Change in cos phi with variable frequency drive
asked 21 October 2016 asked by LR06 (420 points)
Hello, It is normal to have a better cos phi if you're using an inverter drive. The cos phi indicated on the engine plate is for direct current or an electronic starter. The capacitors and the inverter technology itself can improve the phase shift between current and voltage. Electrical measurements are more reliable upstream of the inverter where the signals are sinusoidal. Downstream of the drive, signals are square-wave, and measures are skewed even with a true RMS multimeter.
Thank you for this. Would there be a difference if I measured cos phi upstream vs. downstream of the inverter?
Measuring upstream and downstream of the inverter: at 50 Hz and with an RMS device, there will be little difference; but the lower the frequency, the more significant the disparity.