ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Shout Box
Recent Posts
Ronald and Nancy Reagan in GE commercials
by Bill Addiss. 03/13/19 08:12 PM
Carflex in an RNC connector?
by gfretwell. 03/12/19 05:21 PM
Reverse-feeding transformer in PV system?
by HotLine1. 03/11/19 08:37 AM
Vintage stage lighting and equipment catalogs
by Albert. 03/09/19 06:21 PM
TJX Recalls Heating Pads
by Admin. 03/08/19 09:33 PM
New in the Gallery:
What is this for?
Plug terminals
Who's Online Now
1 registered members (Scott35), 18 guests, and 8 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Another brain teaser....480 on a 240 volt delta #61107
01/16/06 11:05 PM
01/16/06 11:05 PM
W
WFO  Offline OP
Member
Joined: Sep 2005
Posts: 202
Cat Spring, TX
I work at a utility. We got called out on a customer complaint to a grocer who had burned up his 3 phase motors.

His service was a 120/240 volt open delta secondary fed from two phases of a 4 wire wye, 12.5/7.2 Kv primary.

When we got there, we read across the "lighting" legs and got 120 volts from A to neutral and 120 volts from B to neutral. A to B read 240 volts, as did B to C.

So far so good. So.....

A to C read 480 volts (instead of 240) and C to neutral read 360 volts (instead of 208).
Neither transformer fuse was blown.

Hint: There had been many outages due to storms a few days before and lots of backfeeding had been going on.

Work Gear for Electricians and the Trades
Re: Another brain teaser....480 on a 240 volt delta #61108
01/16/06 11:12 PM
01/16/06 11:12 PM
G
gfretwell  Offline

Member
Joined: Jul 2004
Posts: 9,343
Estero,Fl,usa
Did the transformers end up on the same input phase?


Greg Fretwell
Re: Another brain teaser....480 on a 240 volt delta #61109
01/16/06 11:14 PM
01/16/06 11:14 PM
W
WFO  Offline OP
Member
Joined: Sep 2005
Posts: 202
Cat Spring, TX
Dammit! Dammit! Dammit!
Didn't even get past the first guy. [Linked Image]

Re: Another brain teaser....480 on a 240 volt delta #61110
01/16/06 11:15 PM
01/16/06 11:15 PM
C
caselec  Offline
Member
Joined: Apr 2002
Posts: 558
San Jose, CA
I don’t know what back feeding has to do with this but you can’t feed a three phase transformer bank with only 2 phases. By feeding both transformers from the same two phases your secondaries are connected in series giving the voltages you see.

Curt


Curt Swartz
Re: Another brain teaser....480 on a 240 volt delta #61111
01/16/06 11:17 PM
01/16/06 11:17 PM
C
caselec  Offline
Member
Joined: Apr 2002
Posts: 558
San Jose, CA
I’ve got to learn to type faster.


Curt Swartz
Re: Another brain teaser....480 on a 240 volt delta #61112
01/16/06 11:44 PM
01/16/06 11:44 PM
W
WFO  Offline OP
Member
Joined: Sep 2005
Posts: 202
Cat Spring, TX
Quote:
"I don’t know what back feeding has to do with this but you can’t feed a three phase transformer bank with only 2 phases. By feeding both transformers from the same two phases your secondaries are connected in series giving the voltages you see."

Right on the second half.
You CAN feed a 3 phase open delta bank with only two phases and neutral. I didn't mean to give the impression that they were going phase to phase on the primary with the common floating. The common is bonded to the neutral.

Quote:
"I’ve got to learn to type faster."

Indeed. The second response was going to win a brand new Porsche.

...oh, wait. I was the second response.

Re: Another brain teaser....480 on a 240 volt delta #61113
01/17/06 02:08 AM
01/17/06 02:08 AM
mxslick  Offline
Member
Joined: Oct 2004
Posts: 803
Atomic City, ID USA
Oh, man lookit what I started.... [Linked Image]


Stupid should be painful.

Featured:

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

 

Member Spotlight
RH1
RH1
California
Posts: 22
Joined: August 2009
Show All Member Profiles 
Top Posters(30 Days)
Admin 9
Albert 3
Popular Topics(Views)
254,001 Are you busy
190,398 Re: Forum
180,110 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.6.1
(Release build 20180101)
Page Time: 0.020s Queries: 14 (0.004s) Memory: 0.9852 MB (Peak: 1.1373 MB) Zlib enabled. Server Time: 2019-03-25 18:48:58 UTC