Pole Mounted Transformer Primary Winding

[W@ttson]

Hello all,

Recently it has come to my attention that utilities do not send two phases from their 3 phase distribution system to pole mounted transformers in residential areas (at least in my region or even greater nearby region).

Is this really the case? I tried looking on line for this and even went outside and took some pictures of the nearby pole mounted transformer. Looks like there is one High voltage line and then the second connection to the primary is ground. Do they really complete the primary side through earth? Is this the case throughout the country wherever overhead distribution is found? What happens for pad mounted distribution?

See attached pictures.

 

[garbo]

The Ultility company in my area never installs a second high vo!tage wire to transformer primary even when they have three phase power ( 13.2 KV ) at the pole so in my eyes its a dangerous auto transformer that use customers grounded conductor ( ya neutral ) , copper water service, gas steel Ultility pipe and even cast iron soil pipe to carry supply power to feed the other side of the primary. They ground this primary to the 120/ 240 center tap then due a poor job of running an aluminum wire down the pole to a ground rod. In our large city often find 8' of ground wire missing that somebody stole and takes a long time to get repaired. Saw one pole where the Ultility company had 5 crimp fittings telling me that ground wire was cut at least 3 times. You would think they would install a heavy non metallic covering to reduce thief of ground rod wires. Several times after I upgraded or replaced a residential service I would place one of my clamp on a monsters on a copper water service & steel gas pipe. Copper water services always had at least 0.25 amps and gas pipe maybe halve as much. Had one copper water pipe carrying 3/4 amps. I rechecked my taps, connections inside meter can & panel and performed voltage drop readings between every point but they were okay. House had 3 window air conditioning units running ( 2 on one side & the third on opposite side of hot wires ) so one leg was drawing maybe 14 to 18 amps more but neither of the hot legs on 200 amp main breaker were above 50 amps.

 

[winnie]

Most utilities use 'multi-earth-neutral' setups for distribution, where the neutral conductor is connected to ground electrodes all over the place.

This means that neutral current will have a parallel path through soil and any metal in contact with the soil.

For the most extreme version of this, see 'single wire earth return' systems. These use a single primary wire and a step down transformer connected between that primary and a ground electrode.

For _benefits_ of this approach, the big one is that the primary wires are regularly referenced to ground, limiting voltage imposed by things such as faults caused by other primary phases or lightning strikes. This is not my area of study, but I believe this is an aspect of utility 'effective grounding', and sometimes the reason that utilities will demand the use of wye:wye transformers at distributed generation sites.

For _downsides_ of this approach, just look at any report of 'stray voltage'. The current injected into the soil can cause shock hazards and issues for livestock.

-Jon

 

[W@ttson]

The Ultility company in my area never installs a second high vo!tage wire to transformer primary even when they have three phase power ( 13.2 KV ) at the pole so in my eyes its a dangerous auto transformer that use customers grounded conductor ( ya neutral ) , copper water service, gas steel Ultility pipe and even cast iron soil pipe to carry supply power to feed the other side of the primary. They ground this primary to the 120/ 240 center tap then due a poor job of running an aluminum wire down the pole to a ground rod. In our large city often find 8' of ground wire missing that somebody stole and takes a long time to get repaired. Saw one pole where the Ultility company had 5 crimp fittings telling me that ground wire was cut at least 3 times. You would think they would install a heavy non metallic covering to reduce thief of ground rod wires. Several times after I upgraded or replaced a residential service I would place one of my clamp on a monsters on a copper water service & steel gas pipe. Copper water services always had at least 0.25 amps and gas pipe maybe halve as much. Had one copper water pipe carrying 3/4 amps. I rechecked my taps, connections inside meter can & panel and performed voltage drop readings between every point but they were okay. House had 3 window air conditioning units running ( 2 on one side & the third on opposite side of hot wires ) so one leg was drawing maybe 14 to 18 amps more but neither of the hot legs on 200 amp main breaker were above 50 amps.

yeah your description of it looking like an autotransformer is interesting.

 

[W@ttson]

Most utilities use 'multi-earth-neutral' setups for distribution, where the neutral conductor is connected to ground electrodes all over the place.

This means that neutral current will have a parallel path through soil and any metal in contact with the soil.

For the most extreme version of this, see 'single wire earth return' systems. These use a single primary wire and a step down transformer connected between that primary and a ground electrode.

