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5.5KW Motor and VFD, Have I got this right?

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  • lakeside53
    replied
    Originally posted by MrSleepy View Post
    He is UK based , so he will not have 240vAC 3 phase , it will be 240vAC single phase. So all he needs is a 6-10kVA 240vAC to 400vAC autotransformer .(which cost me £465 last time I had one built by Louth Transformers.).

    Then he can feed that into a derated VFD.



    Rob


    Considering he's replacing a 2.2kw motor, that's a lot a vfd to work derated single phase input with 5.5kw output. Unless I had a 10-15kw surplus unit lying around, I'd also change the 5.5kw motor before doing that. Some VFD are good at 50% derating, but other are way lower. My 7.5hp ABB are only 1.5hp on single phase. You can on some vfd add your own external ac-dc stage to plug into the DC buss, but not for the inexperienced.


    I'm not sure that the two speeds shown on the motor plate are a result of delta/Y, but simply 50hz verses 60 hz. Not a good plate layout no matter.
    Last edited by lakeside53; 12-31-2013, 02:15 PM.

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  • janvanruth
    replied
    Originally posted by PStechPaul View Post
    400V phase to phase * 11A/phase * 3 phases / sqrt(3) = 7.6 kVA * 0.73 PF = 5.5 kW.
    I see, wish they had explained it to me in those words back in my schooltime!!

    thanks

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  • MrSleepy
    replied
    Originally posted by lakeside53 View Post
    The transformer I was referring to was on the input, not the output. i.e. step up the 240 3 phase to to 480 (or whatever) three phase to feed the vfd.
    He is UK based , so he will not have 240vAC 3 phase , it will be 240vAC single phase. So all he needs is a 6-10kVA 240vAC to 400vAC autotransformer .(which cost me £465 last time I had one built by Louth Transformers.).

    Then he can feed that into a derated VFD.

    He could also purchase a "modified" VFD from Direct Drives. Direct Drives modify some of their 10kW 3ph VFDs to give 400vAC from 240vAC (single phase) , by creating a "Delon" Bridge voltage doubler.(they add a shorting wire and cut one link). (but must surely nullify any EMI/EMC certification).

    But that round trip is going to cost £1500. I would source a more suitable motor... The one shown also has an unusual speed range vs pole arrangement.... it may be a Dahlander two speed , as usually the speed does not change when using Star/Delta as a method to reduce starting currents.

    Rob
    Last edited by MrSleepy; 12-31-2013, 07:03 AM.

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  • lakeside53
    replied
    Originally posted by ironmonger View Post
    Not to sure that you can drive a transformer with a vfd... isn't there a problem with feedback? Just wondering???

    paul

    The transformer I was referring to was on the input, not the output. i.e. step up the 240 3 phase to to 480 (or whatever) three phase to feed the vfd.

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  • PStechPaul
    replied
    I rewound a 2/3 HP single phase 120V induction motor to 8 VAC, three phase, eight pole, and I was able to run it using a 2 HP VFD powered from 240 VAC single phase, into two step-down transformers (120 to 12V) from A-B and B-C. It worked fine up to at least 180 or 240 Hz. You do need to set up the VFD parameters correctly, but it's not very critical, and VFDs are generally rugged and forgiving of most mistakes.

    BTW, I have fallen off the floor...
    Last edited by PStechPaul; 12-30-2013, 09:42 PM.

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  • ironmonger
    replied
    Originally posted by lakeside53 View Post
    The motor does not show that 240 volts is an option, so probably not. If you use a three phase step up (from 240) transformer you can do it with a 400v class vfd. Connect as Delta for 400, Y for 690. 5.5kw on Y, 6.6kw on Delta. If you go this route and you are not experienced, consult with someone that really knows what they are doing. There are several no-so-obvious code requirements for transformers (fusing, grounding, clearance etc) , and it's easy to die from 400 or 690.
    Not to sure that you can drive a transformer with a vfd... isn't there a problem with feedback? Just wondering???

    paul

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  • Noitoen
    replied
    CFL's and SMPSU and VFD don't supply the "final" equipment with DC. It changes the original 50 or 60Hz to dc so that it can convert it back to high frequency, more efficient AC.

