CLICK HERE AND JOIN OUR COMMUNITY TODAY, IT'S FREE!
Go Back   Electrician Talk - Professional Electrical Contractors Forum > Electrical Trade Topics > Commercial Electrical Forum

Reply
 
Thread Tools Search this Thread Display Modes
Old 10-01-2011, 02:38 AM   #1
Member
 
Join Date: Dec 2010
Location: Maui/Hawaii/US
Posts: 88
Rewards Points: 75
Default Grounding Transformer

The utility is telling me I need to hook up a grounding transformer in order to hook up my 200KW PV inverter to their grid.

My 10 minute google education on what the heck grounding transformers do suggests they are for protecting circuits being fed by an ungrounded delta or in my case a high impedance ground.

From what I read a grounding transformer hooks in parallel with said ungrounded circuit to protect it.

since I have no clue how much a grounding transformer costs and one of the largest transformer distributors in the us had to go through several salesman before they found someone who knew what it was to try and get me a quote, I take it they are rare and could possibly cost big bucks.

What i was wondering is that rather than going the grounding transformer route and hooking in parallel to the circuit why not just hook up to an isolation transformer, I could hook my PV inverter to the delta side of a 480 to 480 volt isolation transformer and ground the crap out of the wye side which i hook up to the utility.

Does that sound like a legit solution?

Thanks for the read and any reply

Rap2 is offline   Reply With Quote
Join Contractor Talk

Join the #1 Electrician Forum Today - It's Totally Free!

ElectricianTalk.com - Are you a Professional Electrical Contractor? If so we invite you to join our community and see what it has to offer. Our site is specifically designed for you and it's the leading place for electricians to meet online. No homeowners asking DIY questions. Just fellow tradesmen who enjoy talking about their business, their trade, and anything else that comes up. No matter what your specialty is you'll find that ElectricianTalk.com is a great community to join. Best of all it's totally free!

Join ElectricianTalk.com - Click Here JOIN FOR FREE


Warning: The topics covered on this site include activities in which there exists the potential for serious injury or death. ElectricianTalk.com DOES NOT guarantee the accuracy or completeness of any information contained on this site. Always use proper safety precaution and reference reliable outside sources before attempting any construction or remodeling task!

Old 10-01-2011, 02:54 AM   #2
Senior Member
 
Join Date: Feb 2007
Location: Eighty Four,Pa.15330
Posts: 7,209
Rewards Points: 2,176
Default

I don't get it. 200kw is a lot of power to all of a sudden say "here I am"! Don't you need approvals and drawings?

bobelectric is offline   Reply With Quote
The Following User Says Thank You to bobelectric For This Useful Post:
seabee41 (09-09-2013)
Old 10-01-2011, 02:58 AM   #3
Heavily Armed Member
 
HARRY304E's Avatar
 
Join Date: Sep 2010
Location: Reporting from the east coast of Moonbatchusetts..
Posts: 39,497
Default

Quote:
Originally Posted by Rap2 View Post
The utility is telling me I need to hook up a grounding transformer in order to hook up my 200KW PV inverter to their grid.

My 10 minute google education on what the heck grounding transformers do suggests they are for protecting circuits being fed by an ungrounded delta or in my case a high impedance ground.

From what I read a grounding transformer hooks in parallel with said ungrounded circuit to protect it.

since I have no clue how much a grounding transformer costs and one of the largest transformer distributors in the us had to go through several salesman before they found someone who knew what it was to try and get me a quote, I take it they are rare and could possibly cost big bucks.

What i was wondering is that rather than going the grounding transformer route and hooking in parallel to the circuit why not just hook up to an isolation transformer, I could hook my PV inverter to the delta side of a 480 to 480 volt isolation transformer and ground the crap out of the wye side which i hook up to the utility.

Does that sound like a legit solution?

Thanks for the read and any reply
Take a look at article 690 in the NEC.

What are trying to produce with the transformer?

