Siemens Robicon Setpoints 3

[nightfox1925]

Does anyone had experience in setting Siemens Robicon Perfect Harmony WCIII? We applied this VFD for a 7500HP motor with input voltage of 7.2kV and an output voltage of 0-7.2kV

I received a worksheet from the vendor requesting for VFD settings with descriptions that I am not familar with like:

Critical Frequency Rejection, Energy Saving Operation, Freq (Auto) Command Bias/Gain, Frequency Command (Upper/Lower) Limits, Momentary Power Ride Through, Over-Torque Detection, Slip Compensation, Speed Coincidence, Speed Search, Torque Compensation, Stall Prevention, V/F Pattern.

What I have at hand are the motor curves, pump curves and at least operating speed ranges as dictated by process operations.

I would like to request some guidance from experts who had set the same and can provide me some kind of direction to start with so I can get the right people necessary to help me out in making the proper settings.

A typical setting sheet of the same equipment may also help or any web link that will provide better info. I am struggling to understand what the manual says.

Thanks

 

[Skogsgurra]

That is such a big (and expensive) drive that you should get a commisioning engineer from Siemens to do the work. That will save you a lot of trouble. And that is what most people do - even experienced drive guys.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[nightfox1925]

Thanks skoggs, we already have the commissioning engineer from Siemens. Unfortunately, the settings indicated above is what he actually requests from us.

I would appreciate all the guidance, tips or direction I would get.

 

[ozmosis]

It sounds like odd requests for the Siemens service engineer to be asking you to be honest.

As Gunnar says, such a big beast of a drive should not be your responsibility to commission. You tell Siemens what the application is, how you want the pump to function, the limits of pressure/flow and then let them do it.
Critical frequency rejection would be application based and sounds like a point of resonance within the load itself.Not sure you would know that up-front.
Energy Saving Operation? well, yes please but how will this affect the application? The service engineer should be able to advise.
Freq command bias/gain? well, once you commission the frequency command then you will know if you need to alter the bias/gain. You do this when you are setting the drive up.
Upper and Lower limits. This you could advise relating to the maximum and minimum speed as a proportion to frequency.
Momentary power ride through: depends on the application and the critical nature of operation. What do you want to do in the event of a power dip? Continue, alarm or trip?
Over-torque detection: I would say yes you might need this on a pump but to what level will be determined at commissioning.
Slip Compensation, Speed Coincidence, Speed Search, Torque Compensation: on a pump? I would say not but a 7500hp MV drive is a special beast.

My thoughts are, throw it back to Siemens and say: we're paying you to commission the drive, you sort it out.

 

[jraef]

Actually, I think it's kind of a fair set of questions. They are for the most part user choices; things that a commissioning engineer would not want to take for granted, call them "Side Dishes" if you like. But if all he did was hand you that on a sheet of paper, his "bedside manner" leaves a lot to be desired. I would have scheduled a meeting and sat down with you to discuss all these issues one by one. For that big of an investment, he owed you that.

Critical Frequency Rejection; Do you know of any critical speeds at which there will be mechanical harmonics that you want to avoid? This would be in the entire driven load and motor system. No way for the VFD guy to know that. You may not either, but he cannot assume that you don't. If you don't, indicate it. But if it turns out there is one, don't blame him. It's not something the VFD guy would know.

Energy Saving Operation; the VFD is capable of operating in a field weakened state which, on some types of centrifugal loads, may end up saving you additional energy when operating at reduced speed. He is asking if you know if your load is a candidate for it, and if you want to take advantage of that.

Freq (Auto) Command Bias/Gain, Frequency Command (Upper/Lower) Limits,; The VFD guy is not the overall automation system provider (unless you specifically contracted for that), so he cannot take responsibility for how your command and control system is configured, i.e. signal conditioning. The VFD is capable of conditioning the signal to match your system, he just wants to know what you want.

Momentary Power Ride Through; The Robicon drive is capable of different levels of ability in surviving a loss of power. The choices are there, he just wants you to tell him what you want to implement. This is something you need to have a conversation about so that you can make an informed choice.

