VFD doesn't trip on over current.

[rQx]

Hi!

This is maybe not the right place to ask this but since many of you have experience from VFDs I'll give it a shot.

We are some what confused regarding the functions of a new series of VFDs from our supplier. I don't want to out the company here so I'll speak in general terms.

We have used many VFDs and ofcourse it has a overcurrent protection in it. On all the other models we have used we are able to set the "motor rated current" in the parameter to a lower level then the motor actually is and the VFD will stall and after a while trip on over current.

On this new VFD we can set the "motor rated current" parameter to 0,5A and run a motor that draws 4A and it just continues to run. No stall, no trip and we have tried this well over 10 minutes. This is a 2,2kW VFD and a 2,2kW motor with no load.

We insist that this is a strange function and we don't want to start to use this new VFD if the company doesn't have an answer to why it doesn't trip. I mean, it's a very important function. We have been trying to get an answer for nearly a year now. Have anybody encountered a problem like this? Or have any ideas as to why this should be correct behaviour for a VFD?

Last I want to say, is there anyone who knows of a good place to ask these sorts of questions? Since maybe it is a bit offtopic for a PLC forum.

 

[osmanmom]

parameters numbers at less to guest

 

[DickDV]

This is a good place to ask VFD questions. We have several people on this forum (including me) that enjoy handling VFD questions. The moderator has made it clear that VFD questions are within the scope of this BBS.

First, the motor nameplate current value should always be entered exactly as marked on the motor nameplate. This value is used for the thermal protection of the motor and should be stated properly. Some modern drives are smart enough to realize that 2.2kw and .5FLA is inconsistent and will attempt to recalculate the FLA or simply fault out on inconsistent parameters.

Second, current limit (if a V/Hz or scalar drive) or torque limit (if a sensorless or vector drive) is a separate parameter and is intended to be used for instantaneous limiting of motor output. This is where you should be setting your limits, not in the motor nameplate data parameters.

Third, we can probably be more helpful if you identify the drive brand and model number more precisely. We deal with brand-specific issues regularly here and we all realize that each brand has its strong and weak spots. I personally have deep roots with ABB and Reliance. Others are Allen Bradley, CT, Yaskawa, DanFoss, or Emerson people. It doesn't matter.

 

[osmanmom]

if you observe again what the default parameters if incoming supply running 2 phase only.

 

[Bering C Sparky]

Not a Drive Expert, but frequency drives are pretty smart usually. However they are only as smart as you tell them to be via the parameter setup process.

I dont see too many drives faulting on overcurent, the drive will usually try to limit the current to stay within its set parameters.

By the numbers you gave and your location I am assuming that this is a 600v 3phase 2.2 kw motor that is Rated for 4 amps FLA.

If you dont have the motor loaded then it is more than likely not going to pull Full Load Amps, and IF you have the overload protection of the drive set very low it is POSSIBLE that the drive is limiting the current to keep it within its parameter setting.

Is the drive running at full HZ? (I am guessing 50 in your case)
Or is the drive limiting the hz in order to limit the current?

Have you clamped the feeder conductor to the motor with a meter to see how many amps you are actually pulling?

Without knowing the Make and Model of the drive we could only guess as to if parameter settings could be an issue.

Sorry for the wall, just throwing some thoughts out there.

BCS

 

[osmanmom]

check attachment,

 

[dginbuffalo]

Hi!

We insist that this is a strange function and we don't want to start to use this new VFD if the company doesn't have an answer to why it doesn't trip. I mean, it's a very important function. We have been trying to get an answer for nearly a year now. Have anybody encountered a problem like this? Or have any ideas as to why this should be correct behaviour for a VFD?

Like the others said, it's hard to say without knowing who's VFD since they all tend to have some different functionality. I know one thing- if I was trying out someones new product and they couldn't give me an answer in a year, I'd be moving along to another one!

 

[rQx]

First, the motor nameplate current value should always be entered exactly as marked on the motor nameplate. This value is used for the thermal protection of the motor and should be stated properly. Some modern drives are smart enough to realize that 2.2kw and .5FLA is inconsistent and will attempt to recalculate the FLA or simply fault out on inconsistent parameters.

Ofcourse when we startup a drive we set it correct, this is only for testing the functionality of the VFD. That is what we thought as well, but we can try to set the motor power rating down to 0,55kW and we had the same problem. Maybe here the drive is smart enough to read the resistance of the linnings and see that there is some sort of problem.

