ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Shout Box
Recent Posts
PLC/HMI Enclosure C2, D1
by ghost307. 10/16/18 03:31 PM
Tingle off the water spigot
by dsk. 10/15/18 02:36 PM
Board tester power supply?
by JoeTestingEngr. 10/13/18 12:14 AM
Voltage sag
by Trumpy. 10/12/18 06:59 PM
New in the Gallery:
What is this for?
Plug terminals
Who's Online Now
0 registered members (), 21 guests, and 20 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Page 1 of 2 1 2
480 Delta #218983
01/06/18 03:09 AM
01/06/18 03:09 AM
G
gfretwell  Offline
OP
Member
Joined: Jul 2004
Posts: 9,298
Estero,Fl,usa
I was talking to a guy from Massachusetts (electronic engineer) and he says 480 delta is common up there for industrial applications. How is that generally grounded? He didn't know but he says he thought it was ungrounded. That did not sound right.
I have seen plenty of 480/277 wye but I have never seen a 480 delta down here.


Greg Fretwell
Work Gear for Electricians and the Trades
Re: 480 Delta [Re: gfretwell] #218985
01/06/18 04:10 PM
01/06/18 04:10 PM
G
gfretwell  Offline
OP
Member
Joined: Jul 2004
Posts: 9,298
Estero,Fl,usa
Never mind, we determined that it was corner grounded delta. He just did not realize it.


Greg Fretwell
Re: 480 Delta [Re: gfretwell] #218986
01/06/18 05:57 PM
01/06/18 05:57 PM
G
ghost307  Offline
Member
Joined: May 2005
Posts: 955
Chicago Illinois USA
We have several mission critical facilities that use an ungrounded delta system.
In the event of a ground fault the system stays energized until it can be corrected.
The only time that the system goes down is when there is a second ground fault before the first one gets cleared.

An ungrounded delta is kinda capacitively coupled to the Earth, so a ground detector device is used.
There are 3 lights wired from phase to a ground rod and all glow continuously at the same brightness.
If one of the phases has a ground fault that light will go out and the other 2 get much brighter.

That tells you which phase the ground fault is on...but finding where it is becomes very challenging.
One of our facilities has had a ground fault on one of the phases for several years...and the maintenance folks are still trying to chase it down.
I think there may be a ground in 2 places on the same phase; which is like trying to find the 2 bad bulbs in an old string of Christmas lights.


Ghost307
Re: 480 Delta [Re: ghost307] #219288
04/28/18 04:27 PM
04/28/18 04:27 PM
W
Wiresmith  Offline
Member
Joined: Apr 2018
Posts: 12
Midwest U.S.
Originally Posted by ghost307
We have several mission critical facilities that use an ungrounded delta system.


An ungrounded delta is kinda capacitively coupled to the Earth, so a ground detector device is used.
There are 3 lights wired from phase to a ground rod and all glow continuously at the same brightness.
If one of the phases has a ground fault that light will go out and the other 2 get much brighter.

.


are you sure that's not a high impedance grounded neutral system?

i was at a plant with a set-up like that and i can't remember the exact fault locator they had but we traced the ground fault with some type of frequency fault locator, even through metal conduit and enclosures, found it pretty quickly ( i think 1 hour)

Re: 480 Delta [Re: gfretwell] #219300
04/30/18 08:47 AM
04/30/18 08:47 AM
G
ghost307  Offline
Member
Joined: May 2005
Posts: 955
Chicago Illinois USA
Nope.
It's a true ungrounded 3 wire Delta.
Since the facilities are critical we can't shut them down unless we do a major upgrade so most of the existing Services are the original ones from the 1930s...or earlier.
One of them still has the oil insulated vertical drawout cast iron MV circuit breakers.
Major upgrades are designed with a conventional 3Ph4W system.


Ghost307
Re: 480 Delta [Re: ghost307] #219317
05/02/18 11:44 AM
05/02/18 11:44 AM
W
Wiresmith  Offline
Member
Joined: Apr 2018
Posts: 12
Midwest U.S.
Originally Posted by ghost307
Nope.
It's a true ungrounded 3 wire Delta.
Since the facilities are critical we can't shut them down unless we do a major upgrade so most of the existing Services are the original ones from the 1930s...or earlier.
One of them still has the oil insulated vertical drawout cast iron MV circuit breakers.
Major upgrades are designed with a conventional 3Ph4W system.



the reason i ask is you said this about the indicator lights

Originally Posted by ghost307
.
There are 3 lights wired from phase to a ground rod and all glow continuously at the same brightness.
If one of the phases has a ground fault that light will go out and the other 2 get much brighter.


i don't think the light would light up if it was completely ungrounded,

this light set-up is what is used on high-impedance grounded systems, a first ground fault will only be low current like 5 amps(i don't remember for sure). the lights do the same thing you are describing.

Last edited by Wiresmith; 05/02/18 11:47 AM.
Re: 480 Delta [Re: gfretwell] #219320
05/02/18 03:42 PM
05/02/18 03:42 PM
G
ghost307  Offline
Member
Joined: May 2005
Posts: 955
Chicago Illinois USA
I may have misspoke, but it's been a while since I've had my hands inside one of these units (for obvious reasons).

The '3 lights' style of ground detector works on a true ungrounded system such as the ones installed back in the 30's because the phase conductors are only capacitively coupled to ground.
There is no physical connection between any energized conductor and ground in our systems.

http://www.ece.mtu.edu/faculty/bamork/EE5223/EE5223TermProj_Ex3.pdf

BTW - Our new installations take advantage of high impedance grounding to maintain system integrity while reducing the potential for catastrophic failure if a second ground fault should occur before the first can be tracked down and cleared.


Ghost307
Re: 480 Delta [Re: gfretwell] #219331
05/05/18 11:06 AM
05/05/18 11:06 AM
W
Wiresmith  Offline
Member
Joined: Apr 2018
Posts: 12
Midwest U.S.
thanks for that link, looks like some good information. do the lights light up dimmly though without a ground fault on a true ungrounded system?

Re: 480 Delta [Re: gfretwell] #219335
05/05/18 07:29 PM
05/05/18 07:29 PM
G
ghost307  Offline
Member
Joined: May 2005
Posts: 955
Chicago Illinois USA
Yes. Under unfaulted conditions all 3 lights are dimly lit.
That also actually acts as a good safety check because if a light burns out you know it right away.
Generally they last forever because they are lit at only a fraction of the voltage that they are designed for.


Ghost307
Re: 480 Delta [Re: ghost307] #219359
05/20/18 09:16 PM
05/20/18 09:16 PM
S
sparkyinak  Offline
Member
Joined: Jul 2007
Posts: 1,335
Alaska
I'm curious. What you done so far to find the fault(s)? Any plans for a powering down the critql systems for maintenance?

I ask since I'm may be transferring soon and be working on ungrounded deltas. Always eager to learn something new


"Live Awesome!" - Kevin Carosa
Page 1 of 2 1 2

Featured:

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Member Spotlight
Trumpy
Trumpy
SI,New Zealand
Posts: 8,250
Joined: July 2002
Show All Member Profiles 
Top Posters(30 Days)
sparky 11
Popular Topics(Views)
250,309 Are you busy
187,948 Re: Forum
177,475 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.6.1
(Release build 20180101)
Page Time: 0.026s Queries: 16 (0.004s) Memory: 1.0266 MB (Peak: 1.2080 MB) Zlib enabled. Server Time: 2018-10-17 03:16:28 UTC