Underground Mine grounding

[tulum]

Hello,

I am looking for any articles/comments on mine grounding systems. Since there are many mining communities in the vicinity of my city, I would like to get familier with mining electrics.

I read an article that said Mines have a SYSTEM ground (ground grid - main susbstation) on the surface of the mine, and a separate grounding system called the SAFETY ground for the underground portion of the mine. Is this always true?

Another thing I came across was there is a standard in the mines to provide a ground bus inside surface control houses (switchgear inside a building) that is mounted on 600v insulators. What is the purpose of this? All the switchgear circuits are tied to this bus, however the switchgear circuits are also bonded to the building...

Any suggestions or article references appreciated.

Regards,
TULUM

 

[cuky2000]

Suggestion:

Search for grounding in the enclose site:

http://www.msha.gov/welcome.htm

 

[tulum]

Thanks cuky,

I will check it out...

One more question though;

I have two pieces of switchgear (same man.) but the ground bus on the one unit is mounted on metal angles spaced every couple of feet (cont. throughout unit). The ground bus on the next unit is bolted flat to the enclosure wall (cont. throughout unit). Are there any electrical issues with laying groundbus directly on enclosure like this?

Regards,
TULUM

 

[mc5w]

The equipment grounds are connected directly to the grounding electrodes. The power sources are resistance grounded even for 110 or 120 volts single phase.

The cords are supposed to have shielding of all conductors so that a broken wire strand will ground out before reaching the surface or an adjacent wire.

Both the branch circuit and the feeder are supposed to have equipment ground fault protection that will trip both the branch and feeder breakers upon a branch circuit ground fault.

The cords also have continuous monitoring of the equipment ground. At the load end of the ground check conductor there is a diode that connects the ground check conductor to the machine frame. At the supply end of the cord a special relay looks for the half wave rectified current that the diode produces. If there is no current the realy cuts the power until the correct polarity current comes back. If the opposite polarity of current or full AC flows through the relay the relay locks out. There is also a way to connect a resistor, a start button, and a stop button to the ground check conductor at the load end so as to remotely control the power relay.

Al 4 of these protection levels produce cords up to 13,800 volts impedance grounded that are as safe as breakfast food. You can deliberately drive a nail into an 1,100 volt or 3,300 volt cord while it is energized and it will not hurt you. You would have to actually cut the cord with an axe ro run it over with a heaby machine to have a fire.