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Recent content by sibeen

  1. sibeen

    Elevator Motor in-rush current on renewable backup power

    You had also best think of what you are going to do with the energy the elevator is going to regen and try to feed back into your inverter. You're going to have to dump that excess somehow.
  2. sibeen

    DC fuse & circuit breaker questions

    I don't live in the IEEE / NEC world but there has to be millions of breakers rated to at least 48 volts installed in all the various telcos which use -48 volts as their standard distribution voltage with exchanges. And a DIN rail breaker mounts on a piece of DIN rail, you don't need a special...
  3. sibeen

    How to use CL CB's let-through curves

    Veritas, look at the 100 kA point and go up to the orange line and then across, it looks like you get approximately 220 kA projected onto the left hand scale. As this is way higher than the calculated symetrical fault current it can only lead to one conclusion :)
  4. sibeen

    Soft starter rating selection

    jraef, could you please expand on why the two phase version of a soft starter is so problematic.
  5. sibeen

    Power Factor Correction

    Check your cals. For 25 kVAR you need an impedance of 0.4j ohms. Assuming a 50 Hz feed 0.4/(2 pi 50) does not equal 7.96 * 10^-6Henry.
  6. sibeen

    VFD and motor contribution to lineside faults

    Bill, one of the first suggestions made was for a load bank to be installed in the generator room and switched in whenever the regen exceeds the load. Haven't heard from the client so they are still mulling over the initial report.
  7. sibeen

    VFD and motor contribution to lineside faults

    Muthu, there's no braking resistors on the drives and no room to install any, and that power has to go somewhere. One option we are kicking around is a load bank installed near the generators that can be quickly electronically switched in when required, but as I said this is very early days and...
  8. sibeen

    VFD and motor contribution to lineside faults

    Yeah, big building Keith, and I've only had a cursory look and kick of the tyres so far. 24 lifts fed from multiple switchboards. They are doing a lift upgrade program. The previous lift system used braking resistors and the new system was put in place for power efficiency. The discovered this...
  9. sibeen

    VFD and motor contribution to lineside faults

    A follow up question. I've come across a site where the lifts are fed via a regenerative drive. When a lift is descending then there's power being fed back into the grid and all is fine. The issue is when the power fails the site then transfers across to on-site backup generators. Now when a...
  10. sibeen

    Isoloated scope probes

    Gunnar, I haven't gotten around to buying one as yet, although I keep promising myself that I'll get around to it. Unfortunately I was bought up in the time where we cut off the earth pin, placed the oscilloscope onto a plastic milk crate and then were very careful about how we changed the...
  11. sibeen

    Isoloated scope probes

    Dave Jones at EEVblog sells a battery powered, Cat 111, 70 MHz diff probe for less than $500. https://www.eevblog.com/product/hvp70/
  12. sibeen

    Motor current during soft stop operation

    jraef, thanks for your post and the information, especially the interesting fault scenario at the end. Something else that I'm going to have to throw into the mix.
  13. sibeen

    Motor current during soft stop operation

    Mark, I'm based in Melbourne. I used to help out Vectek (I hope I have that name right) with UPS issues many years ago and would fly over on occasions to give assistance. I still know a few of the olds and bolds from those days and keep in touch once in a blue moon. As to the problem, one...
  14. sibeen

    Motor current during soft stop operation

    Mark, thanks for the reply and I have to do a ROFL. On Friday I was searching around for papers to read and came across some from AuCom which mentioned your name. The name immediately set off some bells in my head but I couldn't work out from where. I hadn't posted over here for three or four...
  15. sibeen

    Isoloated scope probes

    What bandwidth and category rating are you looking for as these are going to affect the price.
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