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Grounding riddle no.3 – EMC and Electronic grounding

In that power plant, the separated hole of electronic grounding is located far from control room, therefore the used cables for suitable interconnection between equipments and earth pit shall be long enough.
The electronic system is safe against effects of corrosion and vibration also grounding system loop currents that usually observed in "multiple point" grounding systems and may cause inadvertent noises. However that control system has some EMC problems. Investigations show a 700 KHZ noise interference existence in system that has created this EMC problem in power plant control system.


How can you explain the reason of existence of inadvertent noises?


Author : Hamid
 
#1
Thu, September 13, 2007 - 11:23

Just because a system is properly grounded doesn't mean it won't be noisy. Things need to be properly designed and shielded to avoid EMI. 
Author : bhankiii
 
#2
Thu, September 13, 2007 - 11:23

The problem with noise in control systems is long standing. Shielding is partly science and often a lot of art.

The push to fibre optic data transmission significantly reduces those problems.

Anything that has high frequency components often get reflected into the controls, such as Variable Frequency Drives, electronic ballast for lights, welding machines, sparking electric motors, radio transmitters etc 
Author : GW
 
#3
Thu, September 13, 2007 - 11:25

The long ground wires are acting as antennae and picking up fields from some other piece of equipement.
It's a common problem in designing monitoring systems. You can either have lots of local grounds and suffer from ground loops or have a single central ground but suffer from noise in the ground lines.
Since your system is digital it would probably be best to have locally grounded instruments and transmit the data back on a differential data bus. 
Author : mgb_phys
 
#4
Thu, September 13, 2007 - 11:26
Thank you very much for wonderful answer. 
Author : Hamid
 
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