Fan motors in series VSD problems

[frankv1]

Hi

We have a problem with Lenze 18kw vsd model ESV183N04TXB suffering output module failure.
The system is composed of two 15kw fans installed in series and each has an 18kw inverter controlling it.
These fans always work toghether.
Normal running operation is at 35Hz when CO sensors reach a certain level and 50Hz when there is a signal from the fire alarm.
Can you please advise if operating fans in series in this way can have any adverse effect on the vsd

Frank

 

[waross]

I have to assume that you mean in series mechanically.
First check the pressure drop across each fan.
Such an arrangement may be causing one fan to be overloaded.
Does the inverter on the same fan fail every time?
Do the inverters fail at 35 Hz or at 50 Hz or both?
The fans may be overloaded at 50 Hz.

And are the VFD outputs suitably filtered for the installation?
The greater the distance between the VFDs and the motors, the more important filters become.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[LionelHutz]

Does one fan drive the other at times and cause the bus voltage to rise on the driven one?

 

[waross]

I have used water pumps in series and it worked well.
For fans, the compressibility of air adds complications.
The second fan may be moving more dense air than the first fan and may be overloading.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[FacEngrPE]

If these are propeller fans in series, the pressure rise is low (free air to a few inches wc), and the air behaves incomprehensibly.
In order to make propeller fans in series work, straightening vanes are requires between the fans, then the drives need to be tuned to indicate equal power input to each fan. The tuning is probably sensitive to minor mechanical differences in the fans.

If your pressure ratio makes the air behave comprehensibly, the engineering gets more complicated for reason cited by waross. You may still get some mileage out of adjusting the drives so that they apply equal power to the two fans.

 

[LittleInch]

This seems to be two separate fans with the output of one feeding into the other.

Without further details it's impossible to comment further.

"Fans" could be anything.
15kW is pretty big so pressure or flow could be significant.

What exactly is " output module failure"??

The power difference between 35 htz and 50 htz is double.

So provide some more info and we might be able to figure this out.
No idea about performance or how the two are actually coupled together.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[jraef]

If one fan is moving more air than the other, then the 2nd fan will run in a constant state of regeneration, eventually resulting in voltage stress on the DC bus.


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