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Participant

Join Date: Feb 2009
Posts: 3

Do Line Filters Remove EMI and RFI?

02/19/2009 3:08 PM

I want to filter out irregulations and noises (power conditioning)coming through power line to PID controls and VFDs.

Do we get suitable filters to filter out line noises coming to electrical panel through 3 phase line?

Prashbh.

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Pathfinder Tags: line filter/power currection/power conditioner
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Guru
New Zealand - Member - Kiwi Popular Science - Weaponology - New Member Engineering Fields - Power Engineering - New Member Engineering Fields - Electrical Engineering - New Member

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#1

Re: Do Line filters sort out RFI and EMI problems?

02/19/2009 5:12 PM

It depends on how good your incoming supply quality is. If the noise is just coming from your VFDs then you are better of placing line filters on the VFD supply input (close to the VFD) instead of the main switchboard (electrical panel). If you are still getting noise issues, then you could use screened motor cables and possibly change the drive switching frequency (to a lower frequency). There should be installation instructions in your VFD manual that cover this, along with suitable filters.

If your incoming supply quality isn't too good and you are getting noise coming in then a filter at the main switchboard would help. However, if your incoming supply quality issues also include voltage sags (drops in supply voltage) that are effecting your equipment, then you would need to consider installing some form of voltage stabilisation device such as putting a UPS on the equipment that is being effected (such as computers the PLCs, DCS, etc).

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Join Date: Jan 2008
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#2

Re: Do Line Filters Remove EMI and RFI?

02/19/2009 11:19 PM

The query title doesn't seem to quite track with the query text itself.

Line filters can indeed filter out EMI/rfi - that is what they are designed to do. But by definition, EMI/rfi covers a spectrum from 150 kHz and up. The regulations imposed to protect radio reception against EMI/rfi start at 150 kHz, because that's where the commercial broadcast band (BCB) starts (in Europe).

Now that start frequency roughly corresponds to an event lasting no longer than a few microseconds. So if the type of noise you are interested in lasts longer than that, the typical EMI/rfi filter will be ineffective.

You will have to rely on your bulk hold up cap and any other distributed hold up (such as electrolytic caps at the power entry point on daughterboard/motherboard interfaces to provide tens of microseconds or longer hold up.

A basic off-line switched mode power supply can provide quite a bit of constant output voltage as long as the line voltage remains within its operating range. For instance, many such power supplies work from 100 - 230 Vac.

If that doesn't work for you, you may need some brute force help like an UPS or a constant voltage output transformer (Sola makes these).

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Guru

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#3
In reply to #2

Re: Do Line Filters Remove EMI and RFI?

02/20/2009 3:17 PM

Regards.

A cheaper & effective solution may be "Power-Line-Conditioners" for "Conducted-Interference"; but "Radiated-Interference"

through "Control" & Power-Cables demand layout of cables. And demands on-site Hit-& Trial metod.

Generic solutions are:

1. Screened Control-Cables.

2. Twisted Power-Cables to avoid Common-Mode Interference.

3. Keeping distance between Power & Control cables & shortest possible lengths.

4. Front-End Line Filters.

.....

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Anonymous Poster
#4

Re: Do Line Filters Remove EMI and RFI?

06/07/2010 10:25 AM

Three phase filters are normally available in chassis mounting style and bigger in size than the single phase filters

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