
Converting "normal" induction motor to "inverter grade" induction motor by rewinding.
#1
Posted 13 April 2006 - 11:48 AM
What are the things that need to be changed, like upgrading the insulation to Class F insulation etc., in the existing motor?
Also is it a good idea to consult the motor manufacturer before running a "normal " motor from an "inverter" / AC Drive.
Thanks in advance
easyser
#2
Posted 13 April 2006 - 10:11 PM
It's always prudent to consult the motor mfr on using a non-inverter rated motor with an inverter, especially at 380V and above.
#3
Posted 14 April 2006 - 02:48 AM
Please, explaine me following:
What does it mean "inverter grade"?
It means that you want to use your "normal" motor as a generator or as motor which is controled by a driver?
#4
Posted 14 April 2006 - 03:12 AM
The inverter grade motor is a motor that is rated to be used with an inverter (VSD). It will usually offer improved cooling to allow for operation at lower speeds and will have muc sbetter insulation in the windings to allow for the high voltage peaks that can come form an inverter. Additionally, it can have conductive bearings to overcome the EDM problems associated with some drives.
Best regards,
Mark Empson | administrator
Skype Contact = markempson | phone +64 274 363 067
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#5
Posted 19 April 2006 - 09:41 AM
proof the winding against the same. In absencence of such measure motor may fail due to insulation failure .
#6
Posted 19 April 2006 - 10:24 AM
easyser
#7
Posted 19 April 2006 - 06:48 PM
#8
Posted 19 April 2006 - 07:54 PM
Would you believe....... Partial Discharge Inception Voltage (PDIV)
Do a Google with the words enclosed in quotes. There's a potpouri of info on the subject available.
Also, if you are fortunate enough to be able to locate Volume 42, Number 1 (Jan/Feb 2006) of the IEEE Transactions on Industry Applications, there are several excellent papers therein; including the following:
-Michael J. Melfi's paper on "Low-Voltage PWM Inverter-Fed Motor Insulation Issues"
- Dennis Bogh, Jeff Coffee, Greg Stone, Jim Custodio joint paper on "Partial-Discharge-Inception Testing on Low-Voltage Motors"
Kind regards,
jΩ
#9
Posted 21 April 2006 - 08:53 AM
Thanks for the clarification.
easyser
#10
Posted 29 April 2006 - 01:52 PM
First of all I would suggest to divide this discussion in two parts:
- converting motors from "normal" to "inverter grade" (many people and end users are interested)
and create a new one:
- PDIV, a not-so-know argument, only for specialized people, not for massive end-users.
-------------------
Regarding conversion to "inverter grade" I would remember that in many cases it is not convenient to modify existing motors. Alternatively, it is possible to act on inverter parameters (i.e.: reducing carrier frequency) or installing a dV/dt filter between inverter and cable to the motor, or calculating the proper cable lenght to avoid undesired voltage reflections on the cable.
Inverter-grade motors could have special lamination, special bearings, special windings, special rotor, special insulation, sensors, too many special things not available on normal AC motors. Using the proper motor for that application means to have the maximum performances using the minimum quantity of energy, having also the maximum reliability and safety.
Regards
Mario
Mario Maggi - Italy - http://www.evlist.it - https://www.axu.it
#11
Posted 02 May 2006 - 02:47 AM
Please, answer me.
What happen if we'll mount a driver between the motor and the power line and we'll do automatic identification the motor by a driver? After that we start the motor.
I think no bad things happen.

#12
Posted 02 May 2006 - 05:14 AM
You can use a standard motor on a variable speed drive, but there is a higher posibility of the motor failing early due to insulation issues and bearing issues.So to answer your question, in the short term, in most cases there will not be any problem.
Best regards,
Mark Empson | administrator
Skype Contact = markempson | phone +64 274 363 067
LMPForum | Power Factor | L M Photonics Ltd | Empson family | Advanced Motor Control Ltd | Pressure Transducers | Smart Relay | GSM Control | Mark Empson Website | AuCom | Soft Starters
#13
Posted 02 May 2006 - 05:40 AM
Thank for your answer.
I have read this topic one again, but I cann't understand one thing.
Why have you decided that is especial motor or this device is very hardworking?
See
It is your reply Marke.
