Never try to switch 450V DC at 3A with a conventional mains switch...

[wrenchone]

The switching situation isn't so bad for AC, as any arc created gets interrupted each 1/2 cycle and thus has a chance (a chance, mind you) to extinguish. If the arc is severe enough (especially inside a closed space) so that the flame/plasma cloud has no chance to dissipate, even an AC arc can continue until all the nearby consumables are, so to say, consumed...

Back in school, the labs were supplied with a 200VDC bus to run things like electromagnets. I remember being able to draw a beautiful green arc with an electromagnet and its associated knife switch. I didn't let the arc run too long, though, as I didn't want to chew up the switch too badly. That was back in 1974 - a safety inspector these days would have a heart attack looking at all the lab setups back then, especially since most of the students playing with them didn't know which end of a soldering iron to grab, and were mostly unsupervised....

[wrenchone]

One more thing - if there is a substantial enough inductance in series with the AC, it can also keep an arc going, and of course, if the AC voltage is high enough to re-establish an arc each cycle, then all bets are off.

[Tweeker]

33.3 MVAR and 500KV will do.

[Bakmeel]

This will clearly show what will happen when the arc persists.

http://video.google.nl/videoplay?doc...5072&q=station


I have built a 5kW load for voltages up to 600V. for short-circuit testing we use a gigavac Vacuum relay. Works like a dream.

Bakmeel

[jamesrnz]

eva,
what was the result of the switch transistors with the removal of the load?

mine explode..... i am trying to find out whether there is some transient turning on opposite pairs (full bridge) or some type of spike exceeding the max voltage level of the fets.

i dont have my current transformer set yet and i was thinking about a mov across the 400v bus.

speaking of current transformers where do you think is the best place for it to live? in the bus to the brige or in series with the bridge transformer.

jimbo

[Eva]

Oh, nothing happened to the PFC because I have put a great deal of thinking into it in order to make it reliable, unlike what I did when I tried to gate the load with a conventional mains switch (no prior thinking )

[kubeek]

I read this sub station explosion happened in CZ, someone took a discarded distribution transformer- and conected it stright to 3x22kV line under his garden. After few days, this happened to him

[Irakli]

Now I am scared, lol.
I am making a power conditioner with 1.5KVA transformer. I was wondering do I need something special for a master power switch (which I assume will be upstream the transformer's primary). Or just robust, high quality, properly rated DPDT switch will do?

I saw people using NTC resistors for soft start, but my heart is not in it. I do not think they are reliable enough.

Thanks for your comments.

[Irakli]

I have built a 5kW load for voltages up to 600V. for short-circuit testing we use a gigavac Vacuum relay. Works like a dream.

Thanks for the link. seems very promising.

[Wavebourn]

Originally posted by Tweeker
33.3 MVAR and 500KV will do.

My uncle worked on a transformer station on LEP-500 line in Syberia, and visiting him I heard switches. I really heard them on a long distance, because they were pneumatic. An air from cyllinders holding springs was released into the gap when switching.