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  1. thinker

    Permanent Magnet Synchronous Motor (PMSM) sizing of conductors (with a VFD)

    We develop various test systems based on VFD driven dynamometer motors (both induction and PM, range 200-3000 kW). In most cases, the motor cable selection is very critical due to required flexibility. We use NEC Art.430.6(C). Its scope perfectly fits a definition of Adjustable Speed Drive...
  2. thinker

    VFD cable ground conductors termination

    Dear colleagues, please advise on the following: typical VFD cable has three symmetrical ground conductors. Can I combine these three ground conductors together and crimp all of them in a single larger compression lug? The site location is in the USA. Will this arrangement be acceptable. or this...
  3. thinker

    Correlation between European and US safety standards

    We order from Europe electrical equipment that complies with the following EU standards: EMC Directive EN61326-1:2013 Low Voltage Directive EN61010-1:2010 Machinery Directive EN ISO 12100:2010 RoHS Directive EN50581:2012 CE Marking The end user in USA specifically requires that the equipment...
  4. thinker

    PM motor with additional external inductor.

    430 kW.
  5. thinker

    PM motor with additional external inductor.

    Thank you, CSWILSON. You made a good point. This specific motor has values of Ld/Lq around 30 microhenry (and not milliHenry's range). Probably, they require another 20 microHenry to minimize thermal effect of current ripples. We just never saw before such justification of additional inductance.
  6. thinker

    PM motor with additional external inductor.

    We have a specification of PM synchronous motor driven by VFD. The motor spec requires external inductance about 20 microHenry. Our understanding was that this inductance is required to reduce dv/dt of PWM voltage pulses, thus reducing a stress applied to motor insulation, reducing accelerated...
  7. thinker

    Inverter duty motor specifications

    We used to refer for inverter duty motor specifications to the standard NEMA MG1, part 31 (for US built motors) and IEC 60034-17 (for EU motors). The NEMA MG1 Part 31 applies only to squirrel cage induction motors. What document/standard (if any) would apply to inverter fed synchronous PM motors ?
  8. thinker

    VFD with seismic rating

    Thank you, gentlemen for response. We will review a Rockwell information. And we do not use MV drives for this project.
  9. thinker

    VFD with seismic rating

    Wea are a big international company, currently bidding for a project in California. The VFD based test systems are standard products for our EU arm. Their (local) VDF supplier has declined seismic compliance requirements. We try to help them to find a suitable replacement for standard VFD. I...
  10. thinker

    VFD with seismic rating

    Dear colleagues, We consider application of VFD systems [range (300-700)HP] in the area El Monte, California. Can anybody refer to EU VFD supplier that would provide seismic rated VFD cabinets?
  11. thinker

    MIL standards acceptable by UL ?

    Our equipment has to have UL listed/recognized components. Some of currently used components have been built to MIL standards. Do we still need to replace them with UL compliant parts, or MIL compliant parts could be acceptable? Is there any general consensus about that?
  12. thinker

    Can autotransformer act like line reactor?

    The VFD operates at 575V, fed by step-up drive isolation transformer 480/575V. Inside that VFD, there is a switching DC power supply (input power three phase, 400V) fed from a dedicated 400VA control transformer 575/400V. This power supply has failed (as we assume, the failure could be...
  13. thinker

    Opinions on non-standard and non-contiguous MV drive configuration

    Generally speaking, most VFD suppliers are reluctant to idea of separation the inverter(s) from the front end converter. We had a 3 MW VFD systems with 4 inverters, and decision to separate inverter sections has been made only after modeling of overall DC bus extension system. The critical...
  14. thinker

    PM motor current

    Thanks for your responses, gentlemen. We found out the source of our confusion - the fact that above the base speed VFD supplies to the motor additional reactive current component to reduce the flux (field weakening simulation) in order to limit raise of the motor generated back EMF at higher...
  15. thinker

    PM motor current

    Thanks for response, Keith. A bit more details. This is a test stand for 4WD vehicle transmission testing, with 4 PMSM wheel dynamometers(absorbers) and a common DC bus VFD system. We selected input drive transformer kVA rating (reduced comparing with rated for full scale system size)based on...
  16. thinker

    PM motor current

    Please advise: for VFD system (unity PF at AFE) with PM synchronous motor - how to estimate total power/current consumed from the grid when the motor is spinning up to max speed with no shaft load.
  17. thinker

    Insulated bearings

    Yes, I understand that. The insulating coating is fractured in several spots and have missing pieces exposing bare metal. As we read in published white papers, the outer ring coating is not the best method of insulation (could be the cheapest). We will suggest the motor MFG to use ceramic ball...
  18. thinker

    Insulated bearings

    We are analyzing a bearing failure on VFD driven PM motor. Motor MFG uses DE and NDE insulated bearings (brand AKN, Germany) and DE ground brush. These bearings have the outer ring surface coating (medium grey color). This seems to be either ceramic or aluminum oxide insulating provision...
  19. thinker

    Equipment voltage ratings

    This could be a very simple question, but after many years in electrical engineering I suddenly realized that can not determine voltage classification of the VFD system (enclosure) that has input voltage 575V AC and DC bus voltage 850 V DC. Is such equipment classification considered to be below...
  20. thinker

    VFD power regeneration

    Gentlemen, thanks for your inputs, very informative and useful. The very last sentence in Bill's posting actually repeats my OP. Yes, we will try to keep the whole 3 MW regen system intact, and add to it a large energy sink. We thought, the best way would be to add DC resistive load bank...

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