We want to reverse phase (same as split phase in this case) our power lines with 4 overhead aluminum cables carrying three phases and neutral (R, Y, B, N, carrying a max of 250 amps on each phase, neutral carrying 0-50 amps). What is the best sequence for reverse phasing on two sets of wires -- is it: R, Y, B, N on the upper set and then the reverse, N, B, Y, R on the lower set? Or would something else be better, such as leaving the neutral in the same location?
how to reverse phase
- Thread starter 570021
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- Wisconsin
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- PE (Retired) - Power Systems
Re: how to reverse phase
I do not fully understand what you mean by reverse phasing.
I assume you are talking about changing the orientation of the conductors on your overhead lines in order to change the interaction (capacitance and inductance) of the configuration. If this is the case then, the best solution depends on factors like existing spacing and length of conductors. Can you provide more information?
I do not fully understand what you mean by reverse phasing.
I assume you are talking about changing the orientation of the conductors on your overhead lines in order to change the interaction (capacitance and inductance) of the configuration. If this is the case then, the best solution depends on factors like existing spacing and length of conductors. Can you provide more information?
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: how to reverse phase
If you are indeed asking about transposing the phases, in order to reduce the mutual capacitance and inductance, then I would wonder why you think it is needed. Utility companies do not go through that trouble on their transmission systems, unless the lines are many, many miles long. I agree with Jim: we would need more information, in order to understand your situation.
If you are indeed asking about transposing the phases, in order to reduce the mutual capacitance and inductance, then I would wonder why you think it is needed. Utility companies do not go through that trouble on their transmission systems, unless the lines are many, many miles long. I agree with Jim: we would need more information, in order to understand your situation.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: how to reverse phase
Utility companies transpose transmission lines from time to time. I might guess (and I?m sure someone else can guess better) that a 500 mile long line might be transposed every 20 miles or so. The point of this exercise is to prevent an imbalance in phase loading that would be caused by differences between phase-to-phase capacitance and inductance. It seems to me that you are talking about something entirely different. It also seems to me that you are talking about something that cannot work.
For most of our installations, we put all three phases within a single conduit. One advantage is that, as seen from the outside of the conduit, the magnetic fields of the three phases cancel each other out (or nearly so). But look at it from inside the conduit. If you are closer to one phase than to the other two, the magnetic field from that one phase will be stronger than the other two, and you will read a significant EMF.
Are you trying to accomplish a similar cancellation on an overhead line? If so, I don?t think it can work. Anyone standing under the lines would perceive the combined field of the three phases, and would not perceive any changes to that field that would result in a transposition a couple hundred feet down the line. You would have to be continuously transposing the lines, effectively twisting the three phases around each other, in order for a person under the lines to see a cancellation of the three fields.
I have to believe that I still do not understand your question. Can you tell us, for example, how long the lines are, how high above the ground, and how often you plan on transposing them?
Utility companies transpose transmission lines from time to time. I might guess (and I?m sure someone else can guess better) that a 500 mile long line might be transposed every 20 miles or so. The point of this exercise is to prevent an imbalance in phase loading that would be caused by differences between phase-to-phase capacitance and inductance. It seems to me that you are talking about something entirely different. It also seems to me that you are talking about something that cannot work.
For most of our installations, we put all three phases within a single conduit. One advantage is that, as seen from the outside of the conduit, the magnetic fields of the three phases cancel each other out (or nearly so). But look at it from inside the conduit. If you are closer to one phase than to the other two, the magnetic field from that one phase will be stronger than the other two, and you will read a significant EMF.
Are you trying to accomplish a similar cancellation on an overhead line? If so, I don?t think it can work. Anyone standing under the lines would perceive the combined field of the three phases, and would not perceive any changes to that field that would result in a transposition a couple hundred feet down the line. You would have to be continuously transposing the lines, effectively twisting the three phases around each other, in order for a person under the lines to see a cancellation of the three fields.
I have to believe that I still do not understand your question. Can you tell us, for example, how long the lines are, how high above the ground, and how often you plan on transposing them?
mdshunk
Senior Member
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- Right here.
Re: how to reverse phase
What are those pole top hangers that hold the phases in a diamond pattern instead of on a crossarm? I see them in town for "twisting" the conductor phase arrangement over a 2 or 3 pole span.
What are those pole top hangers that hold the phases in a diamond pattern instead of on a crossarm? I see them in town for "twisting" the conductor phase arrangement over a 2 or 3 pole span.
rcwilson
Senior Member
- Location
- Redmond, WA
Re: how to reverse phase
IEEE Power Engineering Society transactions had some papers on this a few years ago. You will need to model the transmission line and perform the field calculations to determine the best configuration for canceling the EMF near the line. Some software packages are available to do this. (I can?t remember the program name.)
The field under the line will be symmetrical but not uniform. Different points under or next to the line will have higher fields. The location of the null points and the high points vary based on the conductor configuration. A configuration that minimizes the field two meters to the left of the line may increase the field directly under the line, or 10 meters from the line.
Model your system and see what works best given your conductor spacing, voltage levels and loads and the location you need to minimize emf.
IEEE Power Engineering Society transactions had some papers on this a few years ago. You will need to model the transmission line and perform the field calculations to determine the best configuration for canceling the EMF near the line. Some software packages are available to do this. (I can?t remember the program name.)
The field under the line will be symmetrical but not uniform. Different points under or next to the line will have higher fields. The location of the null points and the high points vary based on the conductor configuration. A configuration that minimizes the field two meters to the left of the line may increase the field directly under the line, or 10 meters from the line.
Model your system and see what works best given your conductor spacing, voltage levels and loads and the location you need to minimize emf.
charlie
Senior Member
- Location
- Indianapolis
Re: how to reverse phase
That is what we call "spacer cable" and the most common supplier is Hendrix Wire & Cable.
charlie
Senior Member
- Location
- Indianapolis
Re: how to reverse phase
The rearranging of the phases on a pole is probably so we can tie two or more circuits together without bucking phases. Our circuits don't act nice when A? from one substation is connected to B? from another substation. Yes, we keep track of our distribution phases so we can switch loads on the circuits.
charlie
Senior Member
- Location
- Indianapolis
Re: how to reverse phase
Why is that Sam?
Why is that Sam?
Re: how to reverse phase
Thanks to everyone for all the information. This is a private installation- generator fed with approximately a 100 ft. run. There is high EMF for some of the residents under the feed. I was given the original question by a local electrician but he just is searching for a way to minimize the EMF. No other specs are available, but any other suggestions would be helpful.
Thanks to everyone for all the information. This is a private installation- generator fed with approximately a 100 ft. run. There is high EMF for some of the residents under the feed. I was given the original question by a local electrician but he just is searching for a way to minimize the EMF. No other specs are available, but any other suggestions would be helpful.
mdshunk
Senior Member
- Location
- Right here.
Re: how to reverse phase
I'm guessing then that passing out Faraday suits to the local population is not an option?
I'm guessing then that passing out Faraday suits to the local population is not an option?
charlie
Senior Member
- Location
- Indianapolis
Re: how to reverse phase
Sam, I think I do; hence, the signature I use.
Sam, I think I do; hence, the signature I use.
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