27kv

[Alwayslearningelec]

I believe this is incorrect. Showing 27kv from utility to manhole. THe 27kv would obviously continue to a xfmr but the xfmr they should is 600V( 120/208 to 277/480). That xfrmr would not work for 27kv, correct? Although it does say 1MVA....that's 1000 volt amps? So maybe the xfrmr is ok. The 120/208 & 277/480 with the 27kv feeders is throwing me off.

 

[Carultch]

You are correct. 27kV cannot connect to either side of a 480V:208V transformer. Perhaps there is an unmentioned 27kV to 480V transformer in the manhole.

Also, the deltas (triangle icon) and wyes (Y icon) are likely opposite what they need to be in this drawing. If you are trying to generate a 120/208V grid, you need a wye on the 208V side. Otherwise, you'd form a 208V ungrounded or corner-grounded delta grid. The deltas should be on the primary, and the Y's should be on the secondary.

What 1 MVA means is 1000 kVA, not 1000VA. M=Mega for million, and k=kilo for thousand.

The reason we say VA rather than Watts, is that current and voltage is not necessarily synchronized. Apparent power, i.e. the product of the RMS voltage and RMS current, is what governs the transformer size required, rather than real power (the time-average product of instantaneous voltage and instantaneous current)

 

[Alwayslearningelec]

So if the incoming is 208v I'm having a hard time figuring xfmr size so the secondary 277/480v side can feed the 2500A main service breaker. They are calling for (6) sets 4#600's on secondary side going to the main breaker. A 1500kva xfmr would only provide 1804 amps on the secondary side.

 

[infinity]

The primary is listed as 480/277 on your drawing.

 

[Alwayslearningelec]

The primary is listed as 480/277 on your drawing.

Yes but it's incorrect as I confirmed.

 

[Alwayslearningelec]

How would calculate xfrmr size here?

 

[winnie]

1) figure out the incoming supply voltage. You know the diagram is wrong, so confirm everything!

2) Figure out the actual load. You say 2500A 480V main service breaker, but this isn't the actual load. 2500A@480V is 2.1 MVA

Jon

 

[paulengr]

So if the incoming is 208v I'm having a hard time figuring xfmr size so the secondary 277/480v side can feed the 2500A main service breaker. They are calling for (6) sets 4#600's on secondary side going to the main breaker. A 1500kva xfmr would only provide 1804 amps on the secondary side.

VA is VA. Works with every voltage.

 

[paulengr]

So if the incoming is 208v I'm having a hard time figuring xfmr size so the secondary 277/480v side can feed the 2500A main service breaker. They are calling for (6) sets 4#600's on secondary side going to the main breaker. A 1500kva xfmr would only provide 1804 amps on the secondary side.

There isn’t an 1804 A breaker. You could use 2000 A but even though distribution breakers are 100% duty often for expansion reasons they get 80% rated which is only 1600 A, pushing you into a 2500 A frame with an 1800 A rating plug.