type polyphase connection of the stator 3 circuitry leading from the transistors 7 8 9 10 11 12 to the stator windings 6 comprises a stator phase excitation circuit the electrical commutation for the operation of the motor drive as a synchronous motor takes place in this manner the spinning rotor 26 is illustrated in fig1 with the appropriate magnetic polarity it constitutes a permanent magnetic rotor of the axial field motor although the permanent magnetic properties necessary for the present invention need not be achieved directly by permanent magnets a rotor made of a magnetically conductive material may also be magnetized by the magnetic field of the stator in such a way that permanent magnetic properties result which are required for the drive as well as for the braking induction in the stator during the braking phase i e during operation as a generator a gas supply line 19 for the supply of gas to the magnet gas bearing is disposed between the stator 3 and the spinning rotor 26 and has a gas pressure gauge 20 the gas pressure gauge 20 can be a simple sensor set to a predetermined gas pressure threshold value and independent of a voltage supply the gas supply line 19 is connected with a gas supply device which is typically a compressor not shown an information line 20 39 sends information from the gas pressure gauge 20 to a control unit 21 embodied as an and gate a further information line 23 which signals a voltage failure also leads to this control unit 21 a control line 21 39 leads from the output of the control device 21 to a first relay 27 which is operationally connected to a switch 27 39 further a control line 24 39.