Utility wires, counting how many on the power line

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copper123

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I have been reading the discussion about transformer and was wondering. I have read a little about on some high voltage installations you will have only three ungrounded wires running for utility distribution and they will use the ground as the return path is this correct? Also around my rural area, we have some utility lines with only two conductors running on the cross arms, and then others that have three conductors. I am sure this is still only single phase and its in the same area. Also, we will have some three conductors running and they look like main distribution and I would imagine its three phase. And then, finely, I have seen a few cross arms with 4 wires. As you can see, I am very unfamiliar with the entire concept of high voltage utility distribution and was wondering if somebody could shed a little light.
Thanks in advance.
 
Re: Utility wires, counting how many on the power line

In rural areas where there is not a lot of electrical demand, a utility company will either run a phase and a neutral to the transformer feeding the customer's home or they may use two phases to feed the transformer. As for using the ground as a neutral (return path), the ground is only a secondary path, the neutral or other phase is the primary return path. On three phase distribution lines, the customer transformer may be connected as a Delta (phase to phase) or as a Wye (Phase to Neutral). This would explain why some three phase lines have 3 wires (3 phases for Delta) and some have 4 wires (3 phases & a neutral for Wye).
 
Re: Utility wires, counting how many on the power line

Normally, the phase and neutral will both be on the arm where you see only two wires. A delta system is very expensive so most electric utilities do not use it. The insulation level is required to be the same for the neutral as it is for the phase wires if it is on the cross arm. I am betting that one of the insulators is a different size or a different color (white or brown instead of gray). The convention of the electric utility will be apparent where all four conductors are on the same arm. For instance, we will use a 15 kV insulator for the neutral and a 23 kV insulator for the phase wire on a 13.2 kV wye system. :D
 
Re: Utility wires, counting how many on the power line

Charlie, tell us why a delta xmission system is more expensive than a wye.
 
Re: Utility wires, counting how many on the power line

I am going to run a 1? tap and install some transformers and secondary lines. I can do that with a single #2/0 AAAC Br. and #2/0 Al. parallel cable (1 2/0 br. and 2 2/0 PE). The parallel cable neutral will be the neutral for both the primary and the secondary. This has a single phase wire and a single secondary cable.

The delta system now takes two phase wires on arms instead of pole top pins. Additionally, the higher voltage two bushing transformers cost more than a single bushing transformer. Also, with the two cutouts and two lightning arresters make the transformer installations cost considerably more. :D
 
Re: Utility wires, counting how many on the power line

Almost every area I have been in I seen pole top neutral. Which seems the best location to catch a lightning strike instead of it hitting a ungrounded conductor. Why in the world does our utility have the neutral at the bottom of the stack? the lowest conductor on the pole? :roll:
 
Re: Utility wires, counting how many on the power line

Every time they need to get the neutral, they have to go between the phases to get to it. Every transformer they hang needs the neutral. We used a static neutral for a while and decided it was not worth the hassle. We now have our neutral down where we can get to it easily. We protect the phases with good insulators and lightning arresters. :D
 
Re: Utility wires, counting how many on the power line

Thanks guys for you help. I have read somewhere that ranchers had a lawsuit against a utility company that was allegedly shocking cows that were on property that had high voltage distribution wires running across it. It was using the ground as a return path.

Also, it still completely baffles me about electricity always wants to get back to its source. When you bond your grounded hot conductor at your service, you will still get a bit of current traveling through your ground rod, through the ground, up the ground rod at the pole at back to the transformer. Why is that? I thought maybe Charlie could answer it for me. It just seems like it would disapate in the ground. For the longest time I always thought Earth was just a big pool that gave us a zero reference point, equalized potential and that was it. So they idea of current traveling back to the transformer is a bit tough to grasp.
 
Re: Utility wires, counting how many on the power line

Copper,

Just remember that current must follow a closed path; the garden hose analogy does't fully explain it. Think of the water pump in your car; it circulates the water rather than just pumping it into a reservoir. Same with electricity, and the current will divide itself if there are multiple paths to be taken. Sometimes the earth itself is one of those paths.
 
