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  1. edison123

    VFD increasing the motor winding temperature

    "I suggest that skin effect and the resulting increase in effective resistance and losses will be greater at VFD switching frequencies." Bill, no, VFD 'big guys' and electricuwe say higher switching frequency reduces the motor loss. I will be testing another motor shortly to check this theory.
  2. edison123

    VFD increasing the motor winding temperature

    Thanks electricuwe. I contacted Yaskawa and they said the carrier frequency is 2 to 10 kHz with 2 kHz as default. They advised to increase it to 5 kHz and try again to reduce winding temperature. Apparently, the drive has to be derated above 5 kHz.
  3. edison123

    VFD increasing the motor winding temperature

    Thanks, Jeff. Do the harmonics overheat the core or the winding mainly? And do they heat to the extent of over 30 deg C, which seems very high? Will adding a sine filter reduce the heating to normal values? Is the cost justified? The motor is running now on load and based on my advice, the...
  4. edison123

    Testing a 100HP Vertical Motor

    No load run at reduced (aka star connected delta winding) is fine as long as you didn't rewind the motor. You check if the vibrations and stabilized bearings temperatures at rated speed are within limits. If you did rewind the motor, the client may require a rated voltage test which will require...
  5. edison123

    VFD increasing the motor winding temperature

    The winding RTD's were connected to the same temp scanner in both the cases and hence no metering error. The winding temperatures did not drop immediately after switching off power in both the cases. The motor has an external blower which was off in both the cases. No shaft mounted cooling fan...
  6. edison123

    VFD increasing the motor winding temperature

    Shaft speed is directly measured as 3000 RPM in both cases by independent digital non-contact speed sensor. The motor is VFD duty rated, and the distance is 5 meters.
  7. edison123

    VFD increasing the motor winding temperature

    I tested a 415 V, 350 KW, 2 pole motor on no-load (open shaft). With utility supply at 50 Hz, the motor winding temperature was 64 deg C with 130 A current. With VFD supply at 50 Hz, the winding temperature went up to 97 deg C with the same 130 A current. The drive is Yaskawa GA 700 model...
  8. edison123

    Power Needed to Rotate a Mass to a Speed in a Specified Time

    Update: We ran the rotor today at 3300 RPM with VFD input of 36 KW with manual control of speed in 5 minutes. Tracks closely with the calculated 28 KW if you account for the VFD losses and two centrifugal fans loss. I thank you all once again for your valued tips. First time, we did a high...
  9. edison123

    API 546 - Sealed winding conformance

    API machines are mostly for Ex applications which are naturally costlier than generic IEC or IEEE machines. Buy the standards and learn the differences.
  10. edison123

    Excitation current on induction motor as a generator via VFD

    Jeff 415 V, 25 KW, 50 A, 1500 RPM motor no load testing with VFD in our shop today VFD input - 396 V, 6.66 A, 2.7 KW, 0.998 PF VFD output - 415.8 V, 19.6 A, 1.2 KW Hope it helps.
  11. edison123

    2MVA generator

    In the rotor DC circuit, the negative slipring will wear out faster than the positive one due to electrochemical reaction. So, to maintain even wear of both sliprings, the polarities are swapped. This has zero effect on the synch generator output / synch motor direction of rotor. For the same...
  12. edison123

    2MVA generator

    Changing the polarity of rotor field winding has zero effect on the synch generator/motor output. If you changed only the bearings, why do you need to test the generator without the prime mover?
  13. edison123

    To replace faulty power alternator with a smaller unit

    https://tgadvisers.com/steam-turbine-and-generator-reduced-minimum-load-considerations/ If you got 20k, have at it. https://www.epri.com/research/products/000000003002013589
  14. edison123

    Generator with low IR

    Phase to phase IR? Is it 6 leads generator? If not, you should be getting zero megohms between phases.
  15. edison123

    To replace faulty power alternator with a smaller unit

    Under powered steam turbine will have water condensation, scaling of blades leading to lower life.
  16. edison123

    Hoists attached to another hoist to rotate load

    I rotate large electric machines up to 20 tons in our shop. I use two 20 ton hoists mounted independently in the same cross travel bridge.
  17. edison123

    Power Needed to Rotate a Mass to a Speed in a Specified Time

    Greg - 5 to 10 minutes is my plan. It's a time vs KW decision. MintJulep - Ok.
  18. edison123

    KW, KVA, KVAR relationship

    "If I reduce the KVA that should equate to a reduction in amps, correct?" Correct. "if there is an amp reduction, shouldn't I be able to calculate an efficiency increase?" The reduced current means less I^2R loss in the generator, cables, transformer, which is indeed a power saving. You need...
  19. edison123

    Power Needed to Rotate a Mass to a Speed in a Specified Time

    I am looking at 3300/600 = 5.5 rpm per sec. That's linear acceleration, right?
  20. edison123

    power factor issue

    govt department advised correctly. 24x7 capacitor with no other inductive load will drop your pf like a stone.

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