LV 3 pole ACB & Neutral

[Mr zezo]

hi there ;
for LV 3pole ACB (without using external ct for Neutral)
1_how the breaker calculate the Neutral current is it the vector sum of L1+L2+L3
and what will be the different of the reading of N if we connect external ct for N.
2_ for ground fault function :
_what is the difference bet ground fault and Neutral protection?
_ how the ground fault function works as it must be external ct for N (for residual GF ) what is the eq of calculating lgf
is it like that (L1+L2+L3+N=Igf) ; then what should happen if Neutral external ct is not connected and gf function is activited; will it deal with neutral in the eq as N=0 so there is aground fault always and it should trip if the value equal to the adjusted value or what ? and does it mean for question no 1 the breaker is read ground current not neutral current but why the cb shows the reading of N although neutral ct is not connected and it may be a false reading ?
thanks.

 

[waross]

The neutral conductor will be connected to the transformer neutral or wye point. Connect a CT in this conductor to monitor neutral current.
The ground conductor will be connected to the transformer neutral or wye point. Connect a CT in this conductor to monitor ground fault or leakage current.
Three CTs may be used to monitor unbalanced current whether neutral current or ground fault or leakage current, without indicating whether the unbalance is neutral current or ground current.
In the absence of line to neutral loads, it may be assumed that any unbalance detected by three CTs is ground current.

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

 

[che12345]

Mr zezo (Electrical)(OP)23 Sep 24 13:13
' for LV 3pole ACB (without using external ct for Neutral). 1_how the breaker calculate the Neutral current is it the vector sum of L1+L2+L3 and what will be the different of the reading of N if we connect external ct for N'.
A 3pole ACB reads only L1, L2 and L3, where IN is not measured/indicated. A 3pole ACB has no provision for the external CT.

' 2_ for ground fault function :
_what is the difference bet ground fault and Neutral protection?'
a) GF is when (I1,2,3,and IN) is NOT = 0.
b) Neutral protection is to protect the Neutral of a 4pole ACB. Attention: This is extremely important for a 4pole ACB which is with half-size (Neutral pole). Another case is the Neutral current may > the line current, due to heavy third harmonics loads.

' _ how the ground fault function works as it must be external ct for N (for residual GF ) what is the eq of calculating lgf
is it like that (L1+L2+L3+N=Igf) ; then what should happen if Neutral external ct is not connected and gf function is activited; will it deal with neutral in the eq as N=0 so there is aground fault always and it should trip if the value equal to the adjusted value or what ?'

Irrespective whether a 3 or 4pole ACB, they are (usually) NOT designed for any external CT to be wired into their system. Usual solution is to have (external) 4 CTs or 1 ZCT wired to operated the GF relay, which trips the breaker by shunt/UV release.

' and does it mean for question no 1 the breaker is read ground current not neutral current but why the cb shows the reading of N although neutral ct is not connected and it may be a false reading ?'

a) A 3pole ACB reads only I1,2,and 3 . Any Neural current indication is to be ignored, as the external CT is NOT wired into it.
b) Only a 4pole ACB reads I1,2,3,and N . In this case external CT is NOT required. It can read I GF, without the external CT.
Che Kuan Yau (Singapore)

 

[davidbeach]

I seem to recall neutral sensors being available options on ACB type 3-pole breakers 20+ years ago. Don't think they would have disappeared.

When one this sentence into the German to translate wanted, would one the fact exploit, that the word order and the punctuation already with the German conventions agree.

-- Douglas Hofstadter, Jan 1982