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variable torque VFD - IGBT over temperature problem 1

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mohpower

Petroleum
May 30, 2006
32
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

 
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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.
 
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
 
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!

 
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.-
 
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
 
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
 
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.

 
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.-
 
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