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ACS850 VFD Reference Meet Problem

04/08/2017 6:08 AM

Hi to All,

We are facing reference meet problem in ACS850 VFD Drive. Our Drive is running ID Fan on boiler. It is 315 KW 992 RPM Motor. When The PID gives its full output to drive it only achieves 750 RPM instead of 992 RPM. We have checked all the parameters 99 group, 10,13,15,21 groups all are normal. Any one having same problem please help?

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#1

Re: ACS850 VFD Reference Meet Problem

04/08/2017 6:46 AM

Contact ABB directly, I am sure they will have an answer.

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#2
In reply to #1

Re: ACS850 VFD Reference Meet Problem

04/08/2017 6:57 AM

Thanx JPool,

This is the matter of last resort. Firstly I read manuals and now I am on forum if anyone could not help then definitely we will go for ABB.

Regards,

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#3
In reply to #2

Re: ACS850 VFD Reference Meet Problem

04/08/2017 7:10 AM

Dear,

Please check Parameter Group 20 LIMITS i-e 20.01 MAXIMUM SPEED & 20.02 MINIMUM SPEED.

Also share information / history whether it is newly commissioned drive or this situation happens from normal operation to this one.

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#4
In reply to #2

Re: ACS850 VFD Reference Meet Problem

04/08/2017 7:16 AM

Sounds like a parameter is off. I am not familiar with the ACS850 but I bought and installed an ACS550 last year and setup was a breeze, It has a start up and motor assistant and it programed itself.

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#5
In reply to #4

Re: ACS850 VFD Reference Meet Problem

04/08/2017 7:39 AM

Dear Aghvel Niazi,

I have already checked these settings. its ok. This problem came after 3 years of successful operation.

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#7
In reply to #2

Re: ACS850 VFD Reference Meet Problem

04/08/2017 2:00 PM

Wrong. If the manual is no help then definitely pick up the phone to the supplier next. Forums are a last resort, Matey.

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#8
In reply to #7

Re: ACS850 VFD Reference Meet Problem

04/08/2017 2:26 PM

Agreed, In my experience, ABB has a pretty good support system. We had to replace a VFD for our thermal oxidizer a couple years back, I was having issues setting the parameters for the 200hp motor, my robotics sales contact was an engineer on the drives previously and came out to my facility on a Saturday to help me dial it in, never charged us a dime.

I get invited and go to their Auburn Hills, MI facility every year for customer appreciation day. Impressive facility, free lunch, good engineering talks, great support, free swag, all because they want me to dump Fanuc and get ABB robots. Works for me.

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#17
In reply to #2

Re: ACS850 VFD Reference Meet Problem

04/10/2017 9:31 AM

I think you should first have contacted the OEM (ABB). A quick telephone call should have already resolved this issue.

As one other poster pointed out, refer the maximum and minimum speed section of the operating manual.

A problem that just now appears after three years suggests poor maintenance of the motor, the fan bearings, etc.

OEM will have the best advice and diagnostics in this situation.

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#6

Re: ACS850 VFD Reference Meet Problem

04/08/2017 12:10 PM

Are you sure, the PID has a sane(accurate) output to the drive and the drive receive the signal as expected? Might as well double-check.

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#9
In reply to #6

Re: ACS850 VFD Reference Meet Problem

04/09/2017 12:25 AM

Thanx Jpool & Gut Monarch,

I contacted the service manager of ABB. He said that change the limits of current. I talked to my manager, his stance is that drive is already taking rated current how can we increase its limits. He said that IGBT Voltages at the drive should be according to the 100 % set value = 100 % Reference. IGBT Voltages actual are 300 V in actual parameters while we are getting at the terminals of cables 370 V. Please help.

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#12
In reply to #9

Re: ACS850 VFD Reference Meet Problem

04/09/2017 5:25 AM

You should have ask ABB on this. Such a poor VFD without reliable faults diagnostics and after sales service.

There is a guy around here named Jraef and other EE specialist, he has some good experience on this matter.

Oh, I answer by common sense and sound principles in my mind(atleast that's how I thought about it/others may have different views than I have) It does not literally means I repair and diagnose VFD on site.

