I am working on a project with a gas engine at constant speed of 1500RPM to drive a permanent magnet generator with magnetic ball bearings. - SKF.function is GENSET - PM generator is water cooled. - PM generator is horizontal positioned.

The permanent magnets Nd-Fe-Bare axial located on the rotor - radial flux PM.

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From the supplier of the generator I received 2 torque ratings:

  • start torque: 2.9 Nm
  • rated torque: 191 Nm

The gas engine has a torque of 97Nm.

The generator is 3phase 400V AC - 45.6A - 4 poles -50HZ - 93% efficiency - PF 1 connected to the grid, and off grid via an inverter to a battery bank.

Will this work properly, or do I need a rated torque of the gas engine greater or equal to that of the generator?

Assume continuous full load, as it is connected to a battery bank.

In another option it is connected to the grid.

Any specs you would need I would able to supply if possible.

  • \$\begingroup\$ best efficiency i can get is 95% for the PMG (permanent magnet generator). PMG is 30kW full load. at full load the gas engine will not be able to provide enough torque to the PMG,and the engine will not work properly.. solution 1 : adjust the construction PMG for higher RPM in order to maintain 400V AC. the gas engine is a 2 cylinder. higher RPM (gas engine) results in higher torque but more gas fuel consumption. cost of generated electricity goes up. solution 2 : 3 cylinder engine - find the sweet spot RPM/Torque /gas fuel consumption in order to have a low cost of generated electricity. \$\endgroup\$ – PERCY V Apr 26 '19 at 12:20

If the gas engine has an output torque of 97Nm at a speed of 1500rpm (= 157 radians/s), that's an output power of 97*157 = 15.2kW.

If your generator is 93% efficient, then you won't be able to draw more than 0.93*15.2 = 14.2kW from it, even if you could with a bigger engine. It will all work properly, up to that power.

The maximum output power is limited by whichever of the generator and the engine has the lower rating. Small engine, big generator, you will be able to stall the engine without overheating the generator. Big engine, small generator, you will be able to overheat the generator without stalling the engine. Either way, it's a good idea to control what the electrical load draws to avoid overloading engine or generator.

  • \$\begingroup\$ I would also suggest that 93% efficiency is likely the best possible at some specific power output level; at 97 Nm it may be less, so it's better to be somewhat conservative. \$\endgroup\$ – anrieff Apr 25 '19 at 10:16

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