For _benefits_ of this approach, the big one is that the primary wires are regularly referenced to ground, limiting voltage imposed by things such as faults caused by other primary phases or lightning strikes. This is not my area of study, but I believe this is an aspect of utility 'effective grounding', and sometimes the reason that utilities will demand the use of wye:wye transformers at distributed generation sites.

For _downsides_ of this approach, just look at any report of 'stray voltage'. The current injected into the soil can cause shock hazards and issues for livestock.

-Jon

Isn't this what I have pictured? One high voltage line hits the transformer primary, then the other transformer primary is connected to ground. On the Primary side the ckt is Hight voltage phase (lets say A) A to primary of transformer -> Winding -> Other side of primary of transformer -> conductor -> ground electrode -> Earth -> Substation ground electrode -> wire -> Substation neutral

 

[winnie]

Isn't this what I have pictured? One high voltage line hits the transformer primary, then the other transformer primary is connected to ground. On the Primary side the ckt is Hight voltage phase (lets say A) A to primary of transformer -> Winding -> Other side of primary of transformer -> conductor -> ground electrode -> Earth -> Substation ground electrode -> wire -> Substation neutral

Not quite. The most common installation in the US has a 'multi-earth neutral' wire that hits all the poles, is connected to grounding electrodes, and serves as the neutral for both the high voltage distribution system and the transformer secondary voltage. This MEN wire is continuous going back to the substation

The 'SWER' system doesn't have that 'multi-earth-neutral' returning to the substation. You might have a small local neutral acting as the local low voltage neutral and the utility high voltage grounded conductor, but it doesn't return back to the substation

Jon

 

[W@ttson]

Not quite. The most common installation in the US has a 'multi-earth neutral' wire that hits all the poles, is connected to grounding electrodes, and serves as the neutral for both the high voltage distribution system and the transformer secondary voltage. This MEN wire is continuous going back to the substation

The 'SWER' system doesn't have that 'multi-earth-neutral' returning to the substation. You might have a small local neutral acting as the local low voltage neutral and the utility high voltage grounded conductor, but it doesn't return back to the substation

Jon

I am getting a bit lost.

To try and clear it up the below is what I believe is going on here:

 

[winnie]

Your sketches are generally correct for SWER, and as such also _almost_ matches standard installation practice.

What you are missing from sketch2 is that the N wire extends in parallel with the H1 wire back to the substation.

The difference between SWER and MEN systems is that the MEN system has a metallic neutral conductor all the way back to the source. The metallic neutral conductor is earthed many times, so earth is used as a parallel conductor for the metallic conductor.

In the SWER system you only have the earth as the conductor.

-Jon

 

[W@ttson]

Your sketches are generally correct for SWER, and as such also _almost_ matches standard installation practice.

What you are missing from sketch2 is that the N wire extends in parallel with the H1 wire back to the substation.

The difference between SWER and MEN systems is that the MEN system has a metallic neutral conductor all the way back to the source. The metallic neutral conductor is earthed many times, so earth is used as a parallel conductor for the metallic conductor.

In the SWER system you only have the earth as the conductor.

-Jon

I went around walking from pole to pole around the neighborhood, if anyone saw me, they probably thought I was quite the weirdo, I tried to confirm if there is a Neutral parallel with the H1 and from what I can see I do not see any. It is just the H1 that runs along. The only way a N would run parallel with the H1 is if the N that is with the set of Low voltage wires is the one that is ran back to the substation.

So basically if that low voltage N is the one that is ran back to the substation that the way it is done here is a MEN system. If that low voltage N is not run back to the substation then it is a SWER.

In any case, what was interesting is that only one High voltage Phase is sent around to the area.

 

[winnie]

The only way a N would run parallel with the H1 is if the N that is with the set of Low voltage wires is the one that is ran back to the substation.

So basically if that low voltage N is the one that is ran back to the substation that the way it is done here is a MEN system. If that low voltage N is not run back to the substation then it is a SWER.

Yup. The same wire is used at the high voltage neutral, the low voltage neutral, the ground bonding, and the messenger wire carrying the low voltage hot conductors. Exactly what I have in front of my own house.

-Jon

 

[electrofelon]

No there is definitely a utility neutral conductor. Sometimes however they may use the triplex messenger as the MV neutral conductor in situations where the triplex is run in a parallel path to the same location as a separate conductor would.

