×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

variable torque VFD - IGBT over temperature problem

variable torque VFD - IGBT over temperature problem

variable torque VFD - IGBT over temperature problem

(OP)
Hi everyone,

I have an issue on 200 HP variable torque VFD driving a 250 HP fan. the issue is the phase B IGBT inverter that goes to overtemperature that causes a VFD tripping. at the beginning we thought the VFD was faulty then we replaced with a new one. the same problem appeared in the second one. so now we think we are getting this problem from the motor. could you please guide me what procedures should we follow to solve this issue?. by the way, we are getting an RPM metter to perform a power quality analysis.

Thank you for inputs

RE: variable torque VFD - IGBT over temperature problem

Phase "B" in likely in the center.  It is likely then, the hottest running one.  You are not allowing it to cool enough, or the VFD's ambient is too high.  How, and where is the VFD mounted?

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: variable torque VFD - IGBT over temperature problem

Hello mohpower

I assume that you have ensured that the drive is operating within its current ratings and ambient temperature ratings.

Over temperature can be caused by a number of things, the first is in adequate cooling. If you have the VFD mounted inside an enclosure, you need to ensure that there is sufficient airflow through the enclosure or the temperature within the enclosure will get too high and there will be inadequate cooling.

Another cause of over temperature, is excessive losses in the VFD and these are usually: excess current, excess cable capacitance or too high a switching frequency.
Ensure that the length of screened cable is within the manufacturers specifications for the switching frequency used. It may be necessary to reduce the switching frequency to reduce the losses.

You could also role the output cables around one terminal to see if it is an issue with the motor and/or cables on that one phase. i.e. shift the cable from L4 to L5, the cable from L5 to L6 and the cable from L6 to L4. This will not alter the direction of rotation but will shift the problem to another phase if it is an external problem.

Best regards,

Mark Empson
http://www.lmphotonics.com

RE: variable torque VFD - IGBT over temperature problem

Although I think that the issues that Marke raised are more likely, I would also check the inertial load of the fan and your accel parameter.  If you had a large inertial load on the fan and a short decel parameter setting I would expect a trip on bus overvoltage but if for some reason your VFD is hunting for a speed and is continuously accelerating a high intertial load at the upper capacity of your drive then it could cause a problem.

RE: variable torque VFD - IGBT over temperature problem

I'm very curious about the drive sizing, but maybe it's a typo? You have a 200HP VT drive on a 250HP fan motor? A typical 250HP motor is going to be rated at 302A FLC (assuming 460V). Looking at a few 200HP VT rated drives on the market, I get a FLC range of between 240 and 304A maximum. If your VFD is on the lower end of that spectrum, I'd be surprised if only one of the IGBTs is hot!

RE: variable torque VFD - IGBT over temperature problem

jraef's observation is reason enough to size drives by amps, not hp.  Look at the motor's continuous running amps and its peak amps under standard load conditions.  The drive must be capable of sourcing both.

RE: variable torque VFD - IGBT over temperature problem

(OP)
Thanks for your answers,

The FLA of the motor is 270 amps (460 VAC, PF=0.9). the load is a fan, so it is a VT and 200 HP drive is supposed to handle it.
if the problem is due to cooling, then phase B is the one which has to get the overtemperature?

RE: variable torque VFD - IGBT over temperature problem

(OP)
the VFD is mounted inside an MCC.

RE: variable torque VFD - IGBT over temperature problem

Hello mohpower

What is the temperature inside the MCC?
If the temperature is over 40 degrees C, this could be a cause of your problem, and you will need to increase the ventilation.

Best regards

Mark Empson
http://www.lmphotonics.com

RE: variable torque VFD - IGBT over temperature problem

(OP)
I don't know the temperature inside the MCC. I will record it this week and letr you know then.

thank you

RE: variable torque VFD - IGBT over temperature problem

Makes sense that phase B would be the one with a problem if inadequate cooling is an issue. It's in the middle and getting radiant heating from the adjacent stacks (depending on the design of course).

