VFD Fault alarms at low speed

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Rob2025

Member
Location
Toronto, Canada
Occupation
Electrician
I am currently working on the issue of Vacon NXS series VFD giving fault signal (NC contact changes status to NO). The motor is running at 20Hz fixed speed. However this happens especially in Summer time when the room temp goes above 25 C
There is no fault alarm in winter time.

Wirings on Vacon drive:
  1. 3-phase power connections L1, L2, L3
  2. Motor connection U, V, W
  3. Drive enable in forward direction
  4. Speed control potentiometer
There is no external Temp sensor connected nor Motor has any overheat temp sensor.

I don’t know why the NC contact changes to NO giving fault alarm
Anyone got experience on VACON drives on faults like above?
Also how to program NXS Vacon drive etc.

Any thoughts, recommendations highly appreciated.

Let me know if any further information is needed.

Thanks
 
ptonsparky said:
NM. That doesn't appear to be an option, at least in the time I allowed to read the fine manual.
Click to expand...
Ok, I should have explained the fault in a correct way. Let me rewrite this. There is no actual fault alarm but what happens is the NC contact changes to NO opening the safety link and the safety relay turns off the output causing the machine to stop.
 
Rob2025 said:
Ok, I should have explained the fault in a correct way. Let me rewrite this. There is no actual fault alarm but what happens is the NC contact changes to NO opening the safety link and the safety relay turns off the output causing the machine to stop.
Click to expand...
Do you need to reset the drive?
The drive does keep a fault history, look at it.
Are you sure it's the relay changing state?
 
No, I am not required to Reset the drive. In fault condition, the NC contact changes to NO and then again goes back to NC .I just reset the Safety relay. and the motor starts running again.
Yes, the Relay (NC contact) inside the Drive changes it's state momentarily.
 
Is this a fault relay only or a relay that is programmable to specified conditions?

Either can possibly be set for automatic reset once the condition/certain conditions clears itself.

If not a physical issue with the relay itself or wiring connections a look at set parameters, maybe fault history will help point you in right direction.
 
Install a line reactor pre-drive. This will reduce the heat on the bus and might solve the issue. Send me the nameplate motor data and drive amp data and I can help you size it.
 
Looks as though the basic I/O board has only an open collector output (i.e. not a "relay" per se), and then you can add option bords to get more relay outputs. You have to PROGRAM what those relay outputs do, so which relay is being used and what it is programmed for? Might not show up as a "fault" because it is not PROGRAMMED as a fault relay. It might be something like a "minimum speed" relay that closes when the speed is above 20Hz, so it opens when it is BELOW 20Hz. In other words, it might be doing EXACTLY what it is told to do. That wouldn't explain why it doesn't happen in winter, but maybe in winter it never goes below 20Hz? We don't know.

But also, if this is on OptA3, relay 2 at terminals 25 and 26, and there is something else wired to terminals 28 and 29, that is a THERMISTOR, which is a temperature sensing device, I think operating that relay at 25/26. Thermistors are used in IEC motors as a form of motor overload. But I would expect that to show up as a Fault if that was tripping the relay.

Honestly though, I devoted a few (too many) minutes to this and I could not find ANY information on how the programming of the relay functions are done or how to read it, so good luck with that...
 
Rob2025 said:
Ok, I should have explained the fault in a correct way. Let me rewrite this. There is no actual fault alarm but what happens is the NC contact changes to NO opening the safety link and the safety relay turns off the output causing the machine to stop.
Click to expand...
A few comments.

In most cases, vfds have a fault history you can look at.

Is it possible the relay is not actually programmed as a fault relay? Usually they can be programmed to be multiple things.

Most times faults trip the drive and you have to reset it. If you are not having to reset the drive, I am suspicious that it is not actually faulting.

How do you know the contact is actually switching states? Could be something else going on like a loose wire or something else in the e stop circuit is actually what is opening up.
 
petersonra said:
A few comments.

In most cases, vfds have a fault history you can look at.

Is it possible the relay is not actually programmed as a fault relay? Usually they can be programmed to be multiple things.

Most times faults trip the drive and you have to reset it. If you are not having to reset the drive, I am suspicious that it is not actually faulting.

How do you know the contact is actually switching states? Could be something else going on like a loose wire or something else in the e stop circuit is actually what is opening up.
Click to expand...

I confirmed all the wires of E-Stop circuit are good and no loose connections there.
Then for test purpose I bypassed all other NC contacts & left with the only NC of the VFD. The safety relay tripped again. That’s how I arrived to the conclusion, it’s only the NC contact of VFD momentarily changing to NO.


Sent from my iPhone using Tapatalk
 
kwired said:
Is this a fault relay only or a relay that is programmable to specified conditions?

Either can possibly be set for automatic reset once the condition/certain conditions clears itself.

If not a physical issue with the relay itself or wiring connections a look at set parameters, maybe fault history will help point you in right direction.
Click to expand...
The NC contacts are inside the drive (Pin# 25, 26). I am trying to find which one of the schematics applies to this one as
  • Control I/O Basic specifies them as Relay Output 2 Fault
  • Control I/O Local/Remote specifies them as Relay Output 2 Fault programmable (P2.3.9)
  • Control IO Fan and Pump Application Relay Output 2 Aux/Autochange 2 Programmable (G2.3.1)
See below from the manaul:

Control IO Basic Application.png


Control IO Local-Remote Application.png


Control IO Fan and Pump Application.png
I don't know under what condition the NC changes to NO momentarily.
 
Jraef said:
Looks as though the basic I/O board has only an open collector output (i.e. not a "relay" per se), and then you can add option bords to get more relay outputs. You have to PROGRAM what those relay outputs do, so which relay is being used and what it is programmed for? Might not show up as a "fault" because it is not PROGRAMMED as a fault relay. It might be something like a "minimum speed" relay that closes when the speed is above 20Hz, so it opens when it is BELOW 20Hz. In other words, it might be doing EXACTLY what it is told to do. That wouldn't explain why it doesn't happen in winter, but maybe in winter it never goes below 20Hz? We don't know.

But also, if this is on OptA3, relay 2 at terminals 25 and 26, and there is something else wired to terminals 28 and 29, that is a THERMISTOR, which is a temperature sensing device, I think operating that relay at 25/26. Thermistors are used in IEC motors as a form of motor overload. But I would expect that to show up as a Fault if that was tripping the relay.

Honestly though, I devoted a few (too many) minutes to this and I could not find ANY information on how the programming of the relay functions are done or how to read it, so good luck with that...
Click to expand...

Thanks Jraef

Apart from Power input L1, L2, L3 and power to the motor inputs U, V, W, only following Terminals are used on the existing drives.
  1. 1, 2, 3 - Speed control 10K potentiometer, Speed range adjustable: 3-15m/min
  2. 11 (CMA) & 17 (CMB) are connected to 13 (Ground)
  3. 6 (+24Vdc) and 8 (Forward Start) - NO contact to start the motor in forward direction
  4. 25 & 26 part of the E-stop link
Terminal# 28 & 29 are not used.
There is no Reset available for the drive.

Further, I got some more info on the Speed & Hz values

Min Frequency 12.50 Hz (3 m/min)
Max Frequency 62.10 Hz (15 m/min)
 
Rob2025 said:
Thanks Jraef

Apart from Power input L1, L2, L3 and power to the motor inputs U, V, W, only following Terminals are used on the existing drives.
  1. 1, 2, 3 - Speed control 10K potentiometer, Speed range adjustable: 3-15m/min
  2. 11 (CMA) & 17 (CMB) are connected to 13 (Ground)
  3. 6 (+24Vdc) and 8 (Forward Start) - NO contact to start the motor in forward direction
  4. 25 & 26 part of the E-stop link
Terminal# 28 & 29 are not used.
There is no Reset available for the drive.

Further, I got some more info on the Speed & Hz values

Min Frequency 12.50 Hz (3 m/min)
Max Frequency 62.10 Hz (15 m/min)
Click to expand...
Well, YOU said the “NC contact changes status to NO”, so SOMETHING is programmed to do that. I was just speculation as to what that might be. You really need to call your Vacon supplier and get their help.
 
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