Overview#
The Generac SG350 is a 350 kW standby (315 kW prime) industrial natural gas generator set powered by Generac's own 21.9L turbocharged and aftercooled V12 spark-ignited engine. Rated at 438 kVA standby and 394 kVA prime at 60 Hz, it is EPA certified for both stationary emergency and non-emergency applications, making it demand response ready. The genset features the Generac Power Zone Pro Sync controller with a 7-inch color touchscreen display, and can accept full load in less than 10 seconds.
Engine and alternator#
The Generac 21.9L (1,336.4 cubic inch) V12 is a spark-ignited engine designed and built by Generac specifically for gaseous fuel applications. Key specifications include a 10.0:1 compression ratio, 5.03-inch bore, 5.60-inch stroke, electronic ignition, 7 main bearings, cast iron cylinder heads, cast steel alloy cylinder liners, forged steel alloy crankshaft, and solid lifters. Intake and exhaust valves are high-temperature steel alloy with proprietary alloy hardened valve seats. The lubrication system uses a gear-driven oil pump with full-flow spin-on cartridge filtration and a 31.7-quart (30L) crankcase capacity.
The standard alternator is the Generac K0350124Y21, a 4-pole revolving-field design with Class H insulation on both rotor and stator. It features permanent magnet excitation, full digital voltage regulation with plus or minus 0.25% steady-state accuracy, and total harmonic distortion below 5% (3-phase). Motor starting capability is 1,001 skVA at 30% voltage dip on 277/480V with the standard alternator, upgradable to 1,560 skVA with the K0600124Y23 alternator.
Power ratings and fuel consumption#
At 277/480V three-phase and 0.8 power factor, the SG350 delivers 350 kW standby / 315 kW prime. The unit supports 120/208V (1,216 A standby / 1,094 A prime), 120/240V (1,054 A / 948 A), 277/480V (527 A / 474 A), and 347/600V (421 A / 379 A).
Natural gas consumption at standby ratings: 4,140 scfh at 100% load, 3,240 scfh at 75%, 2,400 scfh at 50%, and 1,620 scfh at 25% load. Prime consumption is slightly lower at each load step: 3,780 scfh at 100%, 3,000 scfh at 75%, 2,220 scfh at 50%, and 1,560 scfh at 25%.
Physical dimensions#
The open set measures 154.4 x 71.0 x 66.5 inches (3,922 x 1,804 x 1,689 mm), weighing 7,286 to 8,650 lbs (3,304 to 3,923 kg). Weather protected enclosures measure 207.4 x 71.0 x 80.0 inches. Level 3 sound attenuated enclosures (steel only) are available at 232.0 x 76.9 x 129.2 inches, weighing 13,224 to 14,285 lbs.
Cooling system#
The cooling system operates at a maximum ambient temperature of 122 degrees F (50 degrees C) before derate for both standby and prime. Coolant flow is 211 gpm (798.6 Lpm) with a system capacity of 15.5 gallons (58.7L). The open set fan delivers 28,004 scfm across the radiator. The pusher fan operates at 1,404 RPM with a 44-inch (1,118 mm) diameter.
Demand response capability#
The SG350 is one of Generac's demand response ready platforms. Its EPA certification for both emergency and non-emergency operation allows participation in utility demand response programs without hour restrictions. The 350 kW demand response rating matches the standby rating, meaning the full output is available for peak shaving and demand reduction.
Our service experience#
Generac's vertically integrated approach means they design and build the engine specifically for gaseous fuel. The 21.9L V12 runs hotter than diesel equivalents (1,277 degrees F exhaust temperature at rated output), making valve train maintenance critical. Spark plug replacement at 1,000-hour intervals is the most frequent recurring service item. For facilities running demand response duty, oil degradation accelerates and we recommend 250-hour oil change intervals rather than the standard 500 hours.
