How to use the Variac 1

[PoliPoliCarps]

How to use this? There are no manual or sort

 

[waross]

What do you want to do with it?

How a Variac works:
The basic Variac has a winding around a toroidal core.
One side of the winding is flattened and bared.
A movable brush makes contact with a movable point on the bared winding.
An AC potential is applied to thee winding.
As the brush is moved, it will pick up a potential of from zero Volts to about 110% of the applied voltage.

Your device is a three phase model.
It has a terminal strip and a set of banana plugs.
When three phase potential plus a neutral connection is applied to the input, (4 wires) a potential will be present at the output. (3 or 4 wires.)
Which is the input and which is the output?

Turn both breakers on.
TEST #1
On the terminal strip, connect an Ohmmeter from the neutral (yellow/green terminal) to a line terminal. (Red wire, white wire or blue wire.)
Rotate the handle from stop to stop while watching the ohmmeter.
TEST #2
On the banana plugs, connect an Ohmmeter from the neutral (green terminal) to one of the other plugs. (Red plug, white plug or blue plug)
Rotate the handle from stop to stop while watching the ohmmeter.
On the input connections, thee ohmmeter should stay constant.
On the output connections, the ohmmeter should vary from zero Ohms to about the same value as in the other test.

A primary breaker will not safely protect the secondary of an auto-transformer.
A secondary breaker will not safely protect the primary of an auto-transformer.
Hence two breakers, primary and secondary.

 

[jraef]

With the clear plastic covers allowing you to see the wiring inside, I would suspect this was from a classroom somewhere.

 

[EdStainless]

What are you trying to do?
Many AC devices will not like being fed low voltages.
Read the marking on the variable transformers.
Make sure that you use the correct input voltage.
Make sure that the input and output breakers are sized correctly.
We used to use them for DC power.
Put a full wave rectifier bridge on each phase and then connect them.
Off of our 240V AC supply we would get 400V DC.
And check the calibration of the meter in the top.
I am guessing that the banana plugs are just for sensing/measuring.
The terminal block is the actual outputs.

 

[waross]

I am guessing that the banana plugs are just for sensing/measuring.
The terminal block is the actual outputs.

You may be correct.

 

[LionelHutz]

There should be at least 6 connections, 3-phase in and 3-phase out, so there aren't enough terminal blocks.

 

[EdStainless]

With a common neutral it only takes 4 terminal for all output voltages.
Based on colors I am guessing that these are output only.
I don't know what the meter on top is measuring.

 

[edison123]

Looks like the top mcb is the output with output voltmeter connected. The connector terminal blocks seem to be unfit for load output. Zero nameplate details.

OP has to engage to more

 

[crshears]

Hmmm, looks like the variac we used for the house lights in the very small theatre/cinema in the R.H. Saunders Generating Station tour centre where the video "From Dream To Reality" was played; incandescent bulbs were used.

 

[pwrengrds]

I used one like that to field calculate the impedance of a very large transformer (138kV, 100 MVA or so). I was impressed with myself that I came up with the same numbers as they did in the factory, it does have it's uses.

 

[waross]

I was impressed with myself that I came up with the same numbers as they did in the factory, it does have it's uses.

I failed when I tried that.
The reason?
The % imp of the transformer had been tested with the transformer at operating temperature.
Testing a cold transformer showed a noticeable error.
This was a small lighting transformer with a fairly low X/R ratio.

 

[davidbeach]

From the test reports I’ve seen the transformer testing is done at ambient temperature and then corrected to the operating temperature. But those are in the size range of a few MW to hundreds of MW.

 

[waross]

From the test reports I’ve seen the transformer testing is done at ambient temperature and then corrected to the operating temperature.

That makes sense, given the energy required to raise a large transformer to operating temperature.