Motor/VFD Question 2

[MagneticFlux]

Greetings all,

I would like some opinions/suggestions on an issue being experienced with a VFD and motor.

Motor Specs:
Volts 460
F.L. Amps 239
S. F Amps 275
RPM 1200
Hertz 60
HP 200
Duty CONTINUOUS
TYPE TD
Frame 447T
Serv. F. 1.15
Phase 3
Design B
Code G
Insul Class F
Eff 100% 96.2
Connection 6 Lead Star-Delta
Link

http://www.leeson.com/CnxDocRequest/PublishedPDF/dwg-006131301_00519001_545780_365.pdf

Drive Specs:
Product: Allen Bradley 23C-D460A103NNMANN
Description: PowerFlex 400, Fan & Pump Packaged Drive

Version Voltage Code 480 VAC, 3 PH
Output Current 460 Amps
Human Interface Module Fixed Keypad
Enclosure IP20 / Type 1
Version RS485
Frame Size H

Setup:
Motor is driving a P type fan via direct coupling
Motor connection = DELTA (connection has been verified twice)
Drive tuned and configured for 200HP motor, all settings default with exception to motor nameplate data, voltage input and auto-tune data.
Motor Data = (matches above info)
Voltage Input = 480 Volt
Auto-tune = calculated by VFD based on above info
Motor Control Mode = V/Hz
Application Mode = None, no PID inputs, being controlled via HMI

ISSUE: (Note that I am not performing the install/setup, I got involved because someone asked me to look into this).

The motor will not come up to full speed before O/C limit is reached. With frequency set-point at 60Hz: as the motor ramps up to speed (ramp time = 30 seconds), at +18HZ an over current alarm is indicated on HMI. Longer ramp times have no effect. The VFD will ramp up to ~18Hz and go into 'current trim mode' as this is highest frequency achievable before current output peaks at ~275 amps(SF amps). Adjusting the frequency beyond 18 Hz triggers O/C alarm.

Motor manufacturer recommends leaving the motor connected in delta and starting ATL to determine if this is a drive or motor issue. This was thought I had as well but Size 5 starters are not laying around like they used to be 20 years ago so, for the time being, that option is off the table. My thoughts are centered on drive parameter settings but the settings are as basic as they need to be for nominal operation. Any thoughts?

 

[jraef]

Uncouple the fan and see if the drive still does this when connected to the motor, but no load on it at all. If it does still go into Current Limit, you have a bad transistor in the drive. If not and the drive goes ahead and ramps the unloaded motor up, it might be that you will need to have that fan (blower) system choked off for no flow until after the motor gets to speed.

Also, double check the programming on A179 (Current Limit) to make sure someone has not accidentally entered some unrealistic value in there. Then also check A182, which tells the drive what to do about an over current situation. From the sounds of it, A182 is probably programmed to a value of 2 which automatically forces it to lower the speed, but if set to a value of 1, it will automatically lower the current limit. If set to a value of 3 it will do both but it will lower the speed first, then lower the current limit setting. See what that is set for.

Lastly, look at the setting of A168, which is the Carrier Frequency (called the PWM frequency for this drive). If someone set the CF to a really high value, like 10kHz, in order to try to make the motor quiet, they did so without paying attention to the fact that you must ALSO de-rate the drive when you do that. So for example if you were to set it to 10kHz, the drive must be de-rated by 50%, so the drive may be trying to let you know it can't handle what you are asking it to do.


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

 

[John2025]

jraef,
Wow, that's a heck of de-rating for carrier frequency. Is that fairly typical of all VFD drives? Definitely something to remember.

 

[jraef]

Yes, it's a function of increasing the switching losses in the transistors because you are switching them more often in the same time frame. All VFDs must be de-rated, some cheap ones just don't make that easily to discover until AFTER you burn them up.


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

 

[edison123]

Thanks jeff. Learnt something new today.

Muthu

http://www.edison.co.in

 

[waross]

Thanks for your contribution to my continuing education Jeff.
Yours
Bill

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[MagneticFlux]

I wish I had good news to report...

@iop95: We input your parameter recommendations which yielded marginal results. Was unable to get past 18Hz before reaching FLC.