Second, current limit (if a V/Hz or scalar drive) or torque limit (if a sensorless or vector drive) is a separate parameter and is intended to be used for instantaneous limiting of motor output. This is where you should be setting your limits, not in the motor nameplate data parameters.

We only have one parameter for the nameplate and this is also where we should get our motorprotection from. There is another parameter but that is the inverter rated current we can manipulate, but this current is when the drive trips instantly.

Third, we can probably be more helpful if you identify the drive brand and model number more precisely. We deal with brand-specific issues regularly here and we all realize that each brand has its strong and weak spots. I personally have deep roots with ABB and Reliance. Others are Allen Bradley, CT, Yaskawa, DanFoss, or Emerson people. It doesn't matter.

Well, I know your right, it's better to know what dirves we are dealing with.
It is: Parker SSD AC10 2,2kW 3*400V

Not a Drive Expert, but frequency drives are pretty smart usually. However they are only as smart as you tell them to be via the parameter setup process.

I dont see too many drives faulting on overcurent, the drive will usually try to limit the current to stay within its set parameters.

Yes, this is we also want, the drive to stall. This is another thing this drive doesn't.

By the numbers you gave and your location I am assuming that this is a 600v 3phase 2.2 kw motor that is Rated for 4 amps FLA.

If you dont have the motor loaded then it is more than likely not going to pull Full Load Amps, and IF you have the overload protection of the drive set very low it is POSSIBLE that the drive is limiting the current to keep it within its parameter setting.

3phase 400V 2,2kW motor and the motor is rated 5A. It is unloaded and it draws 4A (well 3,8A) according to the panel on the drive and our instruments.

Is the drive running at full HZ? (I am guessing 50 in your case)
Or is the drive limiting the hz in order to limit the current?

Have you clamped the feeder conductor to the motor with a meter to see how many amps you are actually pulling?

Without knowing the Make and Model of the drive we could only guess as to if parameter settings could be an issue.

Sorry for the wall, just throwing some thoughts out there.

Yes, it runs in full HZ (50) and we have confirmed that it runs in 3.8A.
I appreciate the wall it's always good to get tips and tricks.

Like the others said, it's hard to say without knowing who's VFD since they all tend to have some different functionality. I know one thing- if I was trying out someones new product and they couldn't give me an answer in a year, I'd be moving along to another one!

Yes, I realized that and have now stated the drive. Well, the product is already on the market and is very good in price and we have used their former models for year and have never had any complains so we really want this to work.

Maybe it is like some of you said, the drive is so smart we can't trick it but then we wan't the manufacturer to say that. Right now it's like talking to a wall.

We did a tuning on the 2,2kW drive with the 2,2kW motor and set the correct nameplate current 4,5A. Then we connected a 5,5kW motor instead and ran it for 10minutes with no trips although it drew 6,7A. I just can't for my life understand how this thing works.

 

[Bit_Bucket_07]

I have, in the past, worked with VFDs that did not provide overload protection. Instead, the documentation made it clear that these drives were intended to be used with customer provided overload relay protection. I don't know if anyone makes drives any longer that do not incorporate overload protection. The drives to which I am referring were used back in the 1990s.

 

[Aabeck]

Frequently the motor overload setting is a separate parameter from the motor full current parameter, Check the VFD manual for parameters & see if it's anothher setting - I know on the AB PowerFlex it is separate and will shut down when it hits the overcurrent trip level.

 

[jraef]

I have never seen this drive before, although it looks suspiciously like a brand-labeled Asian drive i have seen before with a slightly different keypad. Regardless of that, it took me about 3 minutes of reading the manual to find a potential issue to explain what you are seeing. I find it hard to believe their tech support had no clue, methinks you got hold of the newbie...

Function 707 is the "Motor Overload Coefficient %" setting. On this drive, the only motor overload protection is provided as a function of the DRIVE current protection function, which is set to begin counting down at 140% of the current rating of the DRIVE. So to protect a smaller motor, you must tell the drive that the motor is smaller than the drive in Function 707, by taking the ratio of the motor size to the drive size x 100%. So for example if you have a 2.2kW drive and a .5kW motor, .5/2.2= .23, so you would set Fn 707 to 23%. That then means the MOTOR overload protection starts counting down beginning at 140% of the expected FLA of a .5kW motor instead of a 2.2kW motor.

