Recent content by jpflying

Keith Thanks for the information. JP

Hi all I am doing some work on a hazardous area classification within a coal mine as per the Australian Standards. There is a difference in the equipment required if the resistivity is greater than 1000ohm.metres. Does anybody have any idea of a range of the resistivity of dry coal dust? Thanls

Thanks for the information and now understand.

Thanks you for the information. I have seen zig-zag transformers used to develop a neutral in an un-grounded system.What is the advantage of the zig-zag winding compared to a simple star winding when purchasing a new transformer? Thanks

Can somebody please help me by explaining how a Dzn0 tranformer is wound or operates. I understand the delta connection, but what is the z winding???? How is a z winding wound and what does it do? Thanks

I guess one of my questions was, is there any disadvantages other than cost??

I am involved with a project where the electrical contractor has used stainless steel bolts and nuts for the connection of the Hv feeder and LV mains cables onto the 11kV/433V 1.5MVA transformer as well as on the connection of the mains cables onto the LV main switch. In the past I have always...

rbulsara Sorry about my poor choice of words. Yes, I should have stated the net sum of the currents should equal zero when there is no fault instead of talking about out of balance. My bigger issue was that I thought the armouring would have acted as a shield and the CT would not sense the...

Thanks PHovnanian. I suspected the installation was OK because I have seen this type of installation of the CT over a shielded cable before, but I did not understand the exact theory behind it. I needed to pay more attention about about Maxwell's Equations when I was at University.

I have an installation which is about 25 years old where there is a current transformer fitted onto a steel wired armoured cable for sensitive ground fault protection. The steel wired cable is grounded at both ends, with the earth at the CT end then passing back though the CT in the opposite...

ScottyUK Thanks for the reply. We are currently reviewing the earthing requirements for generators in surface coal mines (Queensland, Australia) and a discussion paper has come to us from our counterparts from another Australian State where they talk about single phase generators with voltage...

Can anybody tell me how a residual voltage device operates. I know how a residual current device (RCD) operators, but not a residual voltage device. Cheers

The Areva BA300 which DiscoP recommneds is a good unit. We have several of them installed and they work fine. Depending on the type of fault detected therelay operates one of two voltage free contacts which are called urgent or non-urgent.

7anoter4 Thanks for the reply. I am based in Australia and the code here only requires the rebar to be tied with tie wire. The job I am looking at has other grounding electrodes in the system - copper sheathed steel vertical rods and copper horizontal grids, but these vary in size in the...

Simmi123 Building foundations can be used as ground electrodes. In this case there are large building foundations adajacent the substations. These foundations are 6m in depth. There are also foundations in the substation compound. The transformes are situated on concrete pads with foudations...