How does a saturable reactor control AC current?

• A. By cooling the core
• B. By adjusting resistance
• C. By changing supply voltage
• D. By controlling core flux density

Answer: (D)

Saturable reactors control AC current by changing the inductance seen by the AC signal through the magnetic state of the core. A DC bias, applied to a control winding, sets the flux density in the core. When the core is not saturated, its permeability is high, giving a large inductance that presents a high impedance to the AC current and limits it. As the DC bias increases and the core approaches saturation, the permeability drops, the inductance falls, and the impedance decreases, allowing more AC current to flow. So the control of the AC current comes from adjusting the core flux density, which alters the reactor’s reactance. It’s not about cooling, changing resistance, or changing the supply voltage.