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  1. Prospero

    Earthing on a black bag landfill

    A client wants to build a new works on a disused landfill. There will be a number of 11/0.415KV substations on site. FYI - there will be a 1-2m aggregate capping layer and hardstanding. Does anyone have any experience of how to approach the earthing in such a situation?
  2. Prospero

    Thyristor Firing

    We have a requirement to soft start a 800kw pump, the ramp time is expected to be around 30secs. Our consultant tells me the soft starts will be 'block fired'. I (partially) remember we had some furnaces which were thyristor controlled and there were issues with harmonics and high earth and...
  3. Prospero

    Earthing or Grounding

    Hello Colin, I too work for a water company in the UK, and I too have wondered where this often quoted 1ohm comes from. Recently I was told that it originates from Engineering Recommendation G12 (PME installations)and, as Isquared states, is applicable where the HV and LV systems share a...
  4. Prospero

    Earth Fault Levels - UK

    ScottyUK + isquaredr Where does the 20 Ohm and 0.35/0.8 Ohm values come from? - I have read the Electricty Safety, Quality + Continuity Regs and there is nothing so specific in there!? The loop Z was taken at the incoming side or our LV ACB Wareagle A large part of our electrical...
  5. Prospero

    Earth Fault Levels - UK

    For the UK . . I work for a large utility in the Sth of England. We have a DNO substation located in a compound on our site, this is a sole supply - we are the only consumer on this transformer. The DNO provides us with a 500KVA supply at 415VAC, the LV tails are 25m long and terminate into...
  6. Prospero

    Audio/Video equipment on same phase?

    Supply quality Maybe quality of the power supply and harmonics are an issue here too . . . With audio/visual equipment there is the possibility that any dirt on the power supply can get through and affect the system. On a digital system a power spike could concievably cause erratic behaviour or...
  7. Prospero

    Mercury Rectifiers

    In olden times mercury was used in rectifiers. Why was mercury used and how did these rectifiers operate ie was there an ionised gas with a grid voltage between anode and cathode?
  8. Prospero

    Inverter calculations

    I need to work out the DC power input to a inverter to supply a 3 phase output of 35KVA at 415V (I'm English) at power factor of 0.8, the inverter effiency is 90%. DC input: 420V. I've had a go at doing the calc but am unsure whether to apply the root 3 factor to the ouput.
  9. Prospero

    Old Cable 11Kv testing

    Thankyou all for the high quality advice. Hot oil test, nitrogen test. . . what are they?
  10. Prospero

    Old Cable 11Kv testing

    I want to know if I can joint an old 11kV cable that's 50yrs old? The cable is an armoured with a 150mm csa, about 0.5 mile long and goes under a stream. It also passes through ground that has injected sewage sludge in it, which I'm told can deteriorate the physical integrity, so . . . i) What...
  11. Prospero

    Cable temperature

    Also, having an idea of how the external temp relates to the conductor temp and hence current, could this be a method to determine the loading on the cable?
  12. Prospero

    Cable temperature

    How can I find out the average conductor temperature of a cable, if I know the th external temp of the cable, the ambient temp/humidity and the cable type/construction? I have got some 4 core (TP&N) XLPE SWA cu conductor cables in the range 35-300mm, which are quite warm to the touch.

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