An electrical machine comprises a four-pole stator (2) provided with a field winding (10) and an armature winding (11), each of the windings (10, 11) being split into two coils (22, 23 or 24, 25) closely coupled and wound so that diametrically opposite portions of both coils are disposed within diametrically opposite stator slots. A two-pole rotor (not shown) without windings is rotatable within the stator (2), and a circuit is provided for energising the armature coils (24 and 25) when direct current is supplied to terminals (26 and 27) of the circuit. Switches (28 and 29) in series with the coils (24 and 25) are switched alternately to effect alternate energisation of the coils (24 and 25) so as to generate, as a result of the opposite winding of the coils, magnetomotive forces in opposite directions. Since each of the closely coupled coils (24 and 25) generates a magnetomotive force in a respective direction, each coil needs to be energised with current in only one direction so that a relatively simple excitation circuit can be used.