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Thread: Harmonics Challenge

  1. #1
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    Harmonics Challenge

    Looking for help/advice regarding harmonics. Consulting at new facility with number of pump VFDs. THD at PCC is 12%. At distribution panel feeding pumps THD is 55%.
    everything I’ve read to date says harmonics are bad for electrical distribution system. EOR says 12% is OK because meets IEEE 519-2014. As I read 519 it is standard concerned with PCC and not internal system. EOR and VFD manufacturer say 55% is OK on panel.
    Looking for resources that address internal system impacts and not at PCC.
    Any references would be greatly appreciated.

  2. #2
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    Is that current or voltage distortion?
    Si hoc legere scis nimium eruditionis habes.

  3. #3
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    Quote Originally Posted by EE259 View Post
    Looking for help/advice regarding harmonics. Consulting at new facility with number of pump VFDs. THD at PCC is 12%. At distribution panel feeding pumps THD is 55%.
    everything I’ve read to date says harmonics are bad for electrical distribution system. EOR says 12% is OK because meets IEEE 519-2014. As I read 519 it is standard concerned with PCC and not internal system. EOR and VFD manufacturer say 55% is OK on panel.
    Looking for resources that address internal system impacts and not at PCC.
    Any references would be greatly appreciated.
    Here is an ECM article.

    We've studied harmonics where they were clearly out of compliance, however the owner was experiencing no observable issues or frequent maintenance. It didn't make sense for them to spend on mitigation.

    There's another facility where they applied 6 pulse in place of 18 pulse on ten or so 300 HP pumps. They have issues with radios not working inside the electrical room. Except when it rains. Then they work fine. A bigger problem is their master antenna for remote production wells is connected in the same room. Communications with the wells is intermittent. Except when it rains. This is an operational issue so the owner is installing mitigation in hopes that it fixes the issue.

    With regards to the panelboard, perhaps it is fine and the breakers will operate as expected. NETA testing can verify this, although it isn't cost effective to test QOU type breakers this way.. It is also possible circuit breakers will nuisance trip due to additional heat loss in the conductors. This behavior would certainly be observed sooner rather than later, if true. What loads are on the panelboard? Is the THD okay to those loads? Are there any computers or digital electronics such as PLCs, instruments or radios connected?

  4. #4
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    Quote Originally Posted by Besoeker View Post
    Is that current or voltage distortion?
    This is an important distinction, it makes all the difference in the world.

    Condensed version: Current Total Harmonic Distortion (I-THD) is what is caused by your non-linear loads and becomes your problem to deal with in your facility, but that is what CAUSES Voltage Total Harmonic Distortion (V-THD), and V-THD travels to your neighbors, where it can exacerbate their I-THD. So IEEE-519 is meant to prevent that. It ALSO requires that the utility not DELIVER greater than 5% V-THD to the PCCs of you and your neighbors, but the utility has little direct control of how much gets put out by you and your neighbors. So what they will do it measure the V-THD at your PCC and if it is less than 5%, it can not possibly get to your neighbors as more than 5%. So their main way of controlling this is by enforcing IEEE-519 at your PCC. They don’t care one iota how you do it or where, they only care about the end result at that one point. But that said, if your nearest neighbor is far enough away that their primary circuit impedance limits the effects of your harmonics so that the utility is not exceeding the 5% V-THD limit at that first neighbor’s PCC, they may not even bother you about it. That’s why some people “get away with” not having to worry about it. It’s just luck.

    If they required you to maintain 5% V-THD at your PCC, HOW you do it is to take steps to keep your I-THD under control. You can do it at each individual contributor, or you can do it all right at the PCC or a mixture of both strategies. Only the end result matters as measured at the PCC. There are more complexities to it in terms of the I-THD being affected by the Total DEMAND of your facility and how much of that demand is non-linear, but that’s another couple of pages of typing...
    Last edited by Jraef; 09-14-18 at 01:05 PM.
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  5. #5
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    Quote Originally Posted by drktmplr12 View Post
    Here is an ECM article.

