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  1. torslum

    Inverter fed Explosion Proof Motors

    Thanks guys. I've got a few technical catalogues on the subject, and I believe you are right in assuming that ABB and Siemens are quite up-to-date. However, they tend to favour their own inverters. A little bit more independent is Loher, which is very well known German company for Ex-motors at...
  2. torslum

    Inverter fed Explosion Proof Motors

    Dear colleagues, I am a little confused regarding ex-certified motors connected to an inverter of any brand. As I live in Europe, I will stick to European/IEC-terms regarding this issue, but I believe that the consequenses should be more or less the same anywhere.... As far as I understand...
  3. torslum

    460V VFD running a 230V motor

    You should also pay attention to the output frequency; if running in open loop, you would most probably get a reduced frequency at 230V (when your drive is 460V) unless you have programmed the drive correctly. The U/f-ratio should be correct, and you can usually program this in your drive. The...
  4. torslum

    Parallel combination of VSD

    Agree with Gunnar; make sure the gatesignals are synchronized or in practice that the vendor you use have done this kind of paralleing before. Some vendors have so-called master-slave applications where gatesignals are not synchronized, but loadsharing is taken care of on a controller-level...
  5. torslum

    star point

    Connecting the starpoint of a transformer, generator et.c. to ground is giving you a TN- or TT- system (the first T means solidly grounded neutralpoint). The other letter is determining how your PE-conductor goes. If the neutral is not connected to ground, you would have a floating neutral...
  6. torslum

    What is the difference between Open or Closed Loop Flux Vector Control

    Pirates wrote: Surely VSD s cannot induce their own amperage!! Why do we get a difference between AC amps going in to the VSD and the amps going into the motor? Amps into motor higher than amps into the VSD. - Well, it can ;) Just as you describied yourself, the V/f-ratio makes the voltage...
  7. torslum

    Precharing of VFDs on a common dc-link

    Thanks for your valuable replies, everyone. I am aware of the derating for regular breakers and fuses, and the increased risk of arcing due to DC. Any good suggestion on equipment that is particularly well suited for such applications?
  8. torslum

    Motor Insulation resistance was bad

    You did not mention anything about age, condition or environment. My first thought is that the motor could be dirty or situated in moist air et.c? Particularly since the insulation resistance seems to increase while you've run it for a while, and the heat could have removed some moist or...
  9. torslum

    Overloading Transformer

    I agree with the above. Also worth mentioning, the only thing that is really interesting when it comes to overloading a transformer, is the winding temperature. If you have measurements of this temperature, then you can overload your transformer whatever you want within the insulation class...
  10. torslum

    Power measurement VSD

    maypot; to me, that sounds like a very strange explaination? What brand is this? Did you read the power as kW directly from the display, or did you calculate it from some other readings? No way a drive should show 100kW less just because you didn't play any magnetizing current right? Good...
  11. torslum

    TT and TN-system and RCD

    According to IEC60364, for TN-systems and protection against electrical shock: 413.1.3.3: It is said that Zs*Ia <= U0, i.e. system-impedancem multiplied by the minimum current that assures that the breaker is disconnected within a given time should be less than the nominal phase-voltage. The...
  12. torslum

    Power measurement VSD

    Sounds strange, I agree.... Guess you've double checked the ratios and settings of the Fluke measurement already? If we assume that the 300kW measurement is definitely, I would check out how the VSD is doing it's power calculation. Is it giving 200kW to the display directly, or is it given as...
  13. torslum

    Precharing of VFDs on a common dc-link

    Dear colleagues, I am doing some brainstorming on how to complete a VFD-system with several large inverters connected to a common dc-link and with one rectifier to supply the DC. First thing on my mind is how to precharge the capasitors which are already in the inverters. I am, ofcourse, aware...
  14. torslum

    Generator output filter

    As explained by rbulsara it might very well be that the harmonics created by the UPS and other equipment is making the AVR go mad, because it is not suited for operation with such large amount of disturbancies. Some manufacturers providing input filters for their AVRs. I guess this is doing...
  15. torslum

    TT and TN-system and RCD

    Not to sure about that the kindergartens. In Norway, we use the Cenelec/EN and IEC-rules also, even if we are not a EU-member. But all countries can add their own, specific additions to such standards. Maybe this is the case, if there is a specific requirement of 30mA or 25V for a kindergarten...
  16. torslum

    TT and TN-system and RCD

    Not sure if we disagree, but just to clearify: zeusfaber: According to the IEC rules, RCDs are not to be used on TN-C systems. If used in a TN-C-S (i.e. a combination of TN-C and TN-S), RCDs should ONLY be used in the TN-S part of the system, meaning after splitting the PEN-condutctor into one...
  17. torslum

    Why can't I run my 60hz motor on 50hz?

    Short quote from Hubert, C.: Electric machines. Operating an induction motor at significantly below rated frequency, such as operating a 60Hz motor at 50Hz, causes a significant decrease in magnetizing reactance and, because of magnetic saturation effets, an out-of-proportion increase in...
  18. torslum

    Transformer 7.5 degrees phase-shift explained?

    Dear all, I'm very familiar with phase-shift transformers supplying for instance large VFD- or other rectifier-loads. I totally understand how and why a phase-shift of 30dgs eliminates the 5th and 7th harmonic on the primary-side on for-instance a three-winding transformer. Of course, the same...
  19. torslum

    Harmonics and Nuisance Earth Fault

    For certain, the magnetizing current of a transformer is containing a large amount of third harmonics (i.e. when starting up the transformer, the inrush current contain a lot of third harmonics), and I guess the same goes for magnetizing a motor. I would guess, as davidbeach says, if the earth...

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