Electric Potential Across a Light Pole During a Storm

[gurusan]

Hello Everyone,

I am new to the forum so please bear with me. I have a pretty interesting problem on my hands and I would like to hear your inputs. The problem is this:

We are a wireless manufacturing firm that develops and manufactures wireless transceivers for transmission of video + data. We currently have a system deployed on a bridge which is causing us issues.

Here is the setup: On a light pole made of metal (not sure which one, probably steel or aluminum), we have a wireless transceiver, lightning arrestors, antennas, a camera on the TOP of the pole. All these devices (wireless unit, lightning surge protector, antenna, camera) are all grounded on to the top of the metal pole. This means that the ground connection on each of these devices is just drilled onto the the body of the pole at the TOP.

Now, this entire setup (wireless unit + camera) is powered by a solar panel + battery combo which is located at the BOTTOM of the pole . The battery is grounded to the BOTTOM of the pole and we have +12 V DC wires going up from the battery to power both the wireless unit + camera.

Finally, here is the problem: This whole setup is working fine until storm clouds pass over the location. During the storm clouds, the unit "lock up" or freeze and the only way to get these units back up and running is to reboot these transceivers after the storm clouds pass.

We think it is a grounding issue at this point as we think the storm winds and water droplets create static charges at the TOP of the pole via friction and create a potential gradient between the TOP and the BOTTOM of the pole. This leads to ground loops and the system performance deteriorates until the storm passes and the wireless units are rebooted.

I know this sounds like a far-fetched theory but I am just an electrical engineer out of college and I could appreciate some insight. Thanks!

 

[walkerj]

Sounds like a problem with the battery, IMSHO.

No sun, no solar power.

 

[bphgravity]

I don't believe it is static or any other charge either. I would tnd to believe it is simply a technical problem such as a faulty device somewhere in the mix and/or moisture in general creating problems.

 

[mpoulton]

Finally, here is the problem: This whole setup is working fine until storm clouds pass over the location. During the storm clouds, the unit "lock up" or freeze and the only way to get these units back up and running is to reboot these transceivers after the storm clouds pass.

We think it is a grounding issue at this point as we think the storm winds and water droplets create static charges at the TOP of the pole via friction and create a potential gradient between the TOP and the BOTTOM of the pole. This leads to ground loops and the system performance deteriorates until the storm passes and the wireless units are rebooted.

I know this sounds like a far-fetched theory but I am just an electrical engineer out of college and I could appreciate some insight. Thanks!

Highly improbable, and as an EE you can verify the improbability easily: The pole is metal. If you create a voltage gradient from top to bottom, what happens? The pole conducts. To create and maintain a gradient of even a couple volts along a metal pole would require a HUGE amount of current - hundreds or thousands of amps. You can calculate it if you want, based on the dimensions and resistivity of the pole. Then figure how many watts (kilowatts) that is. Bottom line is that triboelectricity does not produce high currents or powers. Triboelectricity is great at producing high voltages at very low currents. This is more likely to be your problem.

You may never know for sure, but it's probably a result of the static charge gradient in the air during a storm - the same effect responsible for Saint Elmo's Fire. During a storm, the electrostatic potential gradient in the air can be thousands of volts per inch. Any parts not grounded or shielded may suddenly find themselves floating at high potential compared to neighboring equipment. It is difficult to make sensitive digital electronics (especially MOS devices!) operate in an environment with huge electrostatic field gradients like a thunderstorm. However, you should probably start by checking the electrostatic shielding of your entire system. Is your entire installation enclosed in a Faraday cage, including continuous shielding of all interconnects? The antenna should be the only device not completely shielded, and it MUST be a DC grounded antenna design. Is there ANY path whatsoever for atmospheric charge to enter your system without being drained to ground? Now check the antenna system again - many are not DC grounded.

Finally, install protective devices on all major interconnections between devices. Got a data line running from one enclosure to another? Put zener diodes from each signal line to ground. A nearby lightning strike can induce huge currents in your wiring, which a Faraday cage will not help. This does not sound like your problem right now, but it certainly may become one eventually.