Modelling of nonlinear rail impedance in AC traction power systems

Nonlinearity in the internal self-impedance of railroad rail can give rise to power frequency harmonics in traction systems. Limiting case analytical models of rail impedance, based on linear complex permeability and complete saturation, are compared with measurements for currents to 800 A and frequencies to 10 kHz. The results show that for accurate representation an effective permeability of the material must be defined by prior modeling of the eddy current flux distribution within the rail iron. The usual assumption of rail, internal self-impedance invariance with current is shown to be unrealistic