Building a scale model of transformers for transformer connections training class

[PUDGUY]

Long time reader, first time poster.

Awhile back I worked at an investor-owned utility that put on annual transformer connections training. They taught us all the different ways we might wire up a pole-mounted distribution transformer bank.

They actually had gone so far as to build a small scale model power transformers using what I assume to be grey PVC conduit and banana jacks. They also had built a single span of three-phase power line. The little transformers (I say little but they were probably 12-14 inches tall and 6 inches in diameter). The transformer itself had banana jack plugs instead of primary and secondary bushings. The transformer could be connected to the overhead lines and the secondary/service lines by using leads with banana jacks on one end and alligator clips on the other end.

Somehow the whole setup was safe for when the transformers were connected incorrectly. When a bank was wired correctly, the guys could use a fluke meter and check voltages on the secondary of the transformer just as if they were checking the voltages on secondaries of a real transformer bank in the field.

Has anyone seen a set-up like this or worked with small transformers? I would be very interested in building a set-up like this to use for joint utility training here in Central Washington. There are several PUD's in the area and we could all use some training on the topic, what better way than hands-on with scale models.

It make take a bit of designing, I think they were somehow using a couple add-a-phase inverters to produce 3-phase AC from a single-phase source. Not sure if they wound their own transformers or bought them off the shelf. I'm not even sure where to buy this kind of stuff - hobby store somewhere?

If anyone knows of reading or places to buy small pre-wound transformers or has any reading material on anything related to this topic, would be much appreciated! If I actually find the time to follow through with building this setup I will be sure to post back schematics and pics so you we can all improve on the design.

 

[PUDGUY]

I re-read my own post, it's not clear, I meant to say that this was all a desktop demonstration. So the "high voltage three-phase power lines" were not really high voltage at all. I didn't have a chance to measure the "high voltage lines" so I'm not sure what voltage they were actually using. But basically a desktop power supply and two add-a-phases were used to create the primary voltage. The training instructor ran jumpers his the desktop power supply and add-a-phases to each training station "Energize" the mini-scale, single-span of three-phase overhead wire. He would kill the power to everything while trainees made their connections, and then bring the power back on when everybody was clear so they could use the fluke to check voltages and check over their work.

 

[HornTootinEE]

We did a similar class like that at the IOU I worked at. I know the instructor used an actual three phase source, but he input it into a "power supply" where he could change the primary system configuration to delta or Wye or similar. The inside of the mini transformers was I think just an off the shelf small power supply type transformer to go from the supply voltage to the desired voltage. DigiKey maybe has something like that? Not sure where he got his stuff, but it was pretty basic but very cool and slick.

I think his supply voltage was 120/208V Y then he could swap it to 208V Delta. The "secondary" of the transformers were typically 120/240 and we'd do all sorts of different connections then check voltage and rotation on the secondary bus. Then he'd have us swap leads and do this and that and show how the voltage or rotation might have changed. Lineman loved the class.

There is also a software out there for this type of thing, not sure where our company was looking at sourcing it from.

 

[LionelHutz]

I would think you'd first pick your 3-phase line voltage and then pick transformers that can't be hurt by the highest voltage level available from those 3-phase lines. In most cases, that would be the line-line voltage. You would then package those transformers into the PVC to make the model pole-mount units.

If you want a decent balanced 3-phase source then you could use a small VFD feeding through a transformer. You can get small 120V 1-phase input, 208V 3-phase output VFDs. Use 3 x 208:120V control transformers connected delta to wye to produce your 208V 3-phase power lines.

As for transformers, use small 208V:120V PC board mount transformers and stick them into the PVC case. If you connect one L-L you'd get 120V and if you connect L-N you'd get 69V. Both of these could be used to drive most voltage or power meter inputs if you were so inclined to try connecting more than a multimeter.

You can also change to using 240V:120V or 480V:120V or 600V:120V transformers if you wanted.

On a somewhat side note, the Littlefuse Startco SE-105 could provide Class A GFCI protection on this system if you use 208V L-L. We use one in our training room.

 

[ScottyUK]

If you use the VFD then make sure it is in the simple scalar V/f control mode.