Damp In 3 Phase Motor

[binky]

If a 3 phase motor mounted externally is getting damp in it, but not enough to short it out completely, would it exhibit any symptoms, such running at a higher current, spinning slower, or not sucking as hard (motor used for extraction fan).

 

[roys]

If the motor is running it is unusual for dampness to creep in due to the heat generated by the windings, problems happen when a motor is of for a while or it is more than just dampness getting drawn in.  Never seen performance etc. dropping off due to dampness usually if the insulation breaks down then the protection will operate be that the fuses, overloads or an earth fault relay if fitted and the motor will no longer go round and round.

 

[Evans Electric]

May be a mechanical problem slowing it down ,  pulley belts, rust, bearings .

Arcing somewhere causing a phase to drop n and out .

What tests have you done ?

Does the motor spin free without the mecanical load ? 

Is my dinder ready ? 

 

[binky]

Mmm interesting. We fitted a Mitsuibishi VSD in line with motor to reduce running costs. VSD was specced by Mitsuibishi - we were fitting for 3rd party. Anyway, having converted from star- delta to delta ( helped by Canoe boy)  we duely left motor running and went home. We had a few other VSDs to fit and have been back over several saturdays to complete works. This particular motor though seems to have to responded by not sucking as hard as it used too, and drawing more current than before (I have since discovered that upping frequency also ups current drawn in non-linear way). Now I strongly suspect lack of filter maintenance is actual cause of poor suction, but according to the senior bloke that works there it is down quite a bit, as shown by guage on filters. Anyway, to cut long story short I was accussed of not having re-sealed motor terminal cover properly allowing water ingress. The fact that for the previuos 5 years a 30mm dia cable had been shoved through a 40mm dia hole seems to have escaped their attention, along with the fact that I had taken some time and trouble to resolve said gaping holes. Fortunately I had photo of terminals, all nice and rusty and with small puddle in one corner. But I'm still curious as to why motor appears to run badly driven by VSD (pretty sure I have set it up correctly after taking advice from ex-Mitsuibishi service engineer and serious manual reading) and was wondering whether damp / water ingress had anything to do with this???

 

[revjames]

I seem to remember from my quarrying days that all circuits had to be tested every 6 months and there was a certain motor that was hardly ever used and as a result IR readings were always low - like 100K ohms. I looked into possible solutions other than actually leaving it running for an hr or 2 every week. I understood at the time there was a way of running a small current through the motor which acted as a rudimentary type of heater which in turn would keep the IR up. Never got round to changing anything, just made sure the conveyor got a run once a week.

would have thought with a VSD there would be a way of employing this by for example periodically applying dynamic braking current to the motor?

 

[poni]

is it running the correct way?, it may still draw, but only about 60% of its suction

 

[batty]

As Poni says is it definitely running the right way. I had this recently with the star delta motor on an extractor it was sucking  but as it was going the wrong way suction was down quite a bit.

 

[OnOff]

Very rough this but you'll find that if the motor has been sitting around in the damp for a while, when then an IR test is carried it out the insulation resistance will gradually creep upwards as the "megger" "dries" it out.

 

[binky]

is it running the correct way?, it may still draw, but only about 60% of its suction

interesting point as this sounds about right. It's down from 120 on the guage to 70

 

[poni]

It’s probably not the damp as the VSD would show a fault code of this, the VSD would also look at the current for the Hz(speed) and torque,



you say that you have gone from star-delta to DOL, are the links all good, again the VSD should pick this up

The most likely fault if you(or anyone else) have not altered the original set up,is the VSD and the fan rotation

(not that it makes any difference but why did you need to open the terminal box of the motor anyway? all the connections would have been at old contactor )

 

[binky]

opened it up as easiest way of wiring inverter in-line with motor - took out star start-up as start-up is controlled by VSD

You didnt say it was on an Inverter !!!

does it make a difference?

 

[OnOff]

Don't forget that some VSD's need to be set up using  laptop and the proper software rather than the "simple" plug in keypad or buttons on the front (of the inverter)  in that they are limited as to what parameters you can set / change. 

