Page 1 of 3 123 LastLast
Results 1 to 10 of 30

Thread: Single phase inverter fed from three phase system

  1. #1
    Join Date
    Sep 2017
    Location
    Santiago, Dominican Republic
    Posts
    12

    Single phase inverter fed from three phase system

    Hello,

    Recently in my worksite we acquired an inverter as back up energy for the offices in case of blackouts (common in my country). The equipment is a TRACE APC6048 Pure Sine Wave inverter which requires 220V input to work properly (according to specs accepts from 194-243V).

    The office building is powered from a three phase, Delta-Y 460-208/120V transformer, and what occurred is that when I tried powering the inverter from that 208V three phase system running two lines to the input side of the inverter, the electronics went haywire (I heard a strong rattling sound coming out of the inverter for 2 seconds and then the sound stopped, but the output of the inverter was out of specs, voltage readings were wrong between the L1, L2 and Neutral).

    I took the equipment back to the seller and then they told me that it can’t feed it from a three phase system but rather from a single phase system, so I needed to get a special transformer in order to change from 208V line-line voltage from the thee phase transformer to 240V single phase and then input that to the inverter.


    • Has anyone here seen any case like it?
    • What difference does it makes for the electronics, being powered from 208V three phase and 240V single phase (given the fact that 208V is within the tolerated range)?
    • What type of transformer do you think this "special transformer" is? Scott-T? Open Delta? Any other?


    Here's a link to a very similar equipment I found:
    http://www.extremeheatsolar.co.za/AP...ersion-4.0.pdf

    Thanks for any reply.

  2. #2
    Join Date
    Dec 2012
    Location
    Placerville, CA, USA
    Posts
    17,986
    The biggest problem with connecting the inverter to two phases and the neutral is that the center tap of a transformer winding from L to L will not be at neutral voltage as it would be with 120/240 single phase. Some parts of the electronics may be relying on that.

    We need more info on how you intend to connect it. Will it be trying to drive three phase loads when running as backup? That simply cannot be done, period.

    There is a transformer config, not Scott-T, that can feed equally from three phases to single phase, but I am pretty sure it would not help you.

    Sent from my XT1585 using Tapatalk

  3. #3
    Join Date
    Jun 2006
    Location
    Ohio
    Posts
    21,120
    If all you did was power up the inverter with no load connected, then the unit was defective and the seller is feeding you a line of BS.
    I will have achieved my life's goal if I die with a smile on my face.

  4. #4
    Join Date
    Jun 2006
    Location
    Ohio
    Posts
    21,120
    Quote Originally Posted by BBGigante View Post
    Here's a link to a very similar equipment I found:
    http://www.extremeheatsolar.co.za/AP...ersion-4.0.pdf
    Similar will not cut it.

    Aside from that, this is a DC to AC inverter. Is your inverter also a DC to AC inverter? If yes, what are you powering it with?

    Something sounds hinky with this whole setup.
    I will have achieved my life's goal if I die with a smile on my face.

  5. #5
    Join Date
    Sep 2017
    Location
    Santiago, Dominican Republic
    Posts
    12
    Wow thank you so much for that quick response.

    The inverter is meant to drive a 6KVA UPS (Eaton Powerware 9170+) which uses split phase power modules to produce 220V output, so I have two lines and a neutral coming out of the UPS thus providing me with two 120V circuits to power all the computers and servers. The inverter also powers all the lighting in the building (fluorescent lamps).

    Right now I have an old inverter, pretty much like a SW5548 which requires 120V input so I simply take one line and neutral from the three phase transformer and feed it straight forward, then at the output I have a step up transformer to make it 220V. The thing is that inverter is faulty and we need to replace it, but now I ordered this APC6048 which provides a 240V output straight forward without the need of the step up transformer.

    I thought I could power it from my three phase system since all my air conditioners are powered from it (220V single phase units) and they run just fine, considering they have an electronic card in the indoor unit to control its operation.

  6. #6
    Join Date
    Sep 2017
    Location
    Santiago, Dominican Republic
    Posts
    12
    The upper drawing is what it looked like before, it was working correctly. The lower drawing is what I tried, and failed.

    As I said before the first inverter is 120V input, and the output was stepped up via a transformer to feed the UPS and some lighting. The new inverter is 220V input and the output goes straight to the UPS, but I couldn’t get the output to work correctly, I tested with no load connected to it.
    Attached Images Attached Images  

  7. #7
    Join Date
    Jun 2006
    Location
    Ohio
    Posts
    21,120
    Quote Originally Posted by BBGigante View Post
    The upper drawing is what it looked like before, it was working correctly. The lower drawing is what I tried, and failed....
    Too small to read text.

    Nevermind. Opened image in new window and zoomed in.
    I will have achieved my life's goal if I die with a smile on my face.

  8. #8
    Join Date
    Jun 2006
    Location
    Ohio
    Posts
    21,120
    Quote Originally Posted by BBGigante View Post
    ...
    As I said before the first inverter is 120V input, and the output was stepped up via a transformer to feed the UPS and some lighting. The new inverter is 220V input and the output goes straight to the UPS, but I couldn’t get the output to work correctly, I tested with no load connected to it.
    Why do you not power the lighting and UPS directly without the inverter?

    The 120-208V labeled 1Ø transformer is not correct. You cannot power 120V lighting with a 208V secondary.
    I will have achieved my life's goal if I die with a smile on my face.

  9. #9
    Join Date
    Sep 2017
    Location
    Santiago, Dominican Republic
    Posts
    12
    I'm sorry my drawing is kind of funky; the lighting circuits are powered from one line of the 208V circuits and the neutral bar on the right, not straight from the 208V lines. What I have is two 120V circuits from those two lines and the neutral.

  10. #10
    Join Date
    Sep 2017
    Location
    Santiago, Dominican Republic
    Posts
    12
    The reason for powering the UPS and lighting from the inverter is that when a blackout occurs, the lighting stays on until the generator kicks up, and the UPS because at night the factory is closed and the generators are not working in case of blackouts, so the UPS would discharge and the servers would go off.

Posting Permissions

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