Fault current

fault current in network system is always higher than radial system, perhaps city connection is network and rural connection is radial, but i am not sure about this answer.

It would be better specify the situation.

Foir instance:

a) under what conditions this ault would occur(same SIR - Source Impedance Ratio)?

b) same cable equivalent length?

c) what is the voltage level?

d)what is the arc extinguishing means considered?

There are some other considerations, but at least those shall be informed.

Regards

Urban networks contain a concentration of electrical devices more so than a rural area, and therefore more to feed into a fault.

Since the available fault current is limited by the impedance of the supply circuit at the location of the fault, the distance is very important. Rural distances are typically much larger than urban ones.

First order approximations of available fault current use an infinite source, which will always give you an answer that is higher than actual. In urban settings, with multiple possible sources (including the contributions of motors in users' locations) and fairly short distances to the substations, this approximation is close enough to reality that the answer is worth using. In rural settings the increasing distances involved lead to a source which is far from infinite , so the available fault currents are correspondingly lower.

Perhaps someone can explain this better using the proper engineering formulas, but I hope my answer helps.

--jmm

Impedance I suppose. If I threw a spanner across line 2 meters from the generator the total system impedance would be low. If the same spanner was thrown across line 20,000 km away from the generator I guess the fault current would be eaten up by the total system impedance.

Can it also be so that the loads themselves inside the concentrated city represent a form of accumulation of short circuit ampacity? Keep in mind this profound statement comes from dumb diesel mechanic whose mother traded her pre-natal vitamins for vodka and cigars. The accuracy of this is likely 2%. Lunch break over now . . . . thank goodness for you readers.

Yes, x2. Who says you are a dumb diesel mechanic? I don't.

My ex mother-in-law says so. She wanted her daughter to marry the dentist, not a bone head welder fabrication mechanic building gen sets and pump sets coming home smelling of diesel each night. My answer was just a wild guess as I've noticed electricity and hydraulics are very very similar.

Thanks for your kindness!

jmueller & PetroPower have the answer. My municipal system is entirely urban, and my average load density per square mile is 4-5 times that of the adjacent investor utility, and over 10 times the nearby rural co-op. Because of this, nearly all of my wire is very heavy gauge, with the longest feeder less than 6 miles. The resultant impedance is almost negligible.

Additional consideration is that generation in a high-density setting is often directly connected to distribution buses, particularly peaking and backup generation. There's no step-up transformer to choke down the fault current.