Water Tank and Lightning

[Duuuuug]

Got a call this morning.
Ground Storage Water Tank at the top of a mountain.
The only electrical at the site is a solar panel that powers a Drexelbrook Level Transducer that sends a 4-20mA signal 2000FT to a pump station to start and stop a pump based on level.
The contractor installed a surge arrestor that has blown on two separate times due to lightning, lost communications and the tank water level went low.
Ground rods are driven every 20FT around the tank circumference and connected with 4/0 cable and then connected to the water pipe underground.

QUESTION
1. Does anyone have any comments about possible solutions?
2. Is there a "re-settable" Surge Arrestor?

 

[ron]

Re: Water Tank and Lightning

First, test the integrity of the grounding electrode system with a tester (typically fall of potential).
Be sure the TVSS is listed as compliant with "second edition UL1449".
Be sure the TVSS is connected with a very short set of conductors.
Be sure the proper modes of protection are provided (L-L, L-N, L-G as needed).
Be sure you have selected the proper category of protection for your installation C3, C2, C1, B3, etc and the proper kA capability per mode.
Multiple levels of TVSS is a good idea to help reduce surges to a more managable level.
Because you have only solar panels, the withstand (short circuit) rating will not be an issue.

They are automatically resettable, unless they are zapped by something that exceeds it ratings.
http://bg.ecmweb.com/ar/electric_surge_protection_selection_2/

 

[justdavemamm]

Re: Water Tank and Lightning

If the LT is the only device powered by the solar panel, I'm wondering why they did it that way. Of the hundreds of process transmitters I buy/use/install each year, only a few (select types of flow meters) need a separate power source.

Most 4-20ma instruments are loop powered, so no power source is needed at the instrument. Since the wire would be sized to allow enough current at the minimum required voltage, a 24 to 48 vdc power supply typically is used at the pump end.

Even if there are other devices needing power, I don't understand why a power cable (A/C or D/C) wasn't run.

Oh well.

 

[tom baker]

Re: Water Tank and Lightning

You don't need power at the tank, if you use a loop powered device. The power would be from the pump station.
I have installed the Drexlebook before, the ones we have were removed as they are inaccurate. I now use a pressure transducer at the bottom of the tank.
You probably need a more robust TVSS.

 

[Duuuuug]

Re: Water Tank and Lightning

More info:
I haven't been to this site at all.
I was just called to look at it and see if I could help them find a solution.
They have had problems with the drxelbrook unit (P/N 505-1100-001) and moisture forming on the face of the transducer causing it to be inaccurate. They added some kind of heater to it to keep the moisture from forming.
AND They are using a dedicated phone line to carry the 4-20mA signal from the Tank to the pump station.
Not Sure yet, but I think the problem surge suppressor is on the phone line.
Will let you know.

 

[physis]

Re: Water Tank and Lightning

I have no experience or knowledge of these transducers or the system arrangment.

A water level transducer that can't handle moisture? Am I the only one who thinks that's bad?

The pressure tranducer that Tom mentioned sounds interesting to me. I've worked with scales that can measure a fly passing it.

Again, not knowing much about this field. It sounds like a good idea to run a conductor at or in the ground to a transducer in the "bottom" of the tank.

 

[justdavemamm]

Re: Water Tank and Lightning

Wow, this sounds like one thing after another.

The 1100 series LT is Ultrasonic and takes either 110vac or 24vdc as a power source and is NOT loop powered.

I only use Ultrasonic if the temperature is to high for a pressure transmitter.

Now to just add a little more *IMHO* I might have used plain old level switches, one for high, one for low and used them for turning the pump on & off.

 

[physis]

Re: Water Tank and Lightning

Now to just add a little more *IMHO* I might have used plain old level switches, one for high, one for low and used them for turning the pump on & off.

Golly gee, is anything that simple anymore?

Must use higher technology? Musn't we?

Sorry, I couldn't help myself. :roll:

 

[hurk27]

Re: Water Tank and Lightning

The problem with any equipment uses very small cable that runs for a long distance is lightning will take all paths to earth and since there is no other conductors between the top and bottom of this mountain it will try to take the path of these cables and most likely blow them apart. It would be impossible to setup a TVSS to protect the cable since each end is "2000'" away from each other. so the next thing would be to invest into a method that does not use a electrical path between the top and bottom of the mountain. Like wireless, fiber optics Etc... This way the transmitter can be protected by fortified fortress style protection, Ie: metal enclosure, single point entrance grounding/bonding, And the TVSS/arrester will have a better chance of protecting the circuit's that enter or leave this enclosure. As it is now you have a great voltage potential between the top and bottom of the mountain that only has the small signal wires inbetween, Not good!

Maybe Dereck will chime in as I'm sure he has dealt with remote micro links for the telco's and could have more to add.

[ August 16, 2005, 01:44 AM: Message edited by: hurk27 ]

 

[physis]

Re: Water Tank and Lightning

All of that is pretty sensible Wayne. And this is by no means an area of expertise for me. Running the signal cable in EMT seems like a good Idea.

Mostly though, I feel compelled to point that there's already a cable from the tank to the station. As far as I can tell from the original post that end of it's holding up.

I'm thinking that when the lightning gets to the ground that it really isn't gonna be very interested in a small signal cable.

 

[hurk27]

Re: Water Tank and Lightning

But sam how good is that gounding 2000' high up on a mountain?

 

[physis]

Re: Water Tank and Lightning

I don't know.

Edit: and morels don't even grow until 4000' so I'm not impressed.

[ August 16, 2005, 03:13 AM: Message edited by: physis ]

 

[petersonra]

Re: Water Tank and Lightning

a couple of things come to mind. most of the time when these type of instruments don't work as expected is because they were either misapplied in the first place or installed improperly. i am not a huge fan of this type of level control in the first place because it is vastly more complex than what you need. A simple pressure (or D/P) transmitter is more than adequate for this type of task and far more robust, and costs less to boot.

there are lightning protection devices you can buy for 2 wire xmtrs that actually do a pretty fair job of protecting the instruments, but there are no guarantees. you can also get a pressure xmtr with the lightning protection built directly into the unit itself, which is about as good as it gets.

<added> you could also try putting in one or more isolators along the way, but how many you can install will be severely limited by the voltage drop, and with such a long run you probably have a lot of voltage drop just in the wires. one of your problems may be that you have a very long antenna stretching down the mountain. This might well be quite attractive to lightning. putting in a couple of isolators along the way might well make it less attractive to lightning.

all in all, i like the wireless idea.

[ August 16, 2005, 07:33 AM: Message edited by: petersonra ]