In DC motor,the field MMF is given by NI.N-no.of field
winding turns,I-excitation and both are constant.Then how
could the main flux decreases due to armature reaction.

Answer Posted / najib

In the absence of armature current if we imagine the field
mmf then it passes through the air gap without any
distortion.However as soon as there is a flow of armature
current the forst effect that comes into picture is
crossmagnetization provided saturation is neglected.Hence
it can be concluded the if saturation is neglected there is
no demagnetization but only crossmagnetization.In reality
saturation does set in and cause demagnetizationalong with
crossmagnetization.

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