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  • Users: edison123
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  1. 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...
  2. edison123

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

    What will be the power needed to rotate a uniform cylindrical rotor weighing 1600 kgs dia 600 mm speed 3300 RPM 5 minutes acceleration time from zero speed to 3300 RPM Any particular equation to calculate this? Will acceleration time play a role in power needed? The cylindrical rotor will be...
  3. edison123

    Single VFD running two motors - One motor temperature much hotter.

    Single VFD running two 400 HP AC motors driving on-shore oil drill via gears. One motor is original winding and one was rewound with 10% more copper area and hence 10% lower DC resistance. Both the motors had the same inductance since the turns are the same. Upon recommissioning, the rewound...
  4. edison123

    Low Frequency (1 Hz to 60 Hz) ammeters, voltmeters and CT's - Any suppliers / OEM's?

    Any suppliers for Low Frequency to Power Frequency (1 Hz to 60 Hz) ammeters (5 A), voltmeters (0 to 750 V) and CT's (0 to 2000 Amp/5 A) ? The standard meters & CT's work only from 45 to 65 Hz. I am looking for meters and CT's that work from 1 Hz onwards. Is it possible?
  5. edison123

    Is an isolation transformer needed on a VFD input side?

    This week, we trialed a 125 KW VFD for testing LV motors in decoupled condition. During the trials, I noticed our LED lights started flickering even though they were switched off. When asked, the OEM drive guru said there will be harmonics fed into the system, and we need to install an...
  6. edison123

    Motor VFD open loop no-load current is much higher than closed loop no-load current. Why?

    We ran a 490 V, 2095 KW, 3000 A, 100 RPM Permanent Magnet rotor motor on no-load via a VFD. In open loop, the motor no-load current is 210 amps while in closed loop (with shaft mounted encoder), it is only 16 Amps. Why this vast difference between open loop and closed loop currents? Edit: It's...
  7. edison123

    KW rating of 4 pole motor at highest speed is low.

    VFD duty 4 pole motor nameplate below. Why is the KW rating at 2200 RPM is lower at 475 KW than that of 2000 RPM (500 KW)?
  8. edison123

    Can two VFD's run in parallel

    For no-load open shaft testing various motors ranging from 50 HP to 1500 HP with maximum no-load current of 500 Amps at 415 V, 50 HZ, I am planning for to go for VFD. If I buy two identical 250 Amps drives, can I parallel them on the output side for 500 Amps? This gives me an option of using...
  9. edison123

    Gas turbine high vertical vibrations at 1X

    5100 RPM (85 Hz) GT driving a 3000 RPM (50 Hz) generator via a gear box is showing high vertical vibrations during startup (after a year-long shutdown) in GT front bearing (NDE) as below. GT rear bearing (DE) also showing similar high vibrations. Both GT and generator white metal bearings are...
  10. edison123

    Calculated neutral current not matching measured neutral current

    3 Ph, 415 V, 50 Hz 4 wire, neutral solidly earthed system feeding a high school with 3 phase ac's, LED & fluorescent lamps, ceiling fans, UPS systems for computers, lab equipments etc. Current and voltage THD's in each phase <3%. Current harmonics 3rd to 13th less than 0.5% in all 3 phases as...
  11. edison123

    Cables termination to busbars - from bottom or from top?

    From bottom From top I personally think from top is better since the cable is not pulling down from the lug. Muthu www.edison.co.in
  12. edison123

    Centrifugal blower input power vs speed

    I hope this is the right forum for centrifugal fans. Below is the nameplate of a centrifugal blower motor. Given the centrifugal fan affinity cube law, how come the power is 1.1/1.27/1.1 KW at 2885/3480/3500 RPM ? Muthu www.edison.co.in
  13. edison123

    Holes in a roof beam. What is the purpose?

    I recently saw this roof beam with circular holes in an airport. What is the reason to cut out those holes? Reduce weight? Make it stiff? Muthu www.edison.co.in
  14. edison123

    Suitable VFD for MV wound rotor motors

    For drive gurus 6.6 KV, 3200 KW, 340 Amps 1000 RPM, 50 Hz Motor. Rotor is 2700 V, 720 Amps. It is driving an induced draft (ID) fan. Motor at present running at variable speeds by rotor resistance manipulation with a PWM slip power recovery system. If we go for stator MV VFD operation, what...
  15. edison123

    Centrifugal expansion of bore of a steel rotating ring

    How much the bore of a steel ring expands under speed? Bore at standstill is 737 mm. Speed is 3000 RPM. Young’s modulus of steel = 210 GPa Muthu www.edison.co.in
  16. edison123

    Recommended VFD rating for 415 V, 16 HP, 25 Amps hoist duty motor

    Our present 10 ton hoist motor is two speed two winding rated for 415V, 12/4 HP, 1440/465 RPM with electrically operated spring brake as shown below. To reduce the high inrush current of about 80 Amps, I plan to rewind the motor for single speed 16 HP/25 Amp/1440 RPM and use a VFD. The VFD...
  17. edison123

    VFD for a 100 Amps, 1500 Hz application

    Not strictly a motor question, more of a VFD question. I need to test a multi-turn 3 phase inductor with a copper cross-section of 30 sq mm at 100 Amps, 1500 Hz. It will be a continuous test for a month. The input source will be 3 ph, 415 V, 50 Hz. Can standard motor VFD's output this high...
  18. edison123

    Which of these structures is stronger?

    Which of these structures is stronger in terms of resisting the bending? Muthu www.edison.co.in
  19. edison123

    Can VFD be set for 3 different speeds with 3 different time &amp; load cycles in a full duty cycle?

    Can a VFD be set for 3 different speeds and 3 different time & load cycles of x1 RPM/t1 sec/a1 amps x2 RPM/t2 sec/a2 amps x3 RPM/t3 sec/a3 amps in a full duty cycle? Motor capacity is 5 KW, 6 pole, 50 Hz with external blower for cooling. Muthu www.edison.co.in
  20. edison123

    Varying difference between constant generated KWH and utility side measured KWH

    A 2100 KVA generator is constantly outputting 2000 KWH every hour but the utility side measured KWH is varying from 1300 KWH to 1800 KWH with difference between them varying from 700 KWH to 200 KWH on hour to hour basis. There is very little power tapped off from the generator for lighting and...

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