Pad mount transformer

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highkvoltage

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I have a large problem. I am installing a 1000 kva. The primary voltage is 4160Y/2400. The secondary voltage is 480Y/277. It was suppose to be a delta primary 4160 and a delta secondary 480 for power. The company ordered the wrong transformer or the manufacture sent the wrong transformer. It really doesn't matter. Also my boss did not have me pull in a primary neutral even though I insisted we have it available just in case something like this happened. Has anyone changed the coil taps to convert it to the delta configuration that I need. I know what has to be changed, paralell to series on both sets I just need to know if it is possible. I am going to call the manufacture tomorrow I would just like to have some input if exspecially if someone has been in the situation before. (I can't wait to be completely on my own.) :confused:
 
Re: Pad mount transformer

My experience is with oil filled transformers, utility type, and there is no way to change the coil configuration. The transformer is built with 2400 volt coils in a wye. There is no way to come up with a 4160 volt rated coil. In general low side connections aren't accessible either. Do you have a dry type, or some other type where different primary coils are available?
Secondly, your 480 wye may suit the customer as well as 480 delta. Be sure they need delta, not just 3 phase 480. On the other hand you must not connect the wye high side to the 4160 system without a grounded neutral. You were right in asking for the neutral. Wye secondaries with ungrounded wye primaries are not for general applications.
I am interested about the coil taps that you have available.
You might be half way home.
Jim T
 
Re: Pad mount transformer

I really don't think that you have the wrong transformer.
You post is a little confusing, though, in that you gave a 'Y' primary voltage of 4160/2400 and a 'Y' secondary voltage of 480y/277.
Then you really didn't provide what the nameplate voltage of the transformer is since if would be very rare at best ever to have a padmounted 4160y/2400-480y/277 transformer.
Reading between the line I would suggest that you really have a 4160v delta-480y/277 transformer. That you may have a 4160y/2400 delta supply.
If so connect the L-L-L to the transformer primary, no neutral requuired.
You did not state what you are supplying but MCCs are commonly feed with a 480y/277v transformer even though the motor loads supplied are simple 3ph-3w loads with no neutral suppied. The MCC is supplied with a place to land the neutral but doesn't have a neutral bus. When the neutral is grounded as is customarily done what's nice about this arrangement is that L-G voltage will be 277v and not 480v.
With a delta secondary one must decide if it is to be corner grounded or not.
 
Re: Pad mount transformer

Generally, on this size of xfmr, the ends of all of the windings are not brought out for the purpose of reconnecting the windings themselves in series or parallel.
It would surprise me if you can simply reconnect, in the field, from wye to delta on both pri. & sec.

Usually what leads are brought out, are simply voltage taps. These are for making adjustments in the transformation ratio & are usually in 2-1/2% or 5% increments.

Study the xfmr closely and/or get a knowledgeable person to check it out for what options are available. Good luck.

Remember, that if somehow, you are able to properly hook-up the pri., then it doesn't matter that the sec. is wye-connected. It doesn't matter whether you have actual 277V. loads or not. Just bond & ground (earth) "X0" & treat as a separately derived system.

Maybe someone has other thoughts on this, but I've always thought of a wye-wye xfmr as a weirdo, for non POCO applications, that is.
 
Re: Pad mount transformer

temp. There is no mistake. The coil configuration are both Y with the primary neutral and secondary neutral sharing a common bushing. I not only quoted from the nameplate both refered to the schematic from the nameplate. Go to the Solomon transformer website and you will see they are available. I mentioned the manufacture because I am sure the error was the company I work fault. A month ago I took readings at the old sub rotation, polarity and phasing and informed them what they needed to order. I believe they did a drive by an already had the order placed.
 
Re: Pad mount transformer

jtester. They are oil filled and I totally agree with you. I have years of substation transformer experience and was 90% sure they could not be changed. But 10% of me said there are many brillant people here and it's always worth a shot.
 
Re: Pad mount transformer

kiloamp. Lineman do this all the time. But they aren't pad mount. Some the older type of pad mounts could be changed but the newer ones within 10 to 15 years depending on manufacture have make this impossible. Transformer manufactures in the 1940 are actually easier to work on than the current ones, but not as reliable or efficent.
 
Re: Pad mount transformer

highkvoltage
I'll be darned. I personally have never heard of a y-y padmounted transformer as they would be a devil to design and manufacture as well as an expensive special. However, I have known large electrical utilities to apply that configuration with transformers in their power distribution grids.
It would be interesting to find out just how they actually built the transformer as a the common d-y transformer has a 3 legged core and a y-y is built on the same core something called ferroresonence and unbalance become a problem which should be addressed as I understand it.
It would not be all that unusual for someone to have provided the manufacturer's "order taker who doesn't have a clue" with a y-y voltage, for the manufacturer to provided pricing as such, the customer accepts the pricing and places the order for same. The manufacturer should have questioned the application and a simple d-d or d-y transformer should have been provided.
Dave
 
Re: Pad mount transformer

Dave,
The major utilities in eastern Wisconsin specify five-legged core padmounts to reduce the ferroresonance problem. This has been their standard for over 20 years starting with WEPCO. But I have never seen them use an "end use" class Y-Y transformer.
 
Re: Pad mount transformer

Even if it is wye/wye, why do you need to connect a primary grounded conductor?
Don
 
Re: Pad mount transformer

Thanks Jim,
Being formerly just in industrial sale from the early 80s I wasn't aware of the use of padmount y-y transformers was common by utilities. I know that Westinghouse had a proprietary 4 legged shell form core design which may have been sold to ABB.
And, Don, one would think that it would be similar to applying a 'y' wound motor wouldn't you think? My reference leads me to believe that not grounding the H0 appears to be a better choice as Fundamental and harmonic frequency zero sequence currents in the secondary lines supplied by the transformer also flow in the primary lines and primary neutral conductor if the H0 is connected. Also, ground relays for the primary system may see load imbalances and ground faults in the secondary system which must be considered when coordinating OCPD.
My reference does indicate that when applying a y-y w/o connecting the H0 it is incapable of furnishing a stabalized neutral and its use may result in phase-to-neutral overvoltage (neutral shift) as a result of unbalanced phase-to-neutral loads.
But sense highkvoltage only needs 3ph-3w with no neutral this may not be a problem.
The appears to be enough red flags that I personally believe that the application should need farther study before I would apply it.
Dave
 
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