 

[binky]

well aware of that, but as 99% of the available parameters were un-used in this instance, laptops were not necessary

 

[OnOff]

well aware of that, but as 99% of the available parameters were un-used in this instance, laptops were not necessary

From my (bitter?) experience: Years ago we used to import kit from abroad. (Access equipment). They used SEW inverters with Bonfiglioli motors at the start. The motors were dying left right and centre and we'd replace with SEW.

A while down the line I had a job where there were 2 bits of kit installed some months apart. The first piece of kit went in and the users said it was the best winch they had ever used (it was quick which meant they could do their job faster). Some months later I fitted the second system and they started complaining that it was far slower than the first system. I went through every parameter I could access on the inverter itself and they all matched. 

I ended up calling SEW. The guy said to connect my laptop, run Movitools and give him a call back. I said "Eh? What are you on about etc?". It was my introduction to the setting up of motors. Turns out that the makers themselves only ever set up the drives and motors using the plug in keypad on the drives.  I had to tell them that they should be using Movitools. On that "best winch they had ever used" the motor burnout where it was a 2-pole motor but the inverter was set for 4-pole (or vise versa, can't remember). This was not accounted for as the only way to match them was by laptop/software. It was never / could never have been seen by just the inverter controls without the computer!

At least with drives and motors from the same maker you tell the drive what motor it's running from a list and the bulk of parameters will be preset - you just then tweak it. If using a different motor you have to set up a lot of the parameters manually.

 

[Marvo]

I think you're in the clear as far as moisture goes, you could do a quick IR test to confirm if you need to convince the customer. The blocked filter theory is also easy to confirm, if you remove a filter or two and it has little effect on the run current or air volume then it's not the problem. My first thought was reverse rotation but also might be worth checking for mechanical obstructions such as a partially closed fire damper or a VDU that's got stuck. The high running current might point to incorrect drive setup.

How high is the run current and how much higher is it now compared to what it was?

What type of fan is it? (FC/BC centrif, axial, mixed flow...)

 

[roys]

Since there has been a fair bit of work done on this circuit, could it be running only in star instead of Delta?  Not sure on your inverter connections so I could be talking rubbish, just thinking out load.

 

[batty]

It has been converted from star delta to delta not sure how as I don't get to involved with motors.

 

[binky]

Since there has been a fair bit of work done on this circuit, could it be running only in star instead of Delta?  Not sure on your inverter connections so I could be talking rubbish, just thinking out load.

defo not - been checked several times

It has been converted from star delta to delta not sure how as I don't get to involved with motors.

yep - motors run more efficiently in Delta, but in-rush current is roughly 6 times higher than running current, so Star is used to get motor running, then timed relay cuts in to convert to Delta after say 20 seconds

I think you're in the clear as far as moisture goes, you could do a quick IR test to confirm if you need to convince the customer. The blocked filter theory is also easy to confirm, if you remove a filter or two and it has little effect on the run current or air volume then it's not the problem. My first thought was reverse rotation but also might be worth checking for mechanical obstructions such as a partially closed fire damper or a VDU that's got stuck. The high running current might point to incorrect drive setup.

How high is the run current and how much higher is it now compared to what it was?

What type of fan is it? (FC/BC centrif, axial, mixed flow...)

maintenance team are saying IR is down to 0.25 M Ohm and have taken motor indoors to dry out - hence trying to blame me!! Current draw is up according to them also, but I'm not sure what that is based on. Reverse rotation still gets my vote, as this happened on one of the other motors, not sure how, but then original installation was a lash-up.

 

[NozSpark]

Is there a chance that since the alterations that the motor is just not getting up to speed?

 

[Technician]

Many years ago I had a conversation witth a senior electrical inspector with

an insurance company about TEFC (Totally Enclosed Fan Cooled) motors.

It was thought that the "damp" problem would be solved by this design.

Not so.  Seems that when opened up, damp had been present at some time

in the past.  Corrosion pools in the end covers etc.  At the time, no-one could

explain it.