Most technical issues on a machine is not that complex and hard. You need a some scientific analysis and isolation of things. Though, it is really necessary to have a solid engineering foundation to make it a convenience. ----Just saying though

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#13
In reply to #9

Re: ACS850 VFD Reference Meet Problem

04/09/2017 1:05 PM

ABB has superb support - and unlike some of their competitors don't start by asking for a PO #.

You state it was working and now is not --- that means something has changed or broken.

-Using parameters verify reference is 100% - if not chase the analog input reference.

-fans are cube law on power - verify that you are not sitting against a current limit.

If you are on a current limit chase down why it has changed in power / torque requirement.

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#14
In reply to #13

Re: ACS850 VFD Reference Meet Problem

04/10/2017 12:25 AM

Thanx GW and ALL,

Now I explain you the whole perspective again. We have ID FAN, FD FAN, SPREADER FAN, MCW Pump and Cooling Tower Fan. All are ACS850 Drives. All of them are taking reference and achieving it except ID FAN. When reference is 100 % we see the reference on local control panel as 100 % but the other parameters are not changing accordingly. The current is maximum however according to the current-speed curve it should be less than maximum. The voltage at IGBTs as read on local control panel is 300 V whereas it should be 380 V according to reference. The frequency at the local control panel is 37 Hz whereas it should be 50 Hz according to reference. The RPM of motor is 750 on local control panel whereas it should be 992 rated according to reference. I hope that now someone may have an idea to solve this problem.

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#15
In reply to #14

Re: ACS850 VFD Reference Meet Problem

04/10/2017 1:20 AM

Have you verified the values for voltage and current with calibrated handheld devices?

Have you swapped the controllers to see if the problem moves (controller issue) or stays (fan issue)?

Or disappears (loose connection)?

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#16
In reply to #15

Re: ACS850 VFD Reference Meet Problem

04/10/2017 5:54 AM

Dear GM1964,

Please note that today we checked the voltages at terminal with new Fluke Digital multimeter and these are found to be 300 Volts instead of 370 Volts which were measured by old fluke digital multimeter. The frequency at the terminals was 37.43 Hz and the current measured at the terminals was 570A rated. It means that the reference at the local control panel is 100 % while at the terminals everything is according to 75% reference. Anyone have any idea about why the 25% less reference is calculated?

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#18
In reply to #14

Re: ACS850 VFD Reference Meet Problem

04/10/2017 11:21 AM

From your description you have hit a torque or current limit.

Look at the speed error parameter and the speed control output (torque).

Verify your limit group settings and compare to actual running values.

I have seen several fan installations where they take more power than anticipated. Fan curves are under given test conditions, once installed you have a different situation.

It can be from bad design, bad bearings, partial blockage in the discharge, or moving more volume than anticipated, gear ratios not correct, etc.

Temporarily open the torque / current limits and see if the speed goes up.

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#20
In reply to #14

Re: ACS850 VFD Reference Meet Problem

04/10/2017 3:27 PM

You said that the drive is at maximum current, but not maximum speed. You have discovered your problem, but now you must get to the root cause of the problem. That is actually a very common outcome of a problem, and in fact you already heard the answer but failed to understand it. I'll try again.

When you program a "Current Limit" into a VFD, that tells the VFD that you want to NEVER allow the current to go higher than that amount. But if you understand how VFDs function, you know that the ONLY WAY for a VFD to limit the current, is to limit the speed. So when the drive hits the current limit setting, it overrides your speed command and ceases to increase the speed, because an increase of speed would result in an increase in current, and you said "NO" in setting up that current limit setting. So in other words, the drive is doing EXACTLY what you have told it to do.

The root cause you must now find is WHY the current is suddenly so much higher than it was in the past. You can rule out that the drive or motor is under sized, because you said it WAS working correctly for 3 years. So obviously something has changed and you need to find out what that is. The buildup of dust and dirt on the fan blades was a good suggestion, you seemed to have tossed that aside without investigating first, I would not be so hasty. Another possibility is failing bearings, which is a known phenomenon on VFD driven loads when proper precautions are not taken.

