I have 2 phases (400v), can I utilise this for running my 3 phase motor?
Close
Login to Your Account
Page 1 of 3 123 LastLast
Results 1 to 20 of 43
  1. #1
    Join Date
    Dec 2019
    Country
    UNITED KINGDOM
    Posts
    19
    Post Thanks / Like
    Likes (Given)
    10
    Likes (Received)
    0

    Default I have 2 phases (400v), can I utilise this for running my 3 phase motor?

    As title, I have two phases of a 3 phase supply coming into my property, is there any way of taking advantage of this to create a 3 phse supply? thanks

    Ive read bout a "Scott connection in a transformer" ???

  2. #2
    Join Date
    Mar 2009
    Country
    UNITED STATES
    State/Province
    California
    Posts
    5,164
    Post Thanks / Like
    Likes (Given)
    97
    Likes (Received)
    951

    Default

    Sounds like you are 2/3 the way there. But the answer is no.
    If you choose to phase shift one of the lines with external capacitors you might be able to get something close.
    I would not do that unless a RPC was part of the equation.

  3. #3
    Join Date
    Mar 2008
    Location
    Marulan N.S.W. Australia
    Posts
    161
    Post Thanks / Like
    Likes (Given)
    81
    Likes (Received)
    41

    Default

    If these 2 conductors are 415v, Yes. So you only need a suitable idler motor.

    Jim

  4. #4
    Join Date
    Dec 2019
    Country
    UNITED KINGDOM
    Posts
    19
    Post Thanks / Like
    Likes (Given)
    10
    Likes (Received)
    0

    Default

    My multimeter shows 400v between(im in the UK)the two lives, how would I hook up the RPC with these two? thanks

    Do I connect these two lives to two of the legs on the idler & then the third leg is generated? What about the neutral wire? thanks

  5. #5
    Join Date
    Mar 2008
    Location
    Marulan N.S.W. Australia
    Posts
    161
    Post Thanks / Like
    Likes (Given)
    81
    Likes (Received)
    41

    Default

    Hi pxr5, Yes. Connect your 2 actives to idler terminals and the third terminal is the generated leg. Make sure motor is connected for 400v operation. Now put a piece of rope around the shaft or pulley and give it a good pull, then switch on the motor and the motor will come up to speed. When you connect a load motor to the idler you may find it runs better with a couple of run (balance) capacitors added.
    In this project the neutral wire does not connect to anything.

    Jim

  6. #6
    Join Date
    Jul 2014
    Location
    MI USA
    Posts
    912
    Post Thanks / Like
    Likes (Given)
    199
    Likes (Received)
    372

    Default Open Wye - Open Delta Transformer Connections

    There exists a transformer method that can utilize two legs and a neutral of a wye system, and convert that into a open delta 3Φ output.

    It's called an open wye - open delta. It's not very common, but is used by utilities to serve small 3Φ loads and single phase loads.

    All of the examples shown use US system voltages, It can work for your voltage and frequency, but some engineering would be required for selection of transformers, suitable for your use.

    openy-open-.jpg
    Diagram provided is from this paper, you will need to do some research, or contact an engineer.
    www.egr.unlv.edu/~eebag/EE%20741%20-%20Transformers%20II.pdf

    Video of a Utility engineer stepping through a worksheet of the process.
    YouTube

    An excerpt from this old article, diagram is missing.
    Unconventional Transformer Connections — Part 1 | EC&M

    Case One: open-wye/open-delta connection (OY-OD). Many light-commercial neighborhoods have 208Y/120V, 4-wire distribution. A small building "saved" money by foregoing the expense of a 4-wire electrical service. Instead, occupants had an uncommon 3-wire lateral network service, consisting of two ungrounded conductors and one grounded conductor served from a 4-wire wye system.

    The tenant shop owner needed to operate his prime electrical appliance: an ancient, but sturdy, cord-connected 3-hp 230V dough mixer. Unfortunately, he had only 208Y/120V 3-wire, single-phase network service available within a reasonable distance. This simple transformer set (OY-OD) was a low-cost solution. Using this connection was cheaper than using a single- to 3-phase upgrade of the electrical service entrance, 125-ft feeder, and subpanel.

