Probably worth looking at the associated thread here https://www.eng-tips.com/viewthread.cfm?qid=491180

There's more data there.

The base cause for me is that you are trying to use a PD pump for the wrong application. If you want to limit pressure with variable flow, use a centrifugal pump and throttle it. running a motor design to run at 50 htz at 10 htz is going to cause you all sorts of pain, not least that the motor cooling fan works much less and hence motor will overheat or trip on high amps.

But I would be interested to hear what the issue is from the motor / VFD end as well.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

Hi Littleinch,

It has forced cooling fan so throttling it as this is membrane application where need to boost the pressure. The pump is designed for the pressure up to what i throttled.

I just trying to troubleshoot of higher current of smaller motor of 11 KW at site with the same pressure but different VFD, The current is slightly larger by 0.2 ampere from rated motor which trip the system.

I believe at aite the VFD is set configured based on constant torque where my VFD is not at workshop.

So from all perspective, i try to isolate each problem at the time. I found no issue on pump after overhauled it.

Just so you know, on a dual voltage 415/240V motor, Delta connections are for the LOW voltage, the higher voltage would be Star. So if you have the motor connected in Delta and are programming the VFD for applying 415V at 50Hz, you will be saturating the windings and causing … high current!

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

Hi Jraef,

The recomennedation for 15 KW from manufacturer is Delta connection.

I also tried star,It has low current when i increases the mechanical load for rated application such as pump pressure, result motor stalled unable to drivs the pump at low pressure.






From this 3 KW above shall be connected in delta.

BMW,

Noted, but you're using a pump at 20% of its rated flow, but 100% of its rated pressure.

Pumps and motors don't like this.

You really need to avoid using motors and pumps at this low a percent of their rated duty.

Can you post a diagram of what the pump and valve you have is set up?

What may work instead is to operate the pump at higher speed, but control pressure and flow using a proper control valve on the the return / relief line back to the tank.

I assume your downstream equipment essentially controls flow based on pressure?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

BMW: You are not very clear in your original post what you're trying to accomplish in terms of power, speed, pressure, and flow. Understanding how the driven load (pump) works, and how the driver (motor+drive) works may help you. Assuming a constant impeller diameter for the centrifugal pump (this is irrelevant for the positive displacement application) we get the following relationships. All variables (power, flow, pressure, and speed) are in PER UNIT where 1.0 pu = rated condition.

CENTRIFUGAL:
(Pressure 2 = (Pressure 1) * ((Speed 2)/(Speed 1))^2
(Power 2) = (Power 1) * ((Speed 2)/(Speed 1))^3
(Flow 2) = (Flow 1) * (Speed 2)/(Speed 1)
POS DISPLACEMENT:
(Pressure 2) = (Pressure 1) * ((Speed 2)/(Speed 1))^(Factor) ... where 1.5 < Factor < 2.5
(Power 2) = (Power 1) * (Speed 2)/(Speed 1)
(Flow 2) = (Flow 1) * (Speed 2)/(Speed 1)

Under constant torque rating, the motor would be capable of delivering
(Power 2) = (Power 1) * (Speed 2)/(Speed 1).
This means that the nominal 15 kW rating would only have 3 kW (20%) of rated power available at 20% speed.
Under constant volt/hz (i.e., variable torque) the motor would be capable of delivering
(Power 2) = (Power 1) * ((Speed 2)/(Speed 1))^2
This means that the nominal 15 kW rating would only have 0.6 kW (4%) of rated power available at 20% speed.
Note that under constant torque application, the motor requires separate powered forced ventilation to operate below about 75% speed for extended periods (longer than a few seconds every 10 minutes or so). For variable torque application, the separate power requirement is not usually necessary.

Converting energy to motion for more than half a century

You need to make sure 100% the VFD is programmed to match the motor properly. Motor voltage, frequency and overload. If you use flux vector control you need to tune it for the motor, and you should probably be using flux vector control.

You need to understand that after doing the above, the power the motor is capable of producing varies linearly with the percentage of speed you try to run it at.

I really can't understand what you are doing exactly, but this is likely a problem.

Quote:

Setting : only set for 25 KW parameter

I don't really agree with this,

Quote (Gr8blu)

Under constant volt/hz (i.e., variable torque) the motor would be capable of delivering
(Power 2) = (Power 1) * ((Speed 2)/(Speed 1))^2

If you want to say that's a safe number that will always work, sure. But, it's not the limit the motor is capable of.

Hi All,

By changing the U/F setting of VFD to 100%, i am able to drive the pump at 50 Bar. Before the setting of UF eas at 30%.

Motor stalled when i loaded the pump to 25Bar.

My objective of this workshop test using 15 KW motor to prove that the old motor of 11 KW at 11 Hz which has been run for last 4 years without any issue until recently has been run with undersized power.

The odd things why before pump maintanance of spares changed the exiating 11 KW motor has no issue running at 11 Hz at 50 Bar ?

I would need to investigate in my workshop with this 15 KW run at 5 different load test conditions. It proves that the VFD could provide torque boost except for 11 KW motor full load has exceeded its FLA.

However,The torque sensor shows much greater torque value vs motor rated torque despite the amperes is within 15 KW full load current.

Maybe you all can enlighten me why despite such high torque demand, the motor can still drive it .

I observed that using Quad which is variable torque has much lower current at maximum load of the pump of 50 Bar at 11 Hz using 15 KW workshop test.

@LionelHutz.

Setting : only set for 25 KW parameter

My apologize this was typo, setting motor parameter as PER 15 kW motor 4 pole.

Sorry for the confusions

@Littleinch,

You mentioned earlier the total power at 50 Bar is only 2HP.

what is your insight wheb we run in VFD the power BKW is getting quadraticly high ? .

You did a bit more work setting the VFD and it started to work kind of. I don't understand how it could work at 50bar but not 25bar which should be less load. How'd you change the pressure? Probably more work properly setting the VFD will get it fully working as long as you don't try to do something the pump and motor are not capable of doing.

@LionelHutz,

I changed the VFD setting U/F setting of VFD to 100%, i am able to drive the pump at 50 Bar.

Before the setting of U/F wass at 30%, Motor stalled when i loaded the pump to 25Bar.

But from torque sensor, it showed high Torque, but the motor current of 15 KW in my workshop was srill within its rated.