kingsmurf

[gar]

080524-1622 EST

Charlie:

There are only three wires on the top of the pole and the transformer primary is bridged across two of the top wires. Neither of these is outwardly, on the outside of the transformer, connected to the secondary neutral. If one of the top wires is the neutral of a Y, then it must be jumpered inside the transformer. There is no secondary neutral running between poles and another transformer that could also be the primary neutral.

If the load was Y, then why bother to run 3 wires instead of just two?

Do you ever use a Y source at the substation and then only load it as delta and not carry the neutral with the distribution lines? One IEEE summary does seem to indicate this is used: "three-wire service, wye-delta". This was from
http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel2/820/3079/00095535.pdf?temp=x .

.

 

[mdshunk]

Gar, can you take a pic?

 

[iwire]

I have been involved working for Connecticut light and power when they have converted areas from delta to Wye, at the same times the line to line voltage was doubled. (My end was only to provide temp power to business that where out while the change over.)

My point being is I think there may be Deltas out there but they are being phased out.

 

[chris kennedy]

at the same times the line to line voltage was doubled.

How is that?

(My end was only to provide temp power to business that where out while the change over.)

Your talking gennys right?

 

[iwire]

How is that?

The hung new transformers all over the area over the course of many days, then came cut over day. They killed a large area swapped over to the new transformers and I imagine at some sub-station they replaced a large transformer.

Your talking gennys right?

Yes, we are contracted by a large generator rental company that has a contract with Connecticut light and power. If there is a long term or planed outage we will be connecting generators. Had to do a 2 MW unit at 1 AM in a stone quarry last fall.

 

[gar]

080524-2014 EST

don:

On millivolt ground voltages. I saw nothing in your two references that would imply a steady-state AC ground voltage of natural causes that would display in the AC mode on my Fluke. This meter has a capacitor in series with the input in AC mode to strip the DC component. At some point I might setup instrumentation to look more closely at the ground voltage. Low cutoff on the model 27 is probably in the range of 10 Hz.


mdshunk:

I just took some pictures, but they are not good. However, more clarification. Maybe morning or midday light may be better. Trees around the transformer make pictures difficult.

Two poles toward the substation from my transformer there are only three primary wires coming to that pole from the substation. Lower down are the cable TV and phone wires. Between these is one twisted wire pair, one of the pair is uninsulated. This supplies the street light on this pole and is supplied 120 or 240 from my transformer. My guess 120 because of the one uninsulated wire. This street lamp wire does not continue toward the substation. The pole is at the SW corner of my lot.

The next pole is at the NW corner of my lot about 150 ft from the SW pole. At this pole only the street light pair extends north to a pole with only a street lamp. All other wires make a 90 deg turn and go along my lot line about 85 ft to my pole transformer. Here my transformer primary, both sides insulated, connect to the outer two primary wires. The street light wires terminate on my secondary. They do not continue to the pole at the NE rear corner of my lot which is 185 ft from the NW pole. Only the primary wires and phone and cable TV extend to the rear pole.

Basically I am on 1/2 of the end of a long irregular block. My primary wires feed all or most of the other houses on my block. The block is about 0.6 miles in circumference and there are 22 houses.

I think there is no doubt that the pole transformers are wired across two legs as a single phase part of a delta load. Whether the substation is Y or delta is not known other than by what you might be able to tell me is common useage. This is clearly not a four wire distribution system on the primary side.

.

