744RSL4058 3-Phase - Marathon | 2300 kW

Model. The 744RSL4058 3-Phase is a Marathon RSL 4-pole alternator. Marathon reads the model as frame 744 followed by the RSL family code and the winding number 4058. The frame sets the mechanical envelope and the family code sets whether the machine is wound for single-phase or three-phase service. It is wound for three-phase service at 60 Hz. Electrical rating. At 0.8 power factor lagging this machine is rated 2300 kW, which is 2875 kVA, delivered as three-phase at 480 V 60 Hz. At 480 V line-to-line that is 3458.1 A per line. At this rating the machine is normally ordered with a PMG excitation system rather than plain shunt excitation, because the fault current available from a permanent magnet pilot exciter is what lets the downstream protection discriminate properly on a set this size. The 1800 rpm figure is synchronous speed, so there is no slip and no speed-dependent voltage droop. Frame and core. The 744 frame carries the 4058 core. Frame size fixes the stator bore and the shaft centre height; the core length fixes how much active iron sits in that bore, and therefore how much output the machine can make at a given temperature rise. The exact finished weight and outline drawing depend on the winding and the coupling, so they are confirmed on the certified datasheet issued with the order. The cooling circuit is direct air cooled, IC01, and the frame is rolled steel frame, cast iron end brackets. Three-phase winding. This is a three-phase machine with a 12 re-connectable winding brought out to 12 re-connectable terminals, so it can be reconnected on site for the usual voltage pairs — 380/220 V, 400/230 V, 415/240 V, 440/254 V and 480/277 V on the 50 Hz build, and the 60 Hz pairs on the 60 Hz build. Reconnection is done on the link board inside the terminal box, not by rewinding, which is why one machine can serve a 380 V job and a 480 V job. The 2/3 pitch design is what keeps the fifth and seventh space harmonics down without skewing the stator, and it is the reason the line-to-line waveform stays within the distortion limits the standards ask for. Four-pole build. A four-pole machine turns at 1500 rpm on 50 Hz and 1800 rpm on 60 Hz. That is the standard choice for generator sets from a few tens of kVA up to the low megawatt range, because the lower rotor speed gives a longer bearing life, a quieter fan, a higher subtransient reactance that is easier to coordinate with downstream protection, and a rotor that can carry a substantial damper cage for parallel operation. The trade is weight: a four-pole machine of a given kVA is roughly twice the mass of a two-pole one. Excitation and voltage regulation. The excitation system is self-excited brushless with SE350E AVR, regulated by SE350E standard / PM500 / DVR2400 with PMG, holding steady-state voltage to +/-1.0%. Marathon fits the SE350E as the standard regulator on the smaller frames, with the PM500 and the DVR2400 available where a PMG is specified. On the Mariner and harsh-duty builds the excitation stator is fully encapsulated and the rotating rectifier is a heavy-duty assembly with a 300% diode margin and sealed welded stud terminations, which is the difference between a machine that survives a damp boat hold and one that does not. Mechanical build. The frame is rolled steel frame, cast iron end brackets. Bearings are sealed for life ball bearings. Mounting is single bearing SAE flange or two bearing. Maximum overspeed is 2250 rpm, and the machine is rated for 1000 m. On the 280 to 430 frames the machine ships with twelve leads and a link board as standard, and the minimum inlet clearance is six inches. On the 570 frame and above the terminal box is mounted on top with the link board inside it, and a selenium surge suppressor is fitted as standard from the 360 frame up. Harsh-duty builds get multiple dip-and-bake cycles on the main stator. Where it fits. Power station and large marine duty. Machines in this band are engineered to order around the prime mover, with the excitation, cooling and protection all coordinated at the system level rather than picked from a catalogue. On a three-phase machine of 2300 kW the practical constraint is usually the downstream protection and the cable, not the alternator itself. Core stack position. The 4058 core is stack position 3 of 3 in the RSL family, roughly 100% of the way along the family's lamination length range. It is the longest stack the RSL family is built with. Long-stack builds carry the rating in the frame with the lowest flux density of the family. The extra iron costs length and weight, and buys a cooler-running core, lower magnetising current, better part-load efficiency and more margin for site ambient above 40 C or for a non-standard voltage. Where it sits in the range. The RSL family is catalogued from 160 kW up to 2200 kW, and this page covers the 2300 kW / 2875 kVA point. The step below it is the 744RSL4056 3-Phase at 2200 kW, 2750 kVA. It is the largest build in the family, so it is the one to quote when the load is fixed and there is no room for a second frame size. Reading the model code. A Marathon