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  1. 230842

    filament temperature

    Thanks nbucska. The problem is to meassure temperature Julian
  2. 230842

    filament temperature

    My purpose was to teach my pupils, by Lab meassurements, the temperature dependence of electrical conductors getting practical curve resistance-temperature. It seems to be a very dificult objective, so any other suggestion will be appreciated. Julian
  3. 230842

    Current Transformers

    Secondary taps should be marked. There have been several ways to identify polarity. If you could read such a marks it could help to give you an answer. Maybe you have to get some covers out. Otherwise, you should test. A ohm reading will probably give you no significative information since CT...
  4. 230842

    Unbalanced load/negative sequence currents.

    Besides eddy current heatings, I think there is other negative impact of reverse-rotating field produced for negative sequence currents: That reverse-rotating field induces a double frequence voltage on excitation dc windings that can damage excitation circuit components. That do not occur when...
  5. 230842

    calculation for current in delta connected system.(unbalanced load)

    I´ll try to answer your questions. 1.- Current phases can be be obtained from some data values to be got from Manufacturer: - Real (active)and reactive powers of every branch: tan(phi) = Reactive/real = Q/P - Voltage and Real Power of every branch: cos(phi) = P/(V.I) - Power...
  6. 230842

    calculation for current in delta connected system.(unbalanced load)

    Current phase (angle) values are missing in your post. So there can be infinity valid results. Kirchhoff ecuations are fully applicable provided that current phasors (complex quantities) are used to. Julian
  7. 230842

    Constant Wattage Autotransformer (Ballast)

    Ballasts are reactors with positive voltage-current characteristic compensating the arc negative performance. That could be done with resistors but resistors waste energy while reactors do not. Besides, reactors allow for arc lightening. Frequently, ballasts combines reactor and trasformer, for...
  8. 230842

    transmission line

    Yes. You'r right Julian
  9. 230842

    CT strikes again

    Hi. After some investigation I've got two first approach formulas giving the turn number correction produced by the use of the auxiliary parallel winding technique: - N, R: Number of turns and resistance of main winding - Na; Ra: Number of turns and resistance of auxiliary parallel winding...
  10. 230842

    CT strikes again

    Wellcome Scottf. I wish my star is the first. Since no documentatios is apparently availabe, I'll try to investigate myself on the matter to find out the technical reasons that could justify that correction procedure. Does it perhaps provide a correction equivalent to a fraction of one...
  11. 230842

    CT strikes again

    Scottf: Your answer looks quite reasonable. Do you know any book, paper or site to get technical information on the matter? I thank you very much. Julian
  12. 230842

    CT strikes again

    scottf The accuracy is rated class .2 Julian
  13. 230842

    CT strikes again

    Thanks togtt. I think your post do no answer my question: it refers to a ring type core CT as displayed in Figs 4B and 4D of ABB's document; the additional winding is directly made close and around the core and its turns are mixed with secondary ones; it is made with a significatively thinner...
  14. 230842

    CT strikes again

    I've opened a low voltage CT rated 300/5A to see internal construction details and have observed the secondary is composed by two parallel windings: One has 60 turns (which seems right) but the other has only 59 turns and is constructed with a thinner wire. Can anybody explain this? Julian
  15. 230842

    Unbalanced Transformer Loads

    If neutral is not earthed at all, then system is floating because it is not referenced to eart. If neutral is earthed (even poorly) neutral voltage is null, since no current can flow to earth. If your question refers to the neutral voltage displacement due to umbalanced loads, then you can...
  16. 230842

    Instrument Transformer

    ANSI/IEEE C57.12.80 defines an Instrument Transformer as "A transformer which is intended to reproduce in its secondary circuit, in a definite and known proportion, the current or voltage of its primary circuit, with the phase relations and waveform substantially preserved". In...
  17. 230842

    Maximum transformer power

    It is not easy to answer your question. Any additional data are needed even to give any advice. The most important concern the rated voltages and the iron and copper weights. Any other procedure needs tests and meassurements procedures and equipments. To determine rated voltages, no load...
  18. 230842

    bandpass filter

    If you contact me at chacon@des.icai.upco.es I can send you a schematic with two op-amps allowing a bandpass filtering with a bandwidth of about 1.3 khz and a quality factor of about 100 Julian
  19. 230842

    line resistance

    What relative (%) difference amount are you referring to? Julian
  20. 230842

    Checking Phase Sequence

    Are you ready to construct your own home-made phase sequence tester? all what you need is two resistors, one capacitor and a simple multimeter (able to meassure line voltage). If you are interested let me know and I´ll mail a simple scheme. Device operates on three lines without neutral. Julian

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