Hedges
I See Electromagnetic Fields!
- Joined
- Mar 28, 2020
- Messages
- 20,960
When running at very low flux density, as we will be doing, flux doubling and inrush is never a problem.
The flux CAN actually double and still remain safely below saturation.
Try starting up your 230v winding through a lamp from 110v. Inrush should be absolutely minimal.
I'm not worried about inrush at half voltage. Full voltage, it can be a problem because they are designed to go part way into saturation with each half cycle. If power is disconnected at the end of half cycle, then reconnected at start of a half cycle of same polarity, that's when they go deep into saturation, can draw many times full load current. Operating at half normal voltage, this effect would only draw a moderate current.
I've measured inrush by repeatedly switching on & off, sometimes got quite high current. Better waveforms with Fluke i2000 Rogowski coil (20 kHz bandwidth) than with CT.
A more obvious and dramatic demonstration is applying DC with a CV/CC supply or any DC source with a series resistor for current limit and measurement. First time I apply nominal voltage, it holds off current for 20 milliseconds before current shoots up. Second time same polarity, only holds off 2 milliseconds. Reverse polarity and again one application holds off 20 milliseconds. (With a different applied voltage, time to saturate would be different, closer to the 8 or 10 milliseconds of one phase.)