4160V Solid grounded system
4160V Solid grounded system
(OP)
I went through the code requirements in terms of the grounding requirements and haven't seen any limitation on Solid grounded system at any voltage levels.
We have a temeperary application with no load testing. There is not much point to ask for a high resistance grounding system for that. The problem is, we would see a 2kA short circuit at 4160V level which will require a huge size of Neutral conductor. Anybody can shed some light on me?
Thanks in advance.
We have a temeperary application with no load testing. There is not much point to ask for a high resistance grounding system for that. The problem is, we would see a 2kA short circuit at 4160V level which will require a huge size of Neutral conductor. Anybody can shed some light on me?
Thanks in advance.






RE: 4160V Solid grounded system
The ground wire size required depends on how long you plan to let the fault last. 480 V systems have very high fault currents when solidly-grounded and the ground wires survive, although much smaller than the phase conductors.
RE: 4160V Solid grounded system
For utility distribution feeders, solid grounding may make sense, and there are still some 4160 V overhead systems around. It is not a good idea for industrial systems.
RE: 4160V Solid grounded system
Think a little further..if the neutral size depends solely on the scc current, what would be the size of the phase conductors? They would also see the same current during a fault!
Rafiq Bulsara
http://www.srengineersct.com
RE: 4160V Solid grounded system
RE: 4160V Solid grounded system
RE: 4160V Solid grounded system
Rafiq Bulsara
http://www.srengineersct.com
RE: 4160V Solid grounded system
RE: 4160V Solid grounded system
The neutral cable should be sized equal in size to the phase cables if you have a 3-phase, 4-wire system with single-phase 2400V loads. The neutral conductor will be protected from Line-to-neutral fault damage by a 51 Relay on each of the phases of the transformer 4160V winding. Again ensure that I^2t damage limits of the neutral and phase cables are greater than the I^2t of the fault current(2000A) and the relay trip time(t). The 51 phase relay pick-up can be set at 1.25 X Transformer secondary full load amps and wired to trip either Generator main breaker or Transformer secondary main breaker.
Since relay protection is a safety system, then I suggest you get a licensed P.E to look at your application and make the necessary recommendations, with the appropriate documentation, as Rafiq alluded to in an earlier post.
RE: 4160V Solid grounded system
Note that a 12 ohm neutral resistor, on the neutral of the step-up transformer, will reduce the ground fault current to 200 amps or less. This assumes the 4160 V supply is a "Wye" configuration with a grounded neutral.
480V systems are solidly grounded because a slight resistance in the fault can reduce the ground fault current to values less than the feeder protection so the fault may not be cleared. Solidly grounded medium voltage system can give you a severe arc flash hazard. I recommned some resistance grounding.
RE: 4160V Solid grounded system
Resistive (impedance) earthing will limit fault current, BIG BUT,This will allow dangerous voltages to appear exactly where you do not want them during a fault.
You are in fact dicing with death.Balance the equation;
Cost of neutral conductor Versus Death damage and injury.
A no brainer I hope.
Keep away from resistance earthing and let the protection do its job as quickly as possibe.
RE: 4160V Solid grounded system
I'm afraid I have to disagree with virtually everything in your post.
Neutral to earth conductor does not have to be equal in size to phase conductor. It must be sized appropriately for the expected current it will see and the duration of the current.
Despite your dramatic phrases, resistance grounding is accepted and recommended practice for medium-voltage industrial systems.
RE: 4160V Solid grounded system
RE: 4160V Solid grounded system
Resistance earthing in an MV system provides the exact opposite of what you have said in your post. The idea is to (a) limit earth fault current to minimise equipment damage under fault and (b) limit the rise of earth potential at the point of the earth fault by dropping the majority of the phase-earth volts across the NER.
RE: 4160V Solid grounded system
Mr DPC, For a single phase to earth fault, the return must be equally capable of conducting as the phase conductor to maximise scc and clear the fault asap.
As faults are unpredictable it makes sense to prepare for worst scenario.
Mr david beach and mr DPC, Utility companies have decided, in certain circumstances, where the provision of a return path is economically unviable, to reduce the fault current by introducing an impedance. This is justifiable where security of supply takes more precedence over spurious short circuits due to contact with vegetation, etc.
I can only assume from the quoted voltage level that this is not distribution per se but an industrial location.
However,at a distribution level, I know that in one case, a lady who went to see why one of her cattle was not moving, also died.
The point being that limiting current by impedance causes voltage rises where they are most damaging.
Mr David Beach; I have worked in the electrical industry for a speck off thirty years. I have commissioned plant at 10, 15, 20,110,220 and 400kV.I have also in my time, been a protection engineer.
This was my first post, and my last.