Groundfault detection query for a mine site 1

[veritas]

Hi

I came across the electrical design for the 480V network for a mineral sands mine in the state if Georgia. The system is high resistance grounded at the supply trfr with the groundfault current limited to 5A. Yet there are no RCD's installed, only fuses on all the final sub-circuits. How is a groundfault then to be detected?

I do not envisage that touch potentials will be an issue and I foresee the touch potentials to be < 50V which is the safety limit here in the IEC world. Not sure what the touch potential safety limit is in the IEEE world.

It being a mine site what would the requirements be regarding groundfault detection?

Thanks in advance.

 

[Kiribanda]

veritas,
In my opinion you may install,
1)SE-701 GF relay from LITTLE FUSE (previously STARTCO)
2)ALLEN-BRADLEY E3/ E3 plus relay for small motors.

 

[veritas]

Thanks, is there however no statutary obligation to have groundfault detection relays installed for a mine site on the 480V high impedance grounded network?

 

[waross]

At the very least I would expect ground detection lights or voltmeters.
I can't put my finger on a requirement in the Canadian code.
However let common sense and good engineering prevail.
The primary reason for impedance grounding is to avoid equipment damage by limiting the ground fault current and to avoid plant shutdowns.
The understanding is that ground faults will be alarmed or indicated and repaired.
If there is no indication of a ground fault and as a result no repair, the fault may persist until a second fault results in a line to ground to line fault.
This may result in the equipment damage and/or an unintended plant shut down that the impedance grounding system was meant to avoid.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[buzzp]

I would check the MSHA requirements. I believe there is a requirement for this with MSHA. The mining industry seems to be only concerned with MSHA vs. common industry practices.

 

[veritas]

Thanks, I am also aware of elevated voltages on the healthy phases during groundfaults on impedance grounded networks which if left unattended could lead to a cross country phase to phase fault. Pretty much what waross alluded to.

Will have a look at MSHA. Thanks.

 

[3I0]

Not familiar with IEC standards but in Canada we have CSA M421 as an electrical standard for mines.

Based on what I have seen in hardrock mining here it is typical for underground LV distribution that in addition to high resistance grounding at the source transformer and overcurrent protection, there is also ground fault plus ground check protection on 600V feeders.