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1000 VA 230 VAC 50 Hz - How Much Inrush Current?

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themadhippy:

--- Quote ---, we are using  up to 5 KVA isolation both EI and toroïdal never seen this
--- End quote ---
But i bet they aint protected by a fast acting protective  device,if the 20A device protecting the ring final is a type B it  only takes 0.1 seconds at 100A for  it to go pop.

--- Quote ---RCCD
--- End quote ---
Hope you mean RCBO as an rccd is just the old name for an rcd as in residual current circuit device and has no overload protection,if it is an rcd/rccd thats tripping your looking up the wrong tree for a solution

Kleinstein:
Magnetic remanence is a problem with high quality toroidial transformers too. The good materials have quite some remanence too, though there seem to be also steel grades optimized for less remanence (likely with downsides in other parameters). It is not so easy to find a good reference - with the graphs often shown it is not really clear if this is real or schematic only.
One example ref I have found is this, where it is about measuring the remanence. The get a range up to 30 / 50% of the actual used magnetization some some 25-40% of the saturation magnetization as there highest measured point.

https://pdfs.semanticscholar.org/e243/dcfd93b3cf368457f06043844cf65367b225.pdf

How high the remanence magentization can also be effected by the ciruit the transformer is used in (load, capacitance) an the moment when the voltage is turned off. So the remanence can vary a bit random.

EI cores usually have enough air gap to reduce the remanence quite a bit. In addition EI cores often use non grain oriented materials and a relatively low magntization. So they have more headroom to saturation.
Torodidial transformers on the other side often use grain oriented steel and this allows to get closer to saturation in normal operation. This is one may point, why the torroid form can get higher power density. As a downside it makes the inrush current from saturation more of a problem. It would be the ones with cheap non oriented material that are less effected by the inrush current problem.

So getting a problem with inrush current is not a sign of poor quality, but more an indication of the use of the better grain oriented matirial and a relatively high magnetization.

Benta:

--- Quote from: jonpaul on March 09, 2022, 10:00:21 pm ---Hi very odd, we are using  up to 5 KVA isolation both EI and toroïdal never seen this.

--- End quote ---

The main problem today is, that transformers are "starved" on material, meaning iron and copper. Everyone wants "Aliexpress" prices and get corresponding products.
The cores operate within a hair's breath of saturation, and the copper operates at too high temperatures. That makes them smaller and cheaper for the same quoted "power".

The soft-starter is one way of getting around this.

In a couple of projects, I've gone a different way: Using 400 V primary transformers for 230 V input.
You'll need to specify the secondary voltages differently, of course, and you'll need to downgrade your power expectations. A 1 kVA would then be specified as 800 VA instead. This due to the thinner winding wires (but lower core losses).
This takes the transformer away from being very close to saturation. I've not had any of those 400 V types blow the fuses yet.

dannybeckett:
Yes I meant RCBO, I'll change the text in my original post. Also attached an image of it for clarity. The fast blow fuses get annihilated along with the RCBO tripping.

I've started the phase detect firmware for the Arduino tonight, should be able to get something going in the next couple days. Once it's working, I'll do an experiment measuring inrush current vs switch phase angle on this big torroid. Very interested to see the results.

dannybeckett:

--- Quote from: Kleinstein on March 09, 2022, 10:54:46 pm ---One example ref I have found is this, where it is about measuring the remanence. The get a range up to 30 / 50% of the actual used magnetization some some 25-40% of the saturation magnetization as there highest measured point.

https://pdfs.semanticscholar.org/e243/dcfd93b3cf368457f06043844cf65367b225.pdf

--- End quote ---

Really interesting paper. It may end up being the case that the simple inrush limiting resistor / relay timer circuit is the way to go as we don't have to worry about any such residual flux.

The engineer in me wants to see if an arduino is capable of making those small signal LCR measurements to determine magnetising inductance and hence remenance. Knowing that will let us energise at the correct phase angle.

Alternatively, there might be an easy way to degauss the transformer before energising.

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