NEED HELP WITH VFD/MOTOR

[bure961]

I could use some help with Altivar 61 vfd rated for/using 75 hp motor. There are 4 units operating at different times each having a 75 hp motor/pump, 3 of the 4 run at a cool temperature about 80f but one is running much hotter about 150f I am told. When it was checked it was running at 45 hz. drawing 45amps. 380 volts on output of drive. Drive is rated for 380 - 480volts. Temp readings done by operator using cheap point and shoot hand held gun type tool.

Each pump / motor has a coolant or antifreeze inside . All were checked and contained the coolant. Amp readings were almost identical when running at the same speed. Motor was never megged . And I am told never tripped out after operating for over 24 hrs. or more .


Does anyone have an idea what could be causing the difference in temp ? All setups are less then a 1.5 yr old. All run at different times. Running times change for each motor. When problem motor is running it takes a few hours of operation before it gets hot. Checked for restriction of flow, found none if this helps. Thanks for anyone with help.

 

[topgone]

I could use some help with Altivar 61 vfd rated for/using 75 hp motor. There are 4 units operating at different times each having a 75 hp motor/pump, 3 of the 4 run at a cool temperature about 80f but one is running much hotter about 150f I am told. When it was checked it was running at 45 hz. drawing 45amps. 380 volts on output of drive. Drive is rated for 380 - 480volts. Temp readings done by operator using cheap point and shoot hand held gun type tool.

Each pump / motor has a coolant or antifreeze inside . All were checked and contained the coolant. Amp readings were almost identical when running at the same speed. Motor was never megged . And I am told never tripped out after operating for over 24 hrs. or more .


Does anyone have an idea what could be causing the difference in temp ? All setups are less then a 1.5 yr old. All run at different times. Running times change for each motor. When problem motor is running it takes a few hours of operation before it gets hot. Checked for restriction of flow, found none if this helps. Thanks for anyone with help.

Did you checked the motor connections? Most motors are wired to run on delta. An inadvertent connection in wye will make the motor run at lower speed and at lower discharge. The motor windings will get 57% of its rated voltage hence a bigger slip. Please check the individual flows if available and compare. Better still, compared the speeds.

 

[bure961]

TOP, Speeds and amp readings were compared and there was not much difference to each other. Operator said flow was good, I will check but I do believe these are delta motors . All are in same ambient area.

 

[Phil Corso]

Bure...

What are the the three line-currents and phase-phase voltages?

Regards, Phil Corso

 

[bure961]

Phil , As best as I remember it was @45 hz pulling 45amp and 380 volts.
There could be fractional numbers added on one of them . These are the readings I remember.

Thanks in advance.

 

[Phil Corso]

Bure...

Line-current imbalance is a major cause of motor overheating. In fact, by Rule-of-Thumb temp-rise due to current-imbalance is proportional to twice the square of %V-imbalance

How was the 70-deg delta-T you cited, determined? By motor-carcass temp measurement or by the coolant's In / Out delta-T?

Can you at least provide the complete Nameplate rating?
Phil

 

[bure961]

Phil, thanks for your help. Motor temp was determine by a cheap non contact thermo gun shooting at the motor frame while running . Will not be able to get name plate data till Monday night.

 

[big john]

Can you expand more on how the coolant system works? That would seen like the logical place to start if you'reoverheating.

Otherwide put the motors under the same load conditions and verify current and frequency on each to be sure you aren't seeing a problem caused by the driven load.

Figure out your % voltage and current imbalnce on the hot motor and compare that to your cold motors.

Just a thought but also check to see if all drives are running the same switching frequency.

If all that checks out then do a vibration analysis because a failing bearing can cause wicked overheating.

 

[Jraef]

Big john's last two comments were where my mind went right away. People sometimes mess with the carrier /switching frequency because increasing it reduces the noise the motor makes from running on PWM. But the consequence is increased losses, which many people are unaware of. The earrings may be experiencing EDM damage as well, as other well known phenomenon. It causes "fluting" of the bearing races, a roughening of the surface that looks like a washboard. That increases friction and right before it fails the bearings get very very hot. That heat will tranfer to the motor case.

