Ralph Michaels
Member
- Location
- United States
I have been having a disagreement with an associate of mine. The subject at hand concerns a small, 3kVA rated gasoline-powered generator. The generator's output is across a transformer secondary (built in) in a wye configuration with 220 & 380V outputs.
I contend that the most the generator can supply, given the ratings of its windings & wiring, and 3-phase math to a single-phase load in a 100% imbalanced condition, connected line-to-line, is 1/3rd of the generators total (3-phase) power rating; or 1kVA. My belief is that it would even be less, due to the imbalance and resulting loss of efficiency. My math has always been to simply divide the total power rating by 1/3rd, regardless of whether the load is connected line-to-line or line-to-neutral. (FYI - the load is an air-compressor; we are well aware of the generator's inability to support the compressor motor's inrush; so this is more of a hypothetical situation.)
My associate believes that because the load wired line-to-line, is across two of the windings, the generator can deliver 2/3rds of its rated power (2kVA) to the load. After first taking that position, my associate lowered his belief to that the generator could put out at least 57.7% (kVA rating/1.732). I believe firstly that the power available across one of the 3-phase transformer's line-to-line connections is equal to the power available across any one of its line-neutral terminals. Secondly, that trying to operate the generator with a load requiring 2/3rds or even 57.7% of its total power rating will cause possible damage to the windings & wiring, as well as severe mechanical instability to the generator and possibly damage its bearings. I can't see how the manufacturer would over-size the windings and wiring so that each one would support 57.7% of the unit's total rating (requiring roughly, the windings & wiring to be sized to support 173% of the unit's total rating (57.7% x 3).
Can anyone provide any thoughts on this? Would the generator be able to put out 2/3rds of its rating to the single-phase load wired line-to-line? 57.7%? Or not even 1/3rd of its rating?
I contend that the most the generator can supply, given the ratings of its windings & wiring, and 3-phase math to a single-phase load in a 100% imbalanced condition, connected line-to-line, is 1/3rd of the generators total (3-phase) power rating; or 1kVA. My belief is that it would even be less, due to the imbalance and resulting loss of efficiency. My math has always been to simply divide the total power rating by 1/3rd, regardless of whether the load is connected line-to-line or line-to-neutral. (FYI - the load is an air-compressor; we are well aware of the generator's inability to support the compressor motor's inrush; so this is more of a hypothetical situation.)
My associate believes that because the load wired line-to-line, is across two of the windings, the generator can deliver 2/3rds of its rated power (2kVA) to the load. After first taking that position, my associate lowered his belief to that the generator could put out at least 57.7% (kVA rating/1.732). I believe firstly that the power available across one of the 3-phase transformer's line-to-line connections is equal to the power available across any one of its line-neutral terminals. Secondly, that trying to operate the generator with a load requiring 2/3rds or even 57.7% of its total power rating will cause possible damage to the windings & wiring, as well as severe mechanical instability to the generator and possibly damage its bearings. I can't see how the manufacturer would over-size the windings and wiring so that each one would support 57.7% of the unit's total rating (requiring roughly, the windings & wiring to be sized to support 173% of the unit's total rating (57.7% x 3).
Can anyone provide any thoughts on this? Would the generator be able to put out 2/3rds of its rating to the single-phase load wired line-to-line? 57.7%? Or not even 1/3rd of its rating?
You have the power to prove yourself, OR your associate wrong (or right):roll: (sorry guess I'm no help!)