Overvoltage conditions damaging VFD's
Overvoltage conditions damaging VFD's
(OP)
I would like to see some opinions on whether a line reactor will really help in this situation. 1 300hp VFD and aprrox. 30 5hp VFD's fed by a 1500kva transformer within 30 feet. All of these drives have a history of overvoltage faults and many have been repaired or replace more than once. The facility is very close to a steel mill and the line voltage is usually around 500 volts. The VFD's will fault on OV at 544 volts. Thanks in advance for any enlightening discussion.






RE: Overvoltage conditions damaging VFD's
Are there capacitors, e.g. for power factor correction, involved?
RE: Overvoltage conditions damaging VFD's
RE: Overvoltage conditions damaging VFD's
RE: Overvoltage conditions damaging VFD's
When the next fault occurs, check the transient recorder for transient overvoltage. If it is there and if it is not in the milliseconds region, then a line reactor with 3 or 4 percent voltage drop will probably do the job.
If you have longer transients - well, I do not know what to do, really. More inductance than 4 percent might cause problems with the inverters since their input voltage drops too much when loaded. I once used a large DC choke in the DC link to make the inverter immune to PF capacitor switching, but that's a hell of a job.
RE: Overvoltage conditions damaging VFD's
RE: Overvoltage conditions damaging VFD's
I second the potential excess capacitors causing momentary or sustained overvoltage, but put main-transformer tap checks on the top of the list. Remember that—almost without exception—a primary-side powerdown must be scheduled before tap change.
It may be that the serving utility has local capacitors on their distribution system that are not disabled during light-load/low-var-demand periods. The capacitors may be unswitched, or the associated control scheme is not operating correctly.
The 544V-trip feature should be verified as indeed happening at the intended time and voltage level.
508 volts steady-state AC is often the consensus upper limit at 480V building service entrance. It may be worth experimenting with installing buck-connected transformers on a few of the smaller “problem” drives. Stock ratings are typically in the range of 12-16-24-32-48 volts. Check the drytype-transformer literature: for a smaller 3ø 3W load, two open-delta-connected buck/boost transformers can be used, or for bulk loads where a neutral conductor is available, three wye-connected units may be more cost effective. Double check the “new” voltage on the buck-transformer load sides before powering drives.
RE: Overvoltage conditions damaging VFD's
544 is less than +10% variance the utility supply will normally have on a 500V bus. I would look at the tranformer tap and adjust to 480 or even 475V first.
Some swithing suirges caused by the adjacent still mill may be involved? Is there a time delay on OV proteciton on the drives?
RE: Overvoltage conditions damaging VFD's
RE: Overvoltage conditions damaging VFD's
RE: Overvoltage conditions damaging VFD's