Currently we have fix speed electric motor to drive our compressor. If we manage to change the driver with variable speed motor (for control and performance purpose), what should we evaluate and what should be our considerations? Thanks before.

Tanya – Alda Adrina

Dear all,

Currently we have fix speed electric motor to drive our compressor. If we manage to change the driver with variable speed motor (for control and performance purpose), what should we evaluate and what should be our considerations? Thanks before.

Tanggapan 1 – roeddy setiawan

Dear Aldina,

Interesting that you plant to add variable to your driver; ie yr motor. The ost important I suggest you study fan laws

if you change speed

new rate proportional to cube of speed

new BHP prop to cube of speed

new head prop to square of speed

So at all time yr new motor must provide enough horse power and torque so talk to yr vendor therefore they can select the right motor for you for all credible operating speed selected.

The compressor side you must ask(if you already had installed, u have this) your vendor to give you new curve shown your choke point on each speed. so you could estimate yr maximum speed applicable. its is no use if u keep add speed, but compressor in choke /stall condition (yr ach number exceed).

Ask your self where are your off design codition, the work back ward to operating condition and yr minium surge line. see if this can be fullfilled with yr cmopressor. if not ask new ipeler that satisfy yr demand

Talk to VSD supplier like siemens or others about yr planned speed, they will back to you with the right proposal. dont forget to ask the parasitic frequency supresion that would damage equipment nearby.

Talk to your power guy, its no use you doing a fancy stuff but off a sudden your power demand could not be satisfy because yr power house do not have an ample reserve power,.

I guest that about all that i remember for frequency/speed control and its not come cheap specially for large motor. I believe others will be glad to share their experience as well.

Tanggapan 2 – Sadikin, Indera

Dear Bu Aldina and Pak Roeddy,

In my opinion, rather than changing to variable speed motor, it is better to keep the old single speed motor and add a frequency inverter to control the speed.

Tanggapan 3 – Alda Adrina

Dear pak Roeddy and pak Indera,

Thanks a lot for your quick response. Very comprehensive and really helpful.

Talking about frequency inverter, is there any drawback of adding this instead of installing a VSD? Or the drawback is on the VSD? Thanks before.

Tanggapan 4 – roeddy setiawan

Dear Pak Sadikin,

I thinks my write up was just equally same with what you suggesting, it was controlling a motor via frequency manipulation.
somehow for most of the case the original motor wasnt sized with future hypotetical demand of frequency manipulation. therefore for increasing sxped demand the motor wasnt just dont have enough power left see cube relationship.

Tanggapan 5 – Sigit kumoro bekti

Dear,

<>Using VSD with any method is making many advantages in operation rather than using IGV. every vendor always attach performance curve for compressor so you can compare on that curve for compressor operation wether the compressor is operating at good point or not.
it’s true what Mr Roedy said, that surge or choke is very important in compressor operation it can lead very serious damage and noisy. Perhaps you can install like flow meter (if N/A) and pressure discharge indicator (usually installed) to monitor your compressor performance while attaching VSD. is it operating at the safe area or not? regarding to performance curve. and obviously, discuss with your vendor about your plan, because vendor design the compressor at efficient and safe operation.
Good luck.

Tanggapan 6 – Dedy Desril A.

Dear Alda

I think you should consider what the purpose is, before you want to change the driver to inverter.
If you do not need to vary your motor speed, that mean if once the motor start is up to speed you need not to change the driver to inverter. but if you want to control the speed depend on the demand, that will work. becoz at the fullspeed condition, fixed speed motor is more efficience than the inverter’s one.
VFD and VSD are the same purpose driver the difference only for AC or DC Drives.