 

[quogueelectric]

perhaps a fresh set of brains can suggest a cure for the following querky problem

rural home . . .pool next to home . . . .X-former 50 feet away from home . . .SE drop to home

Problem:...current felt at pool edge when on the wet concrete edge

reseached thus far: . .everything . . .and still current shock on an low
order at pool

Querker: . . .finally removed SE connductors from mains . . ungrounded
and grounded conductors swinging in the cool air and
STILL getting low order shock at pool

Question : considering there is now nothing from POCO connected . .
and next closest POCO service is quite a ways off . .home
served by well and septic tank/leech field


? is there any possibilty that the current is from an natural
phenomenon? . .or a now present current due to an
galavanic reaction under ground?


with meter popped...and neutral open . .cannot be anything
POCO related now . .but WhollyJumpin'JesusPalimino . .I am at
an loss to explain this

any suggestions? . . .( keeping in mind that with all contact severed with POCO . .we still have current in the pool . . .no other service even
remotly close to this home )

You didnt disconnect the downground on the xformer did you just the magnetizing current could be conducting to ground off the primary but I susspect there are more than 1 house connected to this pole pig and is the water main copper??

 

[frizbeedog]

Help. Why is this thread called kingsmurf.:-?

 

[don_resqcapt19]

Gar,
What about the secondary conductors? The utility often uses the same conductor for both the primary and secondary grounded conductor.

I missed that you said AC voltage, but I expect that you will find that almost everywhere because of all of the grounding electrodes on power systems. This places the earth in parallel with the grounded conductors, both primary and secondary.

 

[ultramegabob]

Help. Why is this thread called kingsmurf.:-?

I was wondering the same thing, but was afraid to ask.....

 

[mdshunk]

I was wondering the same thing, but was afraid to ask.....

There seems to be a trend among posters who intend to "hit it and quit it" to name the post after their user name so that they can find it quickly.

 

[gar]

080525-1721 EST

mdshunk:

I have loaded some photos on my web to display the primary wiring to my pole transformer. I will leave these for a while but unrelated items I do not leave for a long time.

http://www.beta-a2.com/misc_TMP_photos.html

I would be interested in your estimate of the KVA rating and expected % impedance of this transformer.

.

 

[charlie]

I would be interested in your estimate of the KVA rating and expected % impedance of this transformer.

I can't believe what I am looking at but it looks like a 4.16 kV primary and the transformer has a 4.16 kV primary coil. It is still up in the air as whether or not the primary is a wye configuration or not. I am guessing again that the secondary of the substation transformer is in a wye configuration and the secondary neutral is not used and is probably not grounded. If one primary phase broke and hit the ground or a fence, you would get a corner grounded "delta" (if the wye neutral is not connected to earth, you will not be able to distinguish between a delta and a wye after it leaves the transformer) and the area around the downed primary would still be relatively safe.

You have a very old (50 years or more) installation with wood pin cross arms and 5 kV insulators. The transformers of that era have 5 kV pocket bushings and your's is probably a 25 kVA. It would be imposable to guess what the impedance is without looking at the nameplate but my best guess is 2?%. It looks like you have an old 3 kV silicon carbide lightning arrester on one side and a more modern MOV lightning arrester on the other side.

The cable feeding the street light is probably #4/6 Al. duplex. The bare #4 is for strength and the insulation is PE. The primary conductors appear to be #6 Br. Cu.

Sorry, I am doing a lot of guessing since I am not familiar with your serving electric utility's system. I do hope this helps a bit though.

 

[gar]

080526-1311 EST

charlie:

Thanks for the information.

The street light wiring is using the uninsulated wire as one conductor, and there is only one insulated wire wrapped around the uninsulated one. This is visible with my binoculars at the NW pole where the T connection is located.

Since my watt-hour meter is 200 A and I expect my neighbor sharing this transformer is probably the same your guess of 25 KVA seems low. But that size and 2.5% impedance is somewhat in agreement with a source impedance measurement I made. However, I have no idea how the power company sizes service rating and continuous full load operation.

This primary line was probably installed in the early 60s. Before 1964 at least.

.

 

[charlie]

. . . I have no idea how the power company sizes . . .

