VFD single phase to three phase conversion 4

[Wedoca]

alright guys .....here is the application ...

sewage pump station with on site generator.

the VFD located inside of a 230V panel,
the oringinal idea was to use the drive as a phase convertor, since the utility only provide us with single phase there...

pump infor .....

10.1 hp, 230V, 60 Hz, 2 pole, 3 phase , FLA 25A, service factor 1.15 ,
rated to pump 99GPM

VFD infor......

20 hp, Culter Hammer SVX drive ..

now I have set up the drive parameter to match the pump .... max RPM, Max Amp (25), Max Frequency (60)

Problem: When turn on the pump, the display on the VFD showed that the frequency would only go up to around 50Hz ....I measured the out put voltage and current and it was around 180 phase to phase(fluctuating), 135 phase to ground (fluctuating), and it was pulling about 27 amps ..... pump phase ground resistance was meggered and all three phase was above 999 Mega-ohms ....

now ...on the previous thread ....some of you (Thanks again) have mentioned that the lack of capacitance due to undersized VFD causeing low output voltage at the VFD (180V) which lead to over current (is that right??) and because of the current limit thats set on the drive ....therefore the drive was not able to get pass 50Hz...( please correct me if I am wrong)

I have checked the VFD and it is a 20HP unit, so it was oversized to compensate the DC ripple problem.... so that pretty much sets me back into the dark ...

ideas anyone????

 

[rockman7892]

I understand how a drive will decrease speed when the voltage drops or is limited in order to maintain a V/Hz ratio.

However it was mentioned above that the drive could also decrease speed when the motor is drawing to much current in order to protect the drive from tripping. How does decreasing the drive speed diminish the current drawn by the motor?

 

[jraef]

... However it was mentioned above that the drive could also decrease speed when the motor is drawing to much current in order to protect the drive from tripping. How does decreasing the drive speed diminish the current drawn by the motor?

Slight correction: the drive MAY also decrease speed when the moor is drawing too much current in order to protect the drive from tripping. That would be dependent upon a function setting that may or may not be a feature provided in the VFD. Most mfrs call it something such as "Stall Prevention" and there may be several choices as to how you want the VFD to respond if it perceives a stall, one of which is to reduce speed. By reducing speed you are reducing power (assuming you are still below base frequency) which means you are lowering current.


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