synchronous machines in the chemical combinat 2

[hakla]

the chemical combinat that manufacture ammoniac work with a gas piston compressors (synchronous motors),the number of these motors may reach 14(all motors are identical and work with the same rotation speed,on parallel).the load on the shaft of motor have a periodecal character,it means that changes reapetedly with a definit law,my question is :when the tacts (bars of pistons)reach their maximum altogether(at the same time),all parameters (current ,voltage..)start fluctuate and consequently a high vibration on the basise(groundwork) these phenomena are indesirable ,so what arrangement is taken in this situation (to prevent vibration and flucuation ).
any help ill be appreciate.
with regards

 

[busbar]

Hakla, no personal offense is meant, but could you work on the form, punctuation and grammar of this posting? Please separate statements from questions. Please detail and clarify—are you asking whether mechanical effects are electrically induced?

Are there chemical reactions that are affecting electrical functions? Perhaps that could be a introduced as separate topic.

 

[hakla]

ok.i meant that when the tacts of pistons reach their maximum, there will be a high vibration on the groundwork .So how to deal with that;and there are no chemical reaction in that at all.
regards

 

[busbar]

ME thread! Sorry if I inconvenienced you in any way.

 

[gjones33]

Hi Hakla,

Can the pistons be staggered so that they do not all reach their maximum power requirement at the same instant.
Cheers,
G

 

[jbartos]

Suggestion: It appears that this needs to be modeled as an electromechanical system since the electrical parameters will vary according to the motor shaft varying loads. The variations will be periodical, which will cause or support the mechanical vibrations. Sometimes, these problems are resolved via flywheels that enable the smooth and low vibration operation of the motor-compressor sets.

 

[hakla]

to jbators:thank you for your care ;in fact this problem is practicle ,having discussed this theme i understood that one arangement can be done in this situation :so when all tacts get their maximum -and all the motors work with the same rotation speed, consequently their rotors have the same angle position (between all rotors the angle is zero)-we can change the rotor angle positions so that not all motors(consequently the tacts of pistons) carry a max load at that moment ,how to get that arangement done i still need help for you .
my speciality's feild is electrical drive and control so my work in principe to work upon elictrical solutions .the mechanical ones may be idon't understand them and the mechanic's do it better .so upon this theme and if anyone work in this feild i would like to know the recent publications and works.
with regards

 

[jbartos]

Suggestion: Post a copy of your postings in this Forum under the Mechanical Engineers and Industrial/Manufacturing Engineers in this Forum.

 

[electricpete]

I definitely don't understand the problem and I'm not too familiar with syncronous motors.

I am aware the sycnrounous motors are susceptible to torque oscillations. If the load torque increases the rotor angle increase and machine torque increases sometimes too much and overshoots... causing oscillation. It sounds reasonable that this type of oscillation would be excited by a reciprocating load. If that is the case, I believe jbartos is right that adding a flywheel will make that resonant frequency lower, which might make your problem worse or better.

I would suggest that you might search for synchronous torque oscillations. Try this forum. Try the mechanical/acoustics/vibration forum on this site. Also try that search at the vibration/alignment/balancing forum at reliability-magazine.com. Finally my favorite general purpose search is dogpile.com

 

[electricpete]

Here is a very extensive discussion of torque oscillations in reciprocating machines.

http://www.engdyn.com/download/86.pdf

Case #10 involves syncronous motor driving reciprocating machine. I don't understand the whole report but my basic understanding is that there is a need to avoid the torsional resonance frequency being a multiple of running speed. (the impacts excite 1x running speed, 2x running speed, 3x running speed etc harmonics). Although it is not discussed in the paper, syncrounous motors are inherently susceptible to torque oscillations since torque varies with rotor angle... induction motors are not.

Also do your oscillations persist at the same magnitude while running, or are they more severe during starting.

If more severe during starting, let me know. I have a copy of IEEE 1255-2000 "Torque Pulsatons during starting of Syncronous Motors".

Can you identify the frequency of vibration? Do you have a standard predictive vibration survey (horizontal, axial, vertical spectra)? Can you identify whether there is in fact torsional oscillation more common radial vibration (your description sounds like torsional to me).