Multiple earth network
Multiple earth network
(OP)
Hi .
For a multiple earthed network(the neutral wire is earthed at the powerhouse, at the point of supply to each consumer and at other points along the line between powerhouse and consumer), I have to use 3 p ACB, that's clear.
But designer wants Ground fault. And CT on neutral.
I know ground fault works like this: is adding all currents in the 4 wires, and vectorial sum different than 0 initiates trip.
Or, in this case... All the time vectorial sum is not 0, since we got earth links everywhere.
Final question: ground fault not applicable to multiple earthed system?
For a multiple earthed network(the neutral wire is earthed at the powerhouse, at the point of supply to each consumer and at other points along the line between powerhouse and consumer), I have to use 3 p ACB, that's clear.
But designer wants Ground fault. And CT on neutral.
I know ground fault works like this: is adding all currents in the 4 wires, and vectorial sum different than 0 initiates trip.
Or, in this case... All the time vectorial sum is not 0, since we got earth links everywhere.
Final question: ground fault not applicable to multiple earthed system?






RE: Multiple earth network
RE: Multiple earth network
1. CT around all phases and neutral, or
2. Current from all CTs summed.
What if you only had one ground at the PEN or a ground only at the PEN and at the load? A ground fault at the load would also bypass the neutral CT.
RE: Multiple earth network
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Multiple earth network
No. Those groundings are all intentional.
Those grounds are the problem, and the normal current(not fault current) will have the shown path in my drawing, i believe! So, the earth fault protection will trip all day long.
Correct?
PS: i talked to an experienced guy; he said that i will have some small, csmall urrent flowing on my shown path(on normal, not fault conditions), but most of current will go through PEN wire. And UEF has smallest setting 40% of ACB current(in this case 0,4*2500=1000 A).
RE: Multiple earth network
Can you describe the physical layout and the distances involved, please?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Multiple earth network
Ground fault protection on multiple grounded neutral systems is set above the maximum zero-sequence load current. Normally, it is either from a summation of the phase currents or from a relay element in the CT residual lead. A separate neutral CT is not normally used for feeders. The ground fault protection for the station transformer would use a CT in the neutral of the transformer as shown by 7anoter4.
RE: Multiple earth network
Best Regards
RE: Multiple earth network
At Transformer side the Ground Fault Relay is connected between transformer star point and the Grounding.
From experience the current imbalance flowing through the neutral conductor will not be more than 50% of the maximum phase current.
For example: S=1000 KVA RatedVoltage=400 V Iphase=1.44 kA let's say maximum per phase current would be 1.2*1.44= 1.73 kA.
The breaker grounding trip current has to be set let's say 0.5*Iphasemaximum.
Then if the setting of ground fault will be Ig=1.73*.5=0.865 kA time=0 sec that means the ground fault will be cleared fast and at still low ground fault current.
At consumer site the GFCI [Ground Fault Circuit Interrupter] will act as usual.
Thanks, waross for your help.
Best Regards