Reactor is belong to the perceptual load, the alternating current render large impedance (according to the core section and coil number of turns), so a small current through the primary winding, to To adjust the size of the reactive load, column to join dc excitation winding in the core, change the winding dc current can reduce the inductance of the primary winding, to adjust the primary winding Current size or the size of the reactive load, and then to match the load size, in order to satisfying the requirements of Marine generator load test. It is the present domestic Marine generator, Capacitors in parallel resonance test device, and other important part of the load test equipment, through the adjustment of the external excitation voltage, make can even, smooth and stable change all kinds of negative The value of load test, which satisfy different power factor testing purposes.