System power factor

[Joethemechanic]

Drive would not run until I disconnected capacitors.

That's interesting.

 

[xformer]

See the beer picture. The less foam, the smaller a glass needed to deliver the desired amount of beer.

If you improve power factor, you need less current to deliver the same power at a given voltage. Less current means smaller cables or lower cable loss.

Jon

Less current also means lower IR loss in cable.

 

[anbm]

In my area the ultility company would charge commercial customers a surcharge if power factor was below 90% . We had to add capacitor banks at several locations. Now with everybody using LED every where you have to watch their power factor. They usually do not list PF on spec sheet or boxes but have seen it as low as 80%. Hope the government make LED manufacturers only produce LED lamps & luminares with a PF of at least 95%. Never install PF capacitors on output side of any VFD'S. We had a contractor install two 30 HP drives on 40 year old air handlers that each motor had a PF capacitor. Drive would not run until I disconnected capacitors.

In your last sentence, do you know why the VFD does not run?

 

[ptonsparky]

In your last sentence, do you know why the VFD does not run?

Feeding power to a capacitive load would certainly be different than the expected inductive.

 

[Joethemechanic]

If the drive is configured to ramp up speed, the capacitors might act much differently at lower frequencies

 

[Besoeker3]

In my area the ultility company would charge commercial customers a surcharge if power factor was below 90% . We had to add capacitor banks at several locations. Now with everybody using LED every where you have to watch their power factor. They usually do not list PF on spec sheet or boxes but have seen it as low as 80%. Hope the government make LED manufacturers only produce LED lamps & luminares with a PF of at least 95%. Never install PF capacitors on output side of any VFD'S. We had a contractor install two 30 HP drives on 40 year old air handlers that each motor had a PF capacitor. Drive would not run until I disconnected capacitors.

Variable speed drives and power factor caps are not comparable. Displacement and distortion factors are different quite things.

 

[Jraef]

Feeding power to a capacitive load would certainly be different than the expected inductive.

To the pulsed transistors in the output of the VFD, the capacitor charging current looks no different than a short circuit. So a good VFD will detect that and protect itself by disabling the transistors, using what’s called a “base block” that immediately opens the circuit to the base emitters. A cheap VFD might just destroy itself. There’s also a risk of damaging the capacitors. Some of the times I have seen this scenario, the results have been catastrophic. They were lucky if all it did was disable the drive…