Checking Earth on an Industrial Equipment

[sarky]

Hi Guys,

Well i am a newbie on here, I have an Industrial Machine and I need to renew the Earthing Rods,
The machine is of 3 Big Units and I want to make sure the earthing I install is enough for the requirement.

The power source is a 350KV Generated power.

Any Info will be welcomed.

Thanks

Sarky

 

[malcolmsanford]

Sarky my old deputy engineer would tell me

"Son the impossible we do immediately, miracles may take a little longer"

I think even our HV experts like Engineer54 and Tony would struggle with the limited information you have supplied.

Why are you renewing earth rods?
What are you trying to achieve?
What is the requirement?

 

[Knobhead]

As Malcolm said, more information needed. I hope you meant 350KVA and not 350KV.
I bloody hope so otherwise you will be toast before your next post!

 

[sarky]

ok got your points as for the KV it is KVA sorry..

Let me give you a bit of my background, I am not a sparkie my field is
mechanical engineer in charge of a Yard which has a few industrial equipment.

Now one question you are going to ask "What the hell is a mechanical engineer doing with
Electricity.", Well This yard is in Nigeria / Africa if anyone of you guys worked this neck of the
wood would understand that proper hands are hard to come by.

The machine is an Asphalt plant, there have been issues with the electrics and tried to get
so called electricians to look at it but they are not able to do it.

The plant is powered by a diesel engine 350KVA FG Wilson, and i think from day one of that
plant there was no proper earthing.

What am i trying to achieve... Right I want that plant to have the proper earthing done, and
i need to know things i can check, Things i know is the TOTAL AMPS the machine consumes when running

Anything else you require do let me know

Sarky

 

[Knobhead]

As to the location Malcolm will be the best to ask regarding ground conditions. But I come from a quarrying background where earthing is a problem. We would normally drill a 10m hole at each corner of the gen set enclosure for rods these would be back filled with a mixture of quarry sand and urea*. All out stations (plants) would be soundly connected via 70 or 95mm earth bonding to a central point at the generator.

*before E54 shoots me down, urea was free, bentonite we had to pay for!

(Funny thing is I went from quarrying to iron making, where we were up to our eyeballs in benonite but no suitable sand!)

 

[malcolmsanford]

That about sums it up Tony.

Though I have seen when the generator was the sole source of power Ufer earthing utilized quote a lot as these generators were fixed via concrete slabs and the ree bar used.

You could if they are bedded down see if you could expose ree bar and try to take your fixed earth from there.

If that is not possible then you can rod as Tony said, or make up a decent mesh and bury that, it will depend on your ground conditions there. Here even though it is a desert here we get pretty good grounding because of the mineral content, but most of my earthing is done ufer style.

What ever method you decide to use, the bottom line is testing it. Have you got instrumentation, or someone there that would understand and interpret the results

 

[Knobhead]

sarky
Have a look at Ufer ground - Wikipedia, the free encyclopedia

 

[sarky]

I got a procedure to test the soil using a meger meter 3 point test, Im a quick learner main reason for joining this forum is to learn
how to do it, having you guys here i am sure i should manage it.

Yeah the Gen is on a concrete Slab, but i would rather not expose the Rebar just do a pit.

When all is done how do you check if the machine has the right Earthing on it ? is there a method...

 

[sarky]

Thanks Tony, an Eye opener as everything over here always rely on Generator being the main source of power.

 

[malcolmsanford]

To get a proper test you need an earth electrode test meter do you have one ?

Why don't you want to expose the ree bar, that will give you the easiest and possibly the best earth ?

There is no right earthing as such, there are degrees of earthing and what values you get will then denote what you do to make the installation safe. The lowest value you can achieve will be your aim, but what value you achieve will denote what you do next, there is no "it must be this value"

I've not asked on your OP what issues are you having, and why do you think the earth is not suitable?

http://support.fluke.com/find-sales/Download/Asset/2633834_6115_ENG_A_W.PDF

This is a good guide.

 

[sarky]

Well I already own Fluke 123 Scopemeter as for Earth Specific no but thinking of getting a Megger meter 4TD to assist me in working what i need.
As for why do i think that exposing rebars, Well i am not sure if the construction was cheap or properly done with enough Rebars.

The reason why i think the grounding is not right, well one of the units on that machine is a scale reading of load cells and the fluctuation is much as soon as the machine
starts up and there is no other reason i can see.

As i asked before if there is a method of checking the machine and its earth then do let me know as that would be my basis of being 100% sure it is that.

