Causes of UPS Fire
Causes of UPS Fire
(OP)
A facility manager I work with recently had a small APC UPS catch fire and burn up. A week before, they had an SCR on a large UPS fail.
We suspect the cause to be some sort of power quality issue on the distribution system. The issues have come up since introducing some large, non-constant DC power supplies to the system.
My first thought was harmonics, but some reading I've done indicates that it might also be voltage fluctuations. I understand why harmonics could cause failures, but I'm not clear on why voltage fluctuations might.
Two questions then:
1) Is it possible for voltage fluctuations to cause this kind of damage?
2) Are there other power quality issues that he should be looking at - like Surge, Sag, etc?
Thanks very much!
We suspect the cause to be some sort of power quality issue on the distribution system. The issues have come up since introducing some large, non-constant DC power supplies to the system.
My first thought was harmonics, but some reading I've done indicates that it might also be voltage fluctuations. I understand why harmonics could cause failures, but I'm not clear on why voltage fluctuations might.
Two questions then:
1) Is it possible for voltage fluctuations to cause this kind of damage?
2) Are there other power quality issues that he should be looking at - like Surge, Sag, etc?
Thanks very much!






RE: Causes of UPS Fire
RE: Causes of UPS Fire
RE: Causes of UPS Fire
If the UPS is heavily loaded and input voltage goes down, then the UPS will compensate the low voltage by drawing more current (needs to get same power from grid) and that does it to the input circuitry.
If this happens often, then check if load is high or if the low voltage limit is set too low (some UPS don't even have a low voltage limit).
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Causes of UPS Fire
How old is the unit and was there regular maintenance performed on it, and to what extent?
RE: Causes of UPS Fire
RE: Causes of UPS Fire
RE: Causes of UPS Fire
UPS systems fail and the small UPS systems fail quite a lot. I used to work for a manufacturer of these units and the failure rate for small units (warranty claims) was calculated to be about 3% in the first year. Most of the failures will be quite benign and the UPS will shut down but in rare cases you'll end up with smoke and flame.
The units are built cheap, especially the magnetics within them so it's not surprising that they fall over quite regularly.
As for the large UPS you state that an SCR failed. What part of the circuit? Was it the rectifier, the bypass (reserve) static switch or the inverter output static switch? Each one could have a different cause and therefore a different set of theories in to what caused the failure or it just may be that the thyristor failed because it was its time, or a manufacturing defect or hit by an energetic cosmic ray.
Two UPSs failing on one site within a week of each other, especially when one is a cheap and nasty, wouldn't send me into a spasm of investigation.
RE: Causes of UPS Fire
RE: Causes of UPS Fire
The corporation I worked for had very stringent design standards in that significant smoke/fire emission under any failure mode circumstance was a no-no.
Not all companies have developed the FMEA (failure mode effects analysis) skills/expertise for design and test verification of circuit boards and power assemblies to not cause fire/smoke under any failure mode. But it has been done.
A simple example is the failure mode carbon resistors in a power circuit can exhibit. Carbon resistors as one might image, in overload conditions can glow red hot for sustained periods and become a source of ignition. Metal film resistors tend to behave more like fuses and safely open the circuit. Base circuit board composition is another factor that can determine the degree of escalation that will occur. Primary fusing alone may not be sufficient depending upon power supply topology and additional internal fusing points may also be needed. Ferro-resonant transformer designs are notorious for this due to ferro fold back on overload.
The core design premise used is that any fault condition capable of producing fire/smoke must "clear" (e.g. design must operate like a circuit breaker) or energy levels be low enough at the point in question to not generate fire/smoke.
The design principle is no different than circuit breaker/fuse trip/clear curves must be consistent with acceptable temperature rise/insulation limits of connected downstream circuits.
I think I would consider using a different UPS supplier.
RE: Causes of UPS Fire
I don't work too closely with UPS's. My general impression is they are complicated devices with lots of design variations and many possible failure modes.
Suggestions for investigation:
1 - if you study the fusing and protection of the device perhaps you could rule out some failure modes.
2 - do a thermography survey of other similar units to look for anything unusual that might indicate a design vulnerability
3 - my very limited experience (2 failures) tends to support sibeen's generalization that magnetic components are more likely suspects.
4 - get the vendor involved. Not only are the familiar with the design, but chances are they have been called by other customers to consult on failures and have some history of weaknesses in your design.
=====================================
(2B)+(2B)' ?
RE: Causes of UPS Fire
We had two UPS's of the same design fail
should have been:
We had two UPS's of the same design catch fire
(There are a whole lot of ways for a UPS to fail and very few of them should result in fire)
=====================================
(2B)+(2B)' ?