Lightening effect on PLC

patelbaroda · Jul 5, 2004

I have YASKAWA U84 PLC with remote I/O installed around 300 Meters away from Main CPU. The YASKAWA is MODICON 486 or 586 model. Recently we have faced a serious problem of PLC hanging along with lightening in the sky. This happend for last four times in just 20 days period. Other wise the PLC works fine. We have dual redundent CPU with switching module, Remote I/O driver, Communication module and ASCII module.

YOKOGAWA DCS CENTUM-XL is connected to the PLC through YOKOGAWA Gateways. The PLC has 1663 installed I/Os in six remote channels.

The communication between CPU and remote rack is through MODICON quad shield coaxial cable. The cables are redundent.

I request all users to share their knowledge and experience with me, if possible. my email ID is [email protected]

The PLC earth pit is seperate from DCS , PANEL earthpit. The coax cable is laid on the top of the cable rack and in the GI pipe of schedule 40 and the GI pipe is grounded to power earth. The PLC earth pit resistance is less then 1 ohms and both remote I/O installed at electrical substation and main CPU rack earthpits are connected through a grounding cable. DCS, PANEL and PLC is not showing any earth connection with each other.

Thanks in advance.
Pragnesh Patel

CaseyK · Jul 5, 2004

Being that you have coax brings on different techniques then I normally run into.

When I was working with 2-way radios for a large city, we made sure everything was grounded, or had a suppressor or arrestor on it. All cabinets, towers, supporting structures were grounded. We had several hundred control lines around the city, dozens out in the country, and many that were regional. Some had a DC current fed over them, some had tones, others were digital. We were able to eliminate most of our lightning problems.

The fire department had firehouses, pull boxes, and alarm bells all over. When lightning came around, all the bells rang.

A feed through arrestor may be available for your type of coax or connectors. For your data, you could also make one, with a MOV Metal Oxide Varistor, with the lowest voltage rating that you can get away with) from each lead to ground, though my personal thoughts is a gas discharge would be a little better suited.

All power lines should have MOV's. That would include a MOV from hot to ground, neutral to ground, and hot to neutral.

Only guaranteed solution is fiber optic, and that is NOT 100%.

regards……casey

Tom Jenkins · Jul 6, 2004

PolyPhaser Corp. has surge suppressors for co-ax cable. You could also look at Phoenix Contact, B & B Electroincs, and Black Box Corp.

Your problem may not be in the comm link. You should make sure you have good surge protection and EMI/RFI filtering on the incoming power. Cutler Hammer, AutomatinDirect.com, Joslyn, MCG, and others have filter / surge suppressor products.

You may also want to look at the field terminal blocks. Phoenix Contact and many others have terminals with MOVs or diodes built in and tied to the DIN rail for surge suppression. You can also consider fused terminals in conjunction with these.

gcere · Jul 7, 2004

See the 300m cable

Hello

I thin this points may be useful:

1) When are lightning in the sky, the there are some difference in potencial between grounds, more even if there are 300m saparated.

2) When the cable is not undergrounded, the cable get potentical through the sky, like a capacitor.
In this case the best thing is to (re-)shield it.

3) See the way of the cables, be careful, that in the frecuency of the lightning surge (1MHz) one 10cm straight cable may take 1kV, when the surge courrent pass across.

Hope this could help.

Regards

Jeffersonian · Jul 7, 2004

I did a job similar to this on a lock and dam on the Mississippi River. We got past the lightning issue by putting fiber optic repeaters on our I/O runs and using them instead of the coax. Never had a problem.

jayesh_vardhman · Sep 27, 2007

Lightning Protection

Dear Mr Patel, Baroda,

Please get protected by experts in the field. LPI - Lightning Protection International Private Limited, 16, Mertonvale Circuit, Kingston, Tosmania, Australia 3050 manufactures systems to provide protections against lightning. Through MAP World Wide Services, Mumbai you can get more details. You need to have protections against the lightning strikes that destroys or damages your system and perhaps you will get right solution.

Jayesh Shah / Surat.

patelbaroda said:
I have YASKAWA U84 PLC with remote I/O installed around 300 Meters away from Main CPU. The YASKAWA is MODICON 486 or 586 model. Recently we have faced a serious problem of PLC hanging along with lightening in the sky. This happend for last four times in just 20 days period. Other wise the PLC works fine. We have dual redundent CPU with switching module, Remote I/O driver, Communication module and ASCII module.

YOKOGAWA DCS CENTUM-XL is connected to the PLC through YOKOGAWA Gateways. The PLC has 1663 installed I/Os in six remote channels.

The communication between CPU and remote rack is through MODICON quad shield coaxial cable. The cables are redundent.

I request all users to share their knowledge and experience with me, if possible. my email ID is [email protected]

The PLC earth pit is seperate from DCS , PANEL earthpit. The coax cable is laid on the top of the cable rack and in the GI pipe of schedule 40 and the GI pipe is grounded to power earth. The PLC earth pit resistance is less then 1 ohms and both remote I/O installed at electrical substation and main CPU rack earthpits are connected through a grounding cable. DCS, PANEL and PLC is not showing any earth connection with each other.

Thanks in advance.
Pragnesh Patel

Lightening effect on PLC

patelbaroda

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CaseyK

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Tom Jenkins

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gcere

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Jeffersonian

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jayesh_vardhman

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