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  1. #31
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    Default Re: neutral grounding @ pole??

    Well I've got to say that you have given me some interesting reading. I must say that there is a lot of misconceptions about electricity out there, even by engineers.

    The biggest misconception is that earth is a good conductor. Its not a good conductor, its a lousy conductor in fact. If it was a good conductor, there would not be a problem with Neutral Earth Voltage (NEV). If earth was such a good conductor, there would be no need for the ground grid recommended in the ERPI reference.

    What earth is, is a giant capacitor. Its a capacitor with a lot of leakage current (lousy power factor). That is what causes the NEV. Most of the current that goes into the ground at the ground rod on one half cycle, returns on the other half cycle.

    Now for the transmission line. In a single phase circuit, if the neutral was not grounded at any point except the generator or substation, one big advantage would be reduced EMI. If the line is balanced, and I'm talking about line balance here, not the kind of balance most electricians think of with three phase circuits, line balance means that the current in the lines is equal in amplitude but opposite in polarity. When the lines are balanced, then the magnetic fields created are equal in amplitude but opposite in direction, so the magnetic fields are suppressed. When the lines become unbalanced, then the uneven currents cause uneven magnetic fields which cause radiation. The radiation that is not suppressed are called stray losses.

    Your SNCMFG reference seems to think that the stray EMI is caused by the ground currents, and of course anytime there is current flow, there is a magnetic field, but as the current flows out concentrically from the ground rod, these magnetic fields would pretty much cancel themselves, not completely but mostly. The measured EMI is coming from the unbalanced lines. But even those fields were pretty weak.

    It is clear that the writer of that reference is not an electrical engineer, but he states that "According to utility engineers, the resistance of the neutral wire causes significant voltage drops along the lines, requiring frequent voltage adjustments." That is not true. I think the author misunderstood the engineers. The resistance of the primary wire causes the voltage drop. If there were no ground rods, then the story would be different. Without ground rods, the primary wire would still cause the same voltage drops, but the return line would see the voltage rising in reference to ground, but diminishing in reference to the primary wire as the distance increases. In a grounded neutral, there is no voltage loss because the neutral is clamped to ground so voltage is always at zero volts, therefore no voltage drop.

    He also makes this statement which really scares me. "In contrast to the present multi grounded system, a totally ungrounded system has the advantage that a person could stand on the ground and touch either the neutral or the high voltage wire, but not both, and not be electrocuted." Where do you start with that one.

    The same author wrote your Mike Holt reference.

    Your Bass Engineering papers are interesting. The author seems to think that isolating the primary winding in the transformer will solve most of the problems. It is feasible, I don't know if it would accomplish anything, but it is feasible. Someone would need to do a study on circuits that were "upgraded" by using phase to phase connections instead of phase/neutral connections. This type of circuit exists where a 2400 volt circuit was increased to 4160 by using two bushing transformers connected between two phases. There is no "neutral" line here. The transformer case is still grounded and the center tap of the secondary is still connected to the case. I don't know if any of these exist on the single phase legs but on the three phase sections, this is used in three phase banks to reduce the current in the neutral line. It actually reduces the current in all the lines.

    The issue with using a two bushing pot on a normal single phase line is that the neutral is grounded somewhere. The panel is also grounded so there is a connection between the HV neutral and the LV neutral, but depending on the spacing between the ground rods, there will be at least some resistance.

    Another misconception cited in several references is that in a perfectly balanced three phase system, there would be no current on the neutral line. The only time this is true is on the secondary side of a three phase transformer that is feeding a three phase motor or motors and there are no other loads on this circuit. That cannot be true in the distribution network. Any single phase appliance on the circuit will return ALL of its current on the neutral. It has no path to the other phases.

    I still question the methodology behind the statement that 60% of the return current comes through the ground connection. There has to be a big misunderstanding here. If that were true, line losses would kill the utility. The stray losses would be astronomical. The utilities would be unhooking all those ground rods as fast as they could, except the phone companies wouldn't let them, at least not without a fight.
    Last edited by keith3267; 01-13-2012 at 11:50 PM.

  2. #32
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    Default Re: neutral grounding @ pole??

    Quote Originally Posted by keith3267 View Post
    Well I've got to say that you have given me some interesting reading. I must say that there is a lot of misconceptions about electricity out there, even by engineers.

    You got that right!

