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Thread: out of ideas

  1. #209
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    Quote Originally Posted by safe123 View Post
    I'm leaning more toward the idea that a large number of fluorescent ballasts are putting a lot of inductive reactance on the system, which could be corrected with power capacitors to change power factor to a more acceptable value.
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    The op says the new lighting is all "low voltage" lighting. I don't know what that means, but I'm thinking its not the usual fluorescent with the ballasts. Maybe "low voltage" means also that their converting ac into low voltage dc which means rectifiers which means non-sinusoidal load. Plus, I just like saying non-sinusoidal.
    Last edited by HeyBob; 01-02-2010 at 09:04 AM.

  2. #210
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    Quote Originally Posted by tipsrfine View Post
    The op says the new lighting is all "low voltage" lighting. I don't know what that means, but I'm thinking its not the usual fluorescent with the ballasts. Maybe "low voltage" means also that their converting ac into low voltage dc which means rectifiers which means non-sinusoidal load. Plus, I just like saying non-sinusoidal.
    Good stuff Tips, but it doesn't exactly apply here. The relevence of your information is for shared neutrals on 120v loads. Shouldn't apply to 240v loads. If the motors, wiring and test equipment are ok, then I'm sticking with power factor for now.
    Anything I say here is only my opinion. Even if you understood what I said.... What I said may not even be what I meant.

  3. #211
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    *

    well was this job figured out yet



    .

  4. #212
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    Quote Originally Posted by tipsrfine View Post
    The op says the new lighting is all "low voltage" lighting. I don't know what that means, but I'm thinking its not the usual fluorescent with the ballasts. Maybe "low voltage" means also that their converting ac into low voltage dc which means rectifiers which means non-sinusoidal load. Plus, I just like saying non-sinusoidal.
    Low voltage lighting generally uses a transformer and then a full wave rectifier. The part exposed to the power panel is the transformer(s). A full wave rectifier would present a sinusoidal load because the entire wave ("full" wave) is being converted from AC to DC.
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  5. #213
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    Been reading a lot about harmonics, voltage harmonics, current harmonics, single phase, 3 phase etc..., havn't read anything that specifically rules it out in a 240 system. Found one article that mentioned very briefly voltage harmonic distortion in a 240v circuit. Some math about adding 10v to 240v bla bla bla.
    Not saying the power factor angle is not the problem, I'm just saying I got side-tracked into harmonics & non-sinusoidal loads and I'm paying hell finding anything specific on it as it relates to a 240v induction motor. I'll keep trying & if I find anything definitive I will post it.

  6. #214
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    Quote Originally Posted by tipsrfine View Post
    Been reading a lot about harmonics, voltage harmonics, current harmonics, single phase, 3 phase etc..., havn't read anything that specifically rules it out in a 240 system. Found one article that mentioned very briefly voltage harmonic distortion in a 240v circuit. Some math about adding 10v to 240v bla bla bla.
    Not saying the power factor angle is not the problem, I'm just saying I got side-tracked into harmonics & non-sinusoidal loads and I'm paying hell finding anything specific on it as it relates to a 240v induction motor. I'll keep trying & if I find anything definitive I will post it.


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  7. #215
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    Quote Originally Posted by ACFIXR View Post
    Thanks for the link. Yeah I've read similar articles, but I guess I need a real dumbed down version to figure out if this could be a problem in a 240v motor like the op's. chuck the moderator stated it should only be a problem in 120v sharing the same neutral. Timebuilder? stated that a full wave rectifier would not be a non-sinusoidal load, but articles I've read say they are. So far my understanding is that harmonics, whether voltage or current, can affect a motor using 240v due to non-sinusoidal loads and that these loads due not have to even be in the same building-some place down the street could be causing it.
    Not trying to highjack the thread, but 'til he gets back to us with more info we can entertain ourselves. I wish Chris would come back. I'm thinking he may know a lot about this & have some good links.

  8. #216
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    Quote Originally Posted by tipsrfine View Post
    Thanks for the link. Yeah I've read similar articles, but I guess I need a real dumbed down version to figure out if this could be a problem in a 240v motor like the op's. chuck the moderator stated it should only be a problem in 120v sharing the same neutral. Timebuilder? stated that a full wave rectifier would not be a non-sinusoidal load, but articles I've read say they are. So far my understanding is that harmonics, whether voltage or current, can affect a motor using 240v due to non-sinusoidal loads and that these loads due not have to even be in the same building-some place down the street could be causing it.
    Not trying to highjack the thread, but 'til he gets back to us with more info we can entertain ourselves. I wish Chris would come back. I'm thinking he may know a lot about this & have some good links.
    Somewhere on Flukes site they have a good explanation of building harmonics. I went to one of their classes and the guy who taught it was great. Plus they have and HVAC instrument division so they apply their instruments directly to us.

