Analysis of an Eddy-Current Brake

The retarding torque of an eddy-current brake is calculated as function of the angular velocity of the rotor and of the stator dc magnetizing current. The electromagnetic field components are found in the rotor medium by solving the field equations. Integration of the power flow vector E X H over the rotor surface yields the total retarding power of the brake. The nonlinear nature of the B-H curve of the rotor iron is allowed for by assuming a variable permeability μ(x) = μ
_s
e
^λx
, where x is the coordinate inside the rotor, λ is a constant, and μs is the initial permeability at the rotor surface. Variable permeability, μ(x) is an increasing function of x so that inside the rotor, where saturation is lower, the permeability becomes higher. This assumption is correct at the first approximation only, as the differential equations for the field components are linear with variable coefficients. Thus, an analytical solution can be found in terms of known functions. It is shown that the retarding torque is proportional to I
_μ
^3/2
, where I
_μ
is the dc magnetizing current.