase-Phase Voltage (V) 208
Transformer Rating (VA) 500,000
Transformer Full Load (A) 1,388
Transformer Impedance (%) 2.30
Transformer Multiplier 43.48
Short Circuit Current at Transformer's Secondary Bus (A) 60,344
Transforemer R/X 0.20
Conductor (kcmil) 500
Conductor Length (ft) 100
Conductor Resistance (Ohm/1000ft) 0.04
Conductor Reactance (Ohm/1000ft)
"C" Value 21,391
"f" Vaule 2.35
"M" Value (Multiplier) 0.30
Short Circuit Current at Gear (A) 18,018

So here's what I'm coming up with using there same excel spreadsheet:
Phase-Phase Voltage (V) 208
Transformer Rating (VA) 500,000
Transformer Full Load (A) 1,388
Transformer Impedance (%) 2.30
Transformer Multiplier 43.48
Short Circuit Current at Transformer's Secondary Bus (A) 60,344
Transforemer R/X 0.20
Conductor (kcmil) 750 ------------------------This doesn't change anything
Conductor Length (ft) 18
Conductor Resistance (Ohm/1000ft) 0.03 -------This figure doesn't change any values either
Conductor Reactance (Ohm/1000ft) ------------This was left blank
"C" Value 21,391 ---------------------------------------\
"f" Vaule 0.42 --------------------------------------------> I'm not sure what these numbers are related to can someone help me?
"M" Value (Multiplier) 0.70 ------------------------------/
Short Circuit Current at Gear (A) 42,411 --- The gear is rated at 42k

Thanks for all the help

Here is results from my shot at it, assuming you have 2 parallel 750 aluminum conductors, 18 feet long, no power factor was mentioned so I entered 100% but a lower power factor will increase final fault current, and I used same size conductor as ungrounded conductors for the neutral. Well beyond your 42k gear with my results.

 

[kwired]

Can you verify the transformer impedance. Charts in my American Electricians Handbook are saying a 500kVA is likely to be more like 4.5% which would make a big difference and would give you about 29kA available at the gear with the spreadsheet I used. It is an older book but I'm still guessing this data has not changed too significantly.

 

[nicknorth]

Can you verify the transformer impedance. Charts in my American Electricians Handbook are saying a 500kVA is likely to be more like 4.5% which would make a big difference and would give you about 29kA available at the gear with the spreadsheet I used. It is an older book but I'm still guessing this data has not changed too significantly.

I have included some pictures so you can see how close the transformer is to this old gear and also included a photo of the gears listing. Here's the specs on all the pad mount transformers that our POCO (PSE) uses. They had the 300kVa installed before and now went to the 500kVa, but if they switched to the 750kVa they would be fine as far as the fault currents go. I don't know if there's enough room for them to install a 750kVa because they 500kVa barely sits on the pad they installed it and it doesn't even have room to bolt it down to the lid of the pad. On the Excel file that our POCO uses that is the Excel file that I wanted to share so everyone can see how they do their math, but I'm still lost on how to send it.

 

[nicknorth]

Here is results from my shot at it, assuming you have 2 parallel 750 aluminum conductors, 18 feet long, no power factor was mentioned so I entered 100% but a lower power factor will increase final fault current, and I used same size conductor as ungrounded conductors for the neutral. Well beyond your 42k gear with my results.

Thanks for the help. Is there a way I can send you the actual file that my POCO sent me that they use to calc these fault currents. All the ways I keep doing it it comes to be over the 42k what the gear is rated at. The POCO has sent me some crazy calcs coming up with 18k but they used 500MCM at 100' long which they know is not correct. This is getting tried-some dealing with them because it seems that they don't care and its someone else dept.

 

[don_resqcapt19]

... It is an older book but I'm still guessing this data has not changed too significantly.

I think it may have. The DOE's rules on the energy efficiency of transformers has resulted in lower impedances.

 

[jim dungar]

This is getting tried-some dealing with them because it seems that they don't care and its someone else dept.

