[Amps] Effects of gapping trnasfomers.

[Will Matney]

A good while back, on a discussion about gapping cores in transformers, 
I forget with who, I found this info today that may be interesting. 
Below is a quote from Magnetics, inc., Div. of Spang & Co.;

"A typical example showing the merit of the cut-core was in the check 
out of the Mariner spacecraft. During the check out of a science 
prototype, a large (8A, 200uS) turn-on transient was observed. The 
normal running current is .06 amps, and is fused with a parallel 
redundant 1/8 amp fuse. The MM'71 design philosophy requires the use of 
fuses in the power lines of all "non-mission-critical" flight equipment. 
With this 8 amp, inrush current, the 1/8 amp fuses were easily blown. 
This did not happen on every turn-on, but only when the core would latch 
up in the wrong direction for turn on. Upon inspection of the 
transformer, it turned out to be a 50-50 Ni-Fe toroid. The design was 
changed from a toroidal core to a cut-core with a 25 micron air gap. The 
new design was completely successful in eliminating the 8-A turn-on 
transient."

 >Keep in mind that a 25 micron air gap is equal to 0.000984 inches! 
Magnetics says this;

"A small amount of air gap, less than 25 microns, has a powerful 
demagnetizing effect and this gap has little effect on core loss. This 
small amount of air gap decreases the residual magnetism by shearing 
over the hysteresis loop. This eliminates the ability of the core to 
remain saturated."

Will Matney