Constant voltage supply for motor applications

If the motor continues to deliver sufficient shaft work despite the occasional low voltage, is it time to reduce the undervoltage trip setting?

Some drives will allow setting the undervoltage trip point.

There is also a rated supply voltage and then typically +/- 10% around that. In some installations I have deliberately tapped the supply transformer on the high side.

Is this a regen SCR phase controlled drive? Or is it non regen etc.

Regen drives operating at close to maximum voltage are not very tolerant of voltage brownouts or dips. Non regen are much more tolerant.

Some of the drives use the control voltage to sense undervoltage and this can be handled with a small PC UPS.

Then there are the "serious" power dip ride through arrangements. In one installation they had a synchronous machine with a very large flywheel. On a power bump or short power outage the flywheel would hold the machine for almost 1 minute as the frequency shifted from 60 hz down to 50Hz. We had to prove our drives would track the frequency shift to qualify as a supplier.

GW you are right on here. Raising the taps on transformers can help a lot. You need to know your power system and what is causing the voltage dips. The flywheel synchronous generator is being done in many industries. I know in the Pulp & Paper industry it is done. The UPS on the control voltage can get you in trouble. The undervoltage is there to protect the drive from overcurrent. AC & DC drives are really current rated devices. Placing the UPS on the control voltage will remove this protection from the drive. Be careful.

Careful is the key.

The particular drive I was playing with had both AC line feedback for synchronizing the gate firing and inverting fault avoidance etc, but on a brown out it gave up because the control circuit dropped out first (duuh) with the low voltage dc supply going undervoltage. That was a fun one to figure out! Drive was plated for 230/460 VAC, you changed taps on the control transformer, and the rest was software scaling.

This requires DC Filter Capacitor Bank of thousands µF to filter Ripples in rectifier O/P

And

support In-Rush current taken by a motor @ start; if it is not thru a "Soft-Starter" .

If the the motors are at different loctions & you have a single-DC-Power-Source then it will be better to have individual Capacitor Banks close to the motor-start-gear.

Or have suitable DC power sources just close to each motor-starting-gear

Use of constant voltage transformer can solve your problem . These transformers are fitted with servo controlled tap changing which gives smooth control of voltage correction at the out put of the transformer. I have been using them for our Electroplating plants and certain critical machines where voltage fluxuation was giving me regular breakdowns. In your case you need not do voltage correction for motors since it is expensive but can purchase a small capacity servo controlled voltage Stabiliser for the control panel only.On load tap changing transformers are also available with automatic voltage correction which can be installed at your substation. For more information contact manufacturers.