A series DC machine with the armature winding resistance Ra=2Ω and the field winding resistance Rf=5Ω is mechanically coupled to the load with linear torque-speed characteristics that can be...

A series DC machine with the armature winding resistance Ra=2Ω and the field winding
resistance Rf=5Ω is mechanically coupled to the load with linear torque-speed
characteristics that can be approximated by the following equation: Tl(ω)=k·ω+T0 where k=-2Nm/(rad/s) and T0=200 Nm. The motor constant Kf is equal to 0.22[Nm/A^2] also[Vs/(A·rad)]). The motor is supplied from a 250VDC source.

a) Calculate all possible operating points and determine the stability of each operating
point