    The biggest misconception is that earth is a good conductor. Its not a good conductor, its a lousy conductor in fact. If it was a good conductor, there would not be a problem with Neutral Earth Voltage (NEV). If earth was such a good conductor, there would be no need for the ground grid recommended in the ERPI reference.

    I've measure anywhere from 2 to 600 ohm grounding systems/rods.

    What earth is, is a giant capacitor. Its a capacitor with a lot of leakage current (lousy power factor). That is what causes the NEV. Most of the current that goes into the ground at the ground rod on one half cycle, returns on the other half cycle.

    Now for the transmission line. In a single phase circuit, if the neutral was not grounded at any point except the generator or substation, one big advantage would be reduced EMI. If the line is balanced, and I'm talking about line balance here, not the kind of balance most electricians think of with three phase circuits, line balance means that the current in the lines is equal in amplitude but opposite in polarity. When the lines are balanced, then the magnetic fields created are equal in amplitude but opposite in direction, so the magnetic fields are suppressed. When the lines become unbalanced, then the uneven currents cause uneven magnetic fields which cause radiation. The radiation that is not suppressed are called stray losses.

    Your SNCMFG reference seems to think that the stray EMI is caused by the ground currents, and of course anytime there is current flow, there is a magnetic field, but as the current flows out concentrically from the ground rod, these magnetic fields would pretty much cancel themselves, not completely but mostly. The measured EMI is coming from the unbalanced lines. But even those fields were pretty weak.

    It is clear that the writer of that reference is not an electrical engineer, but he states that "According to utility engineers, the resistance of the neutral wire causes significant voltage drops along the lines, requiring frequent voltage adjustments." That is not true. I think the author misunderstood the engineers. The resistance of the primary wire causes the voltage drop.

    True, the primary wire has voltage drop (because it has current flow) but the return line must also have voltage drop.

    But the return path is similar to parallel conductors, a fairly low Z wire(s) and whatever the soil Z (and ground rod effective Z) happens to be on any given day.


    If there were no ground rods, then the story would be different. Without ground rods, the primary wire would still cause the same voltage drops, but the return line would see the voltage rising in reference to ground, but diminishing in reference to the primary wire as the distance increases. In a grounded neutral, there is no voltage loss because the neutral is clamped to ground so voltage is always at zero volts, therefore no voltage drop.

    He also makes this statement which really scares me. "In contrast to the present multi grounded system, a totally ungrounded system has the advantage that a person could stand on the ground and touch either the neutral or the high voltage wire, but not both, and not be electrocuted." Where do you start with that one.

    Maybe he was just stating a well understood electrical fact i.e. the bird on the wire. I too don't think an ungrounded primary or secondary system would be the way to go. It would work fine with the first ground fault but you don't want to be around the second etc.

    The same author wrote your Mike Holt reference.

    Your Bass Engineering papers are interesting. The author seems to think that isolating the primary winding in the transformer will solve most of the problems. It is feasible, I don't know if it would accomplish anything, but it is feasible. Someone would need to do a study on circuits that were "upgraded" by using phase to phase connections instead of phase/neutral connections. This type of circuit exists where a 2400 volt circuit was increased to 4160 by using two bushing transformers connected between two phases. There is no "neutral" line here. The transformer case is still grounded and the center tap of the secondary is still connected to the case. I don't know if any of these exist on the single phase legs but on the three phase sections, this is used in three phase banks to reduce the current in the neutral line. It actually reduces the current in all the lines.

    The issue with using a two bushing pot on a normal single phase line is that the neutral is grounded somewhere. The panel is also grounded so there is a connection between the HV neutral and the LV neutral, but depending on the spacing between the ground rods, there will be at least some resistance.

    Another misconception cited in several references is that in a perfectly balanced three phase system, there would be no current on the neutral line. The only time this is true is on the secondary side of a three phase transformer that is feeding a three phase motor or motors and there are no other loads on this circuit.

    Most users are refering to 120/240V single phase homes where only the current difference between the two "hot lines" returns to the power company ("un-balance") on the neutral. This assumes the neutral is doing 100% of it's job and there are no earth return problems.

    That cannot be true in the distribution network. Any single phase appliance on the circuit will return ALL of its current on the neutral. It has no path to the other phases.

