Inverter Duty Motors Running Hot. Current within specifications.

Join Date
Aug 2016
Location
Virginia
Posts
343
Good Morning ,

I am working on a new project and I am using 3 Inverter Duty motors. 2 - 5 HP motors and 1 - 3 HP motor. I am using PowerFlex 525 drives and using them in SVC mode. I tuned the motors before installing them in the machine.
I ran them , somewhat loaded , for about 4 hours yesterday , and the motors , during the tail end of these 4 hours , got somewhat hot. I could hold my hane on them , somewhat.

What would cause these motors to heat up so much ? Do you think the drives are causing these motors to heat up ? If so , what setting would be causing this ? Should I re-tune the motors while they are attached to the gearboxes and the rollers they are turning ?

Thanks so much for you advice. Have a great day .
 
Hot is a relative term. Most inverter duty motors will have Class H insulation, which allows for the motor winding temperature to run as high as 180 degrees C (356 degrees F). The outer surface temperature would be a few degrees lower but to put that in context, you would receive a first degree burn by touching a surface that is just 70 degrees C (158F) for just one second. So if it just felt uncomfortably “hot” to you, it was far below the allowable operating temperature of the motor.
 
I would assume these are TEFC motors? Like OkiePC said, slower speeds will have less airflow so the temps will be higher.

Jraef is one of the experts on motor/drives.
 
Yeah depending on what speed/load you are actually operating them and for how long, it may be worth considering a electric fan on the back to help keep things cooler. However as Jraef said, 180C is scorching, so uncomfortably hot to the touch doesn't sound too bad.
 
:DBack in the day we used to check motors that way. If you could hold your hand for a second or so the motor was running well. If you spit on it and is sizzled it was too hot. If the paint was getting darker it was due for replacement.:D:D
 
:DBack in the day we used to check motors that way. If you could hold your hand for a second or so the motor was running well. If you spit on it and is sizzled it was too hot. If the paint was getting darker it was due for replacement.:D:D
And if there was no budget for replacement, you repainted it with BBQ paint, which only comes in black so it makes identifying the priorities when the new budget comes in a little easier...
 
Baker,
To answer the other part of your question, yes, VFDs cause additional heating in motors, that's why motor mfrs will also tell you that if a motor has a 1.15 Service factor, that becomes 1.0SF if operated from a VFD; the VFD operation "consumes" the margin of heating capacity built-in to a 1.15SF design. This is one reason why you always want a good quality motor designed to be operated by VFDs.

But also be careful, the term "Inverter Duty" is not officially defined by anyone, so some manufacturers take advantage of that and slap that label onto very marginal products, or use more vague terminology such as "inverter ready", which means next to nothing. Look at the actual specifications for your motor. They should include what's called a "Turn Down Ratio", which means the expected low speed you can run it at without having to supplement the cooling. So for example if it is a 4 pole (1800 srpm) motor with a 6:1 Turn Down Ratio, that means the motor is DESIGNED to be run as low as 300 rpm without needing added cooling. Typically 20:1 is the best you will see on a TEFC or TENV motor, if you want better than that, you usually need a motor with a separately powered blower (TEBC).
 
What mode is your VFD in and how critical is the speed?
You might try reducing fixed boost, to the point just above that which causes issues under load.
Also if your application can Tolerate slip, if its a pump and pressure is the PV rather than RPM for example, you may want to try basic VF rather than sensor-less vector.

To be fair I am no expert but have reduced temperature on several AFE-VFD based turbines this way. (VF being more effective than a boost reduction in my experience)

Al
 

Similar Topics

Good Evening , I am using Inverter Duty Washdown Motors for the first time for a small project. How different are they ? It is a 5 hp and...
Replies
12
Views
3,370
Cost not being an issue what are the best vfd duty motors out there. We currently have some of everthing but i have not been here long enough to...
Replies
2
Views
2,554
Motor: 60HP (44.8Kw), 480V, 60Hz, 1200RPM Application: Axial piston hydraulic Pump, w/ electronic volume and pressure comp controls. Motor will...
Replies
6
Views
4,357
Good Morning , I have an application that I would like to put a regular fan cooled motor on a drive instead of purchasing a inverter duty...
Replies
7
Views
2,958
I have Toyopuc PLC PC10G-CPU and some communication modules of it. With this modules I'm able to connect with Ethernet, Ethernet/IP, FLnet, FRMT...
Replies
0
Views
52
Back
Top Bottom