Hi There,

I'm currently trying to solve arcing occurring in one of my clients siding. At the loading station of the mine, there is an area called RLO (Rapid Load Out station), where they load coal. As a general rule, we design the rail such that it has block joints / insulation on both sides of the RLO. We do this for many reason, one of them to protect the RLO from any stray currents that may result to electrolysis etc. The rail is our negative return path back to the substation, meaning it's our DC earth.
Now, here is my question, this particular clients siding is built next to the power station and the area has a very good AC earthing system in place. Our System design is 3kV DC. Rail must be 100% insulated from AC earth at all the time. There isn't a good insulation and therefore there is some huge arcing from time to time. At some point +/-300VDC voltage was measured across the insulation on the rail. What I need to find out is:
1. What happens when AC and DC at different potentials meet?
2. Could the big transmission lines in the area be the reason for voltage measured on the rail or arcing?
3. Any ideas?

Tnx.
Prof. SLK.

 

It would be helpful if you can provide us with a diagram showing the overall system.

 

If I understand your description, the AC system uses an actual earth, dirt grounding scheme, while the DC system uses a metal rail as a negative leg. The DC leg is not grounded to earth anywhere? This will give you a large voltage potential between the AC ground and either the positive or negative leg of the DC system.

Only if both, the DC and AC system, are grounded together would you not expect to find a potential difference between them.