We use the following information based on years of experience:

Total electric, 7 1/2 watts per square foot.
Gas or other heat winter load, 4 1/2 watts per square foot.
Gas or other heat summer load, 5 1/2 watts per square foot.
# Cust????EH?????Win. gas??????Sum. gas
????1??????100%?????100%??????????100%
????2???????78%???????62%????????????72%
????3???????72%???????50%????????????63%
????9???????60%???????33%????????????51%

​

This demand factor chart continues for several customer on the same transformer. It is not my intention to post all of the information but to just give you an indication of how we do the loading on new homes. If you have a mix of electric heat and gas (the two most common here), you would use the average of EH (electric heat) and summer gas (that would include AC load) and use the demand factors to develop a table (the details are in a training module I have written for our engineers).

 

[don_resqcapt19]

Gar,
There are seven houses connected to the 25kVA transformer that serves my house. Mine is a 200 amp service and most of the rest are 100s with one or two 60s.

 

[gar]

080527-2014 EST

Thanks again charlie and don. I will get back to the transformer sometime later.


won4thewoad:

Back to your problem.

First, I think we have established that in my home yard there is no direct primary neutral current. Thus, my experiments are based on the assumption that voltages in my yard are from local transformer secondary sources.

Tonight I reran my previous voltage measurements using an oscilloscope as the measuring instrument and I did not parallel it with the Fluke. My minimum range is 5 MV/div or +/-20 MV full scale vertically.

This paragraph is probably of no use to you, but it provides information about my experimental setup. The scope is about 100 mHz bandwidth and thus when you put a long unshielded wire on the input you see local broadcast modulated signals. To remove these I used an input filter that passes low frequencies. This is a four section (stage) filter with each section being 10 k and 0.1 ufd. I isolated the scope power cord from ground.

Note: the bandwidth of a Simpson 260 is several hundred kHz. My 27 and 87 Flukes are more in the useful range of 20 to 30 kHz.

A wire from the copper water pipe below the water meter to the scope chassis or to your meter provides the reference point for all measurements. Any wire from #24 to larger is fine for the wire to the probe. But for the most part I used #18 and #16 extension cords because they are more manageable than smaller wire. For the probe I used a ground clamp on a screwdriver. The one I use allowed about 6" penetration in the soil. You need to consider safety for this probe and you may want a long insulated rod to hold the probe. Some way of holding your digital meter on this probe would be useful. Others will provide more safety information for you.

For those that questioned my previous measurements this test was done with an oscilloscope to prove that the source was current from the power distribution system.

I believe that there is some instrumentation error from induced voltages in the one turn loop that inherently exists in this measurement. This is probably not more than 10 to 20 MV. I was not interested in trying to estimate that tonight. I could have used better techniques in terms of controlling the loop of wire that I pulled around, it was about 200 ft.

My copper water line runs about 175 ft across my lot from the street. Remember my common reference for the scope or meter is the water pipe where it enters the basement.

One experiment I ran was to measure the ground potential near the street where the city shutoff valve is located. This was 15 MV peak and about 60 deg lag phase shift. This is a good check in relation to the other measurements because it is a low value indicating that my water pipe has a significant effect on the ground potential in its vicinity. I do not remember the depth of the water line but it may be 12 to 14 ft below the surface.

In the ground very close to my meter I get 15 MV peak and a lag of 90 deg.
At the transformer pole 22 MV and 90 deg lag.

My highest reading is at my lot edge adjacent to my east neighbor on a line approximately perpendicular to my water line and his service entrance. 175 MV at 50 deg lag. Very good sine wave here.

Under my primary wires:
At the SW pole 10 to 20 MV and leading 90 deg. Near the middle of the front yard about 30 to 40 MV and in phase. At the NW pole 40 to 50 MV and 70 deg lag.

Being below the primary lines there may be a substantial inductive effect. This might account for the leading to lagging phase shift as I moved from one lot corner to the other.

The neighbors across the street are in the 100 ft to 300 ft range and there ground currents are going to have less effect than my east side neighbor.

The fact that I can get these kind of results should imply that if you are dealing with voltages in the range of 1 V there should not be much instrumentation error.

I took many more points, but these are enough to give you an idea of how to approach your problem.

.