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A harmonic power flow algorithm which predicts the levels of low audio range frequency harmonics in a power system produced by several types of nonlinear loads has been recently developed [1-5]. Specifically, the new method solves for the truncated Fourier series of bus voltages and line currents in a balanced three phase network with line commutated converters and nonlinear resistive loads. Most harmonic signal analysis techniques previously developed assume sinusoidal network voltages or known current injection levels. In many cases, especially in resonant or other conditions of relatively high harmonic voltages, considerable inaccuracy results. The new algorithm uses a Newton-Raphson solution technique and does not require these assumptions. Modeling emphasis is restricted to harmonic orders in the low audio range (fundamental to the 25-50th multiple). Interaction between voltage and current harmonics of different order in a nonlinear device is permitted. The power system is considered to be balanced i.e. the nonlinearities are assumed to be equally distributed among the three phases. Gaseous discharge lighting (such as fluorescent, mercury arc, high pressure sodium) is a significant source of power system harmonics, particularly in metropolitan areas. The electrical characteristics of this type of lamp are quite nonlinear. Lamp ignition occurs during each half cycle when the applied ac voltage reaches some required firing potential. During conduction, the lamp exhibits a negative resistive characteristic, and a nonlinear ballast circuit is placed in series with the lamp to limit the current.