frequency inverters to controll flow rates

[themroc]

Instead of using control valves in order to control the flow I intend to use Frequency inverters to regulate the motor speed of a centrifugal pump (2.2kW)
With this type of controll I had quiet good experience in the past.
Now my Question: The FI Inverters I intend to use are Siemens Micromasters, they will be used on a test rig with lots of meassuring devices, mainly for temperature, flow and pressure.

Is there any danger that the signals are interfered by the frequency Inverter. What would be your recommendations is it better to shield the inverters in a metal panel or is it o.k. to mount the without enclosure?

 

[Valvecrazy]

You did not say how you were controlling flow. However, if you are using a PID loop to maintain a constant pressure, you should read this thread.

http://www.eng-tips.com/viewthread.cfm?qid=205555&page=1

 

[gepman]

If you ask this question in the "Electric motors and motor controls engineering" forum you will get a lot of replies. PWM VFD's put out a lot of noise. My experience is that unless the instrumentation signal is a 4-20ma current signal or similar there will be problems with signal level wiring in close proximity to the VFD or the VFD motor leads. No matter what the signals are, to be safe I would have the instrumentation I/O and the VFD in separate enclosures and all instrumentation cable should be shielded while the VFD motor leads should be in steel (not aluminum) conduit.

 

[themroc]

Thanks gepman, I will consider this and post it maybe there.
Only one stupid Question, what does PWM and VFD stand for?

One other think, All my signals are 4 to 20mA except for the temperature sensors which are T-Type thermocouples and 4 wire PT-100. The cables of all instrumens are shielded is there any issue with the temperature sensors?

The sensors are powered in general by 24V or 110V supply Voltage, does a frequency inverter effect this voltages in any adverse way.

One last thing, the noise of these Frequency inverters is there any health issue associated with this?

thanks

 

[ScottyUK]

PWM - Pulse Width Modulation. The means by which the drive produces a variable frequency, variable amplitude output.

VFD - Variable Frequency Drive. The means by which the drive varies the speed of what is essentially a fixed speed motor. Usually taken to be synonymous with VSD (Variable Speed Drive) although some people will argue that the latter has a broader meaning covering mechanical and other electro-magnetic types of drive.

If you follow good installation practice there should not be any problems with either a thermocouple or RTD. Pay attention to the grounding of screens and shields, both on the instruments and on the power circuit. Use twisted pairs / triads for the instrument circuits and maintain segregation from the power circuit.

Your power supplies should not be adversely affected if they are of good quality and installed correctly.

There are no recognised health hazards caused by electrical noise from a VFD. Maybe on a very large drives older design you might get a sound level where PPE becomes necessary due to audible noise.


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If we learn from our mistakes I'm getting a great education!

 

[Valvecrazy]

I found a few things about the health effects of "stray voltage". Here is one of them.


"Stray Voltage" has been well documented as causing health problems with dairy cattle. Excessive stray voltage at a dairy can cause reductions in milk production, mastitis of the udder, loss of unborn calves, sore feet and other problems.

The dose response curve and replication (50 or more cows per herd) makes it obvious. With humans, each one of us is viewed in isolation. There has been extreme reluctance to examine electrical exposure via plumbing, ground currents, dirty power on wires or any other source. People are much more likely to be treated symptom by symptom, illness by illness.

While the human health effects of exposure to electrical ground currents have gotten little media attention, that is not because they are non-existent. Electrical ground currents are pretty conclusively linked to an increase in the risk of childhood leukemia. The high frequencies that pollute our electricity and cause the electrical ground currents have been linked to increased blood glucose levels, multiple sclerosis symptoms, asthma, allergies, migraines, chronic fatigue syndrome and an assortment of other symptoms.

 

[ScottyUK]

Electrical ground currents are pretty conclusively linked to an increase in the risk of childhood leukemia. The high frequencies that pollute our electricity and cause the electrical ground currents have been linked to increased blood glucose levels, multiple sclerosis symptoms, asthma, allergies, migraines, chronic fatigue syndrome and an assortment of other symptoms.

Please cite references for this. I haven't seen anything resembling consensus on this side of the pond to support these claims, only scaremongering by minority interest groups who only acknowledge results of studies which support their agenda and ignore those which don't. Granted there are SOME studies which suggest a link between EM fields and leukemia and other illnesses, and others which show there to be no link at all. Hardly conclusive is it?


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If we learn from our mistakes I'm getting a great education!

 

[Valvecrazy]

Following is the link where I found that quote. Lots of stuff like this when searching for "stray voltage".

http://www.electricalpollution.com/

 

[BigInch]

I'm not saying these EM effects are or arn't true, just that I have personal reasons to believe they may be, so you might want to be cautious.

It is my understanding that electromagnetic related "illnesses" are a recognized workers health hazard in both Sweden and Russia, elligible for medical treatment including paid recouperation time. In Sweden, it is also my understanding that the offending equipment must be corrected or removed. I am interested to know if true.

http://virtualpipeline.spaces.msn.com

"We can't solve problems by using the same kind of thinking we used when we created them." -Albert Einstein

 

[ScottyUK]

I can't honestly consider that as an unbiased and objective website. I am definitely not saying that there isn't a potential problem, but I do expect some properly documented and repeatable scientific research to be presented. I work in the power industry and we have some very powerful magnetic fields in certain areas of the site where personnel may be from time to time. I am very interested in knowing if there are long term health risks, but I'm pretty sure there has been no conclusive result regarding leukemia clusters near electrical plant, and that those clusters have other equally plausible explanations.

What might be of interest is the following report

http://www.hpa.org.uk/radiation/publications/hpa_rpd_reports/2005/hpa_rpd_010.pdf

which does acknowledge that some people may suffer from a variety of other ailments due to exposure to EM radiation.


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If we learn from our mistakes I'm getting a great education!

 

[Valvecrazy]

That is an interesting article but, it really doesn't end up with a conclusion. I have personally seen the adverse health effects in dairy cattle. My test was no more elaborate than to simply remove the equipment that was producing the stray voltage, and the health of the cattle improved drastically and almost immediately. The milk production also increased by 50% within a couple of days. I do not see how stray voltage could have such obvious health effects on cattle, and not have a similar effect on humans as well.

 

[ScottyUK]

That is an interesting article but, it really doesn't end up with a conclusion.

Of course it doesn't - it was published by the Government! More seriously, I think there is a lot more research needed to understand the mechanisms through which EM radiation interacts with living things before we can make any meaningful judgement.

I have heard of the problems with cows before. It's not so much stray voltage as stray current which is flowing in the mass of earth rather than in a line or neutral conductor. The current directly passes through the body because the cow forms a parallel path with the ground. I guess cows are susceptible because of their size - greater potential difference between their front and back legs compared to a smaller animal - and propensity to be found in very damp conditions giving a good connection to earth.


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If we learn from our mistakes I'm getting a great education!

 

[BigInch]

EU Joint Research Center,

http://web.jrc.ec.europa.eu/emf-net/

http://virtualpipeline.spaces.msn.com

"We can't solve problems by using the same kind of thinking we used when we created them." -Albert Einstein