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  1. bfuchs

    Voltage too high

    Gents, Video of substation fire : http://au.youtube.com/watch?v=qvoDNKJX7SU Although I cannot confirm the cause of THIS specific fire one could expect that this is the way most oil-filled transformer which have 'small' internal arcing fault problems would fail : internal arcing faults cause...
  2. bfuchs

    Crculating currents in a neutral

    ...r / D ). In fact "Elements of power system analysis" by William D. Stevenson, Jr (the favourite book of our senior resident elec engineer) states that Xc = 2.862/f * 10e9 * ln (D/r) (and that gives a linear reactance value .. ie per meter) I am sure you have the answer to this question, Boris
  3. bfuchs

    Crculating currents in a neutral

    Thanks for that ! I tried searching for the document mentionned above (EPRI-Power Plant Electrical ref. series VOL.4-WIRE AND CABLES), and have not been successful in locating it. Is downloadable from their website ? Where can I access it (free ? what price ?) Cheers
  4. bfuchs

    Crculating currents in a neutral

    Waross, Can you detail more ? The 4 cables are in a "square" configuration, so the N conductor touches A and C, and is fairly close to B. I would suspect the problem is due to the fact that N is not as close to B (as suggests 7anoter4) as it is to A and C.. Boris
  5. bfuchs

    Crculating currents in a neutral

    Further investigation was conducted on site and this phenomena was discovered on all 3 generators !!! I agree (in principle) that a loose phase cnnection could induce a similareffect, but the fact that 3 generators have the similar issue seems to imply that it is not linked to the cable...
  6. bfuchs

    The difference between a Shunt Trip and a Trip Coil

    A "trip coil" can be either : - shunt trip coils : were the application of voltage causes the coil to trip the breaker - an undervoltage trip coil : where removing the voltage causes the coil to trip the circuit breaker (or application of voltage of voltage is required to close and maintain the...
  7. bfuchs

    Crculating currents in a neutral

    7anoter4, I am interested in your calculations.. can you detail the method ? But to confirm the cable installation : (a) there are 4 groups of cables (b) each group contains 3 phase (400sqmm), 1 neutral (500sqmm) and 1 earth (120sqmm) (c) by starting top left and going clockwise, the groups...
  8. bfuchs

    Crculating currents in a neutral

    The cables are all single-core double-insulated XLPE/PVC outer-sheath. No steel wire armour, and no metal outer shield, so nothing that can be earthed.
  9. bfuchs

    Crculating currents in a neutral

    Additional information : "Gland earthing" : I am assuming reference is made to the what we call the "gland plate" here in Australia, which is the plate through which the cable passes as it enters the switchboard. Both gland plates are earthed, and the slots are cut in the gland plate between...
  10. bfuchs

    Crculating currents in a neutral

    Hi guys, I have a case of circulating currents in a Neutral circuit. The neutral circuit is made up of 4x500 single core cable on a 3 phase 4 wire TNC supply from a generator to a switchboard (Phase are 4x400sqmm per phase). The 'combined' neutral curent on the N circuit was measured at 20A or...
  11. bfuchs

    LV system neutral grounding

    The earthing system I think you are looking for is referred to in IEC60364 as the IT system. The star point is isolated (I) from the earth via a big impedance (a couple of kiloOhms or so), the neutral is connected to the star point of the supply (if you have a neutral, and a star point...
  12. bfuchs

    Three-Lifting Surface

    Hi, There are quite a few pout there ... check out http://www.velocityaircraft.com/ http://www.eracer.org/ http://www.siinc-sources.com/Dragonfly/ etc... All you need in the canard, to ensure stability under stalling is to get a profile for the forward wing to stall before the rear wing. That...
  13. bfuchs

    Increasing wing span

    All these comments are spot on, but there is another which you might want to consider, especially on experimental planes. You might have a swept wing (forward or back), in which case, increasing the span of the wing will change the position of the centre of lift in relation to the centre of...
  14. bfuchs

    One 240mm¦ or 2x120mm¦ solution ?

    Thanks to all for your feedback.<br><br>Khodges,<br>Are you sure about your calcs ?<br>On the 120mm² solution, there will be roughly half the current flowing through the each cable than there would be on the 240mm².<br>So by using your formulas, we would actually be getting less voltage drop...
  15. bfuchs

    Short Circuit

    When two conductive parts at different potentials touch, then you have a short circuit.<br>Once they touch, they are forced to the same potential (at that point), and to compensate for this new forced potential, a new current (aka short circuit current) will develop.
  16. bfuchs

    One 240mm¦ or 2x120mm¦ solution ?

    If you needed to choose, which solution would you go for :<br>&nbsp;&nbsp;- install 2x120mm² cable per phase<br>&nbsp;&nbsp;- install 1x240mm² cable per phase<br><br>We assume of course that both are possible. (2 separate 120s can carry more than 1 240, but we'll assume here that a mutual...
  17. bfuchs

    small 9 volt motors

    Hi,<br><br>Graupner and Plettenberg are two well known names in the Remote controlled (planes, cars, ...) industry for small electric motors (&lt;9V, 20A DC, 20,000 rpm off load ).<br><br>In any case those are what I use in my plane models.<br><br>Is this what you are looking for ?
  18. bfuchs

    What is the most effective way to bring down percentage ofT H D and

    If you have mainly triplen harmonics (3rd, 9th, ...), and these are balanced on the phases, then using an isolating transfomer will prevent these harmonics from spreading up to the main transformer, and will remain confined to the isolated part of the network.<br><br>This works well with 3rd...
  19. bfuchs

    What is the most effective way to bring down percentage ofT H D and

    Fritz,<br><br>THD (Total Harmonic Distortion) is a measure of the harmonic disturbance on your network due to the loads connected. One can talk about THD in Volatge or Current.<br><br>Certain loads draw harmonic current.<br>In a normal installation, this current flows through the...
  20. bfuchs

    Diesel Generator Problem

    Are you measuring the voltage on load ? or off load ?<br>I assume you want to ensure 208V on load, right ?<br>In this case, it is not unusual to have an off load voltage slightly higher (there is ususlly a 5% difference on transformers for instance...).<br><br>

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