 

[malcolmsanford]

Well the oscilloscope will not be of much use for what you want, but the meggar earth electrode meter will.

It is so hard trying to fault find from a distance, Yes if your earth is not good you can get a "float" on the system which will cause the installation to be unstable.

Does the genny have a management centre attached to it. I would honestly have thought if you having these type of problems the genny would cut out.

 

[sarky]

thats why i am trying to work backwards, Do a solid earth near the Gen then hook it up and work backwards at least then i know what i have or have not done.
as for the Gen it has PowerWizard panel, in this country if it cuts of due to Earth I am sure they wouldn't be able to sell as no house or machine has a proper earthing.

The ground here is moist water table is about 150feet and rises up in the rains..

 

[Engineer54]

Hi Sarky,

What you need is a combination of what's already been suggested on this thread. As Tony stated a rod system at each corner of the Generator pad linked together with bare hard drawn copper conductor, 50mm should suffice. As Malcolm suggested, break into the pad to pick-up the re-bar, connect a 50mm earth conductor and link onto the hard drawn copper conductor linking the earth rods. Take an insulated earth conductor from the accessable earth rod position to the generators frame main earthing position, and make absolutely certain that the neutral point of your generator is solidly linked to the generators earth, by a short length from generator earth position to the neutral point connection....

Depending on the soil type you have at the generator pad area, will dictate how you position your rods. If decent soil, you can drive your rods in with a decent heavy SDS type drill (with rotation off) using rod connectors to extend rod lengths, you will need at least/minimum 3 metres depth, to achieve a meaningful and stable Ra value. If sand then you need to drill 75 to 100mm bore holes, fill with bentonite or a conductive mortar and drop your rods into the bores. You need to make at least one of the rod positions your accessable test point, in that the connection to that rod are removable. The rest of the connections can be braise welded exothermically welded, or bolted and protected with a good covering of amalgamating tape or similar, and left buried as such.


For the materials you may need, check out the FURSE website, i'm pretty sure they have an outlet in your part of the world...

Let us know if you need any further pointers....

 

[Engineer54]

Any chance of posting some photo's of your generator installation and it's surroundings?? As they say a picture is worth a thousand words. ...lol!!

At least you have a decent generator there, F. G. Wilson, out of N Ireland, is most definitly one of the better manufacturers and have used them many time's over the years, albeit on a far bigger scale than your 350 KVA unit. But i'm sure just as reliable.

 

[sarky]

Right there ya go some pictures for ya.

 

[Engineer54]

Thank's Sparky,


OK so this generator is within an enclosed building along with at least one other Genny that i can see. So scrub the my first post, that was for a single pad/generator in it's own enclosure/building.

You would now need a small linked earth field of say 3 or 4 deep earth electrode/rods in a straight line or in a ''crows foot configuration'' outside the generator building. Same as before on the rod positions, (ie driven, or bore hole) just make certain that the distance between the rods is at least the same as the depth/length of the rod in the ground, maybe add a half metre to the distance for good measure. Again link them out with at least a 50mm CSA copper conductor (can be cable or copper tape)!! Also again, leave one rod/electrode accessable, as your test position, (nearest the building is best) ...ie, having removable connections.

You could also do the same for the other generator(s) Taking out a separate string of rods for that installation. Try and keep the two (or more rod fields) as distant from each other as you can, then solidly link them, possibly by a common earth bar located in the Genny building. The earth bar should be one that has a removable link(s) between the two sections of earth bar, this is for testing and fault finding exercises. You you can also use the Ufer earth of the buildings foundation re-bar, but again, linked to the earthing system/earth bar, via a removable bolted connection...

Just a thought here, ...If you have any changer-over switches (manual or automatic) from one generator to another, make sure that they are 4 Pole switches, and NOT 3 Pole switches... ie, never solidly link the neutral connections of 2 generators, or mains and generator!!

 

[sarky]

thanks for the comments, As soon as i get the megger tester will do the test on the soil at least so i can go through the learning curve, but for sure will require your assistance to figure out what i am doing and why i need to do it

Thanks again

 

[Knobhead]

HeHe they bring back memories. That looks like Goodwin and Barsby kit :teeth_smile:
The s**t looks the same.

 

[sarky]

lol its a parker blackmobile plant i think 70's and still running but going to be changed in a year or so..

 

[sarky]

right guys just did the test and using 2000 Ohms as directed in the Manual and got the Earth Resistance of 27 Ohms,
Don't know what it means method used.

Used the Existing Earth Rod in ground and the Stakes as directed and got the above result.

Thanks