2 Which voltage is recommended for industrial applications?

We define two nominal voltages depending on the type of connection to the AC supply grid and a voltage band in which devices shall have full functionality: 

1.    For uncontrolled rectifiers on 400 V AC (typically B6 type) 540 V nominal voltage with a voltage band between 485 V and 750 V.
2.    For uncontrolled rectifiers on 480 V AC and for controlled, bi-directional active infeed converters (AIC) the nominal voltage is 650 V with a voltage band between 600 V and 750 V.