What type of building?
HARRY304E is offline   Reply With Quote
Old 10-01-2011, 03:01 AM   #4
Member
 
Join Date: Dec 2010
Location: Maui/Hawaii/US
Posts: 88
Rewards Points: 75
Default

Quote:
Originally Posted by bobelectric View Post
I don't get it. 200kw is a lot of power to all of a sudden say "here I am"! Don't you need approvals and drawings?
Yes, we have submitted drawings for approval, just like our many installations of the like in the next county over(different utility), except this is the first time they have been sent back saying we need a grounding transformer... I have a meeting on Monday to discuss the matter with the utility, but I want to have my ducks in a row....
Rap2 is offline   Reply With Quote
Old 10-01-2011, 03:16 AM   #5
Senior Member
 
Join Date: Feb 2007
Location: Eighty Four,Pa.15330
Posts: 7,209
Rewards Points: 2,176
Default

Understood,rap2. PV here of that size is only a concept we read about.
bobelectric is offline   Reply With Quote
Old 10-01-2011, 03:22 AM   #6
Member
 
Join Date: Dec 2010
Location: Maui/Hawaii/US
Posts: 88
Rewards Points: 75
Default

Quote:
Originally Posted by HARRY304E View Post
Take a look at article 690 in the NEC.

What are trying to produce with the transformer?

What type of building?
I am trying to isolate my not so grounded PV circuit from the utility and provide them with a conventionally grounded one through a 480 volt to 480 volt delta wye transformer, and grounding the neutral side of the wye in order to provide a more conventionally grounded circuit.

690 does not have much on grounding transformers.

This is a large refrigerated packing plant.
Rap2 is offline   Reply With Quote
Old 10-01-2011, 07:06 AM   #7
Donuts > Fried Eggs
 
Big John's Avatar
 
Join Date: May 2010
Location: Portland
Posts: 15,076
Rewards Points: 2,366
Default

If the utility is specifying a grounding transformer, especially if you already have a high-resistance-ground, then I would bet money they want it for protective relaying in order to shut your system down properly in the event of a fault.

Not sure if they'd find a hard ground more acceptable or not.

-John
__________________
Spend $86 to keep yourself safe. Always wear your gloves.
Big John is offline   Reply With Quote
Old 10-01-2011, 11:54 AM   #8
Senior Member
 
Join Date: Nov 2008
Location: east coast
Posts: 1,058
Rewards Points: 518
Default

Most of the high resistance grounding (HRG) units that I have seen have a resister bank in series between the center point of the Wye and ground.
the resister bank is taped and there is a thumping contactor around a small portion of the bank. This is used for ground fault location.

A grounding transformer is used with a Delta power transformer and they are a zig zag transformer and their center point is grounded giving the ungrounded Delta a ground reference. Those that I have seen are not that big and they will fit in a vertical section of switchgear. Now I must say that I have no idea how to size a zig zag transformer.

I would talk to Powell Electric in Houston TX or Controlled Power Corp North Canton Ohio for guidance.
__________________
What tools do I need to carry? Use the NEC as your guide keep all your tools ACCESSABLE but keep your everyday tools READILY ACCESSABLE.

Last edited by Lone Crapshooter; 10-01-2011 at 11:58 AM.
Lone Crapshooter is online now   Reply With Quote
The Following User Says Thank You to Lone Crapshooter For This Useful Post:
cuba_pete (09-20-2013)
Old 10-01-2011, 02:07 PM   #9
Member
 
Join Date: Dec 2010
Location: Maui/Hawaii/US
Posts: 88
Rewards Points: 75
Default

Quote:
Originally Posted by Lone Crapshooter View Post
Most of the high resistance grounding (HRG) units that I have seen have a resister bank in series between the center point of the Wye and ground.
the resister bank is taped and there is a thumping contactor around a small portion of the bank. This is used for ground fault location.

A grounding transformer is used with a Delta power transformer and they are a zig zag transformer and their center point is grounded giving the ungrounded Delta a ground reference. Those that I have seen are not that big and they will fit in a vertical section of switchgear. Now I must say that I have no idea how to size a zig zag transformer.

I would talk to Powell Electric in Houston TX or Controlled Power Corp North Canton Ohio for guidance.
Thanks for the contact I will give them a call on Monday.

