weird lighting transformer issue
weird lighting transformer issue
(OP)
I am working on a lighting project which is using 230VAC through some Lutron dimming modules to toroidal transformers (230:12 VAC).
I have seen some very weird things happenning with the primary fusing on the transformers. Basically if a short occurs on the secondary side of the transformer, it does not always blow the primary fuse. There is a much larger current supplied than the VA raing of the transformer should allow, but somehow the circuit holds at a certain current, which is often not enough to blow the fuse. This happens both when attached to the dimming module, and when the transformer is connected directly to the line voltage. The current limit seems to be somewhat affected by cable length, which I initially thought was a result of voltage drop in the cable, but the voltage drop calculations and measurements don't add up with the measurements. I can't understand what could be limiting the current. HELP!
I have seen some very weird things happenning with the primary fusing on the transformers. Basically if a short occurs on the secondary side of the transformer, it does not always blow the primary fuse. There is a much larger current supplied than the VA raing of the transformer should allow, but somehow the circuit holds at a certain current, which is often not enough to blow the fuse. This happens both when attached to the dimming module, and when the transformer is connected directly to the line voltage. The current limit seems to be somewhat affected by cable length, which I initially thought was a result of voltage drop in the cable, but the voltage drop calculations and measurements don't add up with the measurements. I can't understand what could be limiting the current. HELP!





RE: weird lighting transformer issue
The wiring on the LV side contributes some resistance, and the transformer itself contributes both resistance and inductive reactance. As you only have 12V available to drive current around the LV side it should be clear that a fairly small amount of resistance can have a significant effect on the current which flows.
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If we learn from our mistakes I'm getting a great education!
RE: weird lighting transformer issue
RE: weird lighting transformer issue
Have you considered that a real-world fault is unlikely to be as 'perfect' a short as you made for the test?
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If we learn from our mistakes I'm getting a great education!
RE: weird lighting transformer issue
As far as a real world short, I have been thinking about that situation, and at the moment the only possible solution I can come up with that I am comfortable with is to fuse all the secondaries. The major problem is that there are about 1000 of these on the project and they aren't all that easily accessed.
FYI this is on a megayacht which was started in Taiwan and I am working on finishing it at a shipyard in Croatia.
RE: weird lighting transformer issue
BTW, make a good job of my yacht!
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If we learn from our mistakes I'm getting a great education!
RE: weird lighting transformer issue
A.
RE: weird lighting transformer issue
RE: weird lighting transformer issue
RE: weird lighting transformer issue
If not, then get a 130 degree thermal fuse inserted into the primary winding. This will blow before it catches fire, and is the common method these days.
If the heavy secondary current on SC is a real problem then secondary circuit fuses will be necessary.
Regards, Ray.
RE: weird lighting transformer issue
RE: weird lighting transformer issue
While overcurrent device coordination would become involved (only a single level though) a relatively firm and predictable maximum secondary current value can be attained.
While some members positively bristle at cross-posting, you might get some more insights on a different forum. Re-posting this thread might work without "getting shot at".