Two Tfrmrs supply one service

Status
Not open for further replies.

karl riley

Senior Member
My last EMF job involved a house with an unusually high magnetic field in the bedroom which backed up to a distribution line. Due to high currents in the water pipes my report recommended that the utility be asked to check the service drop neutral connections. They read the report and to their credit took action.

They came out, made some changes, and the magnetic field in the house dropped to almost nothing. OK. Here is my question:

According to an electrician the utility man talked to, it sounds as if they had been feeding this service drop with two of the transformers along the line. Their idea was that if one Tfmr had a problem the other would keep feeding. I have never heard of this. Maybe Charlie knows about this strategy.

The result was that currents in the line behind the client's house were unbalanced and the resulting net current created the fields in their house. Leaving aside the phases, the service drop neutral had two ways to go once it reached the secondary line.

The utility's fix was to feed from just one Tfmr (what a fantastic idea!) and the net current and its field were gone.

Any comments about this double feed?

Karl
 

wirenut1980

Senior Member
Location
Plainfield, IN
Re: Two Tfrmrs supply one service

I must admit, I am in disbelief that this house had a dual radial setup and that they had both transformers feeding at the same time. :eek: The utility might want to make sure their equipment is rated for the increase in available fault current that comes from having parallel paths. I never thought about their being an EMF issue from a dual radial setup, but then again, I have never seen a dual radial setup where both sources are on at once for an extended period of time. Unless I am reading this wrong?
 

charlie

Senior Member
Location
Indianapolis
Re: Two Tfrmrs supply one service

Unfortunately, you are not wrong. It is my understanding that some electric utilities use a modified network of sorts for their overhead distribution system. They will set up an ally or an easement with a continuous run of secondary and several transformers on the same primary phase. The idea is to provide better service with less voltage drop and the ability to replace a single transformer without the customers experiencing an outage.

From a utility standpoint, it is dangerous unless you really know their system. Also, it is difficult to know when you have lost a transformer because the voltage will just sag until there is enough load to burn down the secondary.

I believe most electric utilities that use this method are moving (have moved?) away from it to a more conventional system. By the way, did I say that I don't like that system? :D
 

rhurey

Member
Re: Two Tfrmrs supply one service

I think NIPSCO uses that system in at least one town in NW Indiana. They've got 3 wire overheads below the primaries with each house just tapped off them every so often. (At least that's how I remember my parent's front yard from last time I was home.) The 120V lines are mounted verticaly with some space (from the ground it looks like a couple of feet) between them.
 

hurk27

Senior Member
Re: Two Tfrmrs supply one service

Here in Portage we have a few areas that have a 120/240 lines ran down the alley or behind the houses that feed multiple houses but they are only fed by one transformer.

rhurey
If you don't mind me asking where are you at up here in this area? I work in all areas from Laporte,Co. to Lake,Co and a few counties south. But we are out of Portage.
I also atend the IAEI meetings at the JATC apprentice school in Hammond
 

charlie

Senior Member
Location
Indianapolis
Re: Two Tfrmrs supply one service

Generally speaking, the open wire secondary is installed on 3 spool racks that have 8 in. spacing between the spools. Insulators are then installed between the ends of the secondary buses to split the secondaries between the transformers. Unless you are looking for them, you will not see them.

The situation I was describing is very rare today so I doubt that Northern Indiana Public Service is using that method. :D
 

rhurey

Member
Re: Two Tfrmrs supply one service

Could very well be, I can't see a transformer from the front deck, and I was spending more time trying to figure out if the cables had any insulation left on them.

Oh, I grew up in Ogden Dunes, but moved to Seattle a few years ago when I got done with school, don't get home much anymore.

[ April 20, 2005, 11:55 PM: Message edited by: rhurey ]
 

karl riley

Senior Member
Re: Two Tfrmrs supply one service

Thanks for info, Charlie and all. This situation occurred in Michigan. The fact that they responded to an EMF complaint by changing back to one Tfrmr means to me they weren't that interested in defending the practice.

Karl
 

bcampell4

Member
Re: Two Tfrmrs supply one service

Hurk, when you said that there were multiple houses on one transformer, are they homeruns to the transformer or are the "T-tapping." The reason that I am asking is that my company has developed an instrument that monitors low voltage (120/240) power lines that are "t-tapped," The only residential neigborhoods that use this type of technology (or lack thereof) is overseas. We have been traveling to the UK to test our equipment. We are obviously looking for a place in the states that is set up like this. Any information that you know would be appreciated! Thanks
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Re: Two Tfrmrs supply one service

A club I belong to was experiencing regular power failures due to UG cable faults. At last count the thing failed 10 times in 6 months,

Comed finally ran a temporary line to an overhead feed, and then added another UG feed from someplace else. The line man told me that way if either feed failed we would still have power.

I think a guy up the street on the same UG cable that kept failing was livid as it was seriously impacting his business, and that is what convinced Comed to bring in a second feed.
 
Status
Not open for further replies.
Top