ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat Box
Recent Posts
Do you count seconds?
by gfretwell - 12/05/19 07:36 PM
"Esoteric" countries and their wiring practices?
by Texas_Ranger - 12/02/19 10:52 AM
Look at this mess...
by NORCAL - 11/15/19 10:21 PM
Fire source!
by sabrown - 11/07/19 08:39 AM
New in the Gallery:
FPE Breaker panel in germany
What is this for?
Who's Online Now
1 registered members (cableguy619), 8 guests, and 11 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Positive Ground on 125 VDC Station Batteries #220088 05/22/19 06:05 PM
Joined: Dec 2001
Posts: 437
The Watt Doctor Offline OP
Member
It's been a long time since I've logged on to this forum. I spent a lot time here back when I was working in the Electrical Contracting world. I'm currently working in a 600 MW Cogen Facility. We have a recurring problem with our 125 VDC station battery system. A ground on the positive bus will mysteriously appear, stick around for a while, and then vanish. It's a nuance more than anything. The trouble is that affects the secondary trip circuits for our Oil Filled Circuit Breakers, Gas Breakers, Breaker Failure Relays, Sudden Pressure Relays on our GSU's (Generator Step-Up Transformers), 86GT Lockout Relays, etc, etc, etc. So, systematically turning off breakers until I find the affected circuit is NOT an option. What I'm looking for may not exist. I'm looking for reading material on how to work on DC systems in industrial plants in hopes that I can develop a strategy to resolve this problem. Any help is appreciated.


The Watt Doctor
Altura Cogen
Channelview, TX
Work Gear for Electricians and the Trades
Re: Positive Ground on 125 VDC Station Batteries [Re: The Watt Doctor] #220089 05/22/19 08:53 PM
Joined: Jul 2004
Posts: 9,414
G
gfretwell Offline
Member
There are Hall effect devices that can detect current in DC circuits if that helps


Greg Fretwell
Re: Positive Ground on 125 VDC Station Batteries [Re: gfretwell] #220090 05/23/19 07:55 AM
Joined: Dec 2001
Posts: 437
The Watt Doctor Offline OP
Member
Thanks, gfretwell. We have Hall Effect devices on our large DC Motor Drives. However, that's not what I'm looking for in the particular case.


The Watt Doctor
Altura Cogen
Channelview, TX
Re: Positive Ground on 125 VDC Station Batteries [Re: The Watt Doctor] #220091 05/27/19 06:57 PM
Joined: Nov 2005
Posts: 806
J
JoeTestingEngr Offline
Member
I have quite a bit of experience tracking down ground faults in traction power substations. I find troubleshooting them as some of my more enjoyable work. Our 125VDC is really 133.8VDC Float and I imagine yours is about the same. And our ground faults aren't usually really ground faults, but skin faults. That means they're elevated above ground by the voltage imposed by the 64 (164) Hot/Grounded Structure relays. So I will often see about 25VDC between battery + and Ground. Of course, I always isolate the charger from the batteries first and the problem almost always stays with the batteries. Then, I can usually lift the power from the 64 relays, one at a time, until I see the battery + to ground voltage drop. The problem is almost always in the DC SWGR Lineup. From there, it's a matter of asking our Power Controllers for permission to open individual power sections. Our breakers have under voltage relays so pulling control power will cause a trip. We just open the control power breakers or knife switches one at a time until the fault goes away. Then we know which cubicle to check. Then we rack the breaker out or to test to check further.

In our recent experience our DC Breaker charging motors have been developing leakage between the + connection and their cases.
Joe

Re: Positive Ground on 125 VDC Station Batteries [Re: The Watt Doctor] #220092 05/27/19 07:08 PM
Joined: Nov 2005
Posts: 806
J
JoeTestingEngr Offline
Member
OK, I just posted the above and it's 7:06 CDT on Memorial Day, 5/27. Why is it showing that I replied "Yesterday at 11:57 PM"???


Featured:

2020 National Electrical Code
2020 National Electrical
Code (NEC)

* * * * * * *

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

 

Member Spotlight
Alan Belson
Alan Belson
Mayenne N. France
Posts: 1,803
Joined: March 2005
Show All Member Profiles 
Top Posters(30 Days)
NORCAL 1
Popular Topics(Views)
261,139 Are you busy
196,274 Re: Forum
185,544 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.3