Sorry, but this is your problem to solve, not the POCO's.
If you do not like the results the POCO is giving you, then you should hire someone with expertise in this area. A good engineer will develop possible solutions, and costs, for mitigating this situation.

My guess is, regardless what is done, you will have to replace the gear, or pay to 'lengthen the secondary' by relocating the transformer or rerouting the conductors.

An oversized transformer will have more losses, than the present set up. Will your customer be willing to reimburse the utility for them?

 

[kwired]

Thanks for the help. Is there a way I can send you the actual file that my POCO sent me that they use to calc these fault currents. All the ways I keep doing it it comes to be over the 42k what the gear is rated at. The POCO has sent me some crazy calcs coming up with 18k but they used 500MCM at 100' long which they know is not correct. This is getting tried-some dealing with them because it seems that they don't care and its someone else dept.

I get about 18kA also, but that is for 100 feet length of 500kcmil aluminum, and only one conductor per phase. You have more than double the CSA of conductor and only 18% of the length they are using. Apparently they just gave you some kind of average of what they typically see connected to that particular size transformer on their system and not what you actually have.

Maybe ask the guy that produced that material if he wants to be standing in front of that gear during a fault event?

 

[nicknorth]

Sorry, but this is your problem to solve, not the POCO's.
If you do not like the results the POCO is giving you, then you should hire someone with expertise in this area. A good engineer will develop possible solutions, and costs, for mitigating this situation.

My guess is, regardless what is done, you will have to replace the gear, or pay to 'lengthen the secondary' by relocating the transformer or rerouting the conductors.

An oversized transformer will have more losses, than the present set up. Will your customer be willing to reimburse the utility for them?

I don't understand why you say it is not the POCO problem? Yes I can come up with ten different ways to solve this problem. The point is this would of never been a problem if the POCO did not upgrade their transformer 100% on their own to a larger size with a larger fault current without ownership ever asking for this and the POCO never checking with anyone to make sure everything was safe. The POCO just did whatever they wanted and never informed anyone. The POCO could of went about this 100 different ways but like always they seem just to do whatever they want and get away with it.

 

[don_resqcapt19]

I don't understand why you say it is not the POCO problem? Yes I can come up with ten different ways to solve this problem. The point is this would of never been a problem if the POCO did not upgrade their transformer 100% on their own to a larger size with a larger fault current without ownership ever asking for this and the POCO never checking with anyone to make sure everything was safe. The POCO just did whatever they wanted and never informed anyone. The POCO could of went about this 100 different ways but like always they seem just to do whatever they want and get away with it.

I don't see it being the problem of the power company. They get to build their system anyway they want too.

Are you sure there was no notification? Most power companies have a notification method. Some put that information on the bill and the person that sees and pays the bill would probably have no idea what the information means so no action would be taken.

 

[texie]

I don't understand why you say it is not the POCO problem? Yes I can come up with ten different ways to solve this problem. The point is this would of never been a problem if the POCO did not upgrade their transformer 100% on their own to a larger size with a larger fault current without ownership ever asking for this and the POCO never checking with anyone to make sure everything was safe. The POCO just did whatever they wanted and never informed anyone. The POCO could of went about this 100 different ways but like always they seem just to do whatever they want and get away with it.

I think the are others are probably right, they'll put this on the owner. Most big POCO's today are bullies and not user friendly. They are way to busy spending other peoples money on all their green projects to care about the lowly individual rate payer. Not all though-I regularly work with a very large investor owned POCO in the western US that would always coordinate a xformer change out like this first with the owner and/or his representatives. All depends on the culture of the POCO.

 

[nicknorth]

I don't see it being the problem of the power company. They get to build their system anyway they want too.

Are you sure there was no notification? Most power companies have a notification method. Some put that information on the bill and the person that sees and pays the bill would probably have no idea what the information means so no action would be taken.

Yes 100% the owners of the property double checked. They would of even never had known if it wasn't for Hazmat out on site cleaning up the old transformer messed when it spew oil everywhere and the huge mess that was still left and the tags on the transformer.