@jreaf: Motor uncoupled from load will run up to base speed (1160RPM) connected delta, current draw ~53 amps (2nd hand information, can not verify as I was not on-site). With load coupled, using the damper to reduce air flow (closed position) did not work as far as getting past 18Hz before reaching FLC. The parameters you suggested be reviewed do not match up to the description you provided. I Included a link to parameters in an above post for review. From the description you provided, I can confirm the following:
420

Drive OL Mode = Disabled​

421

Current Limit Sel = Port 0 : 422​

422

Current Limit 1 = 390.00​

38

PWM Frequency = 2.0 kHz​

I have more accurate information on the fan:
Fan Diameter: 72 inches
Fan Width: 19 inches
P Type, Forward Pitch
Design CFM: 51000

We re-connected the motor Y to see if we got any improved results. We did see improvement; was able to get to 48Hz with current at ~260amps. We reduced frequency to 40Hz bring the current down to ~240amps (name plate current). However the motor leads were not sized for Y connection, so we reduced to 30Hz which brought current down to ~120amps. Although the Y connection yielded improved results, it was not designed to run on the Y (high slip, reduced HP, etc..). I contacted AB tech support on Monday and shared our results. Was informed their drive would not function correctly on a delta connected motor which is why we saw some improvement when the motor was connected Y. I questioned this statement and was not given a solid answer. We have a AB PowerFLEX 400 VFD driving a 200HP delta connected motor on site with no issues. Parameters are identical (2nd hand information). The nameplate on the Leeson motors states that it is VFD Rated (see above photo). Can anyone explain the voltage and current ratios shown on the nameplate and how those correlate to a VFD?

 

[waross]

We have a AB PowerFLEX 400 VFD driving a 200HP delta connected motor on site with no issues.

If this is driving a similar fan, or if you have any similar fans on site, can you compare the fan dimensions?
I wonder if the fan has been designed for a much lower speed?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[MagneticFlux]

@waross: The difference in fans are as follows:

EXISTING FANS:
~36 inch diameter, ~24 inch width, belt driven, running ~1800+ RPM

NEW FAN:
~72 inche diameter, ~19 inch width, direct coupled, 1160 RPM

 

[edison123]

Looks to me comparing apples to potatos?

Muthu

http://www.edison.co.in

 

[MagneticFlux]

@edison123: Please explain...

 

[davidbeach]

Neither of those fans is a substitute for the other.

 

[edison123]

@OP - above my current pay grade.

Muthu

http://www.edison.co.in

 

[iop95]

With no load, 53Amp?! That mean 42kVA... about 30kW considering 0.7 PF. I think is too high value... motor have a so powerfull internal fan? May you clarify.
Fan models are too different for any comaparison.
If do some calculation for Y connection with values showed above, result motor torque values above nominal... up to 1800Nm, that is not possible and make me to think about driver current accuracy reading.
2kHz PWM may lead to high current spikes, worse in delta and drive go in current limit... but is far away of limit; a trueRMS clamp meter may help to clarify.
May you increase PWM to 4-5kHz and/or add a reactor?

 

[waross]

The motor will not come up to full speed before O/C limit is reached. With frequency set-point at 60Hz: as the motor ramps up to speed (ramp time = 30 seconds), at +18HZ an over current alarm is indicated on HMI. Longer ramp times have no effect. The VFD will ramp up to ~18Hz and go into 'current trim mode' as this is highest frequency achievable before current output peaks at ~275 amps(SF amps). Adjusting the frequency beyond 18 Hz triggers O/C alarm.

250 kW (200 kW)
Continuous Amps 456 (367)
60 Sec Amps 501.6 (550.5)

Looking at this information there should be no way that this drive will reach a current limit of 275 Amps in 30 seconds.
Possible causes.
1 The drive is configured for less than 250 kW or 200 kW
2 The drive has other configuration issues
3 The drive is faulty
It seems strange that the 60 seconds Amps is lower for 250 kW than for 200 kW.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

53A is quite typical for the no-load motor current, possibly even lower than typical. You certainly don't get a 0.7 power factor on the motor with no load. Maybe 0.1.

Still, if you want to make sure the no load idle current is reasonable then monitor the input current to the VFD. Without the load coupled, the input current should be very low, likely under 10A.