    I still question the methodology behind the statement that 60% of the return current comes through the ground connection. There has to be a big misunderstanding here. If that were true, line losses would kill the utility. The stray losses would be astronomical. The utilities would be unhooking all those ground rods as fast as they could, except the phone companies wouldn't let them, at least not without a fight.
    I've seen the 60% number somewhere and it sure got my attention. But my collection of articles is quite large and I haven't had the time to try and find it. Since it would not have been very agreeable with POCS's (who pay EPRI's operating expenses) it may have been squashed.

    And yes, it would be a huge problem, and is a huge problem, to those who have had to deal with it.

    I appeciate your interest because it's from the utility side, which I (and most) are not too familiar with. Let's keep up the dialog, since it affects us all.

  3. #33
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    Default Re: neutral grounding @ pole??

    These posts are getting lengthy and I think we have gotten off the original question somewhat, but that IMO has made it a bit more interesting,

    The 60% number, 59% actually was in one of those articles you posted, but it was an interpretation of something the author read coming from another source. And that could have come from another source, etc.

    "True, the primary wire has voltage drop (because it has current flow) but the return line must also have voltage drop.

    But the return path is similar to parallel conductors, a fairly low Z wire(s) and whatever the soil Z (and ground rod effective Z) happens to be on any given day"

    The return line would have a voltage drop IF it wasn't earth grounded all along the way. The earth ground clamps the voltage on the return line to zero volts, so it can't have a voltage drop. BTW, when you use the term Z in reference to wires, you are talking about something completely different than resistance. Normally impedance (Z) is the resistance plus the capacitive reactance plus the inductive reactance. In transmission lines, the term Z usually refers to the characteristic impedance, Zo (pronounced Z sub oh). Zo is responsible for developing the line voltage and does not cause any losses. Line losses are due to resistance aka I2R (I squared R) and stray losses.

    "Maybe he was just stating a well understood electrical fact i.e. the bird on the wire. "

    A bird on a wire is not standing on the ground. He said "standing on the ground".

    Another misconception is that the difference in current on the 120/240 side of the transformer are returned as unbalances to the power company. The unbalance on the secondary side of the transformer are NOT sent back to the power company, even in a one bushing pot. The unbalance only goes back to the secondary windings of the transformer, that is it.

    There are two separate secondary windings in a residential transformer. If the hots are unbalanced, that means that one secondary is working harder than the other.

    Here is a scenario that would work, don't know if the utility companies would go for it as a regular practice though. They come out of the substation as a 3 wire, 3 phase feed with a separate ground line. After passing through the commercial areas that have 3 phase customers, the lines feed the single phase customers with 2 phases working as the supply and return. Both insulated and a ground wire below and equal distance from the two phases. That will be three wires on the poles instead of two.

    All the transformers will have to be changed out because now they will need two HV bushings and the ratio has to be different because a normal 7200 volt circuit will now be 12470 volts. The transformer case will be grounded and each bushing will have a surge protector and a CL fuse for ground faults, but only one bushing will need a load or dual sensing fuse.

    The X2 bushing that is the return line will not be grounded at the transformer, it will only be grounded at the service panel.

    This configuration will have fewer stray losses, but I don't know what the payback time to the utility would be or if it would ever fully payback. It would solve the NEV problem to some extent on the farm, but only if the transformer feeds the barn directly. The house and the barn would have to have separate transformers. If they daisy chain the barn from the house panel, then they will need a 4 wire system between the house and the barn or barns.

    If there is a lot of separation between the barn(s) and the house, separate transformers could be very cost effective. BTW, around here, some of the farms have a 3 phase service so the house and the barns (called sheds around here) have separate services.

    I must add that the company I retired from would love the configuration above, it would be a real boon to the business. Other than my pension, i have no other vested (economic that is) interest in them.

  4. #34
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    Talking Re: neutral grounding @ pole??

    ***! Lots of brain cells smoking on this one. Kinda drifted into some pretty gray areas. The original question was about whether a missing GEC connection would be OK because of the pole ground. As a 40 year utility meter/relay tech, I've heard this question a lot. Here's what I've learned. Most people fail to separate utility interests from homeowner interests. The utility's job is to supply power. Safety and reliability are paramount. Cost is secondary, since costs are ultimately passed on to the customer in electric rates. That said, transmission and distribution systems are totally different animals. Transmission is only between substations, and it's function is to get power from generation to substations. Higher voltages mean smaller wire means lower cost (sort of). Basic Ohm's Law. These voltages can anywhere from 34KV to 1 million KV, AC or DC. But this conversation is about distribution. Whether 3 wire delta, 3 wire ungrounded wye, 4 wire grounded wye, or single phase, it's function is to get power from the transmission system to the customer.

