Power factor correction of car lift motor

[Guineafowl]

One for @Carl Wilson ? You did a good vid on selecting a Steinmetz capacitor by calculating reactance.

I have a 7.5kW rotary converter that is struggling to power the 400V 3ph 3.5kW lift motor near capacity (2.7 tonnes). Screw-type lift. There’s plenty of power available (1ph supply to the rotary is within 5% voltage drop under load).

Motor plate:


It seems to be a problem of power delivery, that crappy power factor being significant, I think. One suggestion has been to connect three motor caps between phases to inject some VARs. What value caps?

I’ve just bought a VFD from @skotl so will piddle around with that, too. It should correct the pf upstream, which might help, and I hoped that changing frequency might make a difference too. You can see that running at 60Hz improves the cosphi, and maybe running at a lower speed will reduce overall loading.

 

[skotl]

One for @Carl Wilson ? You did a good vid on selecting a Steinmetz capacitor by calculating reactance.

I have a 7.5kW rotary converter that is struggling to power the 400V 3ph 3.5kW lift motor near capacity (2.7 tonnes). Screw-type lift. There’s plenty of power available (1ph supply to the rotary is within 5% voltage drop under load).

Motor plate:
View attachment 530419

It seems to be a problem of power delivery, that crappy power factor being significant, I think. One suggestion has been to connect three motor caps between phases to inject some VARs. What value caps?

I’ve just bought a VFD from @skotl so will piddle around with that, too. It should correct the pf upstream, which might help, and I hoped that changing frequency might make a difference too. You can see that running at 60Hz improves the cosphi, and maybe running at a lower speed will reduce overall loading.

One point to note - not sure how accurate it is but the VFD product page states it can't be used with a motor that has capacitors on it. So I might start with the VFD + motor without caps to see how that gets on.

 

[Guineafowl]

One point to note - not sure how accurate it is but the VFD product page states it can't be used with a motor that has capacitors on it. So I might start with the VFD + motor without caps to see how that gets on.

Yes, I’ll do the caps/VFD approaches separately.

As a start, taking the motor plate values of 400V, 11A, 50Hz and cosphi 0.65:

Cosphi 0.65, assumed lagging, gives a current angle of -49.5*. So, our impedance Z = V/I = (400V<0*) / (11A <-49.5*) = 36.4 ohm <49.5*.

In rectangular form, that is 23.6 + j27.7 ohm. So I need a capacitive reactance to match the imaginary part, an Xc of 27.7 ohm.

C = 1 / 2piF(Xc) = 115 uF. Seems quite high.