In your case, you are attempting to test this based on an artificially arbitrary current value, which the drive apparently does not recognize as a motor overload. The factory default of Fn 707 is 100%, which means that of a 2.2kW motor, so .5A doesn't even register to it yet. Unfortunately for you, Fn 707 cannot be set any lower than 20%, so essentially .44kW is the smallest motor this drive can protect. That by the way is not unusual, most drives have a limit as to how small of a motor they can protect, because there is a functional limit to the accuracy range of current sensors.

That said, my opinion of the motor protection scheme of this drive, from what I just read in the manual, is well below "**** Poor". I would not use it without an exterior motor thermal overload relay. In fact I read in the "Compliance" section of the manual that indeed, although the drive is UL listed as a "Power Converter", it is NOT listed as a motor controller and in fact tells you, in tiny little footnote letters, that it does NOT provide motor thermal protection! Surprise! You MUST use an external OL relay with this drive!

Welcome to the world of stealth marketing... That little trick is employed by many of the bottom feeder drive mfrs from China who sell at impossibly low prices, I'm a little surprised at Parker for having fallen for that trick.

 

[rQx]

I have never seen this drive before, although it looks suspiciously like a brand-labeled Asian drive i have seen before with a slightly different keypad. Regardless of that, it took me about 3 minutes of reading the manual to find a potential issue to explain what you are seeing. I find it hard to believe their tech support had no clue, methinks you got hold of the newbie...

Function 707 is the "Motor Overload Coefficient %" setting. On this drive, the only motor overload protection is provided as a function of the DRIVE current protection function, which is set to begin counting down at 140% (I think we missunderstand the manual here, it begins count on 100% but if you have 140% it will trip on 60sec) of the current rating of the DRIVE. So to protect a smaller motor, you must tell the drive that the motor is smaller than the drive in Function 707, by taking the ratio of the motor size to the drive size x 100%. So for example if you have a 2.2kW drive and a .5kW motor, .5/2.2= .23, so you would set Fn 707 to 23%. That then means the MOTOR overload protection starts counting down beginning at 140% of the expected FLA of a .5kW motor instead of a 2.2kW motor.

Yes, we know of this parameter but this is a setting if I drive a lower powered motor. The support has told us to "set this", but right now I have a 2,2kW motor and a 2,2kW drive. So I shouldn't change it? And have tested with 5,5kW motor and 2,2kW drive. And the manual doesn't state anything that I have to change this to get a motor protection function (if I'm not driving lower powered motor). It doesn't make any sense that I should have to change this parameter, the DRIVE rating is 6,5A, this mean that the protection only is active over 6,5A? Since when does a 2,2kW motor draw 6,5A? The manual doesnt say we should change this UNLESS you have e lower powered motor. So why should we change it? Gaaah, so many questionmarks is makes me sick.

I think the explanation of the parameter is somewhat confusing:

"For example: 7.5kW inverter drives 5.5kW motor, F707=5.5/7.5 ×100％≈70％. When the
actual current of motor reaches 140% of inverter rated current, inverter overload protection will
display after 1 minute."

What does the inverter rated current have to do with my motor protection, and the only thing stated in the manual is that I should set F803. So all the drives they sell and people install have no motor protecion in that case. And what the F doesn F803 have to do with anything? Is it just a motorcontrol parameter?

I meen, the F707 parameter should corrspond to F803 (motor nameplate current), 100% of F803 in my opinion. I will test this at work tomorrow if it correspond to the DRIVE rating instead. Maybe this is where it all comes down to, a bad manual and directions.

They talk about setting F707 regarding the POWER of the inverter and motor, but if this is the parameter I should use, it should state DRIVE CURRENT vs MOTOR CURRENT.

That said, my opinion of the motor protection scheme of this drive, from what I just read in the manual, is well below "**** Poor". I would not use it without an exterior motor thermal overload relay. In fact I read in the "Compliance" section of the manual that indeed, although the drive is UL listed as a "Power Converter", it is NOT listed as a motor controller and in fact tells you, in tiny little footnote letters, that it does NOT provide motor thermal protection! Surprise! You MUST use an external OL relay with this drive!

Welcome to the world of stealth marketing... That little trick is employed by many of the bottom feeder drive mfrs from China who sell at impossibly low prices, I'm a little surprised at Parker for having fallen for that trick.