I have read a little on zig zag transformers. How big were the delta circuits you were hooking up? It sounds promising the zig zag transformers where physically small in comparison. It may be the cheaper route to go.
Rap2 is offline   Reply With Quote
Old 10-01-2011, 09:54 PM   #10
Senior Member
 
Join Date: Sep 2009
Location: kentucky
Posts: 9,488
Rewards Points: 2,422
Default

Quote:
Originally Posted by Rap2 View Post
The utility is telling me I need to hook up a grounding transformer in order to hook up my 200KW PV inverter to their grid.

My 10 minute google education on what the heck grounding transformers do suggests they are for protecting circuits being fed by an ungrounded delta or in my case a high impedance ground.

From what I read a grounding transformer hooks in parallel with said ungrounded circuit to protect it.

since I have no clue how much a grounding transformer costs and one of the largest transformer distributors in the us had to go through several salesman before they found someone who knew what it was to try and get me a quote, I take it they are rare and could possibly cost big bucks.

What i was wondering is that rather than going the grounding transformer route and hooking in parallel to the circuit why not just hook up to an isolation transformer, I could hook my PV inverter to the delta side of a 480 to 480 volt isolation transformer and ground the crap out of the wye side which i hook up to the utility.

Does that sound like a legit solution?

Thanks for the read and any reply
I don't understand why the utility would demand the way you ground your system. However, if you choose to use a zig-zag auto transformer to ground, it would be less of an I2R loss to you than using a resistive grounding system. They have been around a long, long time.

Last edited by RIVETER; 10-01-2011 at 10:05 PM.
RIVETER is online now   Reply With Quote
Old 10-01-2011, 10:57 PM   #11
Member
 
Join Date: Dec 2010
Location: Maui/Hawaii/US
Posts: 88
Rewards Points: 75
Default

Quote:
Originally Posted by RIVETER View Post
I don't understand why the utility would demand the way you ground your system. However, if you choose to use a zig-zag auto transformer to ground, it would be less of an I2R loss to you than using a resistive grounding system. They have been around a long, long time.

All good stuff to know, any idea how much they cost or how to size one?

Thanks so much for the info.
Rap2 is offline   Reply With Quote
Old 10-01-2011, 11:08 PM   #12
Senior Member
 
Bkessler's Avatar
 
Join Date: Feb 2007
Location: CA/MI
Posts: 5,659
Rewards Points: 2,000
Default

One guy whats it done his way. That's typical with neighboring utility's.
__________________
When ls lunch?
Bkessler is offline   Reply With Quote
Old 10-02-2011, 10:26 AM   #13
Senior Member
 
Join Date: Jan 2011
Location: united states of america
Posts: 4,579
Rewards Points: 2,500
Default

Also keep in mind if using an isolation transformer with different winding connections there will be a 30 degree phase shift which can be a problem when parelleling the inverter to the utility.
meadow is online now   Reply With Quote
Old 10-02-2011, 01:58 PM   #14
Member
 
Join Date: Dec 2010
Location: Maui/Hawaii/US
Posts: 88
Rewards Points: 75
Default

Quote:
Originally Posted by meadow View Post
Also keep in mind if using an isolation transformer with different winding connections there will be a 30 degree phase shift which can be a problem when parelleling the inverter to the utility.
Well I'm hooking up an inverter that syncs to the utility (or whatever is coming into it) so if the utility is on one side of a transformer that is 30 degrees out of phase and my inverter syncs to the other side based on what it sees coming in I don't believe that would be a problem.
Rap2 is offline   Reply With Quote
Old 10-10-2011, 01:16 PM   #15
Member
 
Join Date: Dec 2010
Location: Maui/Hawaii/US
Posts: 88
Rewards Points: 75
Default

I forgot to post.... the utility accepted my re-design using a standard delta wye transformer to isolate my PV inverter from their stuff.

