VFD noise

[MTUgEEk]

I have an electrical room with many large VFD's(200+hp). We know we have a problem with install (not grounding the shields on the power cables correctly) and need to fix this issue. I was wondering if someone could suggest a measurement means (EMC/EMI meter) to quantify the fixes and record the before and after.

Thanks

 

[magoo2]

Your best bet is to pay for a qualified engineer to come in and handle it. Sounds like you don't have any idea what to do. There's a lot of safety issues with just trial and error.

 

[MTUgEEk]

Although not to far from the truth, not entirely accurate. I guess I am not sure from the post why you would say I don’t have any idea what to do. I don’t believe following the vendors suggested installation practices ,as well as consulting and working with the manufacture to install suggested hardware is trial and error. I was not in-charge of the install, i was handed it after construction and would like to hand the engineering firm that designed this, a before and after to stress the importance of following the rules. I was hoping to get a few suggestions on hand held meters to measure the noise on the present install. Does anyone have a suggestion?

 

[ozmosis]

EMI is a wide spectrum covering the lower frequency band (Harmonics typically within 150Hz to 3kHz) through to the high frequency band from 120kHZ to 30MHz.
If by noise you mean Radio Frequency interference then you need something to measure HF band and these are not typically handheld. You would need an oscilloscope and also the knowledge as to where to measure.
EMI comes in two distinct areas: radiated and conducted emission and conducted emission is a lot easier to measure than radiated, when you know the limits you need to adhere to and what would specifically be a problem.
Usually you are measuring 'where you have problems'. For example, if you have serial communications controlling your VFD's and this is via a RS485 network. You would pop your scope on the RS485 signal and look for deformation of the waverform and "grass" on the top of the peaks as this is a likely indication that you are getting RFI onto your commsn network.

It is a wide ranging topic and issue and does require specialist help and equipment.
A useful booklet, is this one published by GAMBICA:

http://www.gambica.org.uk/web_image...allation_Guide_Power_Drive_Systems_3rd_ed.pdf