Cause of RFI during chiller compressor operation 1

[PQ101]

As soon as the newly installed chiller starts-up the reception on AM radio signal disppears for appx. 5-6 blocks. The 200Ton chiller is equipped with harmonic filter. Equipment manufac. has replaced all circuit boards, the SCR panel, installed isolation transformer, chokes around the cables, installed PVC on incoming power conduit, etc. but made no change.

You can basically hear compressor motor whining-distortion on AM radio anywhere from AM500 thru AM1500.

To start with grounding from 480V Main panel to isolation transformer to chiller starter enclosure to compressor motor was checked for proper installation as per NEC and verified OK. Plan was to set power analyzer to check for waveform distortion including the equipment ground.

As soon as chiller is shutoff the AM radio signal comes back to normal. Appreciate any help to narrow down the cause.

 

[Skogsgurra]

You didn't say that the motor is fed from a frequency inverter. But I put one thousand dollars on the table and say it is. If it isn't, you can take the money.

PWM inverters emit powerful HF noise and that is what your AM radios are picking up. NEC doesn't have anything with HF pollution to do, FCC has. So, you have to apply other knowledge than power electrical to this.

A power analyzer will not show what is going on simply because it doesn't have the necessary frequency range. Use an HF high-pass filter plus an oscilloscope to see what is going on.

The simplest and usually quite efficient remedy is to use common mode filters (HF ferrites of the correct quality) on the mains and motor cables. You need a specialist to deal with this. I would talk to the supplier of the compressor first. If that doesn't help, I would talk to the VFD manufacturer.

Where in the world are you?

Gunnar Englund

http://www.gke.org

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

 

[PQ101]

SKOGS, of course it's a VFD, and yes the manufacturere has implemented many many remedies to fix but the problem still exists. In the process they did make changes to grounding i.e. multiple ground rods, disconnected grounding-bonding to conduit piping by placeing PVCs in between, chokes-ferrites,etc. So I had to check and bring grounding up to code. Using Radar Engineers Model 240 RFI Locator, I can see the waveform distortion at compressor end, SCR module, and it is clear operation of VFD is causing it. The point is which component is the suspect cause!!!

The question is that this is a brand new unit, and apparently something is wrong. I just started on this case, and plan to check for cable/wiring seperation at inside chiller enclosure all the way to sensors, etc.

Has anyone experienced this same situation? we are talking professionaly so "please do not respond if did not experience this same issue before". Thanks a lot.

 

[Skogsgurra]

I think that you should check my background. I do not respond without having something to say.

Gunnar Englund

http://www.gke.org

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

 

[dpc]

You come for free advice and then offer advice on how to give advice to a recognized expert in the field who normally gets paid for this type of assistance. Not a great way to encourage further contributions.

 

[PQ101]

My apology. You guys are right. I've attached some pictures for clarity and all advice are welcomed. This case is unique in a sense that unit is brand new, pre-wired, design expert from factory floor has implemented at least 12 changes (but RFI on AM radio reception still exist during compressor run).

The 480V incoming cable enters the enclosure from the top (conduit piping shown), 3-phase lands on chiller disconnect switch (ground conductor on GRD lug, power feed goes thru VFD/SCR, departs to compressor disconnect (with ground), and then to compressor peckerhead.

Plan was to start investigation and check for electrical/control wiring seperation, collect data and determine why only this unit is causing RFI and no other York unit according to factory floor, crack the case and share the information to help others.

 

[PQ101]

Field pictures are attached, showing departing cables from chiller controller enclosure thru SCR, CTs, to compressor disconnect, to motor housing. At compressor terminal I see some control wiring near power cables.

 

[PQ101]

More pics

 

[PQ101]

Chiller control eclosure for information.

 

[PQ101]

480V Cables departing from SCR panel thru CTs and out to compressor disconnect.

 

[PQ101]

Conduit piping to chiller enclosure.

 

[PQ101]

Isolation transformer.

