ungrounded star system

[Mr zezo]

delta star distribution transformer(11/.38). the neutral of the transformer star is solidly grounded,
if the system is converted to ungrounded system as the neutral grounding is removed ,then what is effect of that during ph to ground fault Specially on single ph loads (220v) line to neutral for each ph even the faulted ph?
thanks

 

[waross]

With one line grounded:
Voltage to ground on ungrounded phases = line to line voltage.
Voltage to ground on neutral = line to neutral voltage.
Voltage line to line, all phases = line to line voltage.

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Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

I have the following opinion for your consideration.
With 3-phase L1,2,3 and Neutral 4-wires, where the Neutral is NOT earthed.
1. The system works fine with 220V loads connected to L1-N, L2-N and L3-N. The loads can be balance or unbalance.
2. When say L1 is dead-short to earth.
a) V (L1-N)= V (L2-N)= V (L3-N) = 220V. but (L1-E) = 0V. where V (L1-L2)= V (L2-L3)= 380V.
b) V (L2-E) = V (L3-E)= 380V !.
2.1 Caution: this rise in voltage from 220V to 380V can be damaging !
3. Suggestion: It is strongly recommend the Neutral shall be either solidly or impedance earthed.
Che Kuan Yau (Singapore)