On Sunday, February 15, 2015 at 1:02:31 AM UTC-8, mike wrote:

As long as you stay out of saturation, the main component of the
primary current is due to the shorted secondary.
I think I'll give my SCR the benefit of switching on when there's zero
voltage.

Not really the best idea; it is then possible that the previous turn-off
happened after a half-cycle (+), and if this ON state starts with a half-cycle (+)
as well, that's two half-cycles of the same polarity. The likelihood
of saturation is very high. Turn-on at peak V is a strategy that
minimizes saturation risk.