You can operate the coil directly from the 110-volt, alternating current house-supply line; or, if you find that it overheats rapidly, you can interpose a resistance in series with one of the leads.

Meanwhile, the voltage rise caused by resonance in course of adjusting is controlled by series damping resistance.

Then the model is applied to simulate the direct start-up process, the reduced voltage starting process and the starting process with series resistance in the armature circuit.