1-phase motor frequency control

[jmaja]

We don't pay for poor power factor and the energy meters count only active power. I don't know which kWh my VFD shows, but likely active as well, since it is very close to some efficiency (90-95%) × energy meter.

I talked with Wilo technical support. They use Franklin motors in borehole pumps. They said it is OK to use a VFD, but not below 34-36 Hz for the 50 Hz three phase Franklin.

0.37 kW three phase 400 V Franklin has 66% efficiency and 0.74 PF at nominal power and 50 Hz. Do you have any guesses what they would be at 34-36 Hz?

I don't understand much about one phase motors. How does it work with the 16 uF capacitor vs. now with three phase input? Too much current to some windings now? The windings were clearly different while a real three phase motor would be symmetrical.

Could this work better with the capacitor in place and with just two phases, if I had a VFD, which didn't trip with one phase not connected?

[jmaja]

I found a Swede who is using this pump with VFD. He gets 50 l/min with only 90-105 W at 30 Hz. And it is even cheap. Hope it fits into my borehole (110 mm).
https://www.erdbohrer.de/Pumpen/fuer-Waermepumpen/Brunnenpumpe-fuer-Waermepumpe-4200l-370W-Franklin-mit-30m-Kabel::795.html

And now I know what to look for and there are a lot of options. E.g.
https://diepumpe.com/Tiefbrunnenpumpen/Speziell-fuer-Waermepumpen:::118_145.html

[cdipak]

Single phase motor frequency can be controlled by a single phase variable frequency drive.There are many companies who manufactures VFD such as Schneider, Mitsubishi, Denfoss and many more.
One can learn more on electrical equipments on https://favreadblogs.blogspot.com/2020/01/what--current-transformer-meaning.html?m=1

[jmaja]

Just to let you all know. I run the pump at 26 Hz for more than a week. Still pumped OK. Now I have ordered a new three phase pump. The one I linked earlier was no longer available with Franklin motor. I bought another one with SUB motor, which should be quite similar to Franklin. It's made in Italy and should work fine with VFD. 0.37 kW, 400 V and should have 63% efficiency (66% for Franklin). I hope I'll get it during next week. 446 € with 40 m cable.
https://duggmbh.de/pumpen-308/4-zoll-tiefbrunnenpumpen/orlando-tiefbrunnenpumpen/orlando-tiefbrunnenpumpen-sp-serie-edelstahllaufraeder/orlando-tiefbrunnenpumpen-sp-18-serie-4200l-h/4-zoll-tiefbrunnenpumpe-orlando-sp-1806-edelstahllaufraeder.html

I think the motor is one of these: https://www.subteck.it/motors/
I e-mailed them and asked what is the lowest recommended frequency. Let's see if they answer.

[Eugenijus]

Let me inform you about Franklin not so pleasant feature - minimum allowable frequency is 30Hz .
Running with lower frequency will cause problems with bearings lubrication and damage the motor

[jmaja]

Let me inform you about Franklin not so pleasant feature - minimum allowable frequency is 30Hz .
Running with lower frequency will cause problems with bearings lubrication and damage the motor

Yes I knew that. 30 Hz is likely low enough. The shaft power should depend on third power. Thus (30/50)^3= 0.22. 78% reduction in power. Let's see how that works out for electrical power and pumped flow rate at the head needed.

I still haven't got any answer from Subteck.

[jmaja]

Now I got an answer from Subteck. Just short "do not use frequency lower than 35 Hz". A bit of disappointment that it was not 30 Hz. Still should be 66% less than 50 Hz and hopefully not more than 200 W, but that will depend on many things.

[jmaja]

I got the new 3-phase pump today. It was not Subteck. It actually had nothing about the manufacturer in the manual and the "plate" that came with it. It said made in Italy. Maybe it is this one: https://conforto.it/images/pdf/en/Submotor.pdf

The "plate" (actually just a sticker not attached to the motor) said Submotor, but it also said 1.8 A (1.5 A in the link above). The manual that came with it said that 30 Hz is the minimum.

How does this actually work? I could get different powers at 30 Hz depending on the settings. If I set the motor voltage to 400 V (as per plate), I get higher power than when I allow VFD to adapt the motor. Then it drives only 365 V at nominal 50 Hz. I can get even lower power, if I set the voltage to 240 V (only 240, 380 and 400 V are available). Maybe I could get something else, if I changed the resistance and reactance settings.

What happens when the voltage is lower, but the frequency is still 30 Hz? Will the motor actually run at lower frequency? I would think it doesn't need much current, since the torque taken by the pump should reduce at rpm^3.

Now (using auto adapt) it takes 1.13 A/220 W at 30 Hz and 1.5 A/650 W at 50 Hz while pumping 45 and 75 l/min.

[jmaja]

Reading the VFD manual it appears I should try one of the variable torque settings. I now have constant torque. A pump has rpm^2 torque.

What do these settings actually do? They use a different voltage, which is actually lower PWM at the same frequency? What thus that actually change? If the motor is running at the desired RPM with lower voltage, what does the higher voltage do? Decrease slip and thus a bit higher RPM? Or just decrease efficiency? Too low voltage increases slip until motor stops?

All I can see is the water flow. If it doesn't drop much, it's fine to use a lower torque setting?

[WattsThat]

It’s the Volts per Hertz output relationship.

Constant torque applications use linear Volts per Hz, matching the torque requirement.

Variable torque uses Volts per Hertz squared. This will will result in lower flux levels in the motor, lowering the current and usually the audible noise. Savings should be proportionally better in smaller machines since flux current is a larger proportion of total motor current.

[jmaja]

There are a lot of options in my VFD for voltage Hz dependence. I could even give my own piecewise linear function.

Should I just lower the voltage as low as the flow rate is still about constant?

