Corner Grounded Delta 3 phase transformer

Status
Not open for further replies.
H

hardworker

Senior Member
I have a Corner Grounded Delta 3 phase transformer running off of 200 amp system. It converts the 3 phase to 1 phase. The transformer is on a 50 amp breaker in the 3 phase panel. It converts to a 1 phase 100 amp panel. The 50 amp breaker in the 3 phase keeps tripping. I have not done a load calculation yet, but I know for sure the 1 phase panel is drawing more than 50 amps.

Please help me understand the situation. Thanks, Steve
 
Is the system supplying the transformer corner grounded, or is it the transformer itself that has the corner grounding?

What is the supply voltage to the transformer?

What is the output voltage of the transformer?

Does the breaker trip immediately after energizing the transformer or does the system operate for a while?

Jon
 
hardworker said:
I have a Corner Grounded Delta 3 phase transformer running off of 200 amp system. It converts the 3 phase to 1 phase. The transformer is on a 50 amp breaker in the 3 phase panel. It converts to a 1 phase 100 amp panel. The 50 amp breaker in the 3 phase keeps tripping. I have not done a load calculation yet, but I know for sure the 1 phase panel is drawing more than 50 amps.

Please help me understand the situation. Thanks, Steve
Click to expand...
There is no reason to convert from three phase to single phase. A single phase transformer can simply be connected to any 2 'hot' conductors from the source.

However you can use a delta configuration to provide both 240V three phase and 120/240V single phase, commonly called a high or wild leg system.

Do you have a wiring diagram of your system? Because you mentioned corner ground. I think you have 2 legs from A 480V system feeding a standard single phase transformer providing 120/240V.
 
winnie said:
Is the system supplying the transformer corner grounded, or is it the transformer itself that has the corner grounding?

What is the supply voltage to the transformer?

What is the output voltage of the transformer?

Does the breaker trip immediately after energizing the transformer or does the system operate for a while?

Jon
Click to expand...
The system supplying the transformer is corner ground 240vt 3phase.
Output of transformer 120/240vt. 1 phase.
System operates fine for a day or two and then trips.
The transformer is supplied by a 50 amp double pole breaker
The panel running off the transformer is 120/240vt 1 phase 100 amp. It is pulling around 75 amp when at maximum load.

I think that 75 amp load is tripping the transformer breaker? I dont quite follow the logic, but there was no problem until the load exceeded the 50 amp breaker. That 50 amp breaker supplies the transformer and not the 120/240vt 1 phase 100 amp panel.
 
Ok, that is pretty easy to explain.

You have a 240V single phase primary and a 120/240V single phase secondary. The fact that it is supplied from a 3-phase system is irrelevant, it is a single phase transformer.

With your transformer current in = current out, at least at 240V. If you draw 75A on the secondary (at 240V) you must supply 75A on the primary.

You are simply overloading the supply circuit to the transformer and the breaker is tripping on overload.

With the numbers you give, it doesn't surprise me that the breaker isn't tripping instantly.

That 75A is probably a peak, and breakers take a long time to respond to a 50% overload.

That 75A might be the worse of the two secondary legs, so the transformer loading might be a bit less.

Breakers have a bit of tolerance; the true trip curve might be off a 60A basis.

You didn't provide the transformer nameplate, but it is likely that the transformer is overloaded.

Jon
 
Status
Not open for further replies.
Top