Hardinge KL-1

[pauly45]

It's been suggested to me by a VFD expert at work that this method of using a step up transformer to power the VFD will result in the current in the secondary of the transformer having too high a peak current, and over time damaging the capacitors within the VFD.

He has done a circuit simulation based on some inductance measurements of the transformer I did which were:

0 to 240V shorted, Inductance and resistance measured across 0 to 415v
50Hz 1.107mH 1.59Ω
100Hz 1.094mH 1.59Ω
300Hz 1.090mH 1.612Ω
1kHz 1.0877mH 1.798Ω

0 to 415V shorted, Inductance and resistance measured across 0 to 240v
50Hz 365.2µH 0.571Ω
100Hz 365.1µH 0.572Ω
300Hz 365.1µH 0.578Ω
1kHz 364.3µH 0.641Ω

The set-up:



And these were the results:



The secondary current can be seen as the narrow/tall "sine" wave, peaking at 13.599A.
This is based on a 1.1kW power, and the transformer inductance measurments above.

It's been recommended that I add some extra inductance in the secondary of the transformer, and before the VFD input to smooth out the peaky "AC" and lower the peak current. This should stop me knocking out the capacitors in the VFD over time. I'll get to that inductor.


Meanwhile, I had got hold of some VFD's while I had been waiting for the lathe, so have ended up with:

For the main motor - a Mitsubishi FR-D740-036-EC. 1.5kW.
For the speed change and coolant pump - two Mitsubishi FR-S520S-0.2K-EC. 0.2kW