This paper presents a methodology that can be used to model the electromagnetic behavior of large disk type air-core reactors when excited by fast transient voltages having a frequency content ranging from 10 kHz to 500 kHz. A lumped parameter white-box model is generated using the design details of the reactor. The model parameters are calculated analytically and verified by measurements and finite element method simulations. The modeling methodology is applied to an actual case study and the simulation results are compared to the measured results. The measured parameter values and the model response closely matches the measured results in the case study.