quick motor check?

[Besoeker]

For Tony

 

[Knobhead]

Cheers, that will help or confuse others. But they can see what we’re talking about.

We used them on stone crushers, as a conventional starter they’ve got the grunt to get a blocked crusher going. For stone sizing the speed is then varied, a slower speed gives a larger particle size.

I had a thyristor pack fail on a 2500HP fan. When the pack fuse blew it put the fear of god up me, I was stood near it.

 

[Besoeker]

Cheers, that will help or confuse others. But they can see what we’re talking about.

We used them on stone crushers, as a conventional starter they’ve got the grunt to get a blocked crusher going. For stone sizing the speed is then varied, a slower speed gives a larger particle size.

I had a thyristor pack fail on a 2500HP fan. When the pack fuse blew it put the fear of god up me, I was stood near it.

Sounds like a quarry or a cement works.
Bad fuse selection if that happens to them.

We design and build our version of the Kramer - it has that step up chopper in the DC link that's in the diagram I posted above. They are usually upwards of 1MW but we have a few in service at about 400kW.

Apart from the merits of starting torque, they have a few other merits. Efficiency is a big plus particularly for 24/7 operation and larger powers. And that sells. I don't want to get into boring technical detail here but just a couple of figures. If you take a typical large variable frequency drive it is is likely to be 12-pulse and have to have a dedicated unit transformer. Between that and the VFD total losses are typically 4% or greater. For the Kramer it is usually under 1%. And harmonics are much lower.

Admin, for the avoidance of doubt, this is not a sales pitch.

 

[shanky887614]

I think I need to brush up on my theory, I had only come across thyristor's In small low voltage cases in electronics

if I remember right don't they only let a set voltage through and disparate the rest through heat?

(edit it's coming back to me from my 2330 at college, my lecturer really like his motors etc)

 

[Besoeker]

I think I need to brush up on my theory, I had only come across thyristor's In small low voltage cases in electronics

if I remember right don't they only let a set voltage through and disparate the rest through heat?

(edit it's coming back to me from my 2330 at college, my lecturer really like his motors etc)

Essentially switching devices, they are either on or off.
Three terminal devices, gate, anode, and cathode.
Think of a diode. It passes current in one direction, anode to cathode, and blocks it in the other. So it will pass current in only the positive half cycle of an AC supply.
Thyristors are sort of similar in that they also can pass current in one direction, anode to cathode so again, only the positive half cycle of an AC supply.

And then only if you tickle the gate. So you can delay the point at which you turn it during that positive half cycle.
So you can vary the conduction period from zero to 180 degrees and you have a means of varying the voltage applied to the load. Often, these are in a "back to back" arrangement such as in dimmers and you can control both positive and negative half cycles.

 

[Knobhead]

The first GEC Kramer drives I worked on were installed in 63.

The one that failed was about 90 again GEC designed.
They had had failures before, non with such spectacular aftermath. Swapped the pack out and switched back to speed control, no problem.
Tested the thyristor in the shop, no fault found?

Got admit one of the beauties of the Kramer system is being able to switch seamlessly from one setup to the other. It’s a bit weird knowing that the drive you’re safely working on, the motor is still running.

 

[Besoeker]

The first GEC Kramer drives I worked on were installed in 63.

The one that failed was about 90 again GEC designed.
They had had failures before, non with such spectacular aftermath. Swapped the pack out and switched back to speed control, no problem.
Tested the thyristor in the shop, no fault found?

Got admit one of the beauties of the Kramer system is being able to switch seamlessly from one setup to the other. It’s a bit weird knowing that the drive you’re safely working on, the motor is still running.

Yes, bypass operation comes more or less as a freebie.
Working on the drive while it is bypass is a feature we have built in to a few with padlockable isolation switches.
But with current site safety requirements it would need something like an act of Parliament to do so.

On thyristor failures, my experience is that, for the most part, the failure is a short circuit which can usually be measured using a standard multimeter. However, I have come across a few that weren't. Pressure mounted devices, disc, hockey-puk and various other names depend on being clamped to make internal contact may look open circuit when not correctly clamped.

I've also had a few that went into degraded mode that not dead checks would pick up.
Sometimes I'd get the chip out to try to determine cause of failure*
Here's one I did earlier

It's a 60mm diameter chip.

Around the 9 o'clock position you can see an aberration near the edge. Over voltage most likely. It helps with design parameters.

*Do not do this at home or anywhere else. Many have toxic beryllium compounds. So don't even attempt it.