Ok. Please, show me, why this motor is especial?!
From this topic I don't undersatnd that it is especial or particular or peculiar.
Sorry me I repeated myself.
#14
Posted 02 May 2006 - 06:29 AM
A standard induction motor is designed to operate of a three phase sinusoidal voltage at rated frequency.
An inverter based variable speed drive does not produce a sinusoidal output voltage. The inverter uses PWM techniques with very fast switching devices to synthesize a sinusoidal current in the motor, but the voltage applied is a high frequency switching waveform.
This places the winding insulation under much higher stress. Additionally, the high frequency fast switching waveforms can result in high earth currents flowing from the rotor of the motor to the frame of the motor. This can cause serious pitting of the bearings. If the motor operates for extended periods at less than rated speed, there can be issues with cooling, shortening the life of the motor.
To sum up, the speed controller places much higher electrical stress on the motor than a standard supply.
Best regards,
Mark Empson | administrator
Skype Contact = markempson | phone +64 274 363 067
LMPForum | Power Factor | L M Photonics Ltd | Empson family | Advanced Motor Control Ltd | Pressure Transducers | Smart Relay | GSM Control | Mark Empson Website | AuCom | Soft Starters
#15
Posted 02 May 2006 - 08:46 AM
I have known about these problems.
I newer asked myself about "Can or cann't any motor be connected to a driver".
Could you show any documentation or any quote of documentation with a mark(note), which explains that "Can or cann't any motor be connected to a driver"?
Please.

#16
Posted 03 May 2006 - 09:21 AM
Hello Tua
A standard induction motor is designed to operate of a three phase sinusoidal voltage at rated frequency.
An inverter based variable speed drive does not produce a sinusoidal output voltage. The inverter uses PWM techniques with very fast switching devices to synthesize a sinusoidal current in the motor, but the voltage applied is a high frequency switching waveform.
This places the winding insulation under much higher stress. Additionally, the high frequency fast switching waveforms can result in high earth currents flowing from the rotor of the motor to the frame of the motor. This can cause serious pitting of the bearings. If the motor operates for extended periods at less than rated speed, there can be issues with cooling, shortening the life of the motor.
To sum up, the speed controller places much higher electrical stress on the motor than a standard supply.
Best regards,
#17
Posted 03 May 2006 - 09:36 AM
Any comments / views ?
Thanks,
easyser
#18
Posted 03 May 2006 - 09:53 AM
Yes, you can connect a sinusoidal filter to the output of a drive to eliminate the high frequency component of the voltage waveform applied to the motor. This is sometimes used with very long cable runs to eliminate the cable capacitance problems on the inverter output. The filter will eliminate the high voltage and transient problems in the motor as well as the standing wave problems in the cable.
The sinusoidal filter would be used more if it were not for the high cost of such a filter.
Best regards,
Mark Empson | administrator
Skype Contact = markempson | phone +64 274 363 067
LMPForum | Power Factor | L M Photonics Ltd | Empson family | Advanced Motor Control Ltd | Pressure Transducers | Smart Relay | GSM Control | Mark Empson Website | AuCom | Soft Starters
#19
Posted 03 May 2006 - 10:25 AM
Ok..
I am understanding all, but I didn't see an answer.
We should use an intermediate filter, we can use an especial motor, but how have you done this conclusion?
May be from your experience, may be from your manufacture's explaination for the motor?
#20
Posted 03 May 2006 - 10:36 AM
This is a pretty well accepted fact in the industry and many of us who have been around for a while have bothe experienced the problems, sorted the problems and read lots of information on the problems.
If you talk to any motor suppliers, or check and motor suppliers web sites, you will find reference to inverter grade motors. For example, at the Weg site, there is a brochure on their inverter grade motors and this lists some of the differences.
http://www.weglibrar...index.asp?ID=4#
You can find plenty more. If you do a goole search, you will finds lots of infomation on this subject.
Best regards,
Mark Empson | administrator
Skype Contact = markempson | phone +64 274 363 067
LMPForum | Power Factor | L M Photonics Ltd | Empson family | Advanced Motor Control Ltd | Pressure Transducers | Smart Relay | GSM Control | Mark Empson Website | AuCom | Soft Starters
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