Assuming the fan is 80% efficient, it could move 51,000 cfm if the fan outlet pressure is under 10psi. So, what is the fan outlet pressure?

The VFD will be fine with a delta connected motor. The motor connection doesn't matter as long as the motor and the VFD V/Hz pattern match.

I find it odd that the manufacturer plated the fan with the HP but without the rpm. That's a really odd thing to do for a fan since the HP is useless without the rpm.

 

[iop95]

Yes, my mistake with 0.7PF... maybe 0.1-0.2 at no load.
Regarding fan.. we don't know torque curve or at least rpm for 200HP power requsted.

 

[MagneticFlux]

@LionelHutz: At ~18Hz, we are drawing less then 1 inch WG on inlet side of duct. It seems to me that there is hardly any load at all.
I agree that the VFD should work fine on a delta connected motor. Can you elaborate on motor and VFD/Hz pattern needing to match?
Again I agree, the fan manufacture indicating the HP without indicating RPM for the equipment is odd. I can only speculate from the motor they installed that the operating speed of the fan is 1160RPM.

 

[jraef]

I don't know who you got connected to at tech support, or how the question was framed, but that issue of the drive not working on delta connected motors is just bunk. That has no bearing on how the drive functions. All that's important is that the motor is connected in the pattern commensurate with the voltage level. Your motor is designed for delta connection at 460V, you must use it that way.

So what I'm curious about is the "old vs new" fan issue. Going from 36" diameter to 72" diameter represents a HUGE difference in inertia of the fan blades themselves. So was the 36" fan using a smaller motor so that when you changed to 72", the motor size was increased too?

Also I agree with LH, stating the fan HP requirement without stating the RPM is very odd. For all we know, that 72" fan was intended to run at 10RPM and the 200HP assumed a 6:1 belt reduction, meaning the torque requirement if directly driven would be the equivalent of 1200HP! I just really think there is some sort of mechanical mistake taking place here and some mechanically inclined person is thinking the VFD performs magic. I've had that happen in more than one occasion.


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

 

[LionelHutz]

The motor is rated 460V @ 60Hz. this means it has a V/Hz ratio of 7.67 and the VFD needs to be programmed to match this ratio. There are various ways this is done and a typical way is programming motor voltage to 360 and a base frequency setting to 60Hz. However, I can't say how to do this exactly with that VFD.

Did you take any rpm measurements when connected in wye? It'd be interesting to know what rpm the motor and fan achieved.

jraef - wasn't there a poster here recently thinking the motor hp was the same at any speed? The basic theory was along the lines of taking a 200hp @ 1200rpm motor and directly connecting it to a load that required 200hp @ 300rpm. Then, use a VFD to run the motor and load at 300rpm. Unfortunately, the theory was wrong because the motor would only be 50hp @ 300rpm.

 

[MagneticFlux]

b]@jreaf:[/b] One of the AB tech support persons made that statement, I was very clear in my question, "Will the PowerFLEX 753 VFD operate a delta connected motor?", long answer was no. I agree with you and questioned it, and again, was not given a clear answer. I contacted AB support again today and got a different specialist who had no reservations about the PowerFLEX 753 drive working on a Y or delta connected motor, said it makes no difference. We went over the motor data and drive parameters. He made some suggestions which we will try this weekend.
There is no "old vs new" fan, this is a completely new baghouse. The reference was to EXISTING system (3 actually) currently in operation vs the NEW system setup.

@LionelHutz: In regards to programming the drive to match the motor V/Hz ratio, AB tech specialist says that is taken care of (calculated) by the V/Hz algorithm.
Yes, at 30Hz we drew ~2 inches WG on inlet side of duct. the RPM was ~550 (can not verify, did not witness the measurement). I will be able to document accurate info this weekend.

wasn't there a poster here recently thinking the motor hp was the same at any speed? The basic theory was along the lines of taking a 200hp @ 1200rpm motor and directly connecting it to a load that required 200hp @ 300rpm. Then, use a VFD to run the motor and load at 300rpm. Unfortunately, the theory was wrong because the motor would only be 50hp @ 300rpm.

That is very interesting, I wonder the poster is somehow involved with this particular fan manufacturer!