Standard LT Motor Failure-VFD Driven

In order for anyone to try and give answer to this question you pose, more info is needed. Such as; Motor load in amps & percent of fully loaded, percent of rpm running under load, ambient air temp where motor was being run. The more info you provide the easier it is to give feed back to your issue.

I have used non vector duty motors for ever and have not had many issues until you get into the lower RPM ranges. These areas can be a problem for these motors. I might add that even when using a non-vectored motor, using a higher rated insulation class will help as well. You should be able to read the insulation class off the motor you had go bad and posted that back with above info.

Hi I agree with FIXITORELSE-- Heat is the #1 killer of motors, even the bearings can

loose there lube and overload or lock up a motor. Most have a 40 Deg.C rise over ambient but we had a new one fail at 4 months (Bearings)! The motors I deal with are 3 phase 460 Volt. I know motors come in a lot of different voltages but I have not seen a 415V one, if you are operating a 460 V motor at 415 Volts it may be a problem if it can not develop the HP it needs. A drive just changes the Frequency thus RPM. The turn to turn short is a fairly common failure and a VFD will "fault" out if anything is wrong with the motor circuit. Also if a motor sits in storage or not running for years the bearings may fail sooner than you think. Inverter duty motors generally have better insulation on the windings and steel in the core and rotor.

Everyone is on the Money GA's..and just FYI we have hundreds of motors on VFD's at this plant and have only one documented "EDM" failure and it was not a run to failure.

We found it with Ultrasonic testing.The Drive end bearing had visible "Fluting". The VFD was not grounded properly to the motor but the motor was grounded to our grounding grid and building steel. Load side Reactors, proper grounding, shaft brushing seals (or clamp on) will stop all that Electrical Discharge Machining.

Correct, and I bet you're following manufacturer's recommendations, standard practices an all codes, just that you missed that one instalation in particular.

But it becomes much more apparent in other scenarios, for example some electric vehicles, they use AC servomotors ran by a high-end VFD. and the bearings are among the most prone to fail parts, much more than the windings.

In my experience working at one major manufacturer of servo motors (almost a monopoly), "EDM" and electrical noise were killing most of them. Wait a minute you may say, electrical noise?... Yup, the bearings featured a built-in pulse coder susceptible to fail due to lose connections on the power leads at the test stations.

Me gusto mucho, bueno trabajo amigo.

Gracias, compadre !

Kindly check the reduction in RPM done by reducing frequency using VFD . IF it is reduced below say 50 % of rated RPM of motor . The cooling fan speed reduces accordingly Thus motor is not cooled by the fan sufficiently as it would have done when running at rated speed . Hence overheating of motor and failuer Hope this clarifies your query As motor used by you might not have forced fan cooling arrangement

In VFD suitable motors

1. Forced fan cooling is provided . Thus even motor runs at lower RPM than rated for long period , the cooling of motor is done by Fan which is run by another small motor

2. The insulation of Motor winding is done by Vaccum Pressure Impregnation ( VPI ) Method as against normal Dip method. Thus Insulation coating is uniform across the entire winding hence points of failuer are reduced drastically Hence better thermal performance of Motor.

However practically if Motor is VPI treated it may not fail if RPM reduction is restricated to say 10 to 15 % of Rated RPM.

Best thing is if you are planning to run motor with VFD kindly ask Motor suitable for VFD from manufacturer.

Thank you very much to all.

I agree with the facts of failure with all above. We have a strange case. Since 3 years, We have installed-8X150 kW pump-motors with 6-pulse Siemens-VFD on an exclusive 2500 kVA transformer-of-course-missed out to install HARMONIC filter. Frequent failure of VFD-control cards are reported. We have taken care about all except harmonic filters. . The I Thd is 45% and V-Thd is 3.5%. Kindly suggest remedies and bad effects of not installing harmonic filters. Management says-that nothing happened except control-card failures and why expensive ACTIVE HARMONIC FILTERS ARE Needed?

• I agree with the facts of failure with all above. We have a strange case. Since 3 years, We have installed-8X150 kW pump-motors with 6-pulse Siemens-VFD on an exclusive 2500 kVA transformer-of-course-missed out to install HARMONIC filter. Frequent failure of VFD-control cards are reported. We have taken care about all except harmonic filters. . The I Thd is 45% and V-Thd is 3.5%. Kindly suggest remedies and bad effects of not installing harmonic filters. Management says-that nothing happened except control-card failures and why expensive ACTIVE HARMONIC FILTERS ARE Needed?

It may have been better to start a new thread on this, but too late now.

I tend to agree with your management on this one, it's unlikely that the control board failures are the direct result of excessive harmonics. The control boards are powered separately, usually off of the DC bus with a DC-DC power converter, but sometimes off of the AC side with an AC-DC switched mode power supply board. Either way, the control voltage going to the board is going to be isolated from the mains.

Control board failure causes tend to fall into two main categories: environmental and electrical noise related.

If the drives are getting too hot inside their enclosures, it is usually the PC boards that fail first, because the drives themselves often have protection schemes to automatically lower the motor speed to protect the transistors from over heating, but if the ambient air is too high, the boards cook anyway. I have also seen cases of air contaminants such as H2S causing corrosion and failure on boards. As I recall, Siemens only offers what is called "conformal coating" of the PC boards as an option.

Improper shielding (screening) of control wiring is a good way to allow introduction of common mode electrical noise to get into the PC board circuits. Most have filtering to help prevent that, but over time, repeated attacks eventually cause the filtering to wear out and fail, then the board circuits are quick to follow. If you are using shielded control cables, make sure that only ONE END is grounded (earthed). That is a common problem.

Good luck.

Great feeling to read through the message/content. I am examining the card failure and will ensure --environmental/noise issues. Your mention that Shielded control cables being grounded at one ned-i feel is very precise for me to examine the site issues. Thank you and my best regards.