    Most systems are 4 wire grounded wye, so that's what I'll talk about. From a utility standpoint, 12,470/7200 is pretty standard. There are common neutral and separate neutral systems. Most common is the first one, which combines the high voltage primary neutral and the low voltage secondary neutral. Both are grounded at the pole. Pole grounds are installed every few poles to insure a good ground return path to the neutral. This is so when a phase becomes unintentionally grounded, the resuting fault current will be high enough to clear the protective device, be it a fuse or relay controlled breaker. It was never intended to serve the same purpose as the GEC/grounding and bonding system, which is for safety and fire protection of the customer.

    All of the talk about impedances, NEV, imbalance, etc. are subjects that can really bend your mind, but I guess what I'd like to get across is that as a utility, we are "exempt" from NEC in most cases because we serve a specific function. Affordable, reliable power. Period. We are not the Evil Empire out to fleece the unsuspecting public.

    Don't you just LOVE this stuff?
    Last edited by meternerd; 01-26-2012 at 02:36 PM.

  5. #35
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    Default Re: neutral grounding @ pole??

    Just to be clear, when I referenced transmission lines, I was not referring to the transmission system. Transmission lines are conductors that carry an electricity, whether it be in the form of power or a signal. A lamp cord qualifies as a transmission line.

    If you ever delve into transmission line theory, it will boggle your mind. It is actually easier to understand how a signal is developed in a computer circuit than how power is transfered down a lamp cord. In fact, the most complex component in a computer is its power cord. I used to troubleshoot (military) computer circuits and airborne radar systems.

    A transmission line has inductance, capacitance, resistance, input impedance, reflected impedance and characteristic impedance. How they all work together can blow your mind.

  6. #36
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    Default Re: neutral grounding @ pole??

    Quote Originally Posted by keith3267 View Post
    ....If you ever delve into transmission line theory, it will boggle your mind....It is actually easier to understand how a signal is developed in a computer circuit than how power is transfered down a lamp cord. In fact, the most complex component in a computer is its power cord. I used to troubleshoot (military) computer circuits and airborne radar systems.

    A transmission line has inductance, capacitance, resistance, input impedance, reflected impedance and characteristic impedance. How they all work together can blow your mind.
    If you really want to get into some deep wire relationships, just check out how RF energy acts within a coaxial cable when the transmitter-coax-antenna set-up is in resonance and when it isn't. It makes transmission line stuff look easy! When you understand how to use a "Snith Chart" http://en.wikipedia.org/wiki/Smith_chart to figure that stuff out post a response Just introducing some humor into the topic here, no offense intended to anyone.

    This has indeed been an eye opener thread and it shows that there's a lot more to things than meets the eye. Yet on the user end where the average person just plugs something in and it works fine everything seems so simple....

    Phil

  7. #37
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    Default Re: neutral grounding @ pole??

    Your link didn't work or the article was deleted. It is also possible that the " just before the link is corrupting it, if so you will have to edit. I always put links on a separate line to prevent this. Maybe you meant this one.

    http://en.wikipedia.org/wiki/Impedance_matching

    Anyway, I read this article and found it not to be very well written, as with most wikipedia articles. The best source of information I have found is the "ARRL Antenna Handbook".

    The Smith Chart is not just for coax cables, it is for all types of transmission lines where there is a mismatch in impedance at the load end and the line is electrically "long", greater than 1/4 wavelength. One wavelength at 60 Hz is about 3100 miles. The Smith Chart is based on a formula. I used to demonstrate the formula for my classes back when I taught this stuff, but it took three complete blackboards to solve even a simple line matching problem. The Smith Chart was a lot faster, but even it wasn't all that easy to use. BTW the wikipedia article above referred to resonant lines which is not the correct term, the correct term is tuned line.

    To be honest, impedance matching in the distribution grid is a non issue. The transmission lines in a distribution grid are electrically "short" meaning they are less than 1/4 wavelength of the applied signal.

    It is an issue on the power grid as some of those lines can be electrically "long" And example would be the transmission lines that go from a wind farm in Texas to users in Chicago.

    BTW, thanks for your post, it was fun. It makes a "flip/flop" circuit, the fundamental circuit used in computers, look simple by comparison.
    Last edited by keith3267; 02-12-2012 at 02:16 PM.

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