Tesla (PIG) Pole Distribution Transformer

Above: The PIG as it was when we acquired it.

We had just finished making my own HV transformer when I saw this Pole distribution transformer (PIG) for sale. Unable to resist it and with no thought given as to how heavy these things are, I decided to buy it. After completing a 435 mile round trip to collect it, with thankfully someone lifting it in for me, We decided to test it by running a Jacob's ladder. Using the 250 volt : 11550v taps I fed in 263 volts which gave 12k out.

As these units are built to a high specification for continuous running in all temperatures, I decided to ballast the transformer for 500 m/a at 12k giving 6kva (original specification was 5kva continuous) The secondary current is therefore slightly overloaded from the manufacturers continuous run' specification of 454 m/a.

PIG transformer out of case

Above: The total height is 16 inches. Weight of cores is 90 Pounds

The two secondaries are each wound over their respective primary winding. I am unable to ascertain the number of turns or the gauges of the wires that have been used.

tesla pig on trolley

The trolley mounting allows it to be much more manoeuvrable for my long suffering wife and son to move around. The front of the case that bulged outwards and housed the two large 11k input insulators has now been cut down. Originally the two small insulators on each side were the 250 volt outlets to the load. By using various combinations of these four terminals an input range of 10.45K to 11.55K could be accommodated.

As I would be wiring the transformer in reverse I used the 11.55K to 250 volt combination. When fed from a variac this gives me 12K out. This now left two terminals that were originally connected to the other two tapping points spare. I therefore altered the wiring inside and now use the spare pair as the 12K output.

The amount of oil is also now reduced but this will not present any problems for short term Tesla use.

Tesla coil PIG transformer with modified case

Tesla coil PIG transformer with modified case

Yes - I know the welding is atrocious.

After cutting some of the side away and bending the front panel upwards, we had a 0.125 inch gap where the two panels met, so we filled this gap with weld. Thankfully the result is oil tight which is the main objective.
Maybe the career change to working in a shipyard as a welder on submarines may have to be put on hold.

Tesla coils PIG transformer

Low voltage (250v) on the left side, HV output on the right (marked red).

The remains of the two cradles that allowed the transformer to be pole mounted are still visible.

Tesla Video

'YouTube Video of my PIG'.

Variable Inductor Ballast

For the Pig's ballast I utilised the transformer from an old welder. With the welder's secondary short-circuited it gave me a variable range of inductance across its primary winding of 20m/H, variable up to 60 m/H
When this is placed in series with the primary feed of the distribution transformer (Pig) this gives an equivalent secondary side inductance for that transformer of 43H to 129H

This is because any inductance on the primary side is 'reflected' to the secondary side of a transformer. In doing so the value of the inductance on the primary side is multiplied by the transformer's turn ratio ^2 (squared).
Conversely a secondary inductance would appear smaller to the primary side and will equal the secondary side value divided by the turns ratio ^2.

This case originally housed a 5H 2500v HV inductor and was oil filled. By turning the welder's core through 90 degrees so that the adjustment handle and its shaft now come out of the top, it made an ideal choice for my variable ballast. The case is once again oil filled allowing the entire core to be under oil to assist with cooling.
The ability to vary the inductance comes about because of a sliding lamination between the primary and secondary coils. This slide is attached to the threaded rod that projects out of the top of the case.

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