The HO Transformer – what are all the bits?

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    This is in reference to my HO Utility Pole Transformers available from Shapeways

    labelsLet’s look at the transformer: This is an overview. I will break it down piece by piece below. One thing that needs to be decided is simply what kind of transformer it will be.

    Electric Power Distribution System:

    Residential secondary systems are predominantly single-phase, but commercial and industrial systems generally use three-phase power. The link above takes you through a SIMPLE look at this. You have decide .. “am I supplying power to a residential home, a commercial business or to an industry”. That should be easy for anyone. I mean .. I have no problem telling the difference between my house and a textile mill.

    Single-Phase: Once that decision is made then if the transformer is supplying power to single-phase residential then you go to the article on Single=Phase transformers.

    Three-Phase: If the power that is being supplied is Three-Phase then you go to the article on Three-Phase transformers.

    This will tell you what bushings to use, what insulators are required. There are multiple ways to do this with one primary wire (single-phase) or .. three or four primary wires which can supply both single-phase and three-phase depending on how it is wired. In other words .. a single primary high-voltage wire will supply electricity to a single-phase user (residential usually). A three or four wire primary high-voltage setup can supply power to a residential user using a single-phase wired transformer or supply three-phase power to commercial or industrial depending on the size of the transformer.

    Oil_Fill_PlugOil Fill Plug: At the top of the transformer we have an Oil Fill Plug at the center. This would be where oil is added if needed. To be honest this was more of a guess on my part. I have seen what *appears* to be an oil fill plug on drawings and photos from early in last century. It seems logical to me that before the EPA acquired snipers and hunter killer teams that topping off a transformer in the field would make sense.
    If you are modeling a modern era and/or upset at the oil fill plug then simply remove it with your X-Acto knife and a swipe of a file.

    Bushing_PadsBushing Pads: On either side of the Fill Plug are two pads. Each pad is 1.2 mm in diameter with a 0.426 mm/0.017” diameter hole in the center. You can use ONE bushing or TWO. It depends on whether you are making a single-phase or three-phase transformer. Sometimes a single-phase will have two bushings .. one to the high-voltage primary .. the other is a lightening arrester.
    These 0.017” dia holes are made so 0.018” dia pins will glue in them. I picked up some “Dritz Quilting Extra-Fine Glasshead Pins” at WalMart. They measure about 0.018” .. are easy to find .. and work for what I need. The difference of 0.001” simply means .. nothing. That 0.1 mm minimum detail for FUD/FXD is about 0.004” .. which is greater than the difference between the hole dia and the pin dia. Ignore it.
    You really need to run the appropriate size drill bit through the holes to clean them up .. 3d printing just is not THAT precise. Sorry.

    Modeling utility pole insulators and transformer bushings

    LidClampsLid Clamps: Next are a series .. umm .. 1,2,3 .. 12. Twelve clamps that hold the lid on the canister. These won’t be but barely visible on a model this small and would be the same color (probably gray) as the transformer case. A thin pin wash would make them pop.

    Lifting_BracketsLifting Brackets: These are what they use to lift the transformer. I haven’t seen this but I can imagine that it would be a couple of hooks on a chain connected to a bar which would be in turn held up by a chain from either end of the bar to a central point that the crane etc. would use.

    Secondary_Wire_LugsSecondary Wire Lugs: These are where the three wires that run to your house originate. Residential housing for example with 240/120 Volt wiring there will be a Neutral and two 120 Volt wires.
    For commercial and industrial the voltage changes since they are supplying higher voltages .. but that shouldn’t be of concern to a modeler since he/she is more concerned with simply how many wires run where.
    The central lug is the neutral, by the way.

    Case_Ground_LugCase Ground Lug: Depending on how the transformer is wired this may .. or may not be used. Evidently that is based on how each power company prefers to do it. The hole for the wire is 0.46mm/0.018”. I think in the next version this should be the 0.32mm/0.013” I used for the Secondary Wire Lugs.

    Pole_MountsPole Mounts: The 1.016 mm / 0.040” holes slide on to 0.040” pins cemented into the pole. This will mount the transformer nicely to the pole.

    Note: I used 0.040″ holes here. The 0.3mm minimum wall constraint for FXD dictated the size of the mounts. I am thinking that a much smaller 0.018″ pin would work fine which would mean that the mounts would be some 0.022″ smaller in size.

    Oil_Drain_PlugOil Drain Plug: I have a photo of an older pole transformer with such an oil drain complete with oil stains

    BaseBase: finally, the base. This is glued into the body to make a solid model.

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