MCC mounting of VFDs is always tricky at best. Heat stacking and air flow issues are a constant source of pain for those who do it. Is it a manufactured / tested package from the MCC supplier, or is it a VFD that was mounted in the MCC after the fact?

RE: variable torque VFD - IGBT over temperature problem

With the motor FLA at 270 and most 200hp VT rated drives at 245-250amps continuous, you likely are in trouble with the drive sizing.  The only possible relief would be if the fan hp at full speed is low enough for the motor to only be loaded to the 245-250amp range.  Otherwise, the drive is simply too small for the load.  

Instead of changing out the drive, why not limit the motor maximum speed to the point at which the amp draw just matches the drive output amp rating.  That will be the most you can hope to get from the drive/motor package in its present form.

As already mentioned, if the drive is in an enclosure that has its interior temp over 40 degrees C, that would be an additional cause of trouble.

RE: variable torque VFD - IGBT over temperature problem

A lot of VFD's these days calculate temperature rise in IGBT's rather than physically measure them. The heatsinks are usually measured but this is not often a constant measurement but a thermastatic measure: i.e. once it reaches (typically) 90degC then the thermastat will come in and trip the drive. The fact that your VFD is picking up the Phase B pair of IGBT's would possibly indicate to me that the measurement is calculated. So, picking up on the point DickDV has said, it is possible that your drive sizing is incorrect and possibly the motor data you dial into the VFD during commissioning does not actually match the real motor data. This can impact the way the internal temperature measurements are defined and calcualted if the base current and voltage are not correct. Typically an IsqT calcualtion is used internally for devices in VFD's and if the base information on the current and voltage is wrong, this can have consequences on the whole performance of the drive.
Mohpower. This is just one of the items to check. Others have already been suggested. The fact you have had two drives with the same issue leads me to think it is an external issue (ambient temp) or, as I mention above, a setting issue with the VFD.
Common problems with VFD overtemp are internal fans not working but this is unlikely if two drives are having the same problem soon after each other.
Have you got enough space around the drive for adequate ventilation (top and bottom)?
A 200hp drive will generate approximately 7~8kw of heat on full load, this needs to be exhausted from around the drive quickly otherwise it will get very hot.

RE: variable torque VFD - IGBT over temperature problem

7kW cannot possibly get out of any enclosure without forced air running thru it.  Or, huge missing areas like no bottom and no top.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: variable torque VFD - IGBT over temperature problem

Hence the problematic nature of mounting large VFDs in MCCs. Ditto what itsmoked said. If the fans are circulating the air already in the MCC, it is just blowing hot air around. You need serious ventilation out the front doors.

Quote (mohpower 15:07):

The FLA of the motor is 270 amps (460 VAC, PF=0.9). the load is a fan, so it is a VT and 200 HP drive is supposed to handle it.

Quote (mohpower 17:37):

I have an issue on 200 HP variable torque VFD driving a 250 HP fan

Caveat: if the VFD is a 200HP Constant Torque rated drive, it should be able to handle a 250HP VT load. But you said it was a 200HP VT drive, in which case it can only handle a 200HP VT load. You need to carefully investigate the CURRENT rating of your VFD; forget the HP claptrap.

RE: variable torque VFD - IGBT over temperature problem

(OP)
Hi everyone,

the VFD is a 200HP Contant Torque used to run a 250 HP fan (considered as variable torque).

