Phase conversion with VFD's

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crawfelect

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We have been working on a pump station that utilizes VFD's to convert 120/240 Volt single phase power to 3 phase power to run two 20 HP 240 Volt pumps. There are two VFD's, one for each pump and the system is designed so the pumps alternate.
On utility power everything appears to work fine.
The station has a backup generator. When a pump starts up and is approaching full speed while running on the back up generator, the generator all of a sudden shuts itself down because of a high frequency output. I measured any where from 88 to 115 HZ. Any ideas, is this a result of the VFD's or is it a generator problem? What can be done to fix this problem?
 
As a rule of thumb the generator needs to be three times larger than the inverter load. Check with the generator manufacturer, they will help. Be persistent. Someone should have sized the generator for this application.
 
Phase conversion with VFD's

If true? The generator is 30 KW, capable of 125 Amps, the FLA of the pumps are 54 amps. Looks like the generator may be undersized and we have an engineering problem?
 
Phase Conversion with VFD's

Phase Conversion with VFD's

If so, the Generator is 30 KW capable of an output of 125Amps, the FLA of the Pumps are 54 amps. Maybe we have an engineering problem?
 
crawfelect said:
We have been working on a pump station that utilizes VFD's to convert 120/240 Volt single phase power to 3 phase power to run two 20 HP 240 Volt pumps. There are two VFD's, one for each pump and the system is designed so the pumps alternate.
On utility power everything appears to work fine.
The station has a backup generator. When a pump starts up and is approaching full speed while running on the back up generator, the generator all of a sudden shuts itself down because of a high frequency output. I measured any where from 88 to 115 HZ. Any ideas, is this a result of the VFD's or is it a generator problem? What can be done to fix this problem?
Click to expand...
Sounds like an electronic governor problem. Gensets will shut themselves off
when a certain RPM is reached by the engine.
Have you started the genset without the load on it to see if it shuts down
without the loads?
If it does, call the Genset rep. Actually you should probably do that anyway.
I cant see the VFD's causing that. If the generator was overloaded by the VFD's it would kick out the field breaker not shut down on overspeed.
 
Is it an older genset? I ask because older ones had sensing circuits for the governor that were sensitive to harmonics caused by VFDs and soft starters and would go squirrelly on you. Genset manufacturers (at least reputable ones) have for the most part solved that problem with filtering on the sensing circuits. Some, like Cat, have retrofit kits for older units. Woodward, a separate governor mfr, has retrofit kits for theirs as well so if yours has a Woodward Governor you may be able to get it through them if your genset mfr. is uncooperative (or ignorant of the issue).

Other than that, you can also add filtering to the VFDs, it's just that this will be a lot more expensive than the filter on the sensing circuit. Go to MTE or TCI for line filters for VFDs.
 
Jraef said:
Is it an older genset? I ask because older ones had sensing circuits for the governor that were sensitive to harmonics caused by VFDs and soft starters and would go squirrelly on you. Genset manufacturers (at least reputable ones) have for the most part solved that problem with filtering on the sensing circuits. Some, like Cat, have retrofit kits for older units. Woodward, a separate governor mfr, has retrofit kits for theirs as well so if yours has a Woodward Governor you may be able to get it through them if your genset mfr. is uncooperative (or ignorant of the issue).

Other than that, you can also add filtering to the VFDs, it's just that this will be a lot more expensive than the filter on the sensing circuit. Go to MTE or TCI for line filters for VFDs.
Click to expand...

Whatever he said.....:smile:

miniMe.....
 
Phase Conversion with VFD's

Phase Conversion with VFD's

The generator is a new 30KW Kohler, runs just fine without the load of the pumps. The FLA of the pumps are 54 amps, unless the genset is too small for the application, it should be capable of an output of 125 Amps. I would think it should handle the VFD load just fine. It is not sized at three times the load though as stated by an earlier reply. Any other thoughts?
 
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