1) Measure input voltage R-N (S-N / T-N)
2) Measure output voltages (at max speed) U-N (V-N / W-N)
The output voltage of about 3V is less than the input voltage
3) Measure the output voltage (min speed) U-N (V-N / W-N)
The output voltage will be about 75 - 100V.
Important to check that beetween a measure and the other the difference is contained within 20%.