harmonics in a 208V service
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Re: harmonics in a 208V service
Hello dereckbc-
You make an excellent point. In this case, the fact that the CDA is the source of the document is not an issue- it presents correct information and follows the recommendations found in IEEE Standard 519 "Practices and Requirements for Harmonic Control in Electrical Power Systems" and IEEE Standard 1100 "Recommended Practice for Powering and Grounding Electronic Equipment".
I used it as an online source as most electricians or engineering firms will not have ready access to the Thomas Gruzs paper.
Here is another URL with the same information as the CDA link that should be fairly unbiased:
http://www.usace.army.mil/inet/usace-docs/armytm/tm5-689/c-5.pdf
Respectfully,
Mark
Hello dereckbc-
You make an excellent point. In this case, the fact that the CDA is the source of the document is not an issue- it presents correct information and follows the recommendations found in IEEE Standard 519 "Practices and Requirements for Harmonic Control in Electrical Power Systems" and IEEE Standard 1100 "Recommended Practice for Powering and Grounding Electronic Equipment".
I used it as an online source as most electricians or engineering firms will not have ready access to the Thomas Gruzs paper.
Here is another URL with the same information as the CDA link that should be fairly unbiased:
http://www.usace.army.mil/inet/usace-docs/armytm/tm5-689/c-5.pdf
Respectfully,
Mark
Re: harmonics in a 208V service
Mark, thanks for the link, I hope I wasn?t coming across as cynical, just pointing out the fact of the source. I am aware of the practices of IEEE 1100, 519, and 142. In fact, I used to religiously follow the practices without question.
After working for MCI and being involved with data center and telephone office power design for several years, I have been fortunate enough to collect a lot of data, and see the industry evolve. In the 80?s & 90?s the practice of over sizing (over 100%) the neutral was a sound practice. But since that time UPS and high-end equipment manufactures have integrated power factor correction technology into there equipment, therefore negating the need in most cases.
In all my collection of data I have found maybe 2 or 3 cases where neutral current exceeded phase currents, and a couple of isolation transformers (non "K" rated) that were overheating from harmonics. As a result I have come to reexamine my own practices I have used for so many years, and have adjusted to the changing technology using what I think is sound principles.
1. 3-phase 4-wire service at 480 or higher and dead-end the grounded service conductor at the service entrance.
2. Segregate critical and non-critical feeders.
3. HVAC, UPS, and DC power plants fed delta 3-wire + EGC.
4. General receptacles fed using a low ?K? isolation transformer and full size dedicated neutral.
5. Critical loads from UPS distributed via PDU?s using full size neutral if needed.
6. Continue to push equipment manufactures into cleaning up the power by using power correction technology and/or filters.
Mark, thanks for the link, I hope I wasn?t coming across as cynical, just pointing out the fact of the source. I am aware of the practices of IEEE 1100, 519, and 142. In fact, I used to religiously follow the practices without question.
After working for MCI and being involved with data center and telephone office power design for several years, I have been fortunate enough to collect a lot of data, and see the industry evolve. In the 80?s & 90?s the practice of over sizing (over 100%) the neutral was a sound practice. But since that time UPS and high-end equipment manufactures have integrated power factor correction technology into there equipment, therefore negating the need in most cases.
In all my collection of data I have found maybe 2 or 3 cases where neutral current exceeded phase currents, and a couple of isolation transformers (non "K" rated) that were overheating from harmonics. As a result I have come to reexamine my own practices I have used for so many years, and have adjusted to the changing technology using what I think is sound principles.
1. 3-phase 4-wire service at 480 or higher and dead-end the grounded service conductor at the service entrance.
2. Segregate critical and non-critical feeders.
3. HVAC, UPS, and DC power plants fed delta 3-wire + EGC.
4. General receptacles fed using a low ?K? isolation transformer and full size dedicated neutral.
5. Critical loads from UPS distributed via PDU?s using full size neutral if needed.
6. Continue to push equipment manufactures into cleaning up the power by using power correction technology and/or filters.
Re: harmonics in a 208V service
Hello dereckbc-
I did not take your post as being cynical, and you make a good point about citing links- one must carefully consider the source.
I'm sure that we have all seen or read "white papers" published by electrical and electronic device manufacturers that support their particular position- most have side stepped the peer reviewed process, and may or may not be accurate.
Most IEEE papers and standards going back to the early 1980's are available in .pdf format. The only reason I don't link to them or cut and paste the info into a thread is due to copyright laws, so I generally try to fine a web site with the same information.
Thanks!
Mark
Hello dereckbc-
I did not take your post as being cynical, and you make a good point about citing links- one must carefully consider the source.
I'm sure that we have all seen or read "white papers" published by electrical and electronic device manufacturers that support their particular position- most have side stepped the peer reviewed process, and may or may not be accurate.
Most IEEE papers and standards going back to the early 1980's are available in .pdf format. The only reason I don't link to them or cut and paste the info into a thread is due to copyright laws, so I generally try to fine a web site with the same information.
Thanks!
Mark
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Re: harmonics in a 208V service
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There is another member here that does PQ work and finds many PQ problems are traceable to work that does not conform to the NEC. Bring the building into NEC compliance and the problems clear up.
How many times do you find overloaded neutrals do strictly to harmonics?
Bob
Mark I do not mean any disrespect it just seems to me you may be in a bit of the same position.
Your profile
Certainly there are buildings with PQ issues, I just have a hard time believing it is as bad as many people would have us believe.
There is another member here that does PQ work and finds many PQ problems are traceable to work that does not conform to the NEC. Bring the building into NEC compliance and the problems clear up.
How many times do you find overloaded neutrals do strictly to harmonics?
Bob
ron
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Re: harmonics in a 208V service
Bob,
I certainly cannot claim to be a PQ guy, but I run into it a lot is the type of work. When I started, I could not believe the number of improper grounded neutrals I found causing wacky problems.
Bob,
I certainly cannot claim to be a PQ guy, but I run into it a lot is the type of work. When I started, I could not believe the number of improper grounded neutrals I found causing wacky problems.
Re: harmonics in a 208V service
Hello Bob-
No disrespect taken. In fact, I agree 100% with your statement that most PQ problems are actually the result of wiring problems. IEEE Standard 1100 recommends that the first step in any PQ survey is verification of wiring and grounding systems. Too many PQ testing firms skip this step and go directly to voltage/current monitoring or thermal imaging, often costing the customer many thousands of dollars and not really finding the problem. I won't post it here, but our website strongly emphasizes building wiring and grounding as the logical starting point for any PQ investigation.
To answer your question, "How many times do you find overloaded neutrals due strictly to harmonics?", the answer would be never if you are using the traditional definition of the word overloaded. If you were to ask me how many times have I measured increased heat on neutral conductors, in motors and transformers due to harmonics, then my answer would be "routinely".
Thanks Bob,
Mark
Hello Bob-
No disrespect taken. In fact, I agree 100% with your statement that most PQ problems are actually the result of wiring problems. IEEE Standard 1100 recommends that the first step in any PQ survey is verification of wiring and grounding systems. Too many PQ testing firms skip this step and go directly to voltage/current monitoring or thermal imaging, often costing the customer many thousands of dollars and not really finding the problem. I won't post it here, but our website strongly emphasizes building wiring and grounding as the logical starting point for any PQ investigation.
To answer your question, "How many times do you find overloaded neutrals due strictly to harmonics?", the answer would be never if you are using the traditional definition of the word overloaded. If you were to ask me how many times have I measured increased heat on neutral conductors, in motors and transformers due to harmonics, then my answer would be "routinely".
Thanks Bob,
Mark
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