×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Currents & Voltages during L-Gnd Fault in HRG System

Currents & Voltages during L-Gnd Fault in HRG System

Currents & Voltages during L-Gnd Fault in HRG System

(OP)
I think this is a simple question, but I can't find any references to determine the answer... perhaps my Blackburn textbook would help...  Here goes:
In a low voltage 600/346VAC, 3ph, 3w, high-resistance grounded system, what are the line voltages and line currents during a line-ground fault, in general?  I understand from what I've read that the line voltages in the unfaulted phases rise to equal the phase voltage, i.e. 600V L-N, but what does the faulted line voltage look like?  How about the currents?  Does the system still deliver current to the load on the faulted phase?  

RE: Currents & Voltages during L-Gnd Fault in HRG System

(OP)
Yeah, I looked on I-Gard's website prior to posting my question... I thought of posing a question to their blog, but figured I'd come here first.  Your attachment is informative, as is the data on their site, but it doesn't answer my question...

RE: Currents & Voltages during L-Gnd Fault in HRG System

Your terminology is confusing to me.  The line-to-line voltage doesn't change.  The line-to-ground voltage in the unfaulted phases goes to full line-to-line voltage.  The fault current in the faulted phase is determined by the resistance in the grounding resistor.  

With HRG, there can be no line-to-neutral loads.  Everything must be line-to-line.  The loads will continue to see line-to-line voltages.  A high-resistance grounded wye system behaves similarly to an ungrounded delta system, but eliminates the worst of the transient overvoltages that were such a problem with the old delta systems.

 

David Castor
www.cvoes.com

RE: Currents & Voltages during L-Gnd Fault in HRG System

A high resistance grounded system behaves pretty much like an ungrounded system.  Instead of treating it like an ungrounded wye, just draw it as a delta system.  Now put a ground on one of the corners.  The phase to ground voltage is zero at that point and the other 2 phase to ground voltages are sides of the delta or phase to phase voltage.

You'll typically get zero fault current for the faulted phase and charging current for the other 2 phases.

RE: Currents & Voltages during L-Gnd Fault in HRG System

(OP)
@dpc, Sorry about the confusion... I tried to be too smart with my question by trying to distinguish between line and phase voltages..
So my understanding is this: during a L-G fault in an HRG system, the load is obviously still connected line-line, the line-line voltages remain at nominal, and rated current is delivered to the load... however, in the faulted phase, fault current also flows, the magnitude of which is determined by the size of the neutral resistor. Line to ground voltages in the unfaulted phases are now 1.73 times their pre-fault values, and the line to ground voltage of the faulted phase is now 0.  Is this correct?
Thanks to all for the help in understanding.   

RE: Currents & Voltages during L-Gnd Fault in HRG System

Sounds about right to me.  The fault current is typically less than 5 amps.  

A great reference is "Industrial Power System Grounding Design Handbook" by Dunki-Jacobs, et al.   

David Castor
www.cvoes.com

RE: Currents & Voltages during L-Gnd Fault in HRG System

(OP)
Thanks to all...  

RE: Currents & Voltages during L-Gnd Fault in HRG System

With a ground on "A" phase the line to line and line to wye point voltages remain the same. Line to ground voltages on "B" and "C" phases rise to line to line voltage and the wye point voltage rises to 1.73 of line to line voltage.
The charging current on "A" phase drops to zero and the charging currents on "B" and "C" phases is now based on line to line voltage rather than line to wye point voltage. There will now be a charging current on the neutral based on 1.73 time line to line voltage.
The fault current will be based on the NGR impedance and line to wye point voltage.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Currents & Voltages during L-Gnd Fault in HRG System

(OP)
@waross, Can you further explain the following part of your response: "the wye point voltage rises to 1.73 of line to line voltage."  So for a 600V 3p, 3 wire system, the wye point voltage would be 600*1.73 = 1038V?  Is this what you are saying?

RE: Currents & Voltages during L-Gnd Fault in HRG System

Sorry, should be "the wye point voltage rises to line to line voltage / 1.73."
347 Volts on a 600 Volt system.
Basically, if "A" phase is grounded, the voltages relative to "A" phase and now ground also stay the same. Of course the exception is "A" phase which is now zero volts to ground.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Currents & Voltages during L-Gnd Fault in HRG System

(OP)
@Waross... Thanks for the clarification...  

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources