Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Helpful Answer
  • Replies 14 replies
  • Helpful Answers 1 Helpful answer
  • Subscribers 39 subscribers
  • Views 372 views
  • Users 1 member is here
Options
You may also be interested in

230V Supply from 400V Line to Line in a Control panel

Pabindu Gamage

Hi, 


I have a situation where I need to install a 230V control system which draws about Max 5A ( at230V) inside a existing Dinrail enclosure. 
However, the incoming (feeder) cable of this enclosure is a 3 Core + Earth and doesn't have a Neutral, as the load is 3 phase with no neutral.

My task is to provide a 230V supply for a control equipment that we are going to install inside this enclosure. I am struggling as there is no neutral available. 
feeder is very long hence we cannot afford to run a neutral from the SDB to this enclosure.  either. 

1) Would it be possible to mount a small control transformer and feed this with 400V supply and then generate a 230V supply ? (below link)

https://www.yesss.co.uk/eris-400va-panel-transformer-230400v-primary-122448110240v-secondary?srsltid=AfmBOoq0MCaJYskcQovSxGEfzGITtVWGUpqrmsWnTT7WLwGIsOa1xMz0


2) and if so, will this be a floating neutral ? and how do I make the neutral 0V then if required? from a practical point of view.

Thank you in advance for your support. 

  • 0

    Yes, a 400 to 230V transformer is a common solution to this sort of problem. Just connect one pole of the output to the supply circuit c.p.c. to make it N (and hence a small TN-S system). (Depending on the situation, other options might also be considered - e.g. a separated (floating) system).

       - Andy.

  • 0
    Pabindu Gamage said:

    https://www.yesss.co.uk/eris-400va-panel-transformer-230400v-primary-122448110240v-secondary?srsltid=AfmBOoq0MCaJYskcQovSxGEfzGITtVWGUpqrmsWnTT7WLwGIsOa1xMz0

    Am I missing something? This is a 400VA transformer, so won't provide the 5A at 230V.

    Also, how big is the regular 3phase current draw? Will the 5A at 230V significantly 'unbalance' the three phase, pushing problems back up the line?

  • 0 in reply to Philip Oakley

    Hi Philip, 
    Many thanks for pointing this out. I need to research on finding a suitable size T/F. 

  • 0 in reply to AJJewsbury

    Thank you Andy, 
    This really helps. I thought of the same but then I was a little worried if I am making a separate earthing island. 
    Thank you for your advice.

  • 0 in reply to Philip Oakley

    Will the 5A at 230V significantly 'unbalance' the three phase, pushing problems back up the line?

    It'll have unequal currents, but will still be balanced (in the sense that the vector sum of L1 L2 and L3 will still be zero) - much like the DNO's HV system where a single phase transformer is hung underneath a 3-wire 3-phase system.

       - Andy.

  • 0 in reply to AJJewsbury

    Well the incomer of this is 125A with the system designed for a 100A load. plus I can balance this by modifying the load at each phase at site. So, that won't be an issue. 

  • 0 in reply to Pabindu Gamage

    I was a little worried if I am making a separate earthing island. 

    By using the supply c.p.c. you make sure it's all part of the same earthing system - so no worries on that point.

    In the case of an earth fault on the control circuit, the immediate fault loop will only consist of the control circuit back through the secondary winding of your transformer (via your PE-N link), but that current has to be "driven" by a corresponding current in the primary - which is limited by the L-L loop impedance at that point. So Zs calculations (if needed) get a bit more complicated, as as well as R1+R2 of your control circuit to consider there's the overall impedance of the transformer plus a proportion of the L-L loop that supplies that (the proportion depending on the winding ratio of the transformer). Note that small transformers can have relatively high impedances. 

       - Andy. 

  • 0 in reply to Pabindu Gamage
    Pabindu Gamage said:
    So, that won't be an issue.

    I'd agree. 5A out of 125A isn't a deal breaker Wink

  • 0 in reply to AJJewsbury

    These 'balance' discussions can get complicated real quick.

    My head's currently spinning about a 'three phase modulation/sampling' scheme that needs to minimise the 'dc' data level around the putative sampling (roughly equivalent to sampling each phase at it's expected peak, in sequence, with an arbitrary zero for the data, and looking for the overall amplitude/phase modulation at LF)

  • 0

    Would it not be more prudent to replace the 3 Core + Earth for a 4 core + Earth?  This would allow for other single phase devices like a dual plug/socket arrangement to plug in a tester or a light to the maintenance technicians laptop.

Community Rules & Guidelines