Yesterday, i took the following measurements at full load(VFD running without tripping).
 - currents : ph A: 255 Amps, Ph B: 252 Amps, ph C: 254 Amps
-motor power was at: 90.6 %
-motor torque was at: 90 %
-motor speed was : 1785 RPM
- unit temperature (the temperature read at the VFD keypad screen): 57 Deg. celsius.
-room temperature was around : 20 Deg. Celius
-the mounted fans on the MCC doors are running and with the right flow of air (three at the bottom sucking air inside the MCC and three at the top sucking out air from the MCC).

i would like also to inform you that the motor is programmed to run at two preset speeds (30hz and 60 hz). sometime the motor can run for weeks at 60hz. i am not sure if this will also affect the selection of the VFD.
the motor drives a gear box of a ratio 1:2 making the speed of the fan to be 3600 RPM.

hope this will help.
let me know if more infos are needed

thank you and happy new year for all

RE: variable torque VFD - IGBT over temperature problem

The one piece of info still missing is the drive continuous current rating.  It should be on the drive nameplate.  Anything under about 270amps will be too small.  Above that, the drive is large enough and the overheating problem is not due to sizing.

If the drive keypad is telling you the heatsink is at 60 degrees C with a 20 degree C ambient and all fans working, I would suggest that the air flow is inadequate or possible not passing over the heatsink properly.  Sometimes, there are baffles or obstructions that keep the air from actually moving thru the drive heatsink.  None of that bypassed air is doing any cooling.  It might be helpful to check the air temperature exiting the drive cabinet.  If the heatsink is at 60 degrees C, I would expect the discharge air to be somewhere in the 50-55 degree C range.  If less than that, I would look for the cooling air bypassing the heatsink fins somewhere.

RE: variable torque VFD - IGBT over temperature problem

I am looking at an A-B catalog that I happen to have on my shelf.  The 200hp Heavy Duty (Constant Torque) Powerflex 700 drive is rated at 300A continuous, 330A one minute, and 450A three second on Normal Duty (Variable Torque) loads and 245A continuous, 368A one minute, and 490A three second on heavy duty loads.  

Did you get your measurements from the drive or from a handheld meter?  Do you have a meter that can read the output of VFD correctly?

Again have you checked the moment of inertia on the fan?  You are running it at over the amps for a heavy duty load for a long time and then perhaps you are asking this high moment of inertia load to accelerate.  Moving the air is a variable torque load but accelerating the fan is not necessarily.  When I size VFD's for centrifuges I have to upsize VFD's due to the long acceleration times.  I have also got into some trouble with large boiler forced draft fans in the several hundred horsepower range and had to adjust the accel parameters.

RE: variable torque VFD - IGBT over temperature problem

DickDV makes a good point - if heatsink temperature is right up into the 60°C range then you need more effective cooling.

Even if you have high enough flow through the MCC enclosure - I'm guessing something around 700 or 800 CFM should do - you could be 'short circuiting' some of it around the drive (if flow paths exists that don't go over the heat sinks then you are).

RE: variable torque VFD - IGBT over temperature problem

The VFD itself will have it's own fans to blow air over the heatsink but if the air being blown is already hot, then it's only going to get hotter.
Ambient temperature means the temperature directly around the drive, i.e. in this case inside the cubicle with doors closed.
mohpower; is the VFD showing any overtemperature alarms? If it is, then you need to do something about it or you will have another power transistor failure and likely compounded problems with capacitors. If your DC link capacitors are drying out then they can cause failure on your IGBT's.
Where is 57degC being measured? If it is actual heatsink temperature then this is not unusual.

RE: variable torque VFD - IGBT over temperature problem

Along the lines of what DickDV said, check that the cable routing inside the cubicle has not created an air baffle that is deflecting or restricting the cooling air path. You are running on the ragged edge of the temperature rating, any restriction will have a bigger effect that you may think.

Also, have you tried rolling the conductors yet as Marke mentioned back at the top of the thread? It would be useful to know if the problem follows the cable.

RE: variable torque VFD - IGBT over temperature problem

If the 57 degrees is the heatsink temperature, then I agree, this is no cause for alarm, however I note that the air temperature outside the enclosure is 20 dregreesC. If the air temperature outside the enclosure is able to rise to say 40C, then the heatsink would rise by the same amount and that would be getting closer to a trip point I would expect.

Additionally, was the 57C measured with the MCC closed, or had it been open recently. If the MCC was open, or had been opened shortly before the measurement was made, then the internal temperature would have dropped and the heatsink temperature would have dropped in sympathy.

