How Much Load Can A 1000 KVA Generator carry

Generators are usually rated in KVA. The KVA rating is the power capacity of the generator. Usually, 1KW=1.25KVA @ 0.8PF, which means that a 1000KVA generator should deliver 800KW of power. 
The formla is =  S(kVA) =  P(kW) / PF

Now when you overload a generator, a lot of things happen. A lot of current is pulled from the alternator, the alternator coils begin to overheat and the drag on the prime mover increases then what happens is that the speed of prime mover will fall, and the frequency will drop. 

If the overload is sustained one of three things would happen. The generator engines will go off when the prime mover stalls or the protection circuits would trip to cut-off the load but in the worst-case scenario the coils of the alternator will saturate and overheat then burn up.

So, to prevent overload we have to monitor how much current we are pulling from the generator as the current basically represents the load on the generator. This is true because as we know Power (P) = Voltage (V) x Current (I). The generator design specs would show the rated voltage and maximum power output. 

Since the voltage and power output are constant, the only variable is the current. As the generator is loaded, more current is drawn from the alternator by the load. However, generators are rated in VA (volt-amperes) for a reason; calculating in watts does not accurately indicate how much current you can draw before overloading the generator. It's important to understand that you cannot draw infinite current from the generator. The power rating sets a limit on the amount of current you can safely draw.

The generator I am using for a case study is a 3phase, 415V,1000kVA Cummins generator. It was supposed to be installed in the workshop. The installed capacity of all the equipment in the workshop would definitely consume more than 1000kVA power. Therefore, it was crucial to know the maximum current we could pull, and we planned to stay within 80% of the max current by monitoring the ammeter as we loaded up the generator.

The solution is simple VA simply means voltage amperes; Voltage multiplied by amperes. For our generator, we know the Voltage we know the rated power so we can easily get current. 

V - 415Vac
S - 1000kVA 
A -?

S = VA
A = S/V

1,000,000VA = 415 x A
A = 1,000,000/415 = 2409.6A

Since it is a 3 phase Balanced system the load should be distributed evenly among the 3 phases and the current through 1 phase should not exceed 2409.6/ √3. Consequently, the current should not exceed 1398A per phase. Considering our plan to run at 80% of full load we would begin load shedding when the ammeter reading gets to 1113A.

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