    We've studied harmonics where they were clearly out of compliance, however the owner was experiencing no observable issues or frequent maintenance. It didn't make sense for them to spend on mitigation.

    There's another facility where they applied 6 pulse in place of 18 pulse on ten or so 300 HP pumps. They have issues with radios not working inside the electrical room. Except when it rains. Then they work fine. A bigger problem is their master antenna for remote production wells is connected in the same room. Communications with the wells is intermittent. Except when it rains. This is an operational issue so the owner is installing mitigation in hopes that it fixes the issue.

    With regards to the panelboard, perhaps it is fine and the breakers will operate as expected. NETA testing can verify this, although it isn't cost effective to test QOU type breakers this way.. It is also possible circuit breakers will nuisance trip due to additional heat loss in the conductors. This behavior would certainly be observed sooner rather than later, if true. What loads are on the panelboard? Is the THD okay to those loads? Are there any computers or digital electronics such as PLCs, instruments or radios connected?
    NEHB breakers in panel board. Only loads are VFDs and three HVAC chillers. THD average 37-45% on individual loads depending on % of hz, though not 1:1 relationship.

  6. #6
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    Quote Originally Posted by Jraef View Post
    This is an important distinction, it makes all the difference in the world.

    Condensed version: Current Total Harmonic Distortion (I-THD) is what is caused by your non-linear loads and becomes your problem to deal with in your facility, but that is what CAUSES Voltage Total Harmonic Distortion (V-THD), and V-THD travels to your neighbors, where it can exacerbate their I-THD. So IEEE-519 is meant to prevent that. It ALSO requires that the utility not DELIVER greater than 5% V-THD to the PCCs of you and your neighbors, but the utility has little direct control of how much gets put out by you and your neighbors. So what they will do it measure the V-THD at your PCC and if it is less than 5%, it can not possibly get to your neighbors as more than 5%. So their main way of controlling this is by enforcing IEEE-519 at your PCC. They don’t care one iota how you do it or where, they only care about the end result at that one point. But that said, if your nearest neighbor is far enough away that their primary circuit impedance limits the effects of your harmonics so that the utility is not exceeding the 5% V-THD limit at that first neighbor’s PCC, they may not even bother you about it. That’s why some people “get away with” not having to worry about it. It’s just luck.

    If they required you to maintain 5% V-THD at your PCC, HOW you do it is to take steps to keep your I-THD under control. You can do it at each individual contributor, or you can do it all right at the PCC or a mixture of both strategies. Only the end result matters as measured at the PCC. There are more complexities to it in terms of the I-THD being affected by the Total DEMAND of your facility and how much of that demand is non-linear, but that’s another couple of pages of typing...
    ”Nearest neighbor” is another service 1 mike away on same property, 165,000 acres, that has had transformer and electronic equipment, FA Panel etc failures. So don’t see 519 as really relavent for neighbor impact and more focused on internal impacts.

  7. #7
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    The impact of harmonics depends upon the connected loads. It is not enough to say 'harmonics are bad', and since the engineer on your team is saying that they are not a problem, you now need to demonstrate that there is in fact a problem that needs fixing.

    VFDs with normal rectifiers draw significant harmonic currents. These harmonic currents are _not_ a problem for the VFD; they are a consequence of the rectifiers and the rectifiers are quite happy with this harmonic current.

    The harmonic currents interact with the impedance of the distribution system, resulting in harmonic voltage distortion. This harmonic voltage distortion can cause problems for _other_ loads on the system.

    Potential problems are things like overloaded neutrals...but if you have 3 phase VFD loads these are not putting any current on a neutral.

    You could also see the harmonics causing problems for line connected motors, such as increased heating. But for this to be a problem depends both on the _specific_ harmonic voltages that the motors see, and how heavily loaded the motors are... I mean if the motor is operating well below maximum temperature and harmonics make it run warmer, is this really a problem?

    Sorry, I guess what you are really asking for are references to help figure out what problems you should be looking for.

    In any case, harmonics are not a problem unless they are actually _causing_ a problem, and then you need to decide if it makes more sense to reduce the harmonics or make the system more tolerant of them.

    -Jon

  8. #8
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    Quote Originally Posted by Jraef View Post
    This is an important distinction, it makes all the difference in the world.

    Condensed version: Current Total Harmonic Distortion (I-THD) is what is caused by your non-linear loads and becomes your problem to deal with in your facility, but that is what CAUSES Voltage Total Harmonic Distortion (V-THD), and V-THD travels to your neighbors, where it can exacerbate their I-THD. So IEEE-519 is meant to prevent that. It ALSO requires that the utility not DELIVER greater than 5% V-THD to the PCCs of you and your neighbors, but the utility has little direct control of how much gets put out by you and your neighbors. So what they will do it measure the V-THD at your PCC and if it is less than 5%, it can not possibly get to your neighbors as more than 5%. So their main way of controlling this is by enforcing IEEE-519 at your PCC. They don’t care one iota how you do it or where, they only care about the end result at that one point. But that said, if your nearest neighbor is far enough away that their primary circuit impedance limits the effects of your harmonics so that the utility is not exceeding the 5% V-THD limit at that first neighbor’s PCC, they may not even bother you about it. That’s why some people “get away with” not having to worry about it. It’s just luck.

    If they required you to maintain 5% V-THD at your PCC, HOW you do it is to take steps to keep your I-THD under control. You can do it at each individual contributor, or you can do it all right at the PCC or a mixture of both strategies. Only the end result matters as measured at the PCC. There are more complexities to it in terms of the I-THD being affected by the Total DEMAND of your facility and how much of that demand is non-linear, but that’s another couple of pages of typing...
    Note that it is unreasonable for POCO to require you to maintain an upper limit of 5%V-THD at your point of common connection if the incoming V-THD from POCO at the PCC is anywhere near 5% when you are not putting any load on the service. Or, looking at it another way, if you have a low I-THD on the current into your facility, then blaming any high V-THD on you is unfair. It might take a little discussion with POCO to settle things though, if this turns out to be the case.

    If you have a very stiff utility service to your PCC you might have 50% I-THD and still not have a problem with V-THD caused by you, but POCO would still be justified in being unhappy.

    So, the bottom line is that you need to measure and understand both types of THD readings.

  9. #9
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    Quote Originally Posted by drktmplr12 View Post
    Here is an ECM article.

    We've studied harmonics where they were clearly out of compliance, however the owner was experiencing no observable issues or frequent maintenance. It didn't make sense for them to spend on mitigation.

    There's another facility where they applied 6 pulse in place of 18 pulse on ten or so 300 HP pumps. They have issues with radios not working inside the electrical room. Except when it rains. Then they work fine. A bigger problem is their master antenna for remote production wells is connected in the same room. Communications with the wells is intermittent. Except when it rains. This is an operational issue so the owner is installing mitigation in hopes that it fixes the issue.

    With regards to the panelboard, perhaps it is fine and the breakers will operate as expected. NETA testing can verify this, although it isn't cost effective to test QOU type breakers this way.. It is also possible circuit breakers will nuisance trip due to additional heat loss in the conductors. This behavior would certainly be observed sooner rather than later, if true. What loads are on the panelboard? Is the THD okay to those loads? Are there any computers or digital electronics such as PLCs, instruments or radios connected?
    Not sure about it but... when we had taxicab or amateur radio problems where the radio worked better when it rained, the problem was always a metal plane ground, where the installer did not grind the paint off at the hole of the antenna so did not get a good ground on the antenna, usually on the NMount or business band antennas... the manufacturers holesaw included a ridge that cut the hole then ground the top edge just for that but the 8nstallers would just go to the hardware store for the cheap hole saw..lol...

    not saying that is the problem on the radios but it was in the taxicab and cb and ham worlds.

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