Square-Loop Core Magnetic Amplifiers H. F. S T O R M

M E M B E R A I E E

THIS ANALYSIS APPLIES to magnetic-amplifier circuits of the center-tap, bridge-type, or a-c variety.

Such circuits are called amplistats, Magamps, trans­ducers, self-saturated magnetic amplifiers, and so forth. Figure 1 shows the circuit diagram of the center-tap connection. The amplifiers under discussion are of the so-called low control-circuit impedance type. In order to reduce the complexity of the analysis, many simplifying assumptions are made. While these assumptions introduce inaccuracies in the equations, the latter still serve effectively in establishing first-order relations among the variables. A large part of the analysis is applicable to core materials whose dynamic B-H loop is not strictly rectangular, such as grain-oriented silicon steel.

The load current IL consists of the exciting component ILx and the saturation component 7Le, and hence the control characteristic (Figure 2) can be synthesized of two components.

Let %c denote the per unit control current

IcNc %C H C W 0 . 4 T T

and \E the per unit exciting current

d)

(2)

The per unit saturation component ILJIL,m becomes a cosine function of the control current (Figure 2A) and the per unit exciting current component IL,JIL,m becomes a linear function of the control current (Figure 2B). The

(B)

Figure 2. Synthesis of control characteristic. (A) Per unit saturation component of load current. (B) Per unit exciting

component of load current versus per unit control current

(AC)

Figure 1. Circuit diagram of center-tap amplistat

sum of both functions represents the control charac­teristic. With cores deviating from the assumptions, the control characteristic is unaffected in the vicinity of t c =— 1, but the upper part of the characteristic may shift to the right or left.

With reverse current present in the rectifiers BECi, REC2, the control characteristic of Figure 2 becomes sheared to the right.

The time constant is proportional to the slope of the curve in Figure 2A; the time constant is inversely propor­tional to the exciting current \E of the saturable reactor. The ampere-turn gain and the dynamic power gain are inversely proportional to \E. The power gain is inversely proportional to %/. The dynamic power gain is inversely proportional to the coercive force He of the dynamic hysteresis loop, and hence, inversely proportional to the width of the dynamic hysteresis loop. Digest of paper 53-284, "Theory of Magnetic Amplifiers With Square-Loop Core Materials," recommended by the AIEE Committee on Magnetic Amplifiers and approved by the AIEE Committee on Technical Operations for presentation at the AIEE Summer General Meeting, Atlantic City, N. J., June 15-19, 1953. Scheduled for publication in AIEE Transactions, volume 72, 1953. H. Γ. Storm is with the General Electric Company, Schenectady, N. Y.

SEPTEMBER 1953 Storm—Magnetic Amplifiers 111