Inability of Earth fault protection system

Do you have a circuit diagram of the installation?

Please refer to our web site for circuit diagram.

REGARDS

MSJ

Basically you have to understand the earth fault system in relation to circuit neutral configuration.

1.In case of Y connected system ie with neutral solidly grounded the Earth fault protection is done by connecting residually connecting all three phases o.current elements and also putting up a stabilizing resistance by a rheostat on the return path to take care of CT uneven saturations during switching and this is very stable and free from spurious tripping if the relay co-ordination is proper.

Apart from that in modern domestic instalations the modern ELCB concept the threephases and the neutral wire all four wires has to be passed through a zero sequence CT and if there is a shield wire in that case the shield wire has to be re inserted through the CT and in the direction of the power flow and then separately grounded.Again this shield has to be grounded on the panel ends only not on the field side.

For Unearthed system where the transformer vector group is Delta connected or neutral is grounded through NGR or NGT ie high impedance grounding the residualy connection does not work in this case there should be zero sequence CT to achieve a proper very sensitive earth fault.

So, what your trying to say, is that when running a Delta type transformer, where you have a high resistance to ground of the 3 phases, your having a problem tripping out the ECLB?

Well, if this is what I'm reading, then of course you will have a problem, but at the same time, the person who is holding on to the live conductor will not be zapped as much, as the current return path to the transformer is already a high resistance, its the same as a bird sitting on a powerline, its common to that line, its not connecting from that line to another potential

in Single-PH ECLB's, you have the A & N lines passing thru the torroid, so, from Active, it goes thru the torroid to the load and back thru the same torroid to Neutral, if there is a earthing of either line (thus bypassing the current path around the torroid) you will get a imbalance, so you will get a voltage on the secondary winding of the torroid, that secondary winding is connected to a solenoid that trips the breaker.

If there is no return path, or it is of high enough resistance (as in your Delta connected transformer) then this imbalance in the torroid will not trip the breaker.

I havn't ripped apart a 3-PH ECLB, but I'd think they are connected in a similar fashion, as below

L1 - T1 - R (Load)
L2 - T1 - S (Load)
L3 - T1 - T (Load)
N - T1 - N (Load)

I hope that worked, Hey, can we bring back ASCII art ;o)

As I said, I havn't ripped one apart, so I'm not fully sure about the construction.

Thank you very much for your trying.

The earthing system is solidly.

REGARDS

MSJ

Do you try to measure/protect against earth faults through the transformer?

As a transformer is a galvanic separation, you will never be able to do this.

Please provide us some shematics, then we can see what is going wrong.

If you fear that everyone on the internet can see them you can send the shematics to us through the mail function (create yourself a nickname and off you go)

I didn't have a problem,

Thank you very much.

In the case of auto- transformer such arrangement does not work. If the CT is placed in the neutral earthing conductor of transformer feeding the autotransformer it will work

Because of electrical and magnetically coupling between primary and secondary windings of auto transformers, the primary and secondary earth fault currents are mixed in neutral point of transformer. The difference phase angle between secondary current and induced primary current is approximately 180 degree, therefore the amount of through earth fault current is the difference of Ip and Is , where the Ip and Is are the primary and secondary earth fault current respectively. So the earth fault protection system in neutral point can not detect actual primary or secondary earth fault currents.