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Discuss Help with apparent power, reactive power etc in the Electrical Forum area at

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  1. Pauly.22

    Pauly.22 Guest


    I've got 8 questions to do for my assignment, i've done 7 of them and im happy with them, i've got down to the last question and im totally stuck.

    this is the question.

    Small Machine shop,

    The supply to this is a TN-C-S system, 400v/230v 50hz. the measured value of prospective fault current is (Ipsc) at the incoming terminal is 884.6amps

    The construction is brick and thermal block, with a smooth plaster finish. The floor is concrete with a 50mm screed. the ceiling is 3.6 meters above the finished floor level, and is constructed from plaster boardwith a s mooth plaster finish, on wooden trusses. The roof is pitched and has a loft hatch space accessible through a hatch (postion no specified)


    Lathes 5kw @ a p.f COS = 0.7 lagging

    Drilling machine 4kw @ a p f COS =0.8 lagging

    Milling machine 3kw @ a p f COS = 0.6 lagging.

    the question is

    Dertimine the total connected power, apparent power, reactive power, and overall power factor in cluding the lighting chose. for each demand above, for lighting power consumption and power factor use manufacturers data.

    so i need to find out some manufacturers data too for the lights too.

    any help will be great just to get me started or some of the question done, even if i just do part of the question, and ill just say i couldn't get any further.

    I know i need to use the triangles sine, can tan etc but im unsure where to start

    Since i was given this work, i have been working away in slough train station, monday to friday, i work in tesco on saturday, so i haven't had much time to complete it.

    Many thanks, Paul.
  2. telectrix

    telectrix Scouser and Proud of It Respected Member

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    tony's your man for this one. he crunches those calculations in his sleep.
  3. Knobhead

    Knobhead Guest

    PM your e-mail address and I’ll send you two spreadsheets of calculations. One is for 3 phase, the other for cumulative PF correction.

    Lathe = 9.38A
    Drill = 6.92A
    Miller = 6.02A

    PS I don't crunch the numbers in my sleep, the computer does it for me.
  4. i=p/u

    i=p/u Electrician's Arms

    is that the same sheet you sent me tony...
  5. Knobhead

    Knobhead Guest

    PPS what the hell has brick walls and a plaster ceiling got to do with it?
    The joys of exam questions, throw a load of garbage in to add to the confusion.
    • Like Like x 1
  6. Knobhead

    Knobhead Guest

    Yes but forgot to send you the PF sheet.
  7. i=p/u

    i=p/u Electrician's Arms

    what ya waiting for sister , gimmi look
  8. Knobhead

    Knobhead Guest

    Say please!

    It's OK it's sent
  9. Pauly.22

    Pauly.22 Guest

    many thanks people, does anyone have a step by step guide to working it out, as they want to see my calculations, and i need to learn how to do it,

    all you get at college is a brief look at it before moving on to the next thing.

  10. i=p/u

    i=p/u Electrician's Arms

    R/Z= pf
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