Lowering frequency in transformers

[kiki_danc]

A transforming winding is like a short circuit.. except there is inductance caused by alternating current and the frequency that produce some resistance. What would happen if the frequency is lowered.. would there be a threshold value that would begin to make it as short circuit? like 30 Hz?

What would happen if the power company is suddenly hacked so the 60Hz becomes just DC (Direct Current)? Would this make all transformers in power lines or homes explode? Did this happen previously? Why not?

 

[CWatters]

Not all power stations can generate DC. Most use rotating machines to generate both the power and the frequency. To reduce frequency down to DC they would have to stop so no power output either.

Solar power stations produce DC and convert it to AC before feeding it into the grid. But I think they also use the grid itself to control the frequency.

There is a bigger problem with your idea. If a power station gets out of sync with the grid frequency they would absorb power rather than generate it. Typically this either forces it back in sync by speeding up the rotating machine or trips it off line.

 

[kiki_danc]

Not all power stations can generate DC. Most use rotating machines to generate both the power and the frequency. To reduce frequency down to DC they would have to stop so no power output either.

Solar power stations produce DC and convert it to AC before feeding it into the grid. But I think they also use the grid itself to control the frequency.

There is a bigger problem with your idea. If a power station gets out of sync with the grid frequency they would absorb power rather than generate it. Typically this either forces it back in sync by speeding up the rotating machine or trips it off line.

Good to know the terrorists can't use this to explode thousands of utlity transformers simultaneously. For a say small home 500VA transformer. How low is the frequency from 60Hz before the induction process ceases and the windings become a short circuit?

 

[anorlunda]

How low is the frequency from 60Hz before the induction process ceases and the windings become a short circuit?

There is no magic number because it is proportional. The impedance of a coil is $2\pi f L$. so if f is halved, impedance is halved.

Did you know that aircraft use 400 Hz because the transformers can be much smaller and lighter. On an airplane, weight is very important.

The power grid normally operates on tight limits. Frequency of the grid and frequency of all generators typically vary less than 0.03 Hz out of 60 or 50 Hz nominal. Protective relays open switches to disconnect equipment if frequency gets out-of-bounds.

 

[kiki_danc]

There is no magic number because it is proportional. The impedance of a coil is $2\pi f L$. so if f is halved, impedance is halved.

If it has become just 2 Hertz. There is still impedance and fluxes, and no winding shorting would occur?

Did you know that aircraft use 400 Hz because the transformers can be much smaller and lighter. On an airplane, weight is very important.

The power grid normally operates on tight limits. Frequency of the grid and frequency of all generators typically vary less than 0.03 Hz out of 60 or 50 Hz nominal. Protective relays open switches to disconnect equipment if frequency gets out-of-bounds.

 

[anorlunda]

If it has become just 2 Hertz. There is still impedance and fluxes, and no winding shorting would occur?

That's right. Damage to windings happens only with excessive voltages or currents. You said nothing about those.

There is a volts per hertz (V/Hz) limit for transformers that has to do with heating. Is that what you're asking about?

 

[kiki_danc]

That's right. Damage to windings happens only with excessive voltages or currents. You said nothing about those.

Let's say you have 120v or 240v at the input and there is no load. If the frequency was decreased to 1 Hz from 60 Hz (by the Utility company (emphasizing I won't try it myself)). Can that 1 hertz still produce inductance and flux or would the current just rush into the windings and short/blow it apart? If you meant it could still produce inductance and flux.. how could mere 1 Hz do that??

There is a volts per hertz (V/Hz) limit for transformers that has to do with heating. Is that what you're asking about?

 

[anorlunda]

Can that 1 hertz still produce inductance and flux or would the current just rush into the windings and short/blow it apart?

It is not either or. Both can be true. That proportionality I talked about in #4 works for all frequencies. However if you hold the voltage constant and reduce the impedance, current increases (that's just Ohm's Law). Too much current will damage the wires.

 

[kiki_danc]

It is not either or. Both can be true. That proportionality I talked about in #4 works for all frequencies. However if you hold the voltage constant and reduce the impedance, current increases (that's just Ohm's Law). Too much current will damage the wires.

If you plug a wire directly to the 2 live line of the outlet, it's either the breaker trips or the wire burns. I'm asking what frequency can you lower the transformer before it acts like a wire directly plugging to outlet.. is it 1 Hz?

Do you consider the winding as like inductor? But DC can also work with inductor. Is this the reason why even at 1 Hz, the winding won't short? Not that I would do it (remember it's only the utility company that can supply the ac and even generators are fixed in frequency so don't worry about us trying it)

 

[anorlunda]

I don't know why you are so interested in this. There is no way that the power mains where you live will ever get below 59 Hz.

But your original question has been answered. Thread closed.