    Harmonics, to me, is simply the left over EMF from not using the entire 60 HZ signal which means the power is really not 60 HR to a degree anymore, there is left over voltage in the lines and that shows up primarily in the neutrals of commercial building, which is a very dangerous thing.

    I've had first hand experience of this in the many commercial building I work in since we tend to be a large software city of the world and the building are full of computers.

    That's why a true RMS meter is now the responsibiliyt of every tech in this world.

    Placing bets on the info given by the poster so far as to what might be the problem, if there is one...I'm still riding in a mis-applicaiton and/or a mis-reading of the posted trouble shooting figures.
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  9. #217
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    Quote Originally Posted by tipsrfine View Post
    Timebuilder? stated that a full wave rectifier would not be a non-sinusoidal load, but articles I've read say they are.

    I do not have an EE degree, so I am open to the idea that someone could convince me that a full wave rectifier could be considered a non-sinusoidal load. Could you give me a link to the doc you saw that suggests this is the case? Thanks!!!!

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  10. #218
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    Quote Originally Posted by timebuilder View Post
    I do not have an EE degree, so I am open to the idea that someone could convince me that a full wave rectifier could be considered a non-sinusoidal load. Could you give me a link to the doc you saw that suggests this is the case? Thanks!!!!

    I'm always learning.
    I'll retrace my steps, but it might take me awhile. I'm tired, got a pot roast to take out and a live-in girl friend who's feelin' frisky. Will find those articles mentioning full wave still producing non-sinusoisdal load first thing in the morning. By the way it made sense what you said about the full wave thing, but maybe it has something to do with how it goes about fully rectifying the ac current. Here is one I havn't had time to read, but I think it shows how the fully wave is actually worse than the half wave.
    http://www.allaboutcircuits.com/vol_2/chpt_7/3.html

    I'll find the other I did read tomorrow.

  11. #219
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    Quote Originally Posted by timebuilder View Post
    I do not have an EE degree, so I am open to the idea that someone could convince me that a full wave rectifier could be considered a non-sinusoidal load. Could you give me a link to the doc you saw that suggests this is the case? Thanks!!!!

    I'm always learning.
    I understand the principle that a full wave rectifier would not effect the sine wave because it uses both the upper and lower part of the wave.
    In actual practice the load is non-linear because it is actually switched by the diodes. Since the load is non-Linear, it alters the sine wave. Harmonics are created and the power factor can be lowered. The problem is increased when a capacitor, or other method is added on the output of the bridge rectifier (full wave) to smooth the voltage output because if you smooth the voltage you amplify the amperage variations. Here is a link which you might find interesting: http://en.wikipedia.org/wiki/Power_factor
    Anything I say here is only my opinion. Even if you understood what I said.... What I said may not even be what I meant.

  12. #220
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    Quote Originally Posted by tipsrfine View Post
    I'll retrace my steps, but it might take me awhile. I'm tired, got a pot roast to take out and a live-in girl friend who's feelin' frisky. Will find those articles mentioning full wave still producing non-sinusoisdal load first thing in the morning. By the way it made sense what you said about the full wave thing, but maybe it has something to do with how it goes about fully rectifying the ac current. Here is one I havn't had time to read, but I think it shows how the fully wave is actually worse than the half wave.
    http://www.allaboutcircuits.com/vol_2/chpt_7/3.html

    I'll find the other I did read tomorrow.
    While the full wave rectifier does generate second-order harmonics, I'm not sure it this is enough to be of large consequence to the op's motor. It's a shame we did not get a graphic of the effect on the waveform to see how much it may have been distorted.

    This makes me wonder about the incredibly large number of motors used in RTU's in non-chiller retail environments such as older shopping malls, and the preponderance of DC power supplies being driven by the mall power grid, especially the newer generation of switching power supplies used in every computer and point of sale terminal in every store. Also, you have fluorescent lamp ballasts that all produce an inductive load on the grid, producing a change in power factor.

    In other words, if the second order harmonic being generated by a full wave supply was a real power problem, I would think it would be very difficult to keep the RTUs running for very long.
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  13. #221
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    Quote Originally Posted by timebuilder View Post
    While the full wave rectifier does generate second-order harmonics, I'm not sure it this is enough to be of large consequence to the op's motor.
    I agree, I am anxious to hear how this comes out.
    Anything I say here is only my opinion. Even if you understood what I said.... What I said may not even be what I meant.

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