Down here, we can buy small stick on temperature indicator labels from Radio Spares. I expect that these are available everywhere. I use these to indicate the maximum internal temperature inside an enclosure when there appear to be issues. It is very simple, you just attach some of these labels around the inside of the enclosure and have a look some time later and you can see the maximum temperature that has been achieved. NB there are two types, one is permanent and show the peak value, and the other shows the actual value at the time. You need the permanent one.
The important area in this installation, is the temperature of the air entering the heatsink, so you put some labels in the airflow into the cooling chamber. (outside the drive is OK)

Best regards,

Mark Empson
http://www.lmphotonics.com

RE: variable torque VFD - IGBT over temperature problem

Marke,
I had never heard of those stick-on devices, they sound like a great tool! Thermochromic paint I suppose, but how they would ensure retention of a peak value is new to me. Found this with Google, gotta get me some!

http://www.drypak.com/THERMAX-dist.pdf

RE: variable torque VFD - IGBT over temperature problem

Jeff;  These things are how produce vendors check to see if their shipper's meet their contractual obligations of keeping the product at the contracted temperature.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: variable torque VFD - IGBT over temperature problem

Hi, all,
Let me see if I've got this straight:
The drive display says the "Unit" temperature is 57deg.C, yet the drive is reporting an over-temperature fault? Does the "unit" temperature mean the heatsink temperature? If so, I'd be surprised if the trip level was this low, given that most drives are capable of running in ambient temperatures of 40 to 50 deg.C. Most VFD heatsinks I've seen have the trip at 90-100deg.C. This is usually measured by means of NTC sensor often inside the IGBT module. In addition, some drives calculate the IGBT temperatures by taking into account switching frequency, output current, etc. This is intended to prevent short term overheating of the devices, given that the heatsink will have a large thermal mass and a long time constant.
So we have over-temperature trips. How often do they occur? What is the VFD doing when this happens?
Over-temperature can have 2 causes: 1. overload of VFD; 2. Excessive ambient temperature (as Ozmosis pointed out, the rated maximum ambient temperature refers to the temperature of the air which is entering the VFD - best place to measure this is just below the VFD fan intake). If the cause was overloading, I would expect to see an overload trip (IsqT) unless the ambient temperature is too high. With ambient of 20degC and "Unit" of 57degC, this sounds about right to me for a drive that is close to its max. continuous output current. However, if the ambient inside the MCC were to rise towards 40 or 50deg.C, then you may run into trouble. Marke's idea about the stickers sounds ideal, I see RS still sell them, search for "temperature label".
Regards,
Mort

RE: variable torque VFD - IGBT over temperature problem

(OP)
the 57 Deg C is the heatsink temperature. at this temperature the drive is runninig (no tripping). we are thinking to add more fans to get the hot air out. we found dust also inside of the MCC, we will need also to clean the heatsinks.

Regards

RE: variable torque VFD - IGBT over temperature problem

A couple of things to note.

The rated cfm of many fans is not a real world number. That is the cfm the fan moves when it is mounted without any restrictions in an open baffle. Add fan grills and an enclosure and the cfm falls, possibly a lot.

In the UL world, a VFD enclosure should have filters on the enclosure fans.

If your VFD moves 600cfm through the heatsink then you can not simply put fans rated for a total of 600cfm into the enclosure. Some air will not go through the VFD heatsink but around the VFD and not contribute to the cooling. You can fix this by putting baffles in the enclosure to force the air through the VFD heatsink. On some VFD's you can baffle the enclosure and then just put big filters top and bottom and the VFD fans will actually do all the work.

RE: variable torque VFD - IGBT over temperature problem

LionelHutz;

I believe the intent is to turn over the air in the cabinet not force it thru the VFD as that is the duty of the VFD's internal fans.  The problem is no/too-little turnover of the air in the cabinet, hence a climb of the ambient.  So using fans to exchange the cabinet air should help as long as they're applied logically.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources