gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
160421-2512 EDT
11bgrunt:
I see no object in building the circuit you have drawn.
If the above discussion was correct the cause of tripping your breaker was the connection of the three wires of a transformer center tapped winding to the neutral and two hot wires of a wye source.
Downsizing from a 15 kVA transformer to a 5 kVA transformer alone reduces the secondary arc current. If you want to lower it further, then simply add some series resistance to a single 5 kVA transformer. 5 kVA at 240 V is about 20 A. A 10% voltage drop (24 V) at 20 A is 1.2 ohms. This is a power dissipation of 400*1.2 = about 500 W. Four 5 ohm Ohmite 100 W resistors in parallel could be used here. These are good for large overloads for a short time. Oven, stove, or water heater elements are other alternatives. I suspect that you don't want the arc to last long.
Any idea of what your arc current would reflect to the primary?
Had your original setup been connected to a single phase center tapped source, then the steady state line currents would have been moderately small even with some unbalance of the two source voltages. The voltages and currents would have been based on approximately the voltage magnitude difference of the two sources divided by the total series impedance of the two load transformers primarys. The series impedance would be possibly 3% and if the voltage difference was 3% we are somewhere in the range of full load current. When those two source voltages are 120 deg apart instead of 180, then you have a big problem.
.
11bgrunt:
I see no object in building the circuit you have drawn.
If the above discussion was correct the cause of tripping your breaker was the connection of the three wires of a transformer center tapped winding to the neutral and two hot wires of a wye source.
Downsizing from a 15 kVA transformer to a 5 kVA transformer alone reduces the secondary arc current. If you want to lower it further, then simply add some series resistance to a single 5 kVA transformer. 5 kVA at 240 V is about 20 A. A 10% voltage drop (24 V) at 20 A is 1.2 ohms. This is a power dissipation of 400*1.2 = about 500 W. Four 5 ohm Ohmite 100 W resistors in parallel could be used here. These are good for large overloads for a short time. Oven, stove, or water heater elements are other alternatives. I suspect that you don't want the arc to last long.
Any idea of what your arc current would reflect to the primary?
Had your original setup been connected to a single phase center tapped source, then the steady state line currents would have been moderately small even with some unbalance of the two source voltages. The voltages and currents would have been based on approximately the voltage magnitude difference of the two sources divided by the total series impedance of the two load transformers primarys. The series impedance would be possibly 3% and if the voltage difference was 3% we are somewhere in the range of full load current. When those two source voltages are 120 deg apart instead of 180, then you have a big problem.
.