LR amps and generator surge capability

[katwalatapan]

Hello,

I wanted to understand the effect of "Locked Rotor" (LR) ratings of a motor and its effect in sizing a generator by reviewing its surge capability.

When a motor powered by a stand-by generator starts, it creates a voltage dip due to starting in-rush currents and requires more wattage.

Generator datasheet mention rated output/running watts and Commercial Surge capability(LR Amps @ 15% Voltage Dip).

For e.g. 40KW single phase generator has running amps of 167A and LR amps @15% voltage dip of 129A. Does it mean that the generator output reduces to 129A until the motor achieves normal running amps? How should this information affect sizing of generator?

Thank you.

 

[waross]

Use three times running current to size the generator. The class of generator, the characteristics of the prime mover, the effect of the UFRO circuit, the type of aspiration of the diesel engine and the type of power supply for the AVR all have some effect.
Use three times running current.

Bill
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