Constant
Current Flux Reset Test
The Constant Current Flux Reset (CCFR)
test is widely used to evaluate core performance
for magnetic amplifier use. The test is described in IEEE Standard 106. The ac
excitation is usually specified at 400 Hertz, but frequencies between 60 and
6000 Hertz may also be specified. The test circuit is shown
in Figure 6.
With
zero dc control current and full wave ac
sine current excitation (S closed),
the current in "R" is set
to a specified value sufficient to give maximum flux change. The flux change
develops a voltage in the pick up winding which is indicated by the integrating
flux voltmeter.
With S open in the ac excitation circuit the current changes to half sine wave
and the core flux then varies between B and B , the residual flux level. The
flux voltmeter now indicates B - B .
Adjusting the dc level in the dc bias winding resets the flux from B to other
values as shown in the B-H loops, drawin in Figure 7. Plotting flux change
against reset magnetizing force gives a curve as shown in Figure 8. Standard
test data
are determined by reading H , the reset magnetizing force required to obtain
a flux change of B. This approximately one-third of 2B . H is the additional
magnetizing force required for an additional one-third flux change. The ratio
of B - B to H is expressed in kilogausses per oersted; and is referred to as
the "gain".
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