designation is read as the frame number, the winding family (PSL, CSL, CSA, RSL, FSL or FDL), and a four-digit winding code. Here that gives 744RSL4058 3-Phase for the model, 744 for the frame, 4058 for the core and three for the phase count, so the code on the nameplate and the code on this page match one for one. Quoting the full code rather than just the frame matters on this family, because the same frame number is built in several core lengths and the winding changes with the voltage. Frame position. The RSL range is built on 12 frame sizes — 431, 432, 433, 572, 573, 574, 575, 740, 741, 742, 743, 744 — and the 744 frame is number 12 of them. No other frame in this range carries exactly this rating, so the 744 is the only build at 2300 kW and there is no cross-frame decision to make. Lead count and reconnectable voltages. This 744RSL4058 3-Phase leaves the factory with 10 leads brought out to the terminal box. Ten leads means two reconnectable groups only: 240Y/480Y and 208Y/416Y. The six winding sections are jumpered for one of those two at installation, and the machine then runs at that voltage for the rest of its life unless the links are physically moved. The ten-lead build is what to quote when the site voltage is already fixed and documented, because it carries the full rating with fewer terminal studs, a shorter link bar set and a smaller terminal box than the twelve-lead version. What each jumper setting actually delivers. With ten leads only two settings exist, and the kVA available is not the same on both. 240Y/480Y gives about 2300 kW / 2875 kVA on this frame — 480 V line-to-line, 277 V line-to-neutral, the usual North American commercial supply. 208Y/416Y gives about 2024 kW / 2530 kVA on this frame — 416 V line-to-line, 240 V line-to-neutral, the usual Canadian and older industrial supply. Quote the voltage group you actually intend to run, not just the frame rating: a machine ordered for 480 V and then rejumpered to 416 V will not deliver the nameplate kW at the lower voltage without exceeding its temperature rise. What the nameplate means once it is wired in. At 2300 kW and 2875 kVA this machine pushes 3458 A down each line on a 480 V three-phase supply. That current, not the kVA figure, is what the switchgear and the cable have to survive, so the outgoing breaker should be a 5000 A frame device set to trip above 4323 A, and the run from the alternator terminals to the first panel should be 630 mm2 copper per phase for a normal 25 to 30 m span. Longer runs, aluminium conductors or tray-installed cable all move that number up, and the volt drop at full load is what decides it in the end. On the mechanical side the prime mover has to deliver about 2576 kW at the coupling. The usual 1.10 to 1.15 margin over the alternator rating covers the fan, the excitation loss and the governor droop, and it is the reason a 2300 kW alternator is normally quoted against a 2576 kW engine rather than a 2300 kW one. Fuel burn follows the electrical load almost linearly in this range. At a realistic 0.29 L per kWh for a modern common-rail set, running this alternator at full rating takes roughly 667 L per hour; at 75 per cent load it drops to about 520 L per hour and at half load to about 367 L per hour, because the fixed losses stay put while the variable ones fall away. Quote the breaker frame, the cable size and the engine rating together with the alternator, because a set that is right on paper and undersized on the cable is the most common way a good alternator gets blamed for a bad installation. Where this rating sits in the frame ladder. Within the 744 frame RSL carries 3 distinct ratings, and this is number 3 of them at 2300 kW. This is the largest rating the 744 frame carries; the step below is the 744RSL4056 3-Phase at 2200 kW / 2750 kVA, 100 kW under this one. Anything bigger moves to the next frame size up. Every step inside one frame is one more lamination stack length. The shaft, the bearings, the foot pattern, the terminal box and the AVR are the same part across the whole ladder, and only the core length and the winding change. That is why the price gap between two neighbouring steps is small while the gap between the last step of one frame and the first step of the next is large. It also sets the value-engineering rule: dropping one core size inside the frame saves money and axial length but eats the margin to the load, while stepping up one size costs far less than jumping to the next frame and buying a bigger skid, a bigger breaker and a bigger cable with it. Supply. Supplied as a genuine Marathon unit — Regal Rexnord, built in United States. Marathon alternators are built by Regal Rexnord in the United States. Each alternator ships with the routine test certificate, the winding connection diagram, and the AVR commissioning sheet. Export packing is seaworthy plywood on a pallet sized to the frame, and the machine is strapped and shrink-wrapped inside it. Tell us the engine make and model, the coupling arrangement (single or two bearing), the voltage and frequency, and whether you need a PMG, and we will confirm the build before it leaves the works.