(a) describe the normal criteria used for setting thermal protection, release and their advantage compare to magnetic types (6)

(b) A series motor runs at 600 r/min when taking 110A from a 230V supply. The resistance of the armature circuit is 0.12Ω and that of series winding is 0.03Ω. The useful flux per pole for 110A is 0.024 wb and that for 50A is 0.0155wb. Calculate the speed when the current has fallen to 50A. (10)