Overload tripping

[edexlab]

At work there has been a problem I've been told about, small 1.8 Kw 3 phase fans tripping the overloads

I'm not really involved in this but I am interested......
The fans are run off Inverters and the OL's for any circuit are usually within the control panels, length of run is upto 35 metres max in SY screened at both ends for the motor and separate cables for monitoring the OL's on 24v ,cable screen at panel end, these are often within the same tray.

Generally they set the OL's to flc plus 10% as a maximum, and occasionally they have this tripping problem and they move the OL's to a new position closer to the fans as requested by the Engineer
I asked what the problem was and was vaguely told its a harmonic thing something to do with frequency,
(this did surprise me as I thought OL's are basically bimetallic strips)

And would moving the OL's nearer solve this issue?

I've looked this up and found nothing so far ???
Can anyone explain this in a bit more detail please

 

[edexlab]

I've just been reading up on harmonics as its something I've heard about before but knew virtually nothing about

So from what I've read it appears to me that part of the problem here is the inductive heating which would cause an overload to trip

So my question still remains

"Would moving the position of the OL's closer to the motor help"

And if so, is this because the harmonic effects increase over distance, and by reducing the distance to the load to a device like an overload, you can minimise the effects?

 

[Marvo]

....The fans are run off Inverters and the OL's for any circuit are usually within the control panels,

Why don't they set up the inverter drives to perform the overload protection?

What types of fans are they and what's their application?

What type of overloads are they using?

It would be nice to have details of the overloads as well as the invertors. It could be a harmonics issue but it could be that the overload devices they're using aren't compatible with the carrier frequency and waveform from an inverter drive especially if it doesn't have comprehensive filtering stages.

I doubt relocating the overloads closer to the motor will have much effect.

 

[edexlab]

As I stated I don't know too much about this subject but the main reason for the question was that it seemed to me to be unlikely that this would solve the problem , more a case of limitation
One of the tech guys said the same re setting the inverter to provide overload protection, but this company has its own doctrine and although they are using new inverters which could replace the software they use to control the systems they are a bit resistant to new ideas.
The fans are used for cooling as part of an environmental system controlling how quickly the end product is dried
I'll try and get more info on the components the inverters are made by emerson and OL's are schneider

 

[Marvo]

Using the drive to provide overload protection isn't what I'd call a new idea.

If they're using a standard thermal type overload or manual motor starter unit it's probably a compatibility issue with the inverter output. Even using a thermistor on the motor windings (if there is one) would be fine for motor protection. The devil is really in the details, without a complete outline of the set up and the components involved it's just a guessing game.

 

[Knobhead]

Fitting O/L’s to a VSD is totally pointless and depending on what the O/L switches it could possibly damage the VSD. Set up correctly the VSD will protect itself and the motor far better than an O/L unit.

Just to add thermal O/L’s should be set to 100%.

 

[Darkwood]

Only time I fit separate O/L's is if the drive runs more than one motor ... do these drives run multiple motors or dedicated motors?

As above if the latter.... pointless practice when the drive is designed to do this, and your Tech guys need to drop there title to domestic Electrician then maybe they would know what they were doing. Like Marvo says ...The devil is in the detail... we could be missing vital info but from what we have been supplied it sounds like your tech guys are just fobbing you off with big technical words.

Yes its best practice to have your drive as close to the motor as possible but not always an option, the drive will give a max distance to motor in its installation guide before additional steps need to be taken like line reactors etc...

 

[edexlab]

Spoke to the engineer this morning who fobbed me off ,
I don't think he knows really ,
I also spoke to the tech guy who said the same as you gents re using the Vsd rather than O/L's and he said he knew the O/L's were not really compatible but this was an issue the Engineer specifying wouldn't change his mind on , so it seems the tech guy knows his stuff but the designer needs educating a little

In this instance it us single motors but they do have systems with multiple motors run from a vsd

Thanks for the answers its given me something to read up on