The Saturable Reactor As a Constant-Current Source

When operating within a range such that the amplitude of the a-c flux does not exceed the saturated value at zero premagnetization, the saturable reactor will furnish practically constant load current over a range of load resistance R_L determined by the value of the control current i_c and the a-c supply voltage V. The resistance of the output circuit is the sum of the load resistance and the gate circuit, i.e., R_L + R'_G. The resistance of the gate circuit R_G equals the resistance of one gate winding R_G for the parallel connection because then only one winding carries load current at a time. When the gate windings are connected in series the resistance of the gate circuit R'_G is 2R_G or twice the resistance per gate winding. The average value of the rectified load current is

[7-25]

A comparison of Eqs. 7-24 and 7-25 shows that

If V and i_c are held constant while the load resistance R_L is increased, the firing angle decreases, holding the load current constant with the limiting value of α equal to zero. For α = 0, the saturable reactor is a short circuit in series with the load resistance throughout the voltage cycle, and the load current is simply a sinusoidal current expressed by

A reduction in the a-c voltage Fhas the same effect as an increase in the load resistance. The effect of inductive load on the operation of saturable reactors is not within the scope of this text, but has been treated in other sources.