Re: Utility wires, counting how many on the power line

Cooper123, most distribution systems in the US use what is known as a multi-grounded-neutral system (MGN). This is especially true in rural areas. On the distribution system the utility grounds the neutral at least four times per mile. This puts earth in parallel with the neutral conductor. So load current flows like in any conductor in parellel.
 
Re: Utility wires, counting how many on the power line

electron flow is from ground to hot, not from hot to ground to utility pole.

paul
 
Re: Utility wires, counting how many on the power line

Paul,

We are talking AC here, the hot wires reverse their potential 120 times per second. You can be shocked just as hard on the negative lobe as you can on the positive lobe. Electrons flow ALTERNATELY from ground to hot and hot to ground--if they have a path, and sometimes that path is Mother Earth.
 
Re: Utility wires, counting how many on the power line

partial oops? are you saying that the earth gets hot enough 120 times a second to actually create electron flow from the ungrounded conductors to the earth at the same potential? I know the same potential exists at the ungrounded conductor as a negative potential, or alternating potential, but I never new the earth potential to alternate at all. A litle confused here. This topic area I generally stay out of as it is not my forte (if I actually have one), but I have heard of hot ground before, but not that hot.

I can understand the jargon saying that current flows back to the pole as the potential, both as a positive wave and a negative wave,seeks it's source. But I never understood the neutral to be a source of potential. please clarify

paul :)
 
Re: Utility wires, counting how many on the power line

Hi Rattus,

I think I understand what you are staying about the water pump. So.. would it be safe to say, if the current could not find its way back to the transformer via the earth, it would not even begin the journey? Simply saying that it has to be a complete loop, so to have flow at all would mean that current must use the earth as a return path?? Its still really wild to think about it. If I have a ground rod that reads 25 ohms resistance to ground, ohms law would say, that with 120 volts potential on the rod, I could only have 4.8 amps of current on it. But, as a parallel ckt goes, electrons will take all paths back. Am I understanding the principles correctly and just have not put the pieces together?
 
Re: Utility wires, counting how many on the power line

By Copper123: I have read somewhere that ranchers had a lawsuit against a utility company that was allegedly shocking cows that were on property that had high voltage distribution wires running across it. It was using the ground as a return path.
Click to expand...
The system that they were talking about is called a "SWER" It stands for "Single Wire Earth Return" It used in very rural locations where the cost of having a return conductor out weighs the cost of the extra grounding electrodes and that most use 20' long ones. Do a search on the net for a SWER system and you will find allot of info out there.

[ February 22, 2005, 07:48 PM: Message edited by: hurk27 ]
 
Re: Utility wires, counting how many on the power line

Paul, it is the DIFFERENCE of potential that causes current. The earth is moreorless neutral, that is at zero potential, but the instantaneous voltages on ALL the hot wires alternate between positive and negative. This leads to ALTERNATING CURRENT (AC) when a load is applied. That is, the electrons go this way and that way, but not very far.
 
Re: Utility wires, counting how many on the power line

Copper, I think you about have it.

If the loop is open anywhere, there will be no current, the electrons just sit there vibrating impatiently. Normally, the resistance of the neutral is so low that only tiny currents flow through the earth. If the neutral is open, then the current returns through the earth, but the earth resistance can be significant, so this is not a good situation.
 
Re: Utility wires, counting how many on the power line

the prvious posts indicated that current would flow back and forth in the ground, using earth as a conductor. I can understand quite well how potential works, but do not understand earth as a fluctuating field. I can understand how the earth on a single phase conducts 60 times per cycle, but not 120 as rattus has implied. If the earth cannot change potential 120 times a second, how can it be part of the reverse flow.

paul
 
Re: Utility wires, counting how many on the power line

Paul,

A complete cycle occurs 60 times per second.

The voltage and current reverse direction twice per cycle, at times 0 and T/2, where T is 16.67 milliseconds. That is 120 times per second.

Except for resistive voltage drop, the "neutral" conducts current without changing potential. Same with the earth except that the resistance can be much higher.

It is the DIFFERENCE in potential between earth and the hot lines that cause the current. The potential of the earth does not need to change, only the potential of the hot lines.
 
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