Grounding/Power Quality Issues

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aelectricalman

aelectricalman

Senior Member
Location
KY
I have a customer that has come to me and said they are having major transformer overload due to harmonic distortion. We are seeing about 11% Vthd. They have some equipment where they have drilled through the concrete floor and drove a separate ground for the new peice of equipment. They have grounding issue and are tripping and burning up drives like NASCAR tires. This is a large primary user.

There are many ways to skin this cat. I understand a power quality study should be the first approach in providing a direction. Once this is done, what type of grounding studies are out there that we could have performed to help determine if there are ground loops, high Vthd, high Ithd. I am looking at some line reactors as well but i don't want to get the cart in front of the horse.

Thanks for your help, all.
 
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GoldDigger

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Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
aelectricalman said:
I have a customer that has come to me and said they are having major transformer overload due to harmonic distortion. We are seeing about 11% Vthd. They have some equipment where they have drilled through the concrete floor and drove a separate ground for the new peice of equipment. They have grounding issue and are tripping and burning up drives like NASCAR tires. This is a large primary user.

There are many ways to skin this cat. I understand a power quality study should be the first approach in providing a direction. Once this is done, what type of grounding studies are out there that we could have performed to help determine if there are ground loops, high Vthd, high Ithd. I am looking at some line reactors as well but i don't want to get the cart in front of the horse.

Thanks for your help, all.
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There should be an EGC for the equipment, and the ground electrode should not be bonded to the EGC.
If the drives are not presenting a high power factor (distortion PF) then there will be a high harmonic content and potentially a high neutral content if it is a wye connection. Line reactors should help this, but there may be better ways.
 
aelectricalman

aelectricalman

Senior Member
Location
KY
Yeah, that was my point. Its is far from correct. They certainly have two different ground potentials. Is there a study I can have performed that will tell if there are ground loops? different potentials?
 
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G

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
aelectricalman said:
Yeah, that was my point. Its is far from correct. They certainly have two different ground potentials. Is there a study I can have performed that will tell if there are ground loops? different potentials?
Click to expand...

You can just use a long section of wire and a meter to measure any differences between the voltages at the different ground electrodes which are not connected by an EGC. You can use a series or clamp ammeter to measure the current. With a suitable probe you can connect the voltage or current waveform to a THD analyzer.
 
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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
130701-1508 EDT

How large is the plant 5,000,000, 1,000,000, 100,000 sq-ft? 100,000 is only 316 x 316 ft. The Ford Sterling Axle plant sits on a 171 acres (about 1/4 sq-mile), and is 3,000,000 sq-ft. Their website did not tell me if distribution is ungrounded delta, but I suspect it possibly is. A million or so sq-ft Dana plant at Ft Wayne is ungrounded delta 480 within the plant. At one time this was over 1,000,000 sq-ft.

What kind of machines in your plant? How large are individual distribution transformers? Why are ground rods being driven at machines? Are there any electric arc furnaces? Is the building a steel frame with good continuity?

.
 
RichB

RichB

Senior Member
Location
Tacoma, Wa
Occupation
Electrician/Electrical Inspector
GoldDigger said:
"A groundloop occurs, when, for various reasons, the front end of your aircraft decides to switch places with the back end. We won't go into just why that happens ..."
Click to expand...

:lol::lol:oops:rant:--kinda like the student who when asked what the wind was--stuck his hand out the vent and found out it was about 100kts--right on the nose!!!
 
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enteng14

enteng14

Member
Location
Manila, Philippines
aelectricalman said:
I have a customer that has come to me and said they are having major transformer overload due to harmonic distortion. We are seeing about 11% Vthd. They have some equipment where they have drilled through the concrete floor and drove a separate ground for the new peice of equipment. They have grounding issue and are tripping and burning up drives like NASCAR tires. This is a large primary user.

There are many ways to skin this cat. I understand a power quality study should be the first approach in providing a direction. Once this is done, what type of grounding studies are out there that we could have performed to help determine if there are ground loops, high Vthd, high Ithd. I am looking at some line reactors as well but i don't want to get the cart in front of the horse.

Thanks for your help, all.
Click to expand...

In my opinion, I should first check and correct the grounding system of the customer then measure the %Vthd after the correction. I think there was an issue on the customer's equipment where they drove a separate ground rod for their "isolated ground" I presume, this may create a "ground loop" or potential difference between the electrical system and the equipment.
 
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