Delta to Y

[fritts]

Have an upcoming job at a vegetable processing farm (Larger type Barn). The incoming service is a corner grounded Delta The main disconnect has two 600 Amp fuses. B phase is connected to earth thru the grounding lug in the main disconnect. First question, should not B phase be connected to a third fuse for short circuit or overload protection?

The barn has 3 small transformers to pick up various 1 phase loads which are blowing fuses during peak season.

The farmer has purchased a used 300KVA generator, transfer switch and 112.5 Delta to Y transformer. The salesman designed it so the generator would produce power transformer would take it from Y to delta then to the transfer switch.

I would like to use the transformer to take care of both Delta to Y and to pick up the load for the peak season 1 phase.

To accomplish this many of the 3 phase motors will have to be connected to the Y output.
Upon speaking with the refrigeration tech that brought up two points that has me questioning the design.
1) He spoke of some of the 3 phase motors not being able to work on the star system.
? Is the star the same as the Y or could he be talking about something else?
? Aren?t 3 phase motors designed to work on both Y and Delta?
2) He spoke of motors working better and longer life if on a Delta system any truth to this?
There are many 1 phase 240volt motors on the 3 phase delta system.
I will check all 3 phase motors for proper phase rotation and insure they have three conductors all ungrounded and an equipment ground.
Is there anything that jumps out as incorrect?

 

[don_resqcapt19]

First the grounded B phase is not permitted to be connected to a fuse. It is a grounded conductor just like the neutral on a 120/240 volt single phase system.

Second, the 3 phase motors do not care if the source is delta or wye (star), they only care that they have a 3 phase supply of the correct voltage.

 

[Smart $]

...
Is there anything that jumps out as incorrect?

Well, yeh.

One, I fail to see how the generator is going to fix the blowing fuse problem. You can shed some loads over to the genset, but if the problem exists for all of the 3 xfmr's systems, you're going to need more than one transfer switch, and panelboards for the loads shed.

Two, I can understand a genset as backup, but in most cases I'm aware of, it's almost always cheaper to spin the meter than spin the gennie. Why not "fix" the service-supplied system?


EDIT— Ohhh... I just read your profile and see you are an inspector... I guess you're out of the decision making loop

...and welcome to the forum!!!

 

[fritts]

Delta to Y

Thanks for the Jab Smart$.
My son signed me up I told him never let the enemy know you are in there camp.
The fact is this is my sons job and his design he ask me to look over. You are correct I dont design or turn a wrench any more. I just critize others work.
His ideal is to select loads for the Em Panel. The farmer claims the utility has left him without power for weeks at a time. The loading my son is still working that out. Picture attached. the way the salesman designed the transformer would only be in use when the genset was on.

 

[Smart $]

Thanks for the Jab Smart$.
My son signed me up I told him never let the enemy know you are in there camp.

Ahhh. So you would have preferred to be in stealth mode

... His ideal is to select loads for the Em Panel. The farmer claims the utility has left him without power for weeks at a time. The loading my son is still working that out. Picture attached. the way the salesman designed the transformer would only be in use when the genset was on.

Missing a picture there, fritts

Too little information about the system to make any calls from this end, so here's some off-the-cuff speculation:

Assuming a 480V 3? service fused at 600A would be 480V ? 600A ? 1.732 = 500kVA service, at best. A 300kVA genset would carry a fair portion of the loads when utility power is out, but not if it is run entirely through a 112.5 kVA transformer.

Actually, I'm not even sure there is any need for a transformer, i.e. simply to convert from delta to wye, e.g. 480 delta to 480 wye, or vice-versa. However, if it is a stepdown transfomer, say 480V (genset voltage) to 208Y/120 for 120V 1? loads, I could understand it either becoming the fourth on-site transfomer or even perhaps replacing the existing three. You didn't tell us their capacities, only their secondary systems were blowing fuses. This is what needs fixed regardless of whether powered by utility or genset. Putting some or all of these loads on the new transformer could be the fix. Again I can't tell from here with the shortage on details...