I dont like putting in a 480 to 480 volt transformer it seems dumb. I started another thread to discuss any advantage there may be in running the PV at 600 volts just to be able to use a 600 to 480 transformer so I am actually transforming something
Rap2 is offline   Reply With Quote
The Following User Says Thank You to Rap2 For This Useful Post:
cuba_pete (09-20-2013)
Old 10-10-2011, 01:30 PM   #16
Senile Member
 
macmikeman's Avatar
 
Join Date: Jan 2007
Location: Honolulu
Posts: 12,482
Rewards Points: 2,468
Default

I have dealt with utility and govt. officials here for years. The secret is to take them out to club gitchi goomi for a hundred rounds of beers first, and possibly also go to your meeting carrying some manapua.
__________________
If fences don't work, why was there two false flag break in's into the White House? It was staged, that's why...

CA2741523A1
macmikeman is online now   Reply With Quote
Old 09-06-2013, 04:04 PM   #17
Junior Member
 
Join Date: Sep 2013
Location: Honolulu, HI
Posts: 1
Rewards Points: 10
Default Transient overvoltages

I know it's late to respond to this thread, but I just came across this today.

The local utility is probably worried about transient overvoltages.

Suppose you have a 3-phase distribution feeder where the only wye transformer with a solid ground is at the start of the feeder (the utility end). If there is a line-to-ground fault on this circuit, the utility's transformer will try to keep line-to-neutral voltages on all three lines at their normal level. This will induce a large current on the ground-faulted line, and the circuit breaker will open, isolating the circuit from the utility power supply.

Now all the lines on this circuit are isolated from the fixed voltage provided by the utility transformer, so they are free to float to new voltages. In this state, the ground-faulted line will move to zero volts (equal to the neutral). If a PV system continues to inject power into this circuit, the other two lines will maintain their normal line-to-line voltage, and since they're free to float relative to the neutral, they will end up with a line-to-neutral voltage equal to their line-to-line voltage (i.e., 1.73x normal line-to-neutral voltage). This overvoltage is bad for other equipment on the feeder, and it will persist until the PV system shuts down (which can take up to 2 seconds).

There is some more information about this at http://pterra.us/blog2/archives/599.
mfripp is offline   Reply With Quote
Old 09-06-2013, 09:42 PM   #18
Senior Member
 
Join Date: Sep 2009
Location: kentucky
Posts: 9,488
Rewards Points: 2,422
Default

Quote:
Originally Posted by Rap2 View Post
The utility is telling me I need to hook up a grounding transformer in order to hook up my 200KW PV inverter to their grid.

My 10 minute google education on what the heck grounding transformers do suggests they are for protecting circuits being fed by an ungrounded delta or in my case a high impedance ground.

From what I read a grounding transformer hooks in parallel with said ungrounded circuit to protect it.

since I have no clue how much a grounding transformer costs and one of the largest transformer distributors in the us had to go through several salesman before they found someone who knew what it was to try and get me a quote, I take it they are rare and could possibly cost big bucks.

What i was wondering is that rather than going the grounding transformer route and hooking in parallel to the circuit why not just hook up to an isolation transformer, I could hook my PV inverter to the delta side of a 480 to 480 volt isolation transformer and ground the crap out of the wye side which i hook up to the utility.

Does that sound like a legit solution?

Thanks for the read and any reply
Zig- zag auto transformers for grounding are not that expensive. They give all of the benefits of an un-grounded system and are not a 24/7 I2R loss as you would have with a hi-resistance ground..

RIVETER is online now   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Transformer Grounding mr_electrician Canadian Electrical Code Forum 4 09-03-2011 02:27 PM
Transformer grounding question BlazeTaco Commercial Electrical Forum 9 07-21-2011 10:08 PM
Grounding transformer GEORGE D General Electrical Discussion 2 07-19-2011 10:27 AM
transformer grounding ronnie General Electrical Discussion 8 04-15-2009 09:00 PM
Grounding and bonding a transformer Jim Workplace Safety 5 08-18-2007 08:08 PM


All times are GMT -4. The time now is 12:20 AM.


Copyright 2006-2014 Escalate Media LP. All Rights Reserved
Our Pro Sites Network
ContractorTalk.com | DrywallTalk.com | HVACSite.com | PaintTalk.com | PlumbingZone.com | RoofingTalk.com