2 Phase Load on 3 Phase Alternator

First, I'm curious. I presume that the 250 amp load is really a single phase load (which you will connect between two of the phases). Yeah, it has to be.

Ok, 2nd question--you don't mention the voltage of the load--what is the actual load in kva or kw?

The main concern is the buildup of heat in the windings. Depending on whether the generator winding is wye or delta, you will be drawing the entire load current from one or two windings instead of all three. I'd feel real safe if you're total load is 1/3 of 500 kva. If higher than that, find out the winding arrangement of the generator--with a Y, I'd consider going to 2/3 of 500 kva.

I suspect that the 2 phase load is actually expecting a single split phase voltage where the voltages are 180° from each other. If this load requires a real 2 phase voltage than the voltage phase angle will be 90°. This is an ancient form of power distribution that may still exist somewhere but the OP must more clearly specify which type of power is required.

For my fellow Americans, people in other parts of the world never had to deal with real "2-phase" power, that which is 90° out. They therefore routinely refer to "2 out of 3 phases" as being "2 phase". We call that single phase here because for us, there is another power system that is (was) really 2 phase power. It's a semantics problem that vexes all international EE forums.

And by the way redfred, phase angles on 3 phase power are 120° out, not 180 , but I know you knew that.

We specify "single phase" (L and N) or "3 phase" (U V W^[1] (and possibly N)).

The term "2 phase" is not used for mains power distribution.

[1] Some may say R G B, or L1 L2 L3 - but you get the idea.

As long as the generator winding can carry the rated current i don't see any problem.

YES is the answer and monitor the heat on the genset. If it becomes excessive, stop the test.

Dear Friends,

Thanks for all the replies and sharing of experiences. The answers to all the queries are as follows :

- The set-up is a heat run test on a single phase loco transformer during prototype testing

- The voltage is 415V (fed through a dimmer & step-up transformer to the test job)

- We are using a DG set as the factory has limited grid power and outages are common

- The testing load is actually 130 kVA which is the full load loss of the transformer under test. But the type testing involves 2 hours of 150% loading i.e. 200 kVA ie. approx 280A @ 415V

- The alternator manufacturer confirms that it is safe to load a 500kVA DG set to the extent of 300A on 2 'legs' with no current in one 'leg' for a period of 8 hours

- As a contingency, if the DG trips on Over-Current / Earth Fault / High Temperature we shall switch to grid power with all other factory loads switched off

- Finally, the testing is scheduled on Friday and I will communicate the results to all

Thanks again....and keep posting !

I think we are talking of loads that are not symmetrical(unbalanced loading) here and since its a three phase 4 wire,the neutral here will take some value of current which i think is not safe.