VFD controlling an Air Handler Failures 2

[enverd]

Hello All,

Recently a new Air Handler Unit was installed and it came with an 9 dedicated VFDs.

After the start up there have been constant issues where the first two weekends we had electrical over-current alarm, the weekend after nothing happened and this past weekend the Unit shut itself down.
ABB start up techs have been involved but they are not able to fix the issue (which is very confusing to me as to why they can't fix the problem).

The first issues gave us the following received alarms:
PC.B1.A160102.SS and PC.B1.A160101SF.VFD.OK.Fault
Four DP Alarms followed:
PC.B1.DP.395.303
PC.B1.DP.391.392
PC.B1.DP.394.135
These were PRI2 Alarms
and the fourth is PC.B1.DP.395.303, this one was PRI1

VFDs faulted and they were reset initially, only 8 of them came back online. #8 stayed in Fault 9 (MOT Overtemp)

Getting the details on the VFDs initially:

Drive # Fault Time Speed @ Fault Freq @ Fault Current @ Fault Torque @ Fault
1 11:30P -2797 RPM 62.5 Hz 1.4A -6.6%
2 11:30P -3259 RPM 54.9 Hz 1.4A -7.4%
3 11:30P -3259 RPM 54.9 Hz 1.4A -5.8%
4 11:30P -3259 RPM 54.9 Hz 1.3A -5.1%
5 11:30P -3259 RPM 54.9 Hz 1.1A -4.8%
6 11:30P 2600 RPM 43.3 Hz 0.5A -3.5%
7 11:29P 2600 RPM 43.3 Hz 0.6A -4.0%
8 Data not available; MOT OVERTEMP fault is most recent fault
9 11:30P -2797 RPM 62.5 Hz 2.4A -4.1%


So this past weekend we are getting the reoccurring electrical over-current alarm.

Can anyone please let me know what the alarms mentioned above mean and what could be driving the over-current alarms on the VFD?

Thank you all in advance.

 

[jraef]

Other than the casual mention of it being ABB drives (presumable because you say it was ABB tech support), how would anyone else know what these faults mean?


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[enverd]

Thank you jraef.
I am sorry for not having any better information and you are correct they are ABB drives and I am asking the same question, how would you know what the faults are.

Looking past that, the obvious alarms/faults are "Motor Overtemp" and "Overcurrent"
Does that indicate anything specific that would cause that, maybe coming from the AHu?

As soon as I hear overcurrent fault or overtemp I think of a fault, draw of too much current etc...
I just don't know enough about AHU's and what would cause that scenario especially when the unit is brand new.

Thanks,

 

[crshears]

Hey there enverd,

Are you employed by the HVAC installing firm, or by the purchaser? Clearly you don't work for ABB...

Provided I was in the position to do so, I'd be putting pressure on ABB and/or the supplier of the AHU and/or the installers and/or commissioning team to work together to sort out the problem...and I'd listen real hard to everything that was said; learning experiences like this can be invaluable. Not only that, you get to know how good or not others are at rising to such challenges, which can serve you well in the future.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[jraef]

ABB makes something like 20 different models of drive, all with different features and manuals and programming. If you make getting information like pulling teeth or a game of 20 questions, this crowd will lose interest in helping you. Please be THOROUGH in describing your issue; What is the MODEL number of the drive? What is the RATING of the drive? What is the motor nameplate information?

As a general rule however, in an AHU load on the motor = flow from the fan. Over LOAD = over flow. Without knowing that drive, I don't know if over CURRENT is the same as over LOAD of the motor. Usually they are not, so that might meat something wrong with the drive itself. But why the ABB guy couldn't figure that out would be a puzzlement.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[enverd]

crshears, you got it, I absolutely don't work for ABB
I am an electrical engineer working for a consulting company and my designs go basically as far as complete specifications and construction documents showing power points of connection.
My first response to the Construction Managers was they need to work this out with ABB, HuntAir etc.. It is their equipment and they really need to fix/figure out whatever is not functioning properly.

On the other hand I do like to be a lid to every pot so I'll try to help as much as possible

jraef, thanks for the suggestion and honesty. Certainly without much information, nothing basically can be solved.
Unfortunately, what I gave so far was the only set of info that was given to me.
If I was one of those people that only points fingers I would simply say "this is not part of my scope and I can't help you" but I am not so I will do as much (or as little it is) that I can to point them in the right direction.

Your explanation helps a bit and you are right, why an ABB guy or any of the AHU techs that are doing this for living can't figure this out is a big puzzle to me.

I'll be onsite tomorrow so I'll figure out as much info as I can. This way I'll either have specifics about the actual problem or I'll have a solution to share.

Thanks for all your feedback gents.

 

[jraef]

I took a look at all the ABB manuals I have, and ACH550, ACS350, ACS150 and an ACS55, the fault codes and descriptions look nothing whatsoever like what you have posted. Now we know that this is second hand information for you, so if I had to guess (and I do), I think these "fault codes" are not from the VFD itself, but rather the display on a BMS (Building Management System) HMI screen. They may have been TRIGGERED by a VFD going off line, but that is not the VFD fault information itself. The "PRI1 and PRI2" are the clues here, those typically are codes used in BMS and Fire Alarm systems indicating Priority Alarm levels so that building mgrs can know which ones to worry about and which ones they can ignore until they finish their coffee.

So it's also entirely possible here that because it might be a balanced air system, if ONE drive faults, the entire system has to shut down. In the HVAC world, having an unbalanced system can create negative (or positive) air pressurization that makes it impossible to open or close doors. So if one air handler trips, the BMS must shut them all down. I'd venture to say that at 11:30PM, VFD #8 tripped on Motor Over Temp, and it shut down all of them. The rest of them were able to turn back on, but not the one with a hot motor.

The motor Over Temp fault diagnostics say this:

Motor is too hot, based on either the drive’s estimate or on temperature
feedback.
• Check for overloaded motor.
• Adjust the parameters used for the estimate (3005…3009).
• Check the temperature sensors and Group 35 parameters.

Given that you ALSO say you got Over Current trips (and by the way, for the ABB drives, OC = OL) I'd say you have an overload on motor #8 that is recurring. So on an AHU, that could be anything from a damper that failed too far open so there is less air flow restriction and the fan tries to move more than the motor is designed to deliver, the belts are too tight, the motor bearings are failing, or the VFD is not programmed correctly for the motor nameplate data as the most common causes.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington