new small relay breaks 300A at 400V

That is seriously impressive. Any idea what they cost?

John

Note the strange operating current specification-- 40-45W for 100msec then it drops down to 4W (for the high current version only). I wonder what's *really* in there- not just a coil, I'll wager.

Best regards, Spehro Pefhany

Probably one of those boosted solenoid things, with a power coil and a holding coil and a limit switch, like the overdrive solenoid on an Austin-Healey.

John

An arc-sweeping "magnet" is mentioned. Maybe it's an electromagnet?

...Jim Thompson

I wonder what its life would be if it was seldom switched under load.

You might ask, what good is a 300A relay if you never switch a load with it...

In a previous life I designed motor control electronics at a forklift company. The forklift had a 600 amp main power contactor that switched power to the motor controllers. But under normal operation the main power contactor was never opened or closed with the motors powered. In the software, the motor controllers were all shut off first, then the contactor was opened. So the contactor only opened in an error situation where the software determined there was something wrong, such as a failed motor controller.

It could even be an electronic switch of some kind-- they say it doesn't need any external snubbing (snubbering?) so maybe they had to add something internally.

They also warn against using a simple diode on the lower-current version, for the usual reasons.

Best regards, Spehro Pefhany

Arc quenching happens in the turnoff direction, so that can't be it.

John

I did something like that. It's a power amp for MRI imaging. There's a BIG 3-phase transformer with multiple secondary windings and rectifiers to give, basicly, floating bipolar power supplies of 100,

There is an aux supply to precharge the filter caps so the relays don't see the surge. It's the world's dumbest switcher: transformer, rectifier, mosfet, and a big power resistor, with the uP turning the fet on/off as needed.

This all works great, and when, rarely, something goes wrong, we get smoke and stuff.

John

Resulting in... what exactly, an explosion?

About 3$ per switch cycle :-)

Francois Choquette

It's to run a compressor that blows the spark/arc out.

Graham Holloway

Aren't there actually explosive things to do that? And I think I've seen tanks of freon or SF6 or something that are used to blow arcs out.

John

I should have said "So the contactor only opened under load in an error situation"

The result was just a bit of a spark. The contactor could switch the full load of the motor controllers, it just makes a spark and causes wear on the contactor tips. Older electric forklifts, such as those that use the GE EV1 controller, switch the contactors under load in normal operation. But it is a regular maintenance item on these forklifts to replace contactor tips.

Nah, in the forward direction it's rated >10**3 cycles, so it's a mere

Contact erosion in DC relays is asymmetrical.

Cheers,

Phil Hobbs

Compressed air most likely, if you are thinking about utility type transmission breakers. The SF6 (and other exotic gasses) are sealed systems, so while there might be some arc-blowing going on within the switch, replenishing the gas isn't a big problem requiring large tankage.

From the '70s until he sold it a few years ago, my dad ran a business rebuilding those compressors (among other electric utility related stuff). They're pretty nifty devices - designed to run in very remote locations under severe environmental conditions, so they do things like periodically change their own oil (every 'X' hours of operation). The air is compressed to around 2000psi, if I remember, and of course has to be very dry.

But I think that SF6 is becoming more common even for the run-of-the-mill utility breakers, except in locations too remote for routine restocking. A couple of tanks of SF6 is cheaper than trying to keep a fancy compressor running.