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Recent content by Pafi

  1. Pafi

    protection for cables in parallel

    Hello! I have a load supplied with 2 cables in parallel per phase and I had to use 1000A/ 690V fuses in order to protect the cables for short circuit. These fuses are hard to find - not on stock, anyway - and size is 4a. Can I use instead one fuse for each of the 2 identical cables in...
  2. Pafi

    problems with contactors

    I made some tests, inspired by the grading capacitors used to diminish - smooth - the TRV curve in HV breakers. I put AC capacitors, 3uF, between the poles of the same phase of the contactor(in parallel with the contact). And the switch-off electric arc has very much diminished. But I don't know...
  3. Pafi

    Power quality analysers

    I think that first you have to check if it is a class A instrument(there is a measurement standard, don't remember the name). I have an older HT analyser and it was very reliable, I still use it today but meanwhile this standard appeared and class A instruments should be manufactured according...
  4. Pafi

    Power quality analysers

    I have Elspec 4500. If you look for something to take easy and fast measurements on the field, don't buy it. If you want a meter for troubleshooting difficult problems or you need data for long time in order to do post processing, it is very good. Post processing takes long time, you need to...
  5. Pafi

    problems with contactors

    I wonder if anyone has an idea about how to protect/ improve maintenance performance for three phase contactors used with shunt reactors. My circuit voltage is 3x660V and I'm using multiple steps with shunt reactors, switched ON and OFF by air type contactors in order to regulate the power...
  6. Pafi

    Impedance in parallel with surge arrester

    I have also read articles about surge protection (for HV motors, transformers) using surge arresters in combination - parallel - with RC filters where R approx.30 Ohms and capacitor approx. 0.25-0.5 uF.
  7. Pafi

    reactor for SVC

    And the second linkhttp://files.engineering.com/getfile.aspx?folder=e9a9df19-4215-4872-89f4-b37736f9183e&file=SVC_page2.pdf
  8. Pafi

    reactor for SVC

    I have attached 2 links, one with the schematic and the second it is a page from Alstom document where at the bottom there is a picture where the main TCR reactor(made from 2 halves) and the much smaller series reactor can be seen. thanks! Pafi...
  9. Pafi

    reactor for SVC

    Thanks for your answers! The replacement reactor had exactly the same parameters - in terms of L. Trench received the technical file of the original. It is not, obvious, exactly the same, it is heating a little more, but the dimensions have been very close. But Trench sent the results of tests...
  10. Pafi

    reactor for SVC

    Hello! I wonder if someone on the forum knows the role of the second much smaller reactor in series connection with each branch of TCR reactor. The TCR reactor is made up from 3 air core reactors - one for each phase. Each phase reactor is devided into 2 equal halves but - at least for this...
  11. Pafi

    20kV reactor surge protection

    Hello! I want to ask you about surge protection for three phase shunt iron core reactor on medium voltage (20kV). I want to use surge arresters and surge capacitors. My problem is that there are 3 single phase reactors which I must connect in wye connection in order to have a three phase...
  12. Pafi

    inverter - motor mismatch

    Thanks for your advice! From what I understood the problem was that they didn't oversized the motor - it is for a pump - and now they cannot fulfill the parameters, so they need the whole 315kW. Anyway, my oppinion is (after reading YOUR oppinion) that there is no other solution but to change...
  13. Pafi

    inverter - motor mismatch

    I have a problem regarding one client who ordered inverter and motor from different manufacturers and not matching characteristics. The inverter is for 315kW/ 3x400V, 50Hz asynchronous motor but the current capability (616A) and kVA rating are under what the supplied electric motor needs. It is...
  14. Pafi

    RC protection for surges

    Hello! I'm looking for hints on how to design the RC protection for large motors started and protected with vacuum breakers. I have read that together with surge supressors there is a need for RC group surge protection to limit the steepness of voltage rise. I know that usually you have to make...
  15. Pafi

    System harmonics

    I think will be better to detail a little: - where did you make the measurements (suppose 11kV, on each transformer) - which THD did you measure - voltage or current, I suppose current - if there are not capacitor banks installed on either of the 2 suppplies, then I would say that the current...
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