Previous in Forum: Discussion Forum for Large Power Generator   Next in Forum: Tap changer burned by Electric spark
Close

Comments Format:






Change Mode
Close

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Close

Rating Vote:







Add Vote
7 comments
Rate Comments: Nested
lifty16
Participant

Join Date: Apr 2008
Posts: 4

Vibration with VSD in elevator application

04/10/2008 6:24 PM

I have a VSD linked to a braked 415v 3 phase motor, 4kW 4-pole, driving a simple cable drum and lift cabin. The system produces vibration, quite severe, at 2 points during the speed curve profile and I can't seem to tune it out by changing switching frequency, or u/f curve etc.

I have heard that if the phases are rotated (motor is wired in Delta) then this can solve the problem. Any ideas please and if true, how does this work?
Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Good Answers:

These comments received enough positive votes to make them "good answers".
2
JRaef
Guru
United States - Member - New Member Engineering Fields - Power Engineering - New Member

Join Date: Sep 2006
Location: California, USA, where the Godless live next door to God.
Posts: 4665
Good Answers: 804
#1

Re: Vibration with VSD in elevator application

04/10/2008 8:21 PM

Mechanical harmonics are a fact of life with VFD use, especially when VFDs are retrofitted onto machinery that was designed for full speed operation. Most VFDs have a feature called something like "Prohibited Frequency Control" or "Speed Skipping" or something like that. it allows you to set up a set of speeds or a bandwidth of speeds at which you know in advance are giving you trouble, then you program how you want the VFD to deal with it. Either you stay below until the commanded speed in higher than the bandwidth, or you immediately skip over it and hold at the higher speed until the command drops below it.

What you are referring to is called "rolling" the conductors and it can sometimes have limited success. It just means that you move the phase conductors from one pole to the next, but keep the same rotation orientation. So for instance, you move phase A leads to the phase B motor terminals, B to C, C to A. What this does is to change any inequities in the phase currents due to imperfections in the motor windings along with any slight variations in the output voltage between the phases. This tends to work better with non-VFD applications however because with a VFD, all 3 phase outputs are supposed to be exactly the same. The only thing that might be affected is if there are any variances in motor lead resistance or induced impedance and if your motor leads are short, i.e. 100 feet or less, that is highly unlikely.

__________________
 ** All I every really wanted to be, was... A LUMBERJACK!.**
Register to Reply Good Answer (Score 2)
No more Good Answers.
lifty16
Participant

Join Date: Apr 2008
Posts: 4
#2
In reply to #1

Re: Vibration with VSD in elevator application

04/11/2008 7:27 AM

Thanks JRaef for your valued reply. I'll try the prohibited frequency at about 35-40Hz and see if that does it. If not we'll do the 'rolling conductor' as a last resort. Failing that maybe we should invest in a better motor?

Regards,

Alan

Lifty16
Register to Reply
nesubra
Guru

Join Date: Nov 2006
Posts: 729
Good Answers: 2
#3

Re: Vibration with VSD in elevator application

04/12/2008 4:04 AM

every rotor has what is known as a critical speed at which vibrations are heavy.Normally 1 st critical speed is kept away from operating speeds by design.In some motors first critical sped is well below the operating spedd and as the motor accelerates it passes through the critical speed.In any case it is kept far away from the operating speed.If it happens that if your motor happens to be near the crtical speed possibility of encountering vibration is high.Normally it will be better to get a motor after giving the application details to manufacturer who can study the speed range and design accordingly.

__________________
 To avoid crticism do nothing,say nothing,be nothing
Register to Reply
nesubra
Guru

Join Date: Nov 2006
Posts: 729
Good Answers: 2
#4

Re: Vibration with VSD in elevator application

04/12/2008 11:59 AM

Further to my reply its quite possible your speed variation takes you closer to critical speed.So better option may be to obtain a motor after specifying the speed variation and range.

__________________
 To avoid crticism do nothing,say nothing,be nothing
Register to Reply
lifty16
Participant

Join Date: Apr 2008
Posts: 4
#5

Re: Vibration with VSD in elevator application

04/12/2008 7:32 PM

Thanks guys for your replies and suggestions. As a result the problem has been solved by using the 'Prohibit Frequency Range' feature in the drive and 'rolling the conductors' once.

Regards,

Lifty16
Register to Reply
JRaef
Guru
United States - Member - New Member Engineering Fields - Power Engineering - New Member

Join Date: Sep 2006
Location: California, USA, where the Godless live next door to God.
Posts: 4665
Good Answers: 804
#6
In reply to #5

Re: Vibration with VSD in elevator application

04/13/2008 12:20 AM

Glad it worked. But did rolling the conductors really do that much for you? Just curious.

__________________
 ** All I every really wanted to be, was... A LUMBERJACK!.**
Register to Reply
lifty16
Participant

Join Date: Apr 2008
Posts: 4
#7
In reply to #6

Re: Vibration with VSD in elevator application

04/15/2008 9:16 AM

There was a marked difference when we rolled them once, so we left it there, then prohibited the rogue frequency and it virtually eliminated the vibration completely. Excellent result! Thanks again,

Regards,

Lifty16
Register to Reply
Register to Reply
Have a Different Question?
7 comments

Good Answers:

These comments received enough positive votes to make them "good answers".
Copy to Clipboard

Users who posted comments:

JRaef (2); lifty16 (3); nesubra (2)

Previous in Forum: Discussion Forum for Large Power Generator   Next in Forum: Tap changer burned by Electric spark
You might be interested in: Vibration Instruments, Vibration Sensors

Advertisement

Got Something to Say?
Ask a Question
Start a Discussion

Search this Forum
Electrical Engineering:
Go

CR4 Sections
Aerospace
BioMech & BioMed
Chemical & Material Science
Civil Engineering
Communications & Electronics
Education and Engineering Careers
Electrical Engineering
General Discussion
Instrumentation
Manufacturing
Mechanical Engineering
New Technologies & Research
Software & Programming
Sustainable Engineering
Transportation

Site Directories
Forum Directory
Blog Directory
User Group Directory
RSS Feeds

CR4 Rules of Conduct
CR4 FAQ
Site Glossary

Who's Online (75 right now)
Show Members
Advertisement