Mains surge blowing eurotherm controllers

[chris_topher]

On Saturday evening there war a huge mains surge that left all our eurtherm controllers fried. All fuses were in tact. How can this happen?

Great forum.

 

[Darkwood]

Are they single to 3 phase inverters if so its possible a lost neutral on supply could have created a floating star point seeing voltages up to 400v on single phase equipment .. was anything else effected and are the drives on common supply? "

 

[chris_topher]

its all on 3 ph, one psu for a laptop died, and an oven in another part of the site failed. I've been told there was a huge power outage on that evening when all our kit went down. How come the fuses don't blow then? I know this is not a new scenario but was just wandering how it can happen

 

[Knobhead]

Quick question first, do you have inductors (chokes) on the supplies?

I've had this happen with Eurotherm before but that was due to a general voltage rise at the weekend. 10 drives smoked over each W/E for 3 weeks. The wholesaler we bought them off was getting a bit pee'd off after the 2nd W/E so we had to stump up for the last lot. That's when I got involved.
One of our own intake transformers had a failed on load tap changer. Our plants were geting 490V instead of 433V when the load on the rest of the work eased off during the W/E. One thing I recommeneded was that when the plant was shut down over night and at the W/E was to isolate the drives.

 

[Darkwood]

Cant ask for a better explanation than tony already given but as for your fuses not blowing query- they are looking at current flow not voltage, so a voltage spike could easily blow sensitive equipment like electronics without operating the fuse, even if your inverters were protected by semi-conductor fuses internally or external as ofter found associated with inverters i still believe this would occur without them operating unless the voltage rise created an internal short circuit but again damage already done in this case.

 

[chris_topher]

excellent, thanks