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?
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
Here's a exemple:
RE: Currents & Voltages during L-Gnd Fault in HRG System
RE: Currents & Voltages during L-Gnd Fault in HRG System
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
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
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
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
RE: Currents & Voltages during L-Gnd Fault in HRG System
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
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"Why not the best?"
Jimmy Carter
RE: Currents & Voltages during L-Gnd Fault in HRG System
RE: Currents & Voltages during L-Gnd Fault in HRG System
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
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"Why not the best?"
Jimmy Carter
RE: Currents & Voltages during L-Gnd Fault in HRG System