 

[Phil Corso]

Come on fellas... bearings?

I agree one or even both bearing could be hot... but we're talking about a 1,000 lb machine whose carcass temperature-rise is indicative of full-load... operating at less than 1/2 of name-plate current... and liquid cooled. The bearings would be screaming!

Bure... Point the thermal gun at the bearing housing!

Phil

 

[Phil Corso]

Bure...

Last question... was the troublesome machine always troublesome?

Phil

 

[bure961]

Phil, When talking to the operator the problem started a few days ago. All suggestions given here will be look into Monday afternoon / night . Right now the motor/pump is locked out till then. Again thanks to all for your input it is very helpful.

 

[bure961]

Just remembered something else the operator said was he checked the level of the coolant and the problem one had more coolant and filled to top would this need room for expansion and cause higher temp. That's all I remember with his conversation.

 

[Besoeker]

If the motors are all the same rating and performing the same duty, might I suggest swapping two of the motors?

 

[iwire]

If the motors are all the same rating and performing the same duty, might I suggest swapping two of the motors?

:thumbsup:

I am a huge fan of doing that kind of straight forward troubleshooting.

Quickly learn if it is the supply or the motor and driven load.

 

[kwired]

:thumbsup:

I am a huge fan of doing that kind of straight forward troubleshooting.

Quickly learn if it is the supply or the motor and driven load.

So am I, but when it comes to something driven by a 75 hp motor chances are it is not something you will swap in just a hour so instead you gather a lot of information and study it before making the next move.

 

[iwire]

but when it comes to something driven by a 75 hp motor chances are it is not something you will swap in just a hour

Could be quick or it could be long, really depends on the specifics does it not?


So many factors involved but typically a 75 HP motor is an essential part of a facility so the cost of it going down unscheduled is a big factor.


Considering this facility is doing preemptive testing I assume unscheduled downtime is unacceptable.

 

[kwired]

Could be quick or it could be long, really depends on the specifics does it not?


So many factors involved but typically a 75 HP motor is an essential part of a facility so the cost of it going down unscheduled is a big factor.


Considering this facility is doing preemptive testing I assume unscheduled downtime is unacceptable.

Correct, I myself may swap drives around before swapping motors - seems like it would be less labor intensive, and those motors are never on grade level with easy access for simple material handling equipment. The drives may all be in same control room - maybe even an air conditioned room:thumbsup:, one may not even need to move drives just re-route conductors.

It just could be some drive setting is different on that one unit that went unnoticed. Then again it still may be like Jraef said and the carrier frequency caused a bearing issue. The same bearing is still bad and switching drives will not cause any immediate noticeable change - problem was not really solved and will come back later after it has a chance to work on a new bearing.

 

[big john]

Just remembered something else the operator said was he checked the level of the coolant and the problem one had more coolant and filled to top would this need room for expansion and cause higher temp. That's all I remember with his conversation.

I've seen motors that had pipes and heat sinks for liquid cooling but nothing where you were filling anything on the motor housing... Does this havecirculator pumps? Fans? How does it work?

You've got an unusual system to remove heat on an overheating motor. Big red flag.

 

[bure961]

I went in early today and was told that the pump/motor was still under a warranty. I finally got the ok to compare the problem motor to a unit running since Friday morning. Both were setup to run at 48 hz. each had 400 v and pulling 48.2amps. No way to check flow rates. Both ran for5 min. The problem motor had a 120f temp. the other motor which was running all weekend had a 80 f temp.
Department manager had unit lockout again and place a call for service , he does not want warranty void by opening up and inspecting/ checking. I agree get someone with expierence, I'll find out when he is coming and be there to get some tips if I can.

For those who ask ...
I was off on original spec.
Less than 1yr old.
460 volts, 3phase delta, 69 hp , In 86.3, [ not sure what In means], 1190 rpm, 4300 gpm, Ta 40 c , This is a sump pump in a dry well. Coolant has a fill plug about 6" from top motor housing. Don' what or how coolant works as far as circulating.

Manager does not want unit switch to other vfd for comparison.
Thanks again for everyones help.