Do transformers produce more power than what is put in?

[David345]

This might sound like a stupid question but I just don't get it.

A electrical engineer at my work who works mainly on the high voltage areas like transformers and sub stations said that the 11kv step down transformers draw only 55 amps on the incoming and that would provide 230v on the outgoing side and provide up to 5kA or 50kA, I can't remember which one he said now, of current on the outgoing side.

Would that mean that the transformer is giving out more power than what is put in, if so how is this possible due to the fact of the laws of physics that you can't get more power than you put in?

Thanks.

 

[James]

Power (watts) = volts * amps
so yes a transformer could have high voltage and low amps input
and have low voltage high amps outgoing.

but it is not providing more power out than coming in.

 

[ElectroChem]

50kA in reference to a transformer is likely to be the secondary circuit prospective fault current.

I.e. if you bolted a copper bar across the terminals you could (briefly) pull that much current before something (hopefully a fuse) went bang.

A 11kW/55A primary works out to about 1MVA, so I'd say the normal rated secondary current for your Tx would be about 1400A.

edit: Missed a (root)3 in the secondary current, Jules had it right.

 

[Julie.]

This might sound like a stupid question but I just don't get it.

A electrical engineer at my work who works mainly on the high voltage areas like transformers and sub stations said that the 11kv step down transformers draw only 55 amps on the incoming and that would provide 230v on the outgoing side and provide up to 5kA or 50kA, I can't remember which one he said now, of current on the outgoing side.

Would that mean that the transformer is giving out more power than what is put in, if so how is this possible due to the fact of the laws of physics that you can't get more power than you put in?

Thanks.

It doesn't.

It will always provide less power out than in due to losses.

A typical size of distribution transformer is 1MVA - although they can be much smaller, and much larger.

This would have a primary current at 11kV of around 53A
The secondary output at 230/400V would be around 1400A

Both these work out to be around the same power - the primary being slightly bigger, due to losses.

 

[David345]

It doesn't.

It will always provide less power out than in due to losses.

A typical size of distribution transformer is 1MVA - although they can be much smaller, and much larger.

This would have a primary current at 11kV of around 53A
The secondary output at 230/400V would be around 1400A

Both these work out to be around the same power - the primary being slightly bigger, due to losses.

Ahh right so using owms law if its 11kv x 53A that = 583000 Watts on the primary and then on the secondary 230v x 1400A = 322000 Watts.

Then using 400 volts on the secondary would be 400v x 1400A = 560000 Watts.

What voltage would you get if you connected all three phases together on the secondary?

 

[ElectroChem]

What voltage would you get if you connected all three phases together on the secondary?

I'd be very interested to find out, just let me know when you plan to try so I can be at least two counties away.

Ahh right so using owms law if its 11kv x 53A that = 583000 Watts on the primary and then on the secondary 230v x 1400A = 322000 Watts.

Then using 400 volts on the secondary would be 400v x 1400A = 560000 Watts.

Not quite. The mathematics of three-phase power conversion go a bit past basic Ohm's law.

Transformers, as a reactive device, are usually rated in KVA (volt-amps) not KW. An 11kV/53A transformer will be 11000x53x1.73 (square root of 3) or about 1,000,000 VA, usually just called 1MVA.

The 400V secondary would then be 1000000/1.73/400 = ~1400A.

 

[Wilko]

how is this possible due to the fact of the laws of physics that you can't get more power than you put in?

You are right, it is not possible !
None the less, there are countless ‘inventions’ claiming to do just that .

 

[Julie.]

Ahh right so using owms law if its 11kv x 53A that = 583000 Watts on the primary and then on the secondary 230v x 1400A = 322000 Watts.

Then using 400 volts on the secondary would be 400v x 1400A = 560000 Watts.

What voltage would you get if you connected all three phases together on the secondary?

A bit of an odd thing with the way we talk about voltages unfortunately.

We use the three phase system, so there are 3 lives each quite different. Each one would have 230-240V between itself and neutral, however if you were to measure between them, there would be 400-415v (a factor of 1.73)

So the "power" would be 1400A x 230V on EACH live, and since there are three of them the total would be 3 x [1400A x 230V] or you could use the 1400A x 400V x 1.73 if you use line to line voltage.

Confusing, but that's just how it is, do a search for "three phase" if you want to understand why this is the case, there should be some good videos on YouTube or similar.

It's the same thing for the higher voltage side, 11000V (11kV) is actually the line to line value - so it is 53A x 11000V X 1.73.

The line to neutral voltage is around 6.36kV (although the neutral isn't generally used) so again you could use 3 x 53A x 6360V.

 

[David345]

A bit of an odd thing with the way we talk about voltages unfortunately.

We use the three phase system, so there are 3 lives each quite different. Each one would have 230-240V between itself and neutral, however if you were to measure between them, there would be 400-415v (a factor of 1.73)

So the "power" would be 1400A x 230V on EACH live, and since there are three of them the total would be 3 x [1400A x 230V] or you could use the 1400A x 400V x 1.73 if you use line to line voltage.

Confusing, but that's just how it is, do a search for "three phase" if you want to understand why this is the case, there should be some good videos on YouTube or similar.

It's the same thing for the higher voltage side, 11000V (11kV) is actually the line to line value - so it is 53A x 11000V X 1.73.

The line to neutral voltage is around 6.36kV (although the neutral isn't generally used) so again you could use 3 x 53A x 6360V.

Right interesting, thanks for the reply, yeah I will do some research on youtube on that as well.

 

[David345]

I'd be very interested to find out, just let me know when you plan to try so I can be at least two counties away.

Yeah don't worry I will be sure to give you plenty of notice before I try this, hahaha.

 

[Mike Johnson]

This might sound like a stupid question but I just don't get it.

Yes it was a stupid question especially the day before April 1st.

 

[David345]

Yes it was a stupid question especially the day before April 1st.

? haha

 

[Soi disant]

What voltage would you get if you connected all three phases together on the secondary?

I'd be very interested to find out, just let me know when you plan to try so I can be at least two counties away.