Mountain panorama or notching?

Commutation notches are a common problem in rectifier and drive applications, even when chokes and filters are equipped. But sometimes even we are astonished, when that much notches can be observed on a voltage waveform.

In the case showed in the picture on the right side, massive faults must be expected, when controls or lighting equipment gets fed by such a grid. Even, when the required 230 or 110 V is generated by an auxiliary transformer from the 690 V grid shown in the diagram.