Does this effect the durability of the motor?

The pump is 15 m below water in the borehole. There is no noice I can hear.

[jmaja]

Found this: https://www.gsengr.com/uploaded_files/Variable%20Frequency%20Drive%20Recommendations%20For%20Centrifugal%20Pumps.pdf
"A voltage proportional to the square of the frequency is recommended for pump applications in order to maintain both motor efficiency and the correct magnetisation level."

Thus a 400 V pump motor should be run at 144 V @ 30 Hz. I have now 220 V and get 1.13 A and 220 W according to VFD. I tried to measure the effective power taken by the VFD using kWh-meter pulses and got just a bit over 300 W. VFD efficiency seems rather low ~70%. Is that expected at lower powers? Would it be better with lower power or newer VFD?

Let's see later today what happens when I change the torque setting to variable torque.

[jmaja]

I did some tests @30 Hz with variable voltage.

220 V gave 1.15 A, 220 W and 46 l/min
180 V 0.88 A 195 W
160 V 0.85 A 180 W
140 V 0.84 A 170 W
120 V 0.865 A 160 W
110 V 0.89 A 150 W and 33 l/min
100 V 0.92 A 150 W.
Variable torque low gave
146 V 0.84 A 170 W and 40 l/min

The last one seems to be about the best. 110 V has already higher current and much lower flow rate. Thus a lot of slip and probably too low rpm for min 30 Hz spec.

I got 240 W from the kWh meter so 70% VFD efficiency.

I'm quite happy with that, if the pump lasts with these values. Probably I'll buy another VFD, since the fan is very noisy and it turns on every now and then even with low power.

[WattsThat]

Changing VFD’s is not likely to change energy usage in any considerable way as simple 6 pulse drive topology is unchanged for thirty plus years.

Perhaps a marginal savings with the lower Vsat voltages with newer IGBT’s and rectifier diodes - but at the power levels you’re running - nah, not worth chasing, IMO. A 10-15 percent improvement would be as much as you could possibly hope for under the absolute best of conditions.

[jmaja]

This VFD should have 96% efficiency at full power. The new ones have the same. But this one is for 1.1 kW shaft power and I only have 0.37 kW shaft power motor. A new 0.37 kW VFD has 93% and 0.55 kW 95% efficiency. Shouldn't these have close to 90% at 170 W electrical power? Or is there something about VFD design that makes it impossible to have good efficiency at low power?

What about using 1-phase input 3-phase output VFD? I could only get 40 Hz due to 240 V max output, but the load would be closer to maximum. Better efficiency?

Saving 50 W is not such a big deal, but having a physically  smaller and less noisy VFD would be more important. Many of the 0.75 kW and smaller seem to be fanless, thus they must be quiet.

I could probably find one at the same price I could sell this one.

[jmaja]

I found this efficiency calculator for current Danfoss models.
http://ecosmart.danfoss.com

E.g. FC-202 0.55 kW should have 94% at 60% frequency and 25% current and 96% at 60% frequency and 50% current. There is one for sale at 140 €.

[WattsThat]

There are no easy answers to efficiency questions. It may appear easy but it’s not as measuring the overall combined efficiency of a vfd, motor and pump, known as watts to water, is problematic at best. Some incredibly pricy and fussy gear is needed to accurately measure the power in and out of a vfd. Measuring motor power is easy but it requires a dynometer, anything less is an estimate. Pumps appear easy as you can measure pressures and flows but still not have all the data since you’re missing the delta T of the water.

It’s not that a smaller drive will be more efficient, it’s just that the measurements with a drive that matches the motor rating will have better resolution, nothing more. If a smaller, quieter drive is a better fit for you, go for it. Just don’t expect any performance improvements.

[jmaja]

Well I already bought the FC-202 0.55 kW a few days ago for 100 €. It has arrived and I'll pick it up tomorrow. Hopefully it is not noisy and a bit more efficient. At least it should be much newer and have a nicer display. It's about the same size.

I have no idea how accurate are the kWh and kW readings of these VFD's show on their display. But it should be easy to see how much energy the new one takes once I have set it up for the same pumping setting (l/min and head).

I guess VLT 5000 series is quite old. From the 90's? I would think the standby current consumption has gotten much better since then, which could show better efficiency at low powers. The ecosmart tool says that FC-202 should have 14 W standby loss and up to 29 W drive loss. I measured about 30 W for VLT 5002 standby.

But let's see. I will report when I get it running.

[jmaja]

Now I have the "new" VFD running. It's much less noisy, but still has a fan. The settings are quite different and I had some dificulties getting the same Hz and flow rate at the same time as the old had. Not much of a difference in efficiency.

I could get the same 40 l/min at 40% variable torque curve at 30 Hz or at automatically optimized 28 Hz. Both took about 175 W according to the VFD and 230 W according to kWh meter of the house. So maybe 10 W less.

The automatically optimized takes about 200 W at 30 Hz (260 W at kWh meter), but then it pumps 44 l/min. 145/190 W at 25 Hz and 35 l/min.

[Envieq]

Hello,
from our huge experience, I can tell you that there is no efficient solution for single-phase motors except Grundfos SQE pumps and Grundfos CU301.
The other solution can be to use the frequency converter that has IN 220V single-phase and OUT 220V three-phase, but in this case, the motor of the pump should be also 220V three-phase. Franklin produces this kind of motor, and there are a few producers that supply this type of frequency converter, one of them is Elentek. The Elentek solution incorporates an ABB inverter which is very easy to set.
Anyway, we can supply all these solutions, but my suggestion remains the same, Grundfos SQE pump + CU301. The pump has built-in all types of motor protection including dry-running protection, what do you want more?
Visit our website, if you have questions, use the online chat also for technical questions
https://www.envieq.com/
Thank you!