VFD line current and max. demand
VFD line current and max. demand
(OP)
Hi All, I have come across this problem again and would like your opinion.
We have several (20+) large motors (>50kW anf 400V) fitted with VFD. When determining estimated maximum demand I have considered them operating at 0.9PF, while all other DOLs operate at 0.75. If I ignore the PF benefits of the VFD the load is too big for the TF.
I am not comfortable with my approach since:
1) While displacement PF quoted by the manufac. is 0.98, distortion PF will be poor. Does distortion power factor contribute to greater current draw?
2) What I have done is take motor kW and converted to Amps at 0.9PF to get the VFD line current. Will the VFD draw more than motor kW amps from the line (even if it is at a good disp. PF)
Thanks all
MB
We have several (20+) large motors (>50kW anf 400V) fitted with VFD. When determining estimated maximum demand I have considered them operating at 0.9PF, while all other DOLs operate at 0.75. If I ignore the PF benefits of the VFD the load is too big for the TF.
I am not comfortable with my approach since:
1) While displacement PF quoted by the manufac. is 0.98, distortion PF will be poor. Does distortion power factor contribute to greater current draw?
2) What I have done is take motor kW and converted to Amps at 0.9PF to get the VFD line current. Will the VFD draw more than motor kW amps from the line (even if it is at a good disp. PF)
Thanks all
MB






RE: VFD line current and max. demand
RE: VFD line current and max. demand
RE: VFD line current and max. demand
RE: VFD line current and max. demand
RE: VFD line current and max. demand
The only information I have is the kW rating of the motors and which are VSD/DOL.
I have to be conservative - I will ignore VSDs, assume full load PF of 0.8, and assume 90% efficiency for kWi/kWo.
Since the client is an EE and knows alot about the process I will get him to apply a diversity factor.
RE: VFD line current and max. demand
NC
RE: VFD line current and max. demand
the PF benefits of the VSD may cancel out the VSD efficiency in this case