 

[PQ101]

Compressor #1 & 2

 

[Skogsgurra]

OK, we can do some work then.

The reason I said you probably have a VFD was that you mentioned an SCR panel, which implies a DC motor. And those do not emit nearly as much EMI as VFDs with IGBTs do.

I do not think that anything is broke or defect in your compressor. IGBTs just output lots of radiated EMI and the fact that the unit is brand new does not change that.

There are two basic methods to keep the inevitable EMI from getting out of the enclosure. One is to block HF. That is done using correct quality (with f0 well abobe 1 MHz) ferrite or nanocrystalline toroids. The other is to short the HF energy to ground. And using short braids to do that. The latter metod means that your ground (and usually same as PE) gets polluted with HF current. So it isn't a good method.

Blocking as close to the inverter as possible and doing it with enough HF ferrite cores is usually what works best. Use ferrite cores both on grid side and motor side, but be sure that you only put the three phase cables through the cores. The toroids will saturate if you do that wrong. They will usually also overheat.

In severe cases, you may need quite a few of those ferrites. See attached picture. I was not allowed to remove the protective grid to take the picture. So you have to 'see through' it. You may also need to make the cabinet HF tight. Removing paint and using metal mesh or beryllium bronze fingers between frame and covers and doors may help.

If you are in Europe, there are limits for permissible emission and you can tell the manufaturer to deliver another unit if it cannot be 'silenced' to levels below these limits. In the US or other places, I don't think that you have that possibility.

Most manufacturers do not understand this very well. Sad but true. I will visit a York compressor for a slaughterhouse on Monday. They have have fitted toroids but now, there is a bearing problem also. What make is your VFD?

Gunnar Englund

http://www.gke.org

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

 

[Skogsgurra]

BTW, I will be in Buffalo, NY week after next. I can pop in and have a cup of coffee and also have a look at the problem. If you are close to Buffalo, that is.

Gunnar Englund

http://www.gke.org

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

 

[rasevskii]

Hello PQ101

You might want to consider adding fine-mesh stainless steel or brass screening to the inside of the louvered panel doors, spot-welded in. In principle it is acting like a radio transmitter. This seems to be the practice on radio transmitter cabinets. Also the doors have to be bonded to the cabinet by braids as said before.

Worth a try.

regards, rasevskii

 

[PQ101]

How long will you be in Buffalo?

FYI-It's a packaged York unit. I will be in Burrie, Ontario on Monday but the chiller facility is located south of Champaign, Illinois. Plan to head there the week after next when the folks come back from Thanksgiving holidays.

One thing I noticed: looking at the pictures received it shows a few ferrite cores installed on cables going to harmonic filter/coil to SCR block. Regarding the ground conductors going to each compressor (from enclosure), I'm not sure if they are solid conductors all the way to the compressoror motor (or is it OK to rely on frame-enclosure ground to provide the path). Reading your comment I gather that RFI is IGBT-related and more ferrite cores are needed to fix the situation to say the least. Wonder why RFI is affecting this unit and not 100 others previously installed.

 

[PQ101]

Thanks Rasevskii.

Louver panels are not equipped with SS or brass screens, but the front doors have braided ground bonded to panel enclosure (side panel).

 

[PQ101]

Power quality data collected during chiller operation indicates voltage sag/waveform distortion on all all 3-phase. Chiller was started several time for abouit 2-3 minute run, with CT clamps on all three phase and ground conductors going back to the isolation transformer and 480V Mains. Ground current increases to 5Amps. Line voltage decreases momentarily to 248volts (from 495volts nominal) during inrush.

 

[ozmosis]

Another point worth noting.
With all cases of EMI, it is not just the aspect of emission that needs limiting but the immunity of other components.
If you are in an industrial environment based on industrial emission levels, then all your products around should be based on "industrial" immunity levels. However, if you have a product in an industrial environment that has "domestic" levels of immunity then you will not achieve parity when looking at compatibility.
Whilst the EU EMC standards are much derided by various circles in North America, they do actually make sense when you have problems.