Over-Torque Detection; Again, how do you want the VFD to react to a situation where it is being asked to deliver more torque than the motor or load may be able to handle? Load related, so again, he cannot ASS-u-me.

Slip Compensation; When operating in basic V/Hz mode, the VFD is capable of tweaking the output as the slip increases under load so that the step change response is quicker (or slower). It used to be what we called "the poor man's vector control" when vector drives were very expensive. If for some reason you need to be in V/Hz mode, then this becomes an issue. Some load profiles need that, some don't. If you are operating in Vector mode, it's moot. Again, if you don't know, just say so.

Speed Coincidence; I can't remember what that means (been a while) but yet another load related issue for sure.

Speed Search; If for some reason the VFD is shut down and then immediately turned back on, do you want it to search and detect the motor speed, match its output and re-ramp up (or down) to your commanded speed? Or do you just want the VFD to immediately jump back to the commanded speed without ramping? Some loads must have that immediacy in the response, some do not. Again, he is not going to know.

Torque Compensation; Like Slip Compensation, only with torque when operating in Vector mode.

Stall Prevention; You can decide how you want the VFD to respond if it detects that the motor is stalling. Do you want it to back off on the commanded speed to prevent it from tripping off line, or do you want it to maintain the speed it is at until it trips?

V/F Pattern; The VFD is capable of having the Voltage and Frequency ratio tweaked, for instance if you know in advance that you need high torque in the lower speed ranges but not at the higher speeds. Again, load related.


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[nightfox1925]

Our application is for a centrifugal pump. I tried to inquire the process individual about process requirements and he only informed me that the pump should be able to be operated 20~60Hz and that's it.

Jaeref, do you have any good web link or book reference for me to get better deal of understanding of a typical VFD system?

 

[Skogsgurra]

Is the pump running? Has the Siemens man finished what he was supposed to do? Or is he using all these questions as an excuse not to finish the job?

I am asking because the questions he has put are rather typical for someone that doesn't quite know what to do and needs some time to discuss with his home-base. Some also use such questions to get more hours on the final invoice - billing the extra time as "analysis" or "engineering". Let's hope that isn't the case here.

If your "process individual" doesn't want more than a certain speed range, then let him have that. All protection and safety features shall of course be included but niceties like energy saving and frequency jumps can easily be added later - if at all necessary.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[nightfox1925]

Thanks Skoggs and Ozmosis for your valuable time and effort to guide me through this dilemna.

I will set a meeting with the VFD Commissioning Engineer and discuss item per item about his list and provide him what we got as an information.

For the protection, I have the SR469 settings to start with. I also have the pump/motor datasheets and curves.
With these information at hand, I would like to get your opinion and guidance based from your collective experience and I will take it from there.

Thank you very much.

 

[nightfox1925]

jaeref,

Critical Frequency Rejection: Is there a way for to determine this using the pump and motor data sheets and curves...or is this going to be determined during operational testing?

Pump Over-torque: Typically, the pump data sheet will show rated torque and this is normally less than the motor rated torque...can we set this based on pump rated torque?

Speed Ramp: Is there any typical rate employed for centrifugal pumps...just figuring out how to decide on this?

Current Ramp: This is associated with soft starting via VFD. Normally, I will be able to determined the %starting current via motor starting studies. However, the ramp time is something I have difficulty...I appreciate any guidance.

Best regards...

 

[LionelHutz]

I am asking because the questions he has put are rather typical for someone that doesn't quite know what to do and needs some time to discuss with his home-base.

How true this can be. I was recently at a site and the customer was also installing a medium voltage VFD in the near future. He was scheduling the start-up around the availablity of a certain factory support person. He'd been through start-ups a few times and this guy was the first one to show up and demonstrate the knowledge necessary to properly do the job.