Maybe you are right, or they just want to have their hands free when something happens because I just found this in the manual:

"In order to protect the motor reliably, it is recommended to use a temperature sensor to detect
the motor’s temperature, and use the drive’s over-load protection device (electronic thermal
relay) instead of an external thermal relay"

 

[osmanmom]

if i have 1.1kw 2.7 AMP AC motor using 2,2 KW using AC10 inverter,

I will set the parameters

F801 = 1.1 KW , F802 = 400 V , F803 = 2.7 AMP , F804 = 4 POLES , F805 =1500 RPM,

for

F707 = 1.1 KW/2.2 KW X 100% = 50 % from default parameters motor amp (5 AMP),probaly new setting 55~60 %.

if the default 5 amp, then 2.5~ 2.7 amp are new setting value for motor overloading.

but can't lower 20 % from this value 1 Amp, as manual description .


for F704 ( Inverter overloading coefficient: the ratio of overload-protection current and rated current, whose value
shall be subject to actual load)

F738 for 2,2kw inverter 15 AMP / 6.5 AMP = 2.3, recommendation 2.5 = 6 AMP

F704 - inverter overloading setting range 50 ~ 100 % ,recommendation 80 % from 6.5 AMP -> 5.2 AMP

new setting for F704 = between 40 ~ 50 %, for ac motor 1.1 kw


F706 Inverter overloading coefficient setting range 120~150 %,default 150 %

from the example inverter 7,5kw (17AMP) to 5,5 kw (~15 amp) AC Motor,

F707 = 70 % FROM Inverter rated current 17 AMP -> ~12 AMP

F706 = 140 /100 X 17 = 23 AMP (inverter overload protection will display after 1 minute)

F706 = 120 / 100 X 17 = 20 AMP

but remember the minima value 120% as manual description.


means,

2,2 kw motor with inverter 2,2 kw ,

1.1 kw motor with inverter 1,1 kw

 

[rQx]

Thanks alot for the very detailed explanation! I will comment on what I find strange thought. And I think that the problem we have is that it doesn't say anywhere that we should set anything other then F803. Thus noone is going to set these parameters and have no motor protection.
And where they say in manual that we shall divide motor power with each other, if this statement should be true it is the motor current we must divide.

if i have 1.1kw 2.7 AMP AC motor using 2,2 KW using AC10 inverter,

I will set the parameters

F801 = 1.1 KW , F802 = 400 V , F803 = 2.7 AMP , F804 = 4 POLES , F805 =1500 RPM,

This is the easy part, I'm with you on these ones. On all the other drives I've commisioned this is enough to have a motor protection. It would refer to F803 to stall and trip.

F707 = 1.1 KW/2.2 KW X 100% = 50 % from default parameters motor amp (5 AMP),probaly new setting 55~60 %.

if the default 5 amp, then 2.5~ 2.7 amp are new setting value for motor overloading.

but can't lower 20 % from this value 1 Amp, as manual description .

This is where the manual must be way off, since the inverter rated current of a 2,2kW drive is 6.5A and the factory default is 100%, it means that my motor at 2,2kW rated 4,5A has no protection. And it says I should divide the power of the motors. Well, if I have a 2,2kW and a 2,2kW drive. 2,2/2,2*100 is 100%. So we must (if this is correct) divide the currents. 4,5/6,5*100=69%.

It seems like maybe F707 is the correct parameter for the overload protecion, but the description of it is completely wrong.

for F704 ( Inverter overloading coefficient: the ratio of overload-protection current and rated current, whose value
shall be subject to actual load)

F738 for 2,2kw inverter 15 AMP / 6.5 AMP = 2.3, recommendation 2.5 = 6 AMP

I didn't quite understand this part. Where do you get 15A from? Anyway this is a protection for the inverter so I think it shouldn't be changed.

F704 - inverter overloading setting range 50 ~ 100 % ,recommendation 80 % from 6.5 AMP -> 5.2 AMP
new setting for F704 = between 40 ~ 50 %, for ac motor 1.1 kw

I'm with you on this one since the inverter rated current is 6.5A so the inverter pre alarm is at 5.2A. However I don't think that I have to set the inverter overload settings since it must be correct from factory to protect the drive?

To sum up I think that we have come up to:

F803 has nothing to do with overload protection what so ever.

F705 motor overload pre alarm coefficient
F707 motor overload coefficient

This is where I should configure the motor overload protection, however the manual state that I shall divide the power of the motorand inverter, and that can't be correct. It must be the current. We'll see tomorrow when I try this if it works or not.

 

[pal]

Bear in mind that inverters don't just vary current , they also vary voltage to the motor , so the power to the motor does not correspond directly to current . I don't know the inverter you are using ,but most inverters will display output voltage as well as output current . Since a normal clamp meter reading of motor current is unreliable because of the inverter chopper frequency , you will get a more reliable reading from the inverter display .

Paul