Forums » Electrical Engineering

TWO TRs connection

    • 9 posts
    June 23, 2019 12:27 AM PDT

    My friends 
    is there any comments for direct connection of two transformers 30/11 - 10 MVA each on the same line as mentioned in the attached drawing. The protection in the 30 kv side will be from the source substation 30kv ( dist. and o/c -EF) and from the 11 kv side will be in the 11 kv substation ( o/c + EF)
    This connection will be temporarily for restoration purpose.
    thanks 

    • 25 posts
    June 23, 2019 12:42 AM PDT

    I think, it is required to have a busbar at the split point between transformers.

    • 37 posts
    June 23, 2019 2:20 AM PDT

    I agree with Edward, it should be drawn like this.


    This post was edited by Ronnie Rana at June 23, 2019 2:21 AM PDT
    • 9 posts
    June 23, 2019 2:39 AM PDT

    Due to site situation it can not be to make busbar at the mentioned point. 

    • 89 posts
    June 23, 2019 3:57 AM PDT

    I am assuming parallel conductors from the upstream breaker that split away from each other at some point ahead of the two transformers.

    With both transformers feed by the same breaker the upstream protection will be less coordinated than it should be. 

    I would like to see fused disconnects ahead of each transformer, since no transformer differential protection is shown. 

    If the transformers high side is a cable connection, a bus bar would not serve any real purpose.


    This post was edited by Steve Ward at June 23, 2019 4:07 AM PDT
    • 25 posts
    June 23, 2019 5:32 AM PDT
    Steve Ward said:

    I am assuming parallel conductors from the upstream breaker that split away from each other at some point ahead of the two transformers.

    With both transformers feed by the same breaker the upstream protection will be less coordinated than it should be. 

    I would like to see fused disconnects ahead of each transformer, since no transformer differential protection is shown. 

    If the transformers high side is a cable connection, a bus bar would not serve any real purpose.

    Assuming parallel conductors is correct, but this depends on number of circuit paralleling. If there are two circuits from the upstream breaker to that split point, and connected each circuit conductors to one transformer, that is right. In this case no need a busbar or node. 

    If there is only one circuit from the upstream breaker to the split point, in order to divide one circuits into two, you need a node or busbars. 

     

    @Fouzi, please give some more information regarding the number of circuits. Is there one circuit with parallel conductors or two circuits?

     

    • 9 posts
    June 23, 2019 6:04 AM PDT

    it is one circuit

    • 25 posts
    June 23, 2019 6:08 AM PDT
    Fouzi Eshtewi said:

    it is one circuit

    you need a node or busbar to split one circuit into two branches or circuits.

    • 148 posts
    June 23, 2019 6:16 AM PDT

    I don't quite follow the diagram as it is unfamiliar to me but it looks like there is a tap so there are many rules for tap conductors, including distance and termination in an overcurrent protective device.

     

    These rules are found in Section II of article 240.... section 240.21

    • 200 posts
    June 23, 2019 11:18 AM PDT

    Thanks for the suggestion of this topic, Fouzi.

    Fouzi Eshtewi said:

    This connection will be TEMPORARILY for restoration purpose...
    Due to site situation it CAN NOT BE TO MAKE BUSBAR...
    it is ONE CIRCUIT

    In my opinion "temporary" installations cannot be used to justify "reduced-cost & reduced-safety" installation..., that is the often way in (wrong) direction to accidents and harmful events.

    Dear Fouzi, if you cannot do the Ideal ONE Circuit installation as advised by the Z4E Members - a tie-breaker is a possibility since just one 30kV OUTGOING source is used, no synchronization issues - due to site limitations, such as the image below:
    [insert image: Ideal ONE circuit.jpg]

    ... at least you can try to make an Alternative of TWO FULLY INDEPENDENT circuits, with all protection devices for both circuits as required by the code of the country you are working at, such as the image below:
    [insert image: Alternative TWO fully independent circuits.jpg]

    The cost of an additional 30kV conductor will not be so high and it will prevent the problems raised here in this topic such as ties and taps, and code conflicts.

    I hope this helps. Regards.


    This post was edited by Alex de Moura at June 23, 2019 11:20 AM PDT