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giselle (Electrical) (OP)
30 Aug 06 8:43
I have some equipment running on a 460V, 60Hz power supply. Main components are a 40h.p. dc motor driven by a variable speed drive and nine other smaller motors ranging from 1.1 to 4.6 kW (460/230V, 3ph). I am considering relocating this equipment to a country with a 415V, 50Hz power supply. After verifying from drive manufatcurer and checking motor specs, is it correct to assume that in order to maintain the same response (V/f) from the motors and drive, I should use a step down transformer to get 383V, 50Hz?
aolalde (Electrical)
30 Aug 06 9:19
385 volts could be short for the DC driver, which will rectify those to DC. Check the motor nameplate for voltage requirements. That driver could work better at 415 V 50 Hz.
The other induction motors will turn without problem at 385V, 50 HZ, but the speed will be reduced proportional to the frequency change. That will mean for instance; less pressure and flow rate in pumps. You must analyze every driven equipment and check that the speed reduction will be acceptable.
itsmoked (Electrical)
30 Aug 06 15:14
Hello giselle; Though you seem to a grip on things, you might want to check this : FAQ237-1224

We may be able to tell you about other possible problems if you give us details on the machine.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

powerjunx (Electrical)
31 Aug 06 6:09

 aolalde, i guess induction motor is out of bound in here.

 With due respect, the issue tackle only on DC machine , DC speed drive and power supply of 460V, 60Hz to be tapped for 415V, 50 Hz. Though, i appreciate your comments.
rbulsara (Electrical)
2 Sep 06 10:53
fbcybil:

Please read the OP's question again, he says one DC motor and other 460/230V, 3 phase motors. aolalde comments are appropriate.

giselle:

What I am wondering is how does a DC motor work on a VFD? Do you have separate DC drive for 40HP DC motor and a VFD for other AC motors?  

I would think you would need a separate transformer for the DC drive to provide 460V. The rectifier would not care for the frequency.  As for the ac motors on VFD see aolalde's comments.

mc5w (Electrical)
4 Sep 06 2:37
I believe that one of the companies that makes aircraft ground power units also makes 50 Hertz to 60 Hz and 60 Hz to 50 Hz frequency changers in addition to the ones that crank out 400 cycle juice to power the lights on airplanes when they are parked.

You might just be better off getting a frequency changer because 415 volts 50 Hertz requires both larger motor frames and larger motor controllers. The other option is to change your belting ratios if anything is belt driven. Centrifugal pumps and blowers that are direct drive would be affected the most.

If the induction motors can be rewired for 416 volts 60 Hertz operation you could use a bunch of variable frequency drives. Alternatively, you could use a wye-wye autotransformer to step up the 240Y416 volts to say 272Y471 volts and then use VFDs to change the frequency for the induction motors. However, the service factor of a motor that is on a VFD has to be dropped down because the VFD produces extra heating because the current and voltage waveforms and not a real sinusoid.

A typical 40 HP DC motor that runs off of 480 volts 3-phase via a Siicon Controlled Rectifier drive is a 500 volt nominal motor. You do not need to step down to 353 volts as the phase delay in the SCR drive will take care of that - it will just simply not use as much phase delay as with 480 volts. The maximum output voltage of such a rectifier when fed with 480 volts AC 3-phase is a little more than 660 volts DC. To get the 500 volts and lower for variable speed action the SCRs are phase delayed. 416 volts 3-phase in produces a little more than 580 volts whcih requires a lot less phase delay to get 500 volts. Almost all of these drives refuse to work at exactly zero phase delay ( full voltage out ) because they have a second set of SCRs for poweer regeneration such as elevators.

Your SCR drive for your DC motor probably can be programmed to accept 50 Hertz and if you use a wye-wye autotransformer to get up to 272Y471 you can easily get the full 500 volts DC output. If you never ever run this motor at full speed then you might not need a stepup transformer. This would be made out of 240 volt primary 32 volt secondary buck boost transformers but getting them in a 50 Hertz rated version could ber difficult. 50 Hz transformers require more steel and conductor than 60 Hertz and are more expensive and heaveir than 60 Hertz.
waross (Electrical)
5 Sep 06 0:38
Hello mc5w;
I have no problem electrically with wye connected autotransformers, but I have found in many actual installations that open delta connected auto transformers are more cost effective. I have used them many times and have never had a problem. You get to use two transformers instead of three. Two transformers in open delta work great for motors, but for lighting, when you are connecting line to neutral, you must use three transformers in wye configuration.
respectfully

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