FYI some parts of the country still have extensive Delta distribution, where transformers are fed with two phases and there is no utility neutral conductor. Where I am in upstate New York is an example, where there is extensive 4800 volt Delta distribution, two bushing transformers fed with two phases.

The advantage of the mgn system is cost. Consider that with an mgn system and all single phase stuff fed line to neutral, you only need one high voltage bushing one high voltage cut out, etc. For underground, you only need one concentric neutral cable versus two for a Delta system. So that is like double the cost to run an underground Delta versus an underground single phase wye. Here in upstate New York one of the utilities allows customer owned primaries where we buy install and own the primary feed to their transformer. You do a few of these that are long and you really start to like the mgn wye system. I'm doing one right now that is 1800 ft long and a Delta system, do the math: four bucks a foot and 1800 ft, that second conductor hurts a bit!

 

[W@ttson]

No there is definitely a utility neutral conductor. Sometimes however they may use the triplex messenger as the MV neutral conductor in situations where the triplex is run in a parallel path to the same location as a separate conductor would.

From the pictures I posted can you highlight the Utility Neutral? There is only one connection to the High voltage line. There is no other connection.

The other connections to the transformer are the 2 Low side Hot conductors, the low side Neutral, and the ground connection which is on the back of the tank.

The Neutral and ground are bonded and a wire is ran down the pole to a ground rod.

That Neutral conductor that is on the low side, is the one that is in question whether it runs back to the substation or not. A messenger cable and two hot conductors are run to each house. The messenger cable connects at the neutral conductor that I mentioned above.

 

[wwhitney]

What you are missing from sketch2 is that the N wire extends in parallel with the H1 wire back to the substation

So the idea is that in areas where the the poles carry both secondary and primary conductors, the POCO doesn't necessarily run parallel secondary and primary neutrals? Rather a single common neutral may be run at the elevation of the secondary conductors (since its voltage to ground is zero)?

In which case to be certain you have an SWER system, you'd need to find a section of poles with no secondary conductors and just a single primary conductor strung between poles.

Conversely if there's a common secondary and primary neutral, then if you find a section of poles with no secondary conductors on them, there should now be two primary conductors.

This is all for the case where the primary is single phase only.

Cheers, Wayne

 

[electrofelon]

From the pictures I posted can you highlight the Utility Neutral? There is only one connection to the High voltage line. There is no other connection.

The other connections to the transformer are the 2 Low side Hot conductors, the low side Neutral, and the ground connection which is on the back of the tank.

The Neutral and ground are bonded and a wire is ran down the pole to a ground rod.

That Neutral conductor that is on the low side, is the one that is in question whether it runs back to the substation or not. A messenger cable and two hot conductors are run to each house. The messenger cable connects at the neutral conductor that I mentioned above.

Yeah looks like they are running the 120/240 to several other houses on those three parallel conductors. one of them is the low voltage neutral conductor, but they are also using it has the MV neutral. If you trace it out you should see it connect back to the dedicated MV neutral at some point.

 

[W@ttson]

Looks like I am going to have some fun getting in the car and driving around. I know where the local substation is so maybe I will drive in that direction to see if I can see anything that clarifies things.

 

[steve66]

In all your photos, I see 3 wires and a top shield wire. So its either a 3 phase system, with the transformer connected to phase wires, or its single phase with one side connected to a neutral - probably the MEN Winnie mentioned.

Yes, even with a MEN some current will flow through the ground, but most would flow on the wire. And don't forget that at higher voltages the currents are lower, and the different currents from different phases (there will be multiple transformers on each phase) will cancel each other out.

Both of those will reduce the actual current running through the earth.

 

[W@ttson]

n all your photos, I see 3 wires and a top shield wire. So its either a 3 phase system, with the transformer connected to phase wires, or its single phase with one side connected to a neutral - probably the MEN Winnie mentioned.

It is not a 3 phase system. It is not a shield. It is the High Voltage (used colloquially) leg that runs in this part of the neighborhood.

 

[W@ttson]

See annotation.

 

[electrofelon]

Yeah Ive never seen a shield conductor on a distribution line.

 

[don_resqcapt19]

From the pictures I posted can you highlight the Utility Neutral? There is only one connection to the High voltage line. There is no other connection.
...

Often the primary and secondary neutral are bonded internally in the transformer, so you don't see the primary neutral connection.