Re: Soft transformer turn on without a variac

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net> 

True when the switch is closed at zero volts the input current is zero.  The
surge current occurs a half cycle later when the next zero volt crossing
occurs.

At steady state, when a neg to pos zero volt crossing occurs, there is
negative current in the transformer.  So during the half cycle period when
the voltage is positive,  current is brought from a negative to an equally
positive value.  Now, if the current at the neg to pos zero volt crossing,
is zero (like at initial turn on with a zero volt crossing switch),  the
current goes from zero to double the normally positive value in this half
cycle time.  But something else can happen, the core saturates and then this
double current goes much higher.  At least, this is what I get out of that
link.

Gerry R

 > Original poster: davep <davep-at-quik-dot-com>
 >
 > >0 volts = zero amps at start up).
 >
 >          Exactly true.
 >          Has to be.
 >          The load _at_ _start_ _up_ is mostly resistive:
 >          the resistance of the windings.  The inductance is
 >          minimal untill the field builds and penetrates the
 >          core.  That latter takes time.
 >
 >          best
 >          dwp