    To apply this configuration, nipple two 3-kVA transformers to a suitable panelboard, and run a three-quarter-inch raceway to a NEMA L15-20 receptacle. Wire as shown in Fig. 1, on page 66 (in the original article). The NEC Sec. 250-5(b) allows you to leave the separately derived 3-phase, 3-wire circuit ungrounded. A 3-pole motor-overload relay in a manual starter will provide secondary-side overcurrent protection for the transformer bank. A 20A 2-pole molded-case breaker furnishes primary short-circuit and ground-fault protection.

    While running the motor, check current in the grounded "neutral" lead of the 208Y/120V single-phase, 3-wire circuit that supplies the transformer pair. To do so, use a clothespin-type current transformer and a digital multimeter. Your reading on this conductor will be similar to the two primary-phase currents with balanced 3-phase load on the secondary. (This particular neutral current has nothing to do with harmonics. You'll find a description of it in the NEC Art. 310 Notes to Ampacity Tables, 10(b).) You cannot apply this configuration on a 120/240V single-phase, 3-wire system. The 120 degrees phase difference between the two phase-to-neutral voltages is absent in this type of circuit.

    Motor phase currents showed reasonable balance under load. No currents exceeded nameplate rating during routine operation. Stator overheating from inordinate voltage imbalance was no problem for this pre-letter-frame induction motor.

    System voltage doesn't matter for this and most other configurations we're looking at. A utility used an OY-OD connection on a remote 115Y/66-kV transmission circuit to provide local corner-grounded 7.2-kV 3-phase distribution service. The rural electric co-op constructed a wood-pole H-frame platform to berth the two single-phase transformers. In each case, transformer ratings must match the application. Case 2 also demonstrates this.


    SAF Ω

  7. Likes JST liked this post
  8. #7
    Join Date
    Aug 2014
    Location
    bainbridge island
    Posts
    1,169
    Post Thanks / Like
    Likes (Given)
    233
    Likes (Received)
    275

    Default

    in addition to the method described by SAF,


    you can acquire the hidden star point of your 415 volt motor (if you have a 6 wire motor it is not hidden)

    and connect the star point to your netural or ground, and two lines to your 230v lines.

    the motor will start on its own because you have a rotating field already, and i think it could safely deliver 2/3rds of its nominal hp if you load it, the third coil of the motor will generate your 3rd phase. --this may be good enough to run all of your equipment. you will have to re-wire all of the motor starters and modify the overcurrent trip points to compensate


    or you can use two transformers. you need a 208v or higher isolation transformer, connect it as an auto transformer and connect it across the 415 volt lines and so you have got 120 volts from its midpoint to ground. you take that 120 volts and use it to drive another 120:240v transformer to create your third phase.

    a motor is probably cheaper than a 240v:240v transformer and a 120:240v transformer.

  9. Likes JST liked this post
  10. #8
    Join Date
    Dec 2019
    Country
    UNITED KINGDOM
    Posts
    19
    Post Thanks / Like
    Likes (Given)
    10
    Likes (Received)
    0

    Default

    Thats really helpfull, thanks very much, I think Ill go the idler route, whats the rule for the idler in terms of size? double the power rating? Im having trouble finding a big 3p motor, my biggest machine neeeds 5.5Kw , thanks again!

  11. #9
    Join Date
    Mar 2009
    Country
    UNITED STATES
    State/Province
    California
    Posts
    5,164
    Post Thanks / Like
    Likes (Given)
    97
    Likes (Received)
    951

    Default

    In general it is double the size.

    5.5Kw x 1 Hp/.746kw = 7.37 Hp

    A 10 to 15 Hp idler motor is what you will need.

  12. #10
    Join Date
    Jul 2007
    Country
    UNITED KINGDOM
    Posts
    4,853
    Post Thanks / Like
    Likes (Given)
    2605
    Likes (Received)
    2362

    Default

    Find out why you don't have the missing phase and get it reinstated!

  13. Likes Illinoyance, hermetic liked this post
  14. #11
    Join Date
    Dec 2019
    Country
    UNITED KINGDOM
    Posts
    19
    Post Thanks / Like
    Likes (Given)
    10
    Likes (Received)
    0

    Default

    The 3 phase power line is under ground out side,it would cost big money & the possibility of having a smart meter fitted.
    This is for my home shop,so I dont need a industrial supply.

  15. #12
    Join Date
    Jul 2007
    Country
    UNITED KINGDOM
    Posts
    4,853
    Post Thanks / Like
    Likes (Given)
    2605
    Likes (Received)
    2362

    Default

    So how did your property get two of the three phases? The only time this would be practical would be with overhead lines .