 

[nightfox1925]

jaeref,Critical Frequency Rejection: Is there a way for to determine this using the pump and motor data sheets and curves...or is this going to be determined during operational testing?Pump Over-torque: Typically, the pump data sheet will show rated torque and this is normally less than the motor rated torque...can we set this based on pump rated torque?Speed Ramp: Is there any typical rate employed for centrifugal pumps...just figuring out how to decide on this?Current Ramp: This is associated with soft starting via VFD. Normally, I will be able to determined the %starting current via motor starting studies. However, the ramp time is something I have difficulty...I appreciate any guidance.Best regards...

I had some pump test sheets which shows vibration results on bearings for 15Hz, 30Hz, 60Hz, 120Hz. Can I use this to determine at what frequency I have to skip in my VFD control (Critical Frequency Rejection)? Or this is determined during pump operational testing?

 

[oldfieldguy]

As a client of the firm mentioned above, we didn't do the drives from their Robicon division, but rather the GM150 series.

Things are getting better, but the GM150 is a German design and the technicians/engineers in the US couldn't scratch their butts around that drive without phone calls and emails to people in Germany who knew the equipment.

It still requires interface with Germany any time we decide we want to do things a bit different or if a failure fix isn't readily obvious to the US guys.

I can say that the whole situation is quite frustrating.

old field guy

 

[Skogsgurra]

Nightfox,

Your questions with comments:

###Critical Frequency Rejection: Is there a way for to determine this using the pump and motor data sheets and curves...or is this going to be determined during operational testing?### Just because there is a possibility to avoid certain frequencies doesn't mean you hav to use it. Pumps do not often have critical speeds. If they have, your "process person" should have told you by now.

###Pump Over-torque: Typically, the pump data sheet will show rated torque and this is normally less than the motor rated torque...can we set this based on pump rated torque?### Again. You do not need to use all possibilities. Set your drive to suit the motor. It needn't be more complicated than that - unless you "process person" has anything to say about it.

###Speed Ramp: Is there any typical rate employed for centrifugal pumps...just figuring out how to decide on this?### The speed ramp can be important if you are moving long columns of fluid (risking water hammer). I would use 10 or 20 seconds if your "process person" doesn't say otherwise.

###Current Ramp: This is associated with soft starting via VFD. Normally, I will be able to determined the %starting current via motor starting studies. However, the ramp time is something I have difficulty...I appreciate any guidance.### The current ramp is to apply excitation current slowly so that there is no sudden movement when the rotor lines up with the stator flux. Usually no problem at all with pumps. Leave it at default setting - which is usually zero seconds.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[jraef]

By the way Nightfox, Gunnar travels...


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[nightfox1925]

Thank you for the guidance Gunnar, Jraef and to all. I'll be dealing with the Siemens fellow at site tomorrow.

Best regards

 

[nightfox1925]

If the VFD motor operates at slow speed, then motor cooling will also decrease assuming the motor is air cooled via coupled fan at the end of its shaft. However, this decreased motor cooling will not lead to excessive motor heating since the voltage applied to it is also proportionately decreased and the V/Hz ratio is maintained.

Is my technical outlook correct?

 

[oldfieldguy]

nightfox--

You are indeed correct. In our installations (7000-9000 HP) we have a cooling system augmentation blower to kick in at lower speeds where the motor-driven fan is less effective.

old field guy

 

[jraef]

...this decreased motor cooling will not lead to excessive motor heating since the voltage applied to it is also proportionately decreased and the V/Hz ratio is maintained (emphasis added)

This part of your statement can get you in trouble. Yes, the decrease in speed results in a decrease in motor consumed power and therefore less heat generated in the motor, but in general, the drop in cooling efficacy is steeper than the drop in heat rise, so without external cooling at the lowest speeds, the motor will over heat. Remember, a portion of the motor losses (heat) are fixed percentages of overall power absorption, so no matter how slow you go they remain relatively constant and become a larger proportion of the total losses. that is usually insignificant at higher speeds but becomes an issue when the cooling capabilities drop off rapidly at the low end.

The motor manufacturer should be able to answer this more definitively though; it has a lot to do with the motor design.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376