Which transformer do I need to use?

Question

In another part of the patent I mentioned in another question about step-up tranformers, it mentions "The voltage is stepped up into the range of thousands of volts using a step-up hi-pot transformer". When it says "thousands of volts" is there a specific type of step up transformer I need? You can only buy them according to watts. Please help. Thanks!

Answer 1

"You can only buy them according to watts" totally wrong. I have no idea where you got this!

Every transformer has a turns ratio. It may be explicitly stated, or it may be implicit in the voltage numbers. For example a transformer rated at 240 volts input and 24000 volts output has a 1:100 turns ratio.

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Answer 2

Transformers are made up of two ' coils' of wire that are electromagnetically joined.  Like the first poster said, one winding ( coil ) will have less turns that the other, and the comparison of the two is called the ratio.  If for instance you had 10 VoltsAC available, and you needed 100 volts, you would use a transformer with the ' output' winding having 10 times more turns than the ' input' winding.

Generally in these types of applications where the ' step up' is in the range of thousands, the output current needed will be small, allowing for the output winding to have MUCH smaller wire diameter than the input.  Remember Ohms law, when the voltage INCREASES the available amperage ( current ) decreases.  One of these can be built rather simply, using a cardboard core from a roll of paper towels.

Wind 400 turns of #16 varnished magnet wire onto the core, and leave the leads long enough to work with.  Cover that  winding with two layers of insulation ( black tape ).  Then over that wind 4000 turns of #24 magnet wire. Be neat! With 110VAC input you will get 1100VAC out.  Modify the ratio as needed.

Professionally built transformers of this type are readily available.

Here's a good site to start:

http://www.powertransformer.us/stepuptra...

Answer 3

Billruss's answer is fine as far as it goes. Let's start with that:

Every transformer has a turns ratio. It may be explicitly stated, or it may be implicit in the voltage numbers. For example a transformer rated at 240 volts input and 24000 volts output has a 1:100 turns ratio.

OK, BUT: this should not be taken to mean that a transformer that steps up from 1 volt to 100 volts is the same as, or can be used in place of, a transformer that steps up 100V to 10,000V.

When you get over a few hundred volts you will have to have terminals, windings, insulation -- in other words, the whole design -- to account for extreme voltages. Thus the "high-pot" part: this stands for high potential.

If you're looking at a source for transformers, and only watts (or kVA) are specified, you can bet those transformers will not work at thousands of volts. That kind of voltage is serious and dangerous and is special purpose.

There may or may not be an OTS (off-the-shelf) transformer for what you are trying to do -- we would have to have full specs. Note also that extreme high voltages are often generated by means other than straight step-up transformers -- it depends on the application. Some applications require high emf but no current, a geiger counter sensor, for example.

Answer 4

It's better to use the kVA rating. Watts is only the resistive component of power. The kVA rating also contains the reactive power, which is power from inductance and capacitance.

For the amount of power you are using, you will also need to take a look at if the transformer is oil filled or not. Also, what is the efficiency of the transformer? Where will it mount? Are you in a hazardous location?

Also, take a look at section 450 of the National Electric Code (NEC) which goes over some other things you will want to consider, like overcurrent protection and grounding.