Phase converter

Discussion in 'General Electronics Chat' started by geoffers, Nov 12, 2014.

  1. geoffers

    Thread Starter Active Member

    Oct 25, 2010
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    Hi all,
    Not sure if this is the right place to ask the question but aac has never let me down yet!
    We have a single to 3 phase converter that runs a motor on a dirty water pump, the over current trip on the motor control keeps tripping out, when I checked the voltages across phases (no load) I get 600v on one phase 360v on another and 200 on the other? Is this because, a. My phase converter is jiggered, b my multimeter on the ac setting doesn't work with 3 phase? Its a old static converter, my thinking is the 600v is driving to much current through the motor (and trip).
    Thanks Geoff
    Ps I'm in the UK 415v three phase.
     
  2. BR-549

    Well-Known Member

    Sep 22, 2013
    1,995
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    First of all...are you pumping sewage or does your pump need cleaned?

    Is there any way you can post a pic of converter with cover off?
     
  3. BillB3857

    Senior Member

    Feb 28, 2009
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    Is the converter a box or is it a rotary converter (looks like a motor)?
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If the convertor is rotary or static, what is the 1ph input voltage if the motor is 415v 3ph?
    1phase in the UK is generally 240v 1ph to neutral?
    Measuring between phases is the same as a 1phase reading to the meter.
    Max.
     
    Last edited: Nov 12, 2014
  5. geoffers

    Thread Starter Active Member

    Oct 25, 2010
    239
    6
    Hi All,
    Thanks for the replies, I've attached a photo (hopefully!). Its a static converter with a 240 single phase input, the motor on the end is a dirty submersable macerator pump, new bearings and seals yesterday and I've been trying it with no load. From the converter I have for wires, guess the black is neutral? Output to the pump from the control is three wires. Measuring with digital multimeter I get 220v input, between blue-red 650v red-yellow 390v yellow-blue 220, this is repeated at the pump connector. (pump dissconected). The pump windings have got a bit damp:mad:! Two phases come in at 8 ohms and one at 10 ohms, no short to earth!
    Thanks again Geoff
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,800
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    Do the measurements relate to the converter output or the controller output? I would have expected a closer match between the three RYB readings. Were you measuring with the R,Y and B open circuit or with a small dummy load? What was the black wire connected to?
     
  7. BillB3857

    Senior Member

    Feb 28, 2009
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    I may be all wrong and hope for correction if I am, but my understanding of static converters (capacitor box) was that it only provided enough phase shift and current to allow a 3 phase motor to start, usually not at full load. After that it would only supply a very small portion of current. After startup, the motor would be running almost like a 3 phase motor that had lost one phase of line power.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Generally the static convertors pass the 1ph 240 directly through to present as 2 of the 3 phases, the third is created digitally from the other two.
    I am assuming the motor is a 240v three phase motor? Otherwise if you are using a 420v motor then either this is different to the static convertors in N.A. or you have the wrong motor?
    Either way the voltages you are getting do not make sense?
    Max.
     
  9. geoffers

    Thread Starter Active Member

    Oct 25, 2010
    239
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    Thanks for all the replies.
    I managed to track down the maker of the phase converter, he said those where the exact readings he would expect from the converter with no load! He said the phases should even out under load. The windings in the motor are "uneven" (8,8 and 10 ohms) and this is enough to throw the current trip? (so I've been told!) Its a 415v motor.
    The motor is being rewound at the moment so I will see what happens! I'm curious how the static converter works, it seems to just be a transformer and capacitor (jolly big one), no digital stuff (made in the late 80's!).
    Cheers Geoff
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    How is it you are trying to run a 415v motor off of a 240v supply?
    Normally a neutral is not needed for a convertor?
    If it is that old, I would have thought the better option is a VFD!
    Max.
     
  11. geoffers

    Thread Starter Active Member

    Oct 25, 2010
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    I'm just working with what I've got, it was all installed in the late 80's. The phase converter claims a 415v output, I guess the idea is to have a brushless motor as its submerged (someone is going to tell me you can a single phase brushless motor!) I shall google vfd in a mo!
    . Cheers Geoff
     
  12. tcmtech

    Well-Known Member

    Nov 4, 2013
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    geoffers likes this.
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If you already have a 3ph motor VFD's are relatively cheap and can be ran off of 240v 1ph they are very common now for anyone wanting 3 phase motor power with only 1ph available.
    Max.
     
    geoffers likes this.
  14. geoffers

    Thread Starter Active Member

    Oct 25, 2010
    239
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    I'm still bashing away at this..... I called a friend who works with generators, between us we decided the phase converter was up the spout, some of the windings were shorted. A new phase converter has arrived but the rewound motor still has wonky currents :mad: ! Without any load on the motor two phases are lower than the other, when the motor is loaded the two phases that were low go higher than they should be and the other drops. I'm suspecting the motor could have been misswound?
    I've got a two channel scope, if I charge the coils with a low voltage and spin up the motor with a drill or on the lathe would I be able to see if the phases are out of phase? I assume they should be at 120 degrees to each other? Any other ideas would be gladly received !
    Cheers Geoff
    Ps, all three phases are 9.5 ohms, I have three wire straight out the stator, there's nothing that can be miss-wired.
     
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