The other distinct possibility is that when initially designed and commissioned, somebody cut corners on cost and either did not order an "inverter duty" motor, or failed to add an output filter to the VFD. So now after after 3 years operation, the motor winding insulation is failing in what is called a "turn-to-turn" short, where the insulation between turns on the same individual stator coils (not phase-to-phase) are shorting out, which decreases the magnetic strength but still pulls the same current, resulting in a loss of torque P.U of current. But instead of tripping the drive on over Load as it would, the drive responds to attempt to keep current under control by reducing speed.

The simple way to test this theory is to go into programming and DISABLE CURRENT LIMITING. Most likely that will result in an Over Load trip, as you would expect. If that is the case, then again, you need to find the CAUSE of the over load condition.

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#22
In reply to #20

Re: ACS850 VFD Reference Meet Problem

04/10/2017 4:24 PM

A lack of understanding is the beginning of failure to diagnose mechanical systems properly. I suspect they have used an improper motor for a cheap HF filter and do have winding to winding short (not phase to phase). The rest of this is just sweeping up the dust and chips.

A new shipment is in their future. I see it in the cards.

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#26
In reply to #14

Re: ACS850 VFD Reference Meet Problem

04/12/2017 1:00 PM

Sounds like it is in current limit, it is common (especially for newer PWM drives) to reduce frequency to control load. There is (usually) a bit set that tells you the speed regulator status, output clamped due to high load.

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#27
In reply to #26

Re: ACS850 VFD Reference Meet Problem

04/12/2017 2:42 PM

So how did that bit get changed? Lightning?

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#21
In reply to #9

Re: ACS850 VFD Reference Meet Problem

04/10/2017 3:30 PM

Check that you have the correct number of poles selected for the motor, 750 rpm indicates an 8 pole motor, but you seem to be operating a 6 pole motor.

6 pole = 1000 rpm, 8 pole = 750 rpm

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#23
In reply to #21

Re: ACS850 VFD Reference Meet Problem

04/10/2017 4:25 PM

How did they change configuration of the motor from three years ago? Where did you get the number of poles?

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#28
In reply to #23

Re: ACS850 VFD Reference Meet Problem

04/12/2017 4:12 PM

Some drives are configured with number of motor poles, not everyone realizes that makes a big difference to the sensorless vector model, if the drive parameters have a slot for it. The typical default of 4 poles covers most applications, so many can go years without realizing the drive is programmed wrong, until it can't reach torque or speed ratings....

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#19
In reply to #6

Re: ACS850 VFD Reference Meet Problem

04/10/2017 11:37 AM

How do you know they are using PID control scheme. It could a simple control band scheme with multiple bands.

Assumptions, assumptions, assumptions.

Something changed, or someone has intentionally or inadvertently changed the control parameters. They need some real engineers to look at output mechanical power available to do the job at hand, compared to the input electrical power, and see what went wrong.

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#10

Re: ACS850 VFD Reference Meet Problem

04/09/2017 1:57 AM

Can we assume the fan has been checked for problems?

Any filters which may be getting blocked, dirt accumulation on blades or obstruction near fan inlet/outlet.

damaged wiring or loosening connections - does not need to be loose enough to move to restrict power to the fan motor. Bearing worn or dry.....

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#11
In reply to #10

Re: ACS850 VFD Reference Meet Problem

04/09/2017 2:34 AM

Dear GM1964,

I have discussed this matter with operations staff, they outrightly rejected the deposits or dust formation on fan blades as there is 135 degrees celsius in ID Fan duct and before it the fly ash arresters catch by cyclone the maxium dust particles. Also, we cannot check it in running plant visually but in upcoming shutdown.

Regards,

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#24

Re: ACS850 VFD Reference Meet Problem

04/12/2017 6:31 AM

Hello,

Steps to follow

1. Please check if you drive is receiving full PID input (20mA if 4-20)

2. Please check maximum and minimum speed of the drive

3. Give me your salary.

Thanks

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#25
In reply to #24

Re: ACS850 VFD Reference Meet Problem

04/12/2017 10:06 AM

Just like an AP to be all greedy and needy!

Where's the cut for the rest of us?

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Users who posted comments:

AA039 (6); Aghvel Niazi (1); Anonymous Poster (1); Crabtree (1); GM1964 (2); gutmonarch (2); GW (2); James Stewart (6); JPool (3); JRaef (1); rwilliams (3)

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