Lets assume an uninterrupted fault at a property.The earth loop impedance at the house is 200 ohms.
Lets break it down
Assuming the line impedance is zero.
The Ra of the house is 180 ohms--- The Ra of the transformer earth is 20 ohms
So 230v/200 =1.15 amps
Voltage dropped at house = 1.15 x 180 = 207 volts
Voltage dropped at transformer = 1.15 x 20 = 23 volts
So all propertys connected to that transformer will see a voltage of 23 volts between the neutral and true earth
This doesn't make sense to me at all - for a start, no one mentioned a fault and Ra shouldn't come in to it.
Let me try to explain my way of thinking a bit better.
We have the Rod that the OP has installed at 'true earth' potential - 0 volts.
We have our incomming 'Line' and 'Neutral' at the cutout - we'll use nominal, so 230v.
NO load:
If we take a 'voltage' reading between '
L' &
'N' we should get roughly
230v
If we take a 'voltage' reading between
'L' and the '
rod' we should get roughly 230v
Neutral to the 'rod' should read
0 volts.
If we then switch some appliances on in the house, applying a load of, say, 12 ohms, and we assume an impedance in the supply neutral of 0.1 ohms.
This will give a total impedance from the cutout(Line) to the star point of 12.1 ohms.
Current flowing therefore = 230 / 12.1 = 19 A.
Volt drop across 'load' (installation) = 19 X 12 = 228 v
Volt drop across supply Neutral conductor = 19 X 0.1 = 1.9 v
So the potential difference between the Neutral connection at the cutout and the star-point(true earth 0 v) is 1.9 v - the same as it will be to the 'rod' (also 0v)
So,
If we take a 'voltage' reading between '
L' &
'N' across the load, we would get 228v.
If we take a 'voltage' reading between '
L' and the '
rod' we should get roughly 230v
Neutral to the 'rod' should now read
1.9 volts, as there is a 19 A current flowing.
This is one reason that they 'rod' the PEN conductor at regular intervals on a PME supply - to hold the Neutral at 0 v.
