How we get optimal resistance reading ?

[230kv]

How we get optimal resistance reading after installed ground rod in transmission lines tower in dry area?

The reason for my question is after we installed ground rod then we take the measurement ....let say ...15 Ohm then after few menthes the reading increase to be 60…80…Ohm !? :confused:

[Koga]

If you use water to work it down. Then once the water soaks in and or dries a little the reading will go up. Alot depends on the soil it self and some times you have to drive 2-3 or more to get an acceptible reading.


Koga

[230kv]

Actually some places we drive 3 to 4 rods on top of each other….I heard if we use coal maybe will be better, but in this case we have to use Digger truck to give place for the coal ,in same time I'm not sure for how long it will work?:cool:

[thrasher]

When trying to get lower resistance the best bet is to go deep with stacked rods. First you get more "shell effect" second you are more likely to hit naturally moist ground down deep. "Shell effect" is imagine a cone forms around a rod, the theory says the width of the cone is equal to the depth of the cone. If you do the math you have more volume in a 30' wide by 30' deep cone then in three 10' by 10' cones. (1580 cubic feet vs 526 cubic feet). I have used loresco brand carbon backfill to ground a 115kv switch yard that was built in an area with lots of granite sticking up out of the ground. We hired a well driller to drill a 200' deep six inch diameter hole then screwed together 200 feet of rod and back filled the hole with the carbon powder. Found it worked best to mix the carbon with some water and laundry soap. Without the soap the carbon just wants to float on the water because it's ground so fine. Probably one of the dirtest jobs i have every been around. Probably not worth it for individual towers but this was a switchyard.

[Stinger]

Tramp's way is the way I was taught. Did a transmission line in Kitty Hawk awhile ago, on some towers we had to put in as many as 6 ground rod cages in different ditrections from the tower to get it down to 25ohms or less.

[duckhunter]

Here in Northern Michigan we are on a pile of sand (Sleeping Bear National Lakeshore). We drive rods on top of each other to try to reach 25 ohms or better. We stop after 10 rods if we do not achieve 25 ohms. We do this at all U.G enclosures and all pole mounted transformers, fuses, OCR's and regulators. It has stooped the lines laying on the ground burning.

[230kv]

Here in Northern Michigan we are on a pile of sand (Sleeping Bear National Lakeshore). We drive rods on top of each other to try to reach 25 ohms or better. We stop after 10 rods if we do not achieve 25 ohms. We do this at all U.G enclosures and all pole mounted transformers, fuses, OCR's and regulators. It has stooped the lines laying on the ground burning.

Interesting, how you install 10 rods on top of each other? Which tools you used for that!
In our area very hard to install more than 5 rods, and we are using Jack Hammer with Air compressor.

[wudwlkr]

How exactly are you measuring the resistance of the grounds? And what type of configuration are the grounds in, single ground connected to pole/tower with ground wire, multiple grounds connected to each other with wire, grounds off each tower leg, etc.?

Also it takes time. I believe it was an A.B. Chance study that showed it can take two years or longer after installing grounds for the earth to properly settle around the rods and give the best/lowest resistance.

[230kv]

How exactly are you measuring the resistance of the grounds? And what type of configuration are the grounds in, single ground connected to pole/tower with ground wire, multiple grounds connected to each other with wire, grounds off each tower leg, etc.?

Also it takes time. I believe it was an A.B. Chance study that showed it can take two years or longer after installing grounds for the earth to properly settle around the rods and give the best/lowest resistance.

We measure by Clamp-On Ground Resistance Tester AEMC proudest. If we get doubt we test by two measures to make sure.
Both of configurations we use single & multiple grounds connected; depend on the reading and area.
One of our 230 kv line was installed ground rods through our company contractor….after almost 7...8 years resistance reading was very high!!:(

[wudwlkr]

We measure by Clamp-On Ground Resistance Tester AEMC proudest. If we get doubt we test by two measures to make sure.

Thought that might be how you were doing it. The AEMC meter is a good tool but is only reliable/accurate when measuring resistance on a single ground rod. If you use it to try and measure a rod connected as part of a group or grid it doesn't work properly. The only real accurate way to reasure resistance to ground in a multiple rod setup is to use the fall-of-potential method.