260 kVA Diesel Generator Drops Under 250 A load


Thread Starter


Hi, there is 260 kVa FGWilson Diesel Genset with Perkins 1300 Series Engine. My problem is generator works well under 0-160 amps. when its under 250 amps load, it drops voltage..

We use this generator on oil pumps which are working on 60-hz - 220 amps.

I changed AVR, fuel pump, injectors but nothing, no any error on ecm of engine.

Please help.

My Best Regards.

Gen. Char:
1500 rpm
380 volts.

When did the problem start, or, has it been ongoing since new?

What exactly is the rating of the generator, from the generator nameplate? Amps? Power Factor?

The formula for three-phase apparent power (VA) is:

S = V * I * (3^(1.2)) * PF

where S = apparent power (the total power, active power (Watts) plus reactive power (VArs))
V = Voltage
I = Amperes
PF = Power Factor

Most electric motors operate at a Power factor of around 0.8-0.9; let's assume 0.85 for this exercise.

V = 380 V
I = 250 A
PF = 0.85

S = 380 * 250 * 1.732 * 0.85 = 128817.5 VA = 128.8175 KVA

So it would seem the engine/generator is not overloaded at 250 A with a rating of 260 KVA.

Let's see what the amperes would be for the rated apparent power, assuming a power factor of 0.8:

260000 VA = 380 * I * 1.732 * 0.8; I = 260000 / (380 * 1.732 * 0.8)
I = 260000 / (526.528) = 493.9 Amperes

So, it would seem that the engine/generator is capable of approximately 494 A at rated output with 380 Volts and a power factor of 0.8.

But, you said the frequency of the load was 60 Hz, yet you said the speed of the generator was 1500 RPM. The two don't jive--for 1500 RPM at 60 Hz the generator would have to have 4.8 poles, and they don't make generators with 4.8 poles. They don't even make generators with 5 poles--they always have an even number of poles. Even if the generator is an induction generator, it's still a very odd application. Are you sure you didn't mean to type 50 Hz? Or, are you trying to drive 60 Hz motors with a 50 Hz generator, or vice versa?

Voltage is a function of excitation (the "AVR"). Amperes is a function of diesel fuel flow-rate. If the voltage is collapsing but the speed is remaining constant, then it's most likely something amiss with the AVR or the devices feeding the AVR (like the voltage or current sensing inputs). If the voltage is collapsing AND the speed is falling off when the load exceeds 220 Amps then it's most likely somethings amiss with the fuel delivery system. Sometimes water can cause paper elements in diesel fuel filters to swell and restrict fuel flow through the filter at higher flow rates (higher amperes; higher loads). And, voltage is also a function of speed--when the speed is rated the voltage should be constant, but if the speed is less than rated, with a constant excitation the generator terminal voltage will be less than rated.

So, is the speed falling off when the voltage drops when the amperes exceeds 250A?

Enquiring minds want to know.