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  • PStechPaul
    replied
    It may be that Edison's DC may win over Tesla/Westinghouse AC even for home use. Incandescent as well as CFL and LED lighting work just as well (if not better) on DC. Electric heating appliances don't care. Tools with universal motors work on DC or AC. Most modern electronic devices such as computers and printers have switching power supplies which convert AC to DC so they will work on DC. Even some appliances like washing machines and blenders now use three phase motors with VFDs which use a DC link, and all other AC only motors such as fans will run just fine on modified AC from automotive type inverters which actually first convert 12VDC to 250VDC and then chop it to get AC.

    About the only things that really need 60 (or 50) Hz AC are electric clocks which rely on the long term absolute accuracy of the line frequency, but now you can get crystal-controlled clocks that are accurate within seconds per month, and some of them can be synchronized via a cable or FIOS connection or by receiving signals from WWV.

    Another advantage of DC is that it is easier to establish a grid-tied solar power system or even a fossil fuel generator because you don't need to synchronize the frequency and phase. And DC is somewhat safer because it does not so readily cause V-Fib electrocution. But it does have a tendency to make you grab and hold a hot conductor. And it is much more difficult to break a DC circuit when there is an inductive load. Having a zero crossing 120 times a second does help extinguish an arc!

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  • MaxHeadRoom
    replied
    Originally posted by Daveb View Post
    Any! Electricity is transmitted from the power station generators (3 phase alternators) at very high voltage,
    A lot long distance transmission is converted to DC now, back to AC at the consumer end.
    Max.

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  • PStechPaul
    replied
    Yes, I see that the rated PF is 0.85. And motors such as this are typically about 85% efficient. Thus 0.85 * 0.85 = 0.72. A premium efficiency motor would be closer to 90% efficiency, and larger ones can be 93% or better.

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  • lakeside53
    replied
    Nearly... pf at full load will be higher than 0.73, but you also need to multiply by efficiency! You could say the product of pf and efficiency is 0.73 to make your math work

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  • PStechPaul
    replied
    400V phase to phase * 11A/phase * 3 phases / sqrt(3) = 7.6 kVA * 0.73 PF = 5.5 kW.

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  • janvanruth
    replied
    power=voltage X current ?

    Originally posted by Daveb View Post
    This is a standard configuration for large motors. They operate at higher voltages. This reduces the current through both the motor and the switchgear. Power (Watts) = Voltage X Current (Amps).
    400 volt x 11 amps = 5.5 kw ??????

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  • Daveb
    replied
    Originally posted by dian View Post
    from what grid can you get 830 volts?
    Any! Electricity is transmitted from the power station generators (3 phase alternators) at very high voltage, this voltage is reduced at local transformer substations for distribution to consumers. Domestic and light industrial premises usually share the same supply with 3 phases being delivered to industrial premises and 1 phase to domestic premises. Large industrial sites usually have their own substation, any required voltage is available but agreed standards are maintained to permit manufacture of motors and ancilliary equipment by others.
    Dave

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  • PStechPaul
    replied
    I stand corrected, and have learned something. However, there is not much reference to 830 VAC, and in the Wiki article it only says it is sometimes used for special installations, such as oil pumping. And in the same search I found an oil pump motor rated at 830 RPM:
    http://www.temcoindustrialpower.com/...nt/M04397.html

    I Googled for 3 phase 830v and came up with only a few genuine hits (I don't count Walmart or other sites that offer the "best deals" on gobbledegook or whatever you search for). There are some analyzers which are rated up to 830V and also some motor controllers. I found an IEEE standard which has been withdrawn, indicating that this is a very rare and perhaps obsolete system:
    http://standards.ieee.org/findstds/s.../464-1981.html

    I did find information on wye-start delta-run motors which are reconnected for effectively lower voltage starting. This is not really needed when VFDs are used:
    http://www.usmotors.com/TechDocs/Pro...-DeltaRun.aspx
    Last edited by PStechPaul; 12-28-2013, 05:37 PM. Reason: wye-delta

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