working on a soft starter for conveyor belt motor,unit is a 480 volt 3-phase 100 hp the problem is that the epoxy encapsulated snubber filter ,mounted about 1 inch from the anode and cathode heat sinks of one of the thyristors caught fire the flame was large enough to travel and discolor the line phase connection and cable,app. 12 inches above it.I think the 3 snubbers should be relocated ,I am concerned that a really bad situation could have happened here as the other phases are about say, an inch apart.May I ask the opinion of the forum on how best to approach this potential hazard and prevent it from causing harm to both man(first) and machine?
soft starter snubber issue
- Thread starter a.bisnath
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- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
The snubbers need to be as close to the SCRs as possible, the farther away you put them, the less they attenuate and the more susceptible they are to failure. Also you have to remember that they are at line voltage, and people are used to thinking small components like resistors and capacitors are low voltage electronics so they often mistakenly assume they are relatively safe to touch. Having them right inside of the heat sinks means they tend to stay away anyway, putting them out somewhere else increases that chance of contact.
Re-designing the equipment is not a great idea in my opinion, you don't know all of the issues that go into the component and design decisions. The fact that yours caught on fire is likely due to a defect, that happens, or a serious voltage spike. But in 25 years of building and supporting soft starters in the field for manufacturers, I have seen RC Snubbers fail less than a dozen times, it's just not that common of a thing. Usually the resistor was bad or a connection was bad, but sometimes if it sat un-powered for a long time, the caps fail when re-energized. If it was an older one with electrolytic caps, they tended to fail messily.
By the way when the RC Snubbers fail, if the soft starter run for a long time afterward, you could have some incremental damage to the SCRs.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Is this part of the soft starter? If so, you should check with the manufacturer of the soft starter. i think some older semiconductors need them but they were part of the soft starter itself.
I can't imagine why someone would add an external snubber to a soft starter. maybe a really old one that came without?
I can't imagine why someone would add an external snubber to a soft starter. maybe a really old one that came without?
snubber is original
snubber is original
the snubber is an original design It is a Westinghouse easy start about 25 years old the scr's have never failed but control card have been changed what I am beginning to researce is if there is a working life for the snubbers and if they need to be changed at intervals these have never been changed,there was a major power outage a few weeks prior whilst it was in use,I am going with not relocating them,probably increasing the wattage of the resistor and voltage rating of the capacitor,any othe possible suggestions from a safety stand point?
snubber is original
the snubber is an original design It is a Westinghouse easy start about 25 years old the scr's have never failed but control card have been changed what I am beginning to researce is if there is a working life for the snubbers and if they need to be changed at intervals these have never been changed,there was a major power outage a few weeks prior whilst it was in use,I am going with not relocating them,probably increasing the wattage of the resistor and voltage rating of the capacitor,any othe possible suggestions from a safety stand point?
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
If you change anything other than the wattage rating of the resistor, you change the snubbing carachteristics. There is no need to mess with the design, it has worked for 25 years. That's about the maximum life expectancy of a snubber board.
I'm not sure if you can still get the replacements from Eaton, but those starters were made by a company called Vectrol that Westinghouse had bought prior to Eaton buying Westinghouse, and the people that left when the deal was done started Motortronics in Florida, who is still around. They did not change the snubber board designs, they still use them today as far as I know. Tell them you was a snubber board for an LS4 starter.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
I think motortronics got bought by emerson and merged into their control techniques division. I heard once they were planning to drop all their manufacturing and relabeling of japanese stuff and going to concentrate on integrating CT drives. that business model never made much sense to me so who knows if what i heard was reliable or not.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
No, that was Saftronics, different "...onics" Florida company in Ft. Meyers, Motortronics is in Clearwater. We (I used to work there) would rob employees back and forth from each other, but otherwise we were not related.
But you are right, Emerson has all but abandoned the old Saftronics VFD brand labeling of Fuji drives (the Yaskawa deal ended over 10 years ago now) and their Soft Starters, if they focus on them at all, are a brand-label product from New Zealand now.
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