Re: Transformer Power
Jross: You still have a few fundamental misconceptions.
Originally posted by jross: Ed - The answer is "10 Amps."
No, the answer is ?Zero Amps.? If you have a delta system, and clamp an ammeter around all three phase conductors, the reading must necessarily always be zero. If it is not, then you have a ground fault. Similarly, if you have a wye system, and clamp an ammeter around all three phase conductors and the neutral, the reading must necessarily always be zero. Here again, if it is not, then you have a ground fault. This is a requirement driven by Kirchhoff?s Current Law, which can be stated as follows, ?The sum of all currents entering and leaving a single node is zero amps.?
I now understand this panel, and all it?s single phase 120 VAC loads (i.e., A-B, B-C, C-A)
I fear that you do not yet understand this panel. If the loads are single phase, 120 volts, then they would be wired A-N, or B-N, or C-N. If instead you are wiring a load A-B, or B-C, or C-A, then you are giving the loads a single phase 208 volt power supply.
The tech data sheet for the system being installed states the total Amp requirement is 150 Amps. It?s now obvious to me the existing bank of 5 kVA transformers won?t meet the bill.
Is that requirement for 150 amps at 120 volts? If so, you need 150 x 120 x 1.732, or 31kVA. At present, you have only half that.
Based on the power source being provided (i.e., 450VAC, 30A, 23382 VA), is it possible to replace the 25A breaker in the 450VAC panel with a 30A breaker and replace the bank of transformers with higher rated units (or a single 3-phase unit) to get the full 23382 VA to the system loads?
First, you need 31kVA for the system loads, not just 23.4kVA. You can get that from a 30kVA transformer (or bank of three 10kVA transformers wired as a delta). But the rated primary current (at 450 volts) would be 38.5 amps. Sure, you could use a 30 amp primary breaker, but it would give you frequent false trips. NEC allows the primary of a transformer to be protected by up to 250% of the primary rated voltage. That means you could use a 100 amp primary breaker. But that is not the only issue. You would need to verify that the primary feeder conductors are capable of handling the current that you propose to put through them.
Please do not take this wrong, but I think you need to let the engineer get back from vacation, and not try to design this project yourself. There are too many variables that you need to understand, and I don?t think you are ready yet.