Light poles inducing damaging voltages?

[Jonelli]

I ran across this forum searching for anything related to this problem. It seemed like the posters here had quite a bit of experience and may shed some light on a problem that we have. I sincerely apologize in advance if this post is irrelevant or not appropriate for this forum.

We are a manufacturer of electronic audio equipment. We have an installation of our products in a foreign country where they have strapped our product to some light poles. I do not know what kind of light poles they are. I only know that they take 10-15 minutes to power up fully.

The light poles are mounted into a raised concrete floor, thus not actually into any earth.

The product mounted to the poles has its own separate 220VAC power with its own ground. It also has two other connections that loop to each other, a twisted pair shielded serial data connection that daisy chains to several products, and an audio twisted pair shielded wire daisy chained to several products.

When the lights are coming on, our products are being damaged by high voltages at the inputs of the data and audio connections.

I can only assume that there is induced voltage somewhere and a path from one pole to another via the data or audio connections is happening.

They have already tried using rubber isolators between the poles and the product's aluminum housing, and are not finding any large voltage potentials between the chassis ground and the light poles (during normal use). I don't know if they have also tested when the lights are powering on.

Any suggestions or a direction to look into would be most appreciated if you've ever heard of such issues.

 

[SG-1]

Some types of modern lighting have an igniter that produces voltage pulses in the KV range during start up, high enough to smoke a modern DMM. That pulse may be finding a path to your equipment.

You stated you equipment has it's own ground. This may also be a contributing factor. Can you give more detail on the grounding & bonding of the lights & your equipment.

 

[hurk27]

The problem your going to have in third world country's is the quality of electrical work, and wiring methods, many will bond poles to current carrying conductors, have loose and open splices, poor wiring which from time to time will short to the pole, many other things that can place a potential between two poles, some even use an ungrounded system, that if L1 was to short to pole 1, and L2 was to short to pole 2, you would have 220 volts between these two poles, yet no OCPD will open, this could happen anywhere in the system, and feed back through your common cables between the poles.

So how do we design a system to ignore this?

Isolation, I presume you audio systems and equipment uses some kind of power supply or transformer prior to your electronics, are you bonding the output of the power supply or the electronics after this point? if so don't, no need to, keep your boards floating and isolated, and use balanced connections between equipment so the all I/O's are isolated from any other reference, like equipment cases, poles, power (220) other then audio systems, and not knowing what fully the other equipment is, there might be other methods of isolation, but with using balanced inputs and outputs, you can avoid most all common connection problems that can occur equipment being fed from more then one source, I have done large venue sound systems, and know all to well how stray current between commonly connected equipment can cause everything from a nice 60 hz hum (50 hz in your case) to voltages damaging input amps on a mixer board to many other things, and each one has to be dealt case by case, but for the most part the most common fix is to isolate, and use balanced I/O's.

I wished many manufactures out there would stop trying to reference the electrical system grounding after their power supply, this would eliminate many problems, for them and us who get a write up to give them less then .5 volts between the neutral and the grounding conductor, very almost imposable in wiring of any circuit with any length to it.

 

[hurk27]

I want to add this, referencing the electrical system grounding, is old school, many manufactures have got away from this but not all, automobile manufactures had to get away from this when they started putting computers into them, how ever they did take a backward approach by isolating the 12 volt loads from the chassis, instead of the signal paths for the computer I/O's but the effect is the same. I think we need more tomorrow designs that incorporate isolation into the lower voltage side of the power supply, and use more balance system for inputs and outputs.

 

[Jonelli]

I'm leaning towards the problem being more related to what SG-1 is describing.
During the day, when the light poles are not on, none of the products fail. All audio and data connections are technically balanced, but not transformer isolated.

What they are telling me (I"m here in the states, trying to help a contractor overseas), the data communications input and audio inputs may fail after the light poles turn on.

I have seen the PCB's from our failed product. There is severe charring at the serial data input and audio inputs where only high voltage 100+ could have caused it.

I'll see if I can get more information on the grounding in our own product.

 

[Speedskater]

You might contact Bill Whitlock at Jensen Transformers:
http://www.jensen-transformers.com/

Jensen manufactures very good and very expensive Audio and Video transformers.
Mr. Whitlock has as much experience and knowledge as anyone about interfacing A/V systems to AC power systems.

A few of Bill Whitlock's papers:
http://www.jensen-transformers.com/apps_wp.html
http://www.jensen-transformers.com/apps_sc.html

 

[SG-1]

I'm leaning towards the problem being more related to what SG-1 is describing.
During the day, when the light poles are not on, none of the products fail. All audio and data connections are technically balanced, but not transformer isolated.

What they are telling me (I"m here in the states, trying to help a contractor overseas), the data communications input and audio inputs may fail after the light poles turn on.

I have seen the PCB's from our failed product. There is severe charring at the serial data input and audio inputs where only high voltage 100+ could have caused it.

I'll see if I can get more information on the grounding in our own product.

Hurk 27 is trying to tell you how to isolate your equipment from the dangers I mentioned & others he knows of. He has experience in your field. Carefully consider his advice.

 

[Open Neutral]

The problem your going to have in third world country's is the quality of electrical work, and wiring methods, many will bond poles to current carrying conductors, have loose and open splices, poor wiring which from time to time will short to the pole, many other things that can place a potential between two poles, some even use an ungrounded system.....

So how do we design a system to ignore this?

One word, but it is not "Plastics"...Rather it is fiber. Not easy, not cheap, but it solves the issue. Interconnect things with not copper but glass (or maybe.... plastics..) and solve your heartburn.

 

[Jonelli]

Thank you all for your constructive ideas.
I do know Bill Whitlock, and I might just give him a call about this. But I did hear back from our engineers and the explanation is that the internal reference is bonded to the chassis to meet safety and EMC regulations and cannot float. We're using digital switching amplifiers and switching power supplies, and by design they must be bonded this way.

One possible suggestions was to use MOV arresters at the inputs of the serial data and audio connections. This might protect in the case of high voltage pulses finding a path to our equipment.

 

[Speedskater]

Remember that a MOV also acts as a capacitor and can couple noise to undesirable places.