CT Secondary Earthing
CT Secondary Earthing
(OP)
Hello,
I need your help regarding with this issue. I'm not an electrical enginnering, but currently i working in this fieid area.
My doubt is: from what i have been reading, the S2 of a Current Transformer should be ground. In that case the current that flows in the secondary will flow to earth in that point (S2)and the circuit will never be closed, because the current never return to S1. If its true, there is a permanent leakedge to earth. How could this work? Peharps this is a huge nonsense, but i have this doubt.
Can somebody help me trying to understand this?
Thanks in advanced
Mike
I need your help regarding with this issue. I'm not an electrical enginnering, but currently i working in this fieid area.
My doubt is: from what i have been reading, the S2 of a Current Transformer should be ground. In that case the current that flows in the secondary will flow to earth in that point (S2)and the circuit will never be closed, because the current never return to S1. If its true, there is a permanent leakedge to earth. How could this work? Peharps this is a huge nonsense, but i have this doubt.
Can somebody help me trying to understand this?
Thanks in advanced
Mike






RE: CT Secondary Earthing
RE: CT Secondary Earthing
I know this is my ignorance speaking, but i would like to understand.
Thank you very much.
RE: CT Secondary Earthing
RE: CT Secondary Earthing
RE: CT Secondary Earthing
In the primary the current flows from the P1 to P2 terminal, and in the secundary the current will
start to flow from S1 (phase) through the load/device, and return to the S2, that is connected to earth for safety precautions. The the current will flow from S2 to S1 and the cycle will repeat.
What would happened if instead of connect S2 to ground, we connect S1, without changing the flows in the primary side?
Thank you all in advanced.
RE: CT Secondary Earthing
RE: CT Secondary Earthing
I must confess that this confuse me...
RE: CT Secondary Earthing
RE: CT Secondary Earthing
In practice, if they were both grounded at the CT terminal, it would short-out the CT secondary winding.
RE: CT Secondary Earthing
And another question, to know the correct secondary to be earthed, we must know the flow in the secondary, ie, P1 to P2, S2 should be grounded and if P2 to P1, S1 should be grounded. Is that correct?
Thank you
RE: CT Secondary Earthing
It does not matter which side of the secondary winding is grounded. It is important to only ground one side at one point. The convention is to have the non-polarity terminal (in this case S2) grounded.
RE: CT Secondary Earthing
When you say "non-polarity" terminal, what does it mean? Because the wire that is connected between the S2 terminal and the load will have a current flow throught it. Am I right?
PS: sorry if my questions seems stupid
RE: CT Secondary Earthing
The polarity dot indicates instantaneous polarity/current direction....which means when the current is flowing into the P1 terminal it flows out of the S1 terminal.
RE: CT Secondary Earthing
RE: CT Secondary Earthing
The convention is to ground the non-polarity side at one point, with a few exceptions. And David is correct about one ground only.
RE: CT Secondary Earthing
My best regards
RE: CT Secondary Earthing
Among less experienced people venturing into system protection and metering, the application of that silly little ground seems to be one of life's larger mysteries.
old field guy
RE: CT Secondary Earthing
ScottyUK (Electrical)5 Mar 15 13:12
The CT secondary circuit forms a closed loop. The loop is connected to earth as a reference at exactly one location. No current flows to earth, it just provides a means of defining the potential at that point in the circuit. If the secondary loop wasn't earthed then the whole secondary circuit could rise to line voltage.
ScottyUk, could you explain me with it more detail this statement: "(...) If the secondary loop wasn't earthed then the whole secondary circuit could rise to line voltage."
Thank you in advanced.
RE: CT Secondary Earthing
Think of the secondary winding at a whole being at some potential...not the potential across the secondary winding, but of the whole winding itself. If one point of the secondary winding is not tied to ground, then that winding could "float up" in potential towards the primary winding's potential.
In all reality, it wouldn't float all the way to the primary winding potential, but it can certainly get high enough to be of serious danger.
So, by tying one end of the secondary winding to ground potential, the maximum voltage that can be present in the secondary circuit is limited to whatever voltage could be developed across the secondary winding itself.
RE: CT Secondary Earthing
RE: CT Secondary Earthing