Generator Current Imbalance
Generator Current Imbalance
(OP)
Hello from a newbie!
I have a question for all of you experts out there. I have a generator application where the customer is specifying both the genset and the equipment. I believe that they have a recipe for disaster with their three phase generator and high, inconsistant single phase loads. The generator is a 10 kW unit and the largest single phase (120V) load is 15 A (20% duty cycle).
Will this imbalance alone cause generator problems? How about if it is in combination with a 28 A/leg (48.4 total amp) 208V three phase load?
I am an ME learning this electrical stuff as I go along. Thanks in advance for all the help!
I have a question for all of you experts out there. I have a generator application where the customer is specifying both the genset and the equipment. I believe that they have a recipe for disaster with their three phase generator and high, inconsistant single phase loads. The generator is a 10 kW unit and the largest single phase (120V) load is 15 A (20% duty cycle).
Will this imbalance alone cause generator problems? How about if it is in combination with a 28 A/leg (48.4 total amp) 208V three phase load?
I am an ME learning this electrical stuff as I go along. Thanks in advance for all the help!






RE: Generator Current Imbalance
HOWEVER, you're three-phase load of 28A at 208V is equal to 10 kVA which is close to the unit rating. Assuming the 10kW rating is at 0.8 pf, the **generator** can produce up to 12.5 kVA. What the engine can produce in kW is another story.
The 15A 120V single-phase load adds another 1.8 kVA to one phase, so you would probably be slightly overloading the unit at that point.
If you're unclear on kW versus kVA and three-phase vs single-phase, I'd suggest enlisting help from an EE.
RE: Generator Current Imbalance
I understand the basics of power generation, but what I was unsure of was the magnitude of the magnetic effect of the unbalanced load. Having one of the "electromagnets" creating a larger field than the others would cause a mechanical imbalance to be reacted by the generator shaft and bearings. I am concerned that this imbalance could cause vibration and the potential for, um, "mechanical interference" (read: brakage) between the rotor and stator.
Am I out of line with my concern?
RE: Generator Current Imbalance
If this was a 3600 rpm, 1000 MW machine, significant imbalance might be of some concern. But these small 10 kW engine-generators should not have any problems with single-phase loads, as long as the winding ratings are not exceeded.
It's always best to balance out the single-phase loads among the three phases, to the extent possible.
The generator manufacturer can be consulted if you still have concerns.
RE: Generator Current Imbalance
At 10 kw and 0.8 pf, the rated current per leg is 35 A. To avoid rotor overheating due to negative sequence flux, it advisable to keep the load current variation in the phases to within 10%.
RE: Generator Current Imbalance
RE: Generator Current Imbalance
I do have a question on Edison's post. Can you please explain "negative sequence flux" and its effects?
RE: Generator Current Imbalance
Refer any good book on "symmetrical components".
RE: Generator Current Imbalance