| Electronics > Projects, Designs, and Technical Stuff |
| Power Transformer Inrush Current Limiter |
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| dave3533:
I always thought the Motorola App Note AN1542 would be fun to try...not at the power levels you're looking at though. |
| jbb:
I haven’t gone that big, but in power systems there’s a lot to be said for big dumb designs. Are you above 1kV? If so, everything will get more expensive... Some options: - A Point On Wave breaker system can be quite effective (calculates and closes relay on a per-phase basis) if you can get them - Big series resistors can be very effective, but bypass switchgear can be expensive (especially for medium voltage). Series resistors can also be made from bulk cast iron or stainless steel sheets cut into meander patterns (with nice wide tabs at the ends to boot the wires on). Remember fuses or thermal protection so they don’t catch fire if the bypass switch doesn’t close. - Can you inject magnetising current through the secondary (or tertiary) winding? (Can be very helpful if primary is medium voltage) |
| schmitt trigger:
What Benta is saying is the optimal solution, but requires to precisely determine the firing angle such that the applied flux is completely opposite from remanence. |
| coppercone2:
https://en.m.wikipedia.org/wiki/Current_limiting_reactor |
| splin:
If you have another source of power from another transformer, or one that can be synchronised to the mains, how about partially magnetizing the core via a secondary winding - just enough to limit the inrush to the required level for a short time when switching on? No danger of rectifying the incoming feed and low voltage, hopefully cheaper switches/relays could be used. [EDIT] Or even discharge a capacitor into a secondary at just the right time? Plenty of current available for the short time required. You can use electrolytics to keep the cost down and use semiconuctor switches to match polarity of the i/c supply at point of switch on. Synchronisation might be tricky if the main switches are mechanical, but triggering by the detection of primary voltage being applied, or even secondary voltage, might be quick enough given sufficient inductance in the primary windings and supply wiring (and the secondary's inductance will be rather less than the primary's). |
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