  16. Likes hermetic liked this post
  17. #13
    Join Date
    Mar 2013
    Location
    Surbiton, surrey, UK
    Posts
    1,621
    Post Thanks / Like
    Likes (Given)
    1996
    Likes (Received)
    1039

    Default

    Quote Originally Posted by pxr5 View Post
    As title, I have two phases of a 3 phase supply coming into my property, is there any way of taking advantage of this to create a 3 phse supply? thanks

    Ive read bout a "Scott connection in a transformer" ???
    I think ive the same setup as you so kind of interested to see how this plays out.

    Heres a pic of how mine looks.
    2-3.jpg

    As I understand things its a 3phase head that only has 2 of the 3 legs and neutral run to it from the underground 3phase line outside. I managed to speak to a neighbour who works for power networks, he said to have 3 phase youd need a cable run and a new head, 3k min + the digging iirc. If I want to use the other line id have to ring up my electrical supplier and have another meter fitted. Testing between the 2 lines gives the expected 400v.

    Currently im running a 30hp transwave rotary off the single line, it starts fine running through a 60amp fuse.

  18. Likes pxr5 liked this post
  19. #14
    Join Date
    Nov 2004
    Location
    Webster Groves, MO
    Posts
    7,329
    Post Thanks / Like
    Likes (Given)
    1850
    Likes (Received)
    3398

    Default

    Before you do anything, you need to define what you have, not someone's opinion. You need to measure the voltage between each leg and the neutral. If is 239 volts, you can do the conversion SAF describes and have a three phase line. If the voltage from each leg to neutral is 208, then you need something like a rotary converter. Voltages subject to some variation, but the difference should still be clear.

    Bill

  20. #15
    Join Date
    Jul 2007
    Country
    UNITED KINGDOM
    Posts
    4,853
    Post Thanks / Like
    Likes (Given)
    2605
    Likes (Received)
    2362

    Default

    The OP is in the UK. We don't do odd-corner three phase!

  21. #16
    Join Date
    Nov 2004
    Location
    Webster Groves, MO
    Posts
    7,329
    Post Thanks / Like
    Likes (Given)
    1850
    Likes (Received)
    3398

    Default

    Quote Originally Posted by Mark Rand View Post
    The OP is in the UK. We don't do odd-corner three phase!
    I didn't say it was. If it was corner grounded three phase, the voltage from each hot lead to the neutral would be 415. If it is single phase with a grounded midpoint, the voltage will be half the 415 and it is single phase. If the voltage is 239 (or 240 or near that), it is part of a wye system and there will be phase differences that can be gyrated into proper three phase.

    Bill

  22. #17
    Join Date
    Jul 2007
    Country
    UNITED KINGDOM
    Posts
    4,853
    Post Thanks / Like
    Likes (Given)
    2605
    Likes (Received)
    2362

    Default

    No The phase to neutral voltage of a 415V system is 240V We don't use split phases in the rest of the world. Neutral is always the star (wye) point...

  23. Likes Jim Kennedy, hermetic liked this post
  24. #18
    Join Date
    Nov 2004
    Location
    Webster Groves, MO
    Posts
    7,329
    Post Thanks / Like
    Likes (Given)
    1850
    Likes (Received)
    3398

    Default

    Quote Originally Posted by Mark Rand View Post
    No The phase to neutral voltage of a 415V system is 240V We don't use split phases in the rest of the world. Neutral is always the star (wye) point...
    If that is the case, the third phase can be produced with two single phase transformers, each connected from a phase to neutral and their secondaries in series with the polarities reversed and connected to the neutral. They need not be very big since each will only supply 1/6 of the total power, although they should have some margin for starting. This would give stable three phase without the noise and instability of a rotary converter.

    Bill

  25. Likes pxr5 liked this post
  26. #19
    Join Date
    Dec 2019
    Country
    UNITED KINGDOM
    Posts
    19
    Post Thanks / Like
    Likes (Given)
    10
    Likes (Received)
    0

    Default

    Bill, thats very good news, what transformers do I need for this? thanks for your help!

  27. #20
    Join Date
    Jul 2007
    Country
    UNITED KINGDOM
    Posts
    4,853
    Post Thanks / Like
    Likes (Given)
    2605
    Likes (Received)
    2362

    Default

    If you've got two phases plus neutral, then the Scott T connection is what is needed.


Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •