ABB ACS800 drive on 3 motor temperature measurement. 1

[martinrelayer]

Hello,

we have 3 motor connected in parallel fed by the same variable speed drive, an ABB ACS800, each motor has 3xpt100.
From parameters, i can only configure 2 motor supervision, i wonder if someone has any idea how to include 3 motor protection either by DriveAP and trip the vsd or sending the 3 temperature to a DCS on fieldbus and controlling there.

regards,
Martin

 

[jraef]

Get a separate RTD monitor and let it provide a trip signal to the VFD.
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[niallnz]

The ACS800 has three analog inputs. As long as you are not using the one of them as your speed reference you could connect PT100's from one of you motors to the spare input and use the DriveAp to do a compare of the measured voltage drop across the PT100's.

You will have to do some calculations from the standard PT100 curve to come up with the voltage that will be the motor trip temperature you want. For this application there are enough DriveAp blocks available that you can convert a temperature setpoint into a voltage to use in the comparison.

Question though, are you sure they are PT100's and not thermistors? (PTC), the above will still work with PTC's but the resistance to temperature relation isn't linear.

Have fun.

 

[martinrelayer]

Hi niallnz,

Good to use voltage levels for warning and trip, and yes, we have 3xPt100.
I was looking and theres no voltage-to-temperature block to send temperature data to fieldbus. I think we can calculate, don't know how reliable this would be.
The next weeks we'll be into this and i'll post what we have done.
thanks!

 

[niallnz]

Hi Martinrelayer

I thought about it over the weekend and what I'm suggesting won't work as you need a constant current source to supply the PT100's. The ACS800 uses an analog output as a constant current source and then reads the voltage required to drive the current through the variable resistor (PT100).

Note that in the ACS800 manual it states that you can only protect two motors if you use the optional analog extension module, hope you've got that. If you haven't then it is going to be easier to do as jraef suggested and use RTD monitor relays to trip the drive. You can configuer one digital input as an external fault, or if you like to play with DriveAp you can program up faults that display a custom meassage.

If you still want to play with DriveAp then you can use an RTD to 4-20mA convertor to provide a temperature signal into the drive analog input.

Sorry for the mis-information.
Cheers Niallnz

 

[martinrelayer]

Niallnz,

Yes we have one analog i/o extension in one AIMA and other in Slot 2 (not in use... some guy connected the third motor rtd there and left).
But can't we set a current output as a constant? using pointer parameter 15.11 or 15.12? I don't remember the current output for 3xPt100... I think is 9,1mA for 1xPt100 but I don't remember for three, have to check.
Also I don't know what can happen if you set a constant current output and the connected circuit opens.
I'll try no to use separate temperature relay because then I have to deal with project management office and modify circuit drawings and other administrative tasks that will involve many people... if there's a possibility, i'll make this way.

 

[niallnz]

I think you should be able to set a constant current using a pointer. PT100 resistance at 130DegC is about 150 ohms. So 3xPT100 I think you'll have to set the current at 20mA, which will give 9V on the analog input. A simple y=mx+c conversion can be programmed in DriveAp to calculate the temperature in Degrees C, remerbering the drive uses integers. So assuming 20mA, the drive reads 9V on the analog input as 9000. For 3xPT100, C=6000 (6V) and m=23.1 but have to use 23.

If the PT100 goes open circuit it won't harm the drive analog output. The anlog input may measure voltage of the analog output and interpret it as high temperature.

Have a look at the attached DriveAp screen shot. I've set up AI1 as the 3xPT100 measure (Par 1.18) and I've used the user constants 85.01 for fault temperature (130 DegC), 85.02 for alarm temp (120 DegC) and 85.03 (10DegC